Micrograph showing HL

LONDON—Results of a small, phase 1 trial suggest CD30-directed chimeric antigen receptor (CAR) T-cell therapy is feasible in patients with aggressive Hodgkin lymphoma (HL).

The trial included 7 patients with relapsed or refractory HL.

Five of the patients achieved stable disease or better after infusions of CAR T cells, and the researchers said treatment-related adverse events were manageable.

William (Wei) Cao, PhD, of Cellular Biomedicine Group, presented these results at the 10th Annual World Stem Cells & Regenerative Medicine Congress.

The research was funded by Cellular Biomedicine Group, the company developing the CAR T-cell therapy (known as CBM-C30.1), as well as by grants from the National Natural Science Foundation of China and the National Basic Science and Development Program of China.

The trial included 7 patients with progressive HL. Two patients had stage III disease, and 5 had stage IV. The patients had a median of 16 prior treatments (range, 8-24) and limited prognosis (several months to less than 2-year survival) with currently available therapies.

The patients received escalating doses of autologous T cells transduced with a CD30-directed CAR moiety for 3 to 5 days, following a conditioning regimen. The researchers measured the level of CAR transgenes in peripheral blood and biopsied tumor tissues by quantitative PCR.

Two patients achieved a partial response to CAR T-cell therapy, and 3 attained stable disease. So the therapy resulted in an overall disease control rate of 71.4% (5/7) and an objective response rate of 28.6% (2/7).

Stable disease lasted 2 months in 2 of the patients and more than 3.5 months in the third patient. Partial response lasted more than 2 months in 1 patient and more than 3.5 months in the other.

Dr Cao said adverse events consisted largely of fever and were manageable with medical intervention. One patient experienced 5-day self-limiting arthralgia, myalgia, and dual knee swelling 2 weeks after cell infusion. There were no delayed or severe adverse events.

“We are very encouraged by the efficacy and toxicity profile of our CAR-T CD30 technology,” Dr Cao said, “given that the [patients] were diagnosed with stage III and IV Hodgkin’s lymphoma.”

Micrograph showing HL

LONDON—Results of a small, phase 1 trial suggest CD30-directed chimeric antigen receptor (CAR) T-cell therapy is feasible in patients with aggressive Hodgkin lymphoma (HL).

The trial included 7 patients with relapsed or refractory HL.

Five of the patients achieved stable disease or better after infusions of CAR T cells, and the researchers said treatment-related adverse events were manageable.

William (Wei) Cao, PhD, of Cellular Biomedicine Group, presented these results at the 10th Annual World Stem Cells & Regenerative Medicine Congress.

The research was funded by Cellular Biomedicine Group, the company developing the CAR T-cell therapy (known as CBM-C30.1), as well as by grants from the National Natural Science Foundation of China and the National Basic Science and Development Program of China.

The trial included 7 patients with progressive HL. Two patients had stage III disease, and 5 had stage IV. The patients had a median of 16 prior treatments (range, 8-24) and limited prognosis (several months to less than 2-year survival) with currently available therapies.

The patients received escalating doses of autologous T cells transduced with a CD30-directed CAR moiety for 3 to 5 days, following a conditioning regimen. The researchers measured the level of CAR transgenes in peripheral blood and biopsied tumor tissues by quantitative PCR.

Two patients achieved a partial response to CAR T-cell therapy, and 3 attained stable disease. So the therapy resulted in an overall disease control rate of 71.4% (5/7) and an objective response rate of 28.6% (2/7).

Stable disease lasted 2 months in 2 of the patients and more than 3.5 months in the third patient. Partial response lasted more than 2 months in 1 patient and more than 3.5 months in the other.

Dr Cao said adverse events consisted largely of fever and were manageable with medical intervention. One patient experienced 5-day self-limiting arthralgia, myalgia, and dual knee swelling 2 weeks after cell infusion. There were no delayed or severe adverse events.

“We are very encouraged by the efficacy and toxicity profile of our CAR-T CD30 technology,” Dr Cao said, “given that the [patients] were diagnosed with stage III and IV Hodgkin’s lymphoma.”

Micrograph showing HL

LONDON—Results of a small, phase 1 trial suggest CD30-directed chimeric antigen receptor (CAR) T-cell therapy is feasible in patients with aggressive Hodgkin lymphoma (HL).

The trial included 7 patients with relapsed or refractory HL.

Five of the patients achieved stable disease or better after infusions of CAR T cells, and the researchers said treatment-related adverse events were manageable.

William (Wei) Cao, PhD, of Cellular Biomedicine Group, presented these results at the 10th Annual World Stem Cells & Regenerative Medicine Congress.

The research was funded by Cellular Biomedicine Group, the company developing the CAR T-cell therapy (known as CBM-C30.1), as well as by grants from the National Natural Science Foundation of China and the National Basic Science and Development Program of China.

The trial included 7 patients with progressive HL. Two patients had stage III disease, and 5 had stage IV. The patients had a median of 16 prior treatments (range, 8-24) and limited prognosis (several months to less than 2-year survival) with currently available therapies.

The patients received escalating doses of autologous T cells transduced with a CD30-directed CAR moiety for 3 to 5 days, following a conditioning regimen. The researchers measured the level of CAR transgenes in peripheral blood and biopsied tumor tissues by quantitative PCR.

Two patients achieved a partial response to CAR T-cell therapy, and 3 attained stable disease. So the therapy resulted in an overall disease control rate of 71.4% (5/7) and an objective response rate of 28.6% (2/7).

Stable disease lasted 2 months in 2 of the patients and more than 3.5 months in the third patient. Partial response lasted more than 2 months in 1 patient and more than 3.5 months in the other.

Dr Cao said adverse events consisted largely of fever and were manageable with medical intervention. One patient experienced 5-day self-limiting arthralgia, myalgia, and dual knee swelling 2 weeks after cell infusion. There were no delayed or severe adverse events.

“We are very encouraged by the efficacy and toxicity profile of our CAR-T CD30 technology,” Dr Cao said, “given that the [patients] were diagnosed with stage III and IV Hodgkin’s lymphoma.”

Blood for transfusion

Photo by Elise Amendola

A patient blood management (PBM) program can reduce transfusion use, cut costs, and improve outcomes in cardiac surgery patients, according to a single-center study.

A PBM program instituted at Eastern Maine Medical Center (EMMC) in Bangor substantially decreased the use of blood products, the loss of red blood cells, the length of hospital stays, the incidence of acute kidney injury, and direct costs.

Irwin Gross, MD, of EMMC, and his colleagues reported these results in Transfusion.

The team compared clinical and transfusion data from cardiac surgery patients treated at the center before the PBM program began (July 2006-March 2007) and after (April 2007-September 2012).

EMMC’s PBM initiative involved pre- and post-operative anemia management, a more restrictive transfusion threshold, the use of single-unit transfusions when necessary, and other measures.

The researchers analyzed data on 2662 patients, 387 treated before the PBM program began and 2275 treated after.

As expected, the rate of transfusions decreased after the PBM program began. The rate of red blood cell transfusion decreased from 39.3% to 20.8% (P<0.001), the rate of fresh-frozen plasma transfusion decreased from 18.3% to 6.5% (P<0.001), and the rate of platelet transfusion decreased from 17.8% to 9.8% (P<0.001).

Red blood cell loss decreased from a median of 721 mL to 552 mL (P<0.001), and pre-transfusion hemoglobin decreased from a mean of 7.2 ± 1.4 g/dL to 6.6 ± 1.2 g/dL (P<0.001).

Patients saw a decrease in the incidence of post-operative kidney injury from 7.6% to 5.0% (P=0.039) and a decrease in the median length of hospital stay from 10 days to 8 days (P<0.001).

Total adjusted direct costs decreased after the program began as well, falling from a median of $39,709 to $36,906 (P< 0.001).

There was no significant difference in the rate of hospital mortality or the incidence of cerebral vascular accident before and after the PBM program began.

Blood for transfusion

Photo by Elise Amendola

A patient blood management (PBM) program can reduce transfusion use, cut costs, and improve outcomes in cardiac surgery patients, according to a single-center study.

A PBM program instituted at Eastern Maine Medical Center (EMMC) in Bangor substantially decreased the use of blood products, the loss of red blood cells, the length of hospital stays, the incidence of acute kidney injury, and direct costs.

Irwin Gross, MD, of EMMC, and his colleagues reported these results in Transfusion.

The team compared clinical and transfusion data from cardiac surgery patients treated at the center before the PBM program began (July 2006-March 2007) and after (April 2007-September 2012).

EMMC’s PBM initiative involved pre- and post-operative anemia management, a more restrictive transfusion threshold, the use of single-unit transfusions when necessary, and other measures.

The researchers analyzed data on 2662 patients, 387 treated before the PBM program began and 2275 treated after.

As expected, the rate of transfusions decreased after the PBM program began. The rate of red blood cell transfusion decreased from 39.3% to 20.8% (P<0.001), the rate of fresh-frozen plasma transfusion decreased from 18.3% to 6.5% (P<0.001), and the rate of platelet transfusion decreased from 17.8% to 9.8% (P<0.001).

Red blood cell loss decreased from a median of 721 mL to 552 mL (P<0.001), and pre-transfusion hemoglobin decreased from a mean of 7.2 ± 1.4 g/dL to 6.6 ± 1.2 g/dL (P<0.001).

Patients saw a decrease in the incidence of post-operative kidney injury from 7.6% to 5.0% (P=0.039) and a decrease in the median length of hospital stay from 10 days to 8 days (P<0.001).

Total adjusted direct costs decreased after the program began as well, falling from a median of $39,709 to $36,906 (P< 0.001).

There was no significant difference in the rate of hospital mortality or the incidence of cerebral vascular accident before and after the PBM program began.

Blood for transfusion

Photo by Elise Amendola

A patient blood management (PBM) program can reduce transfusion use, cut costs, and improve outcomes in cardiac surgery patients, according to a single-center study.

A PBM program instituted at Eastern Maine Medical Center (EMMC) in Bangor substantially decreased the use of blood products, the loss of red blood cells, the length of hospital stays, the incidence of acute kidney injury, and direct costs.

Irwin Gross, MD, of EMMC, and his colleagues reported these results in Transfusion.

The team compared clinical and transfusion data from cardiac surgery patients treated at the center before the PBM program began (July 2006-March 2007) and after (April 2007-September 2012).

EMMC’s PBM initiative involved pre- and post-operative anemia management, a more restrictive transfusion threshold, the use of single-unit transfusions when necessary, and other measures.

The researchers analyzed data on 2662 patients, 387 treated before the PBM program began and 2275 treated after.

As expected, the rate of transfusions decreased after the PBM program began. The rate of red blood cell transfusion decreased from 39.3% to 20.8% (P<0.001), the rate of fresh-frozen plasma transfusion decreased from 18.3% to 6.5% (P<0.001), and the rate of platelet transfusion decreased from 17.8% to 9.8% (P<0.001).

Red blood cell loss decreased from a median of 721 mL to 552 mL (P<0.001), and pre-transfusion hemoglobin decreased from a mean of 7.2 ± 1.4 g/dL to 6.6 ± 1.2 g/dL (P<0.001).

Patients saw a decrease in the incidence of post-operative kidney injury from 7.6% to 5.0% (P=0.039) and a decrease in the median length of hospital stay from 10 days to 8 days (P<0.001).

Total adjusted direct costs decreased after the program began as well, falling from a median of $39,709 to $36,906 (P< 0.001).

There was no significant difference in the rate of hospital mortality or the incidence of cerebral vascular accident before and after the PBM program began.

Pedicle subtraction osteotomies (PSOs) have been used in the treatment of multiple spinal conditions involving a fixed sagittal imbalance, such as degenerative scoliosis, idiopathic scoliosis, posttraumatic deformities, iatrogenic flatback syndrome, and ankylosing spondylitis. The procedure was first described by Thomasen¹ for the treatment of ankylosing spondylitis. More recently, multiple centers have reported the expanded use and good success of PSO in the treatment of fixed sagittal imbalance of other etiologies.^2,3 According to Bridwell and colleagues,² lumbar lordosis can be increased 34.1°, and sagittal plumb line can be improved 13.5 cm.

PSO is a complex, extensive surgery most often performed in the revision setting. Multiple authors have described the technique for PSO.^4,5 There are significant technical challenges and many complications, including neurologic deficits, pseudarthrosis of adjacent levels, and wound infections.⁶ Short-term challenges include a large loss of blood, 2.4 L on average, according to Bridwell and colleagues.⁶ Time of closure of the osteotomy gap is a crucial point in the surgery. Blood loss, often large, slows only after the gap is closed and stabilized.

In this article, we describe a technique in which an additional rod or pedicle screw construct is used at the periosteotomy levels to close the osteotomy gap during PSO and simplify subsequent instrumentation. In addition, we report our experience with the procedure.

Materials and Methods

Seventeen consecutive patients (mean age, 58 years; range, 12-81 years) with fixed sagittal imbalance were treated with lumbar PSO. The indication in all cases was flatback syndrome after previous spinal surgery. Mean follow-up was 13 months. Mean number of prior surgeries was 3. Thirteen PSOs were performed at L3, and 4 were performed at L2.

Radiographic data were collected from before surgery, in the immediate postoperative period, and at final follow-up. All the radiographs were standing films. Established radiographic parameters were measured: thoracic kyphosis from T5 to T12, lumbar lordosis from L1 to S1, PSO angle (1 level above to 1 level below osteotomy level), sagittal plumb line (from center of C7 body to posterosuperior aspect of S1 body), and coronal plumb line (from center of C7 body to center of S1 body).²

Good clinical outcomes in the treatment of spinal disorders require careful attention to the alignment of the spine in the sagittal plane.^7,8 When evaluating the preoperative radiographs, we measured and documented pelvic parameters. Figure 1A shows how pelvic incidence was determined. We measured this as the angle between a line drawn from the center of the S1 endplate to the center of the femoral head and the perpendicular off the S1 endplate. Figure 1B shows pelvic tilt as determined by the angle between a line drawn from the center of S1 to the femoral head and a vertical line originating from the center of the femoral head. Figure 1C shows the sacral slope, which we measured as the angle between a line drawn parallel to the endplate of S1 and its intersection with a horizontal line.

Surgical Technique

The overall surgical technique for PSO has been well described.^4,5 Here we describe the “outrigger” modification to osteotomy closure (Figures 2, 3).

Most of our 17 cases were revisions. In these cases, new fixation points are first established. All fixation points that will be needed for the final fusion are placed. If a pedicle above or below the osteotomy level is not suitable for a screw, it can be skipped.

Wide decompression of the involved level is performed from pedicle to pedicle, ensuring that the nerve roots are completely decompressed. The dissection is then continued around the lateral wall of the vertebral body. While the neural elements are protected with gentle retraction, the pedicle and a portion of the posterior aspect of the vertebral body are removed with a combination of a rongeur and reverse-angle curettes. Resection of the vertebral body can be facilitated by attaching a short rod to the pedicle screws on either side of the osteotomy level and using it to provide gentle distraction.

Once sufficient bone has been removed to close the osteotomy, short rods are placed in the pedicle screws in the level above and the level below the osteotomy site. These rods are attached with offset connectors that allow the rods to be placed lateral to the screws. Before the surgical procedure is started, the patient is positioned on 2 sets of posts separated by the break in the table. The break in the table allows flexion to accommodate the preoperative kyphosis and allows hyperextension to help close the osteotomy site. Now, with the osteotomy site ready for closure, the table is gradually positioned in extension along with a combination of posterior pressure and compression between the pedicle screws above and below the osteotomy. Once the osteotomy is adequately compressed, the short rods are tightened, holding the osteotomy in good position. With the osteotomy held by the short rods and table positioning, decompression of the neural elements is confirmed and hemostasis obtained.

Final instrumentation is then performed with long rods that can bypass the osteotomized levels, allowing for simpler contouring. If desired, a cross connector can be placed between the long rod of the fusion construct and the short rod holding the osteotomy. The rest of the fusion procedure is completed in standard fashion with at least 1 subfascial drain.

Results

Our 17 patients’ results are summarized in the Table. Mean sagittal plumb line improved from 17.7 cm (range, 5.9 to 29 cm) before surgery to 4.5 cm (range, –0.2 to 12.9 cm) after surgery, for a mean improvement of 13.2 cm. At final follow-up, mean sagittal plumb line was 5.1 cm (range, –1.4 to 10.2 cm).

Mean lumbar lordosis improved from 10° (range, –14° to 34°) before surgery to 49° (range, 36° to 63°) after surgery, for a mean improvement of 39°. Mean PSO angle improved from 3° (range, –36° to 23°) before surgery to 41° (range, 25° to 65°) after surgery, for a mean improvement of 38°. At final follow-up, mean lumbar lordosis remained at 47° (range, 26° to 64°), and mean PSO angle was 39° (range, 24° to 59°).

Mean thoracic kyphosis improved from 18° (range, –8° to 52°) before surgery to 30° (range, 3° to 58°) after surgery, for a mean improvement of 12°. At final follow-up, mean thoracic kyphosis was 31° (range, 2° to 57°).

Fourteen patients did not have complications during the study period. Of the 3 patients with complications, 1 had an early infection, treated effectively with irrigation and débridement and intravenous antibiotics; 1 had a late deep infection, treated with multiple débridements, hardware removal, and, eventually, suppressive antibiotics; and 1 had cauda equina syndrome (caused by extensive scar tissue on the dura, which buckled with restoration of lordosis leading to cord compression), treated with duraplasty, which resulted in full neurologic recovery.

Discussion

In the present series of patients, the described technique for facilitating PSO for correction of sagittal imbalance was effective, and complications were similar to those previously reported.

The benefit of the outrigger construct is that it allows controlled compression of the osteotomy site and can be left in place at time of final instrumentation, locking in compression and correction. Other techniques involve removing the temporary rod and replacing it with final instrumentation^4,5—an extra step that complicates instrumentation of the additional levels of the fusion construct and possibly adds pedicle screw stress and contributes to loosening when the new rod is reduced to the pedicle screw. The final long rod construct can bypass the osteotomy levels and allow for simpler instrumentation.

 Mean age was 58 years in this series versus 52.4 years in the series reported by Bridwell and colleagues.² Given the higher mean age of our patients, though no objective measures of bone quality were available, this technique is likely applicable to patients with poor bone quality.

The complications we have reported are in line with those reported in previous series, and maintenance of radiographic parameters at final follow-up indicates that this osteotomy technique allows for solid fusion constructs.

The outrigger technique for controlling PSO closure is an effective method that simplifies instrumentation during a complex revision case.

Pedicle subtraction osteotomies (PSOs) have been used in the treatment of multiple spinal conditions involving a fixed sagittal imbalance, such as degenerative scoliosis, idiopathic scoliosis, posttraumatic deformities, iatrogenic flatback syndrome, and ankylosing spondylitis. The procedure was first described by Thomasen¹ for the treatment of ankylosing spondylitis. More recently, multiple centers have reported the expanded use and good success of PSO in the treatment of fixed sagittal imbalance of other etiologies.^2,3 According to Bridwell and colleagues,² lumbar lordosis can be increased 34.1°, and sagittal plumb line can be improved 13.5 cm.

PSO is a complex, extensive surgery most often performed in the revision setting. Multiple authors have described the technique for PSO.^4,5 There are significant technical challenges and many complications, including neurologic deficits, pseudarthrosis of adjacent levels, and wound infections.⁶ Short-term challenges include a large loss of blood, 2.4 L on average, according to Bridwell and colleagues.⁶ Time of closure of the osteotomy gap is a crucial point in the surgery. Blood loss, often large, slows only after the gap is closed and stabilized.

In this article, we describe a technique in which an additional rod or pedicle screw construct is used at the periosteotomy levels to close the osteotomy gap during PSO and simplify subsequent instrumentation. In addition, we report our experience with the procedure.

Materials and Methods

Seventeen consecutive patients (mean age, 58 years; range, 12-81 years) with fixed sagittal imbalance were treated with lumbar PSO. The indication in all cases was flatback syndrome after previous spinal surgery. Mean follow-up was 13 months. Mean number of prior surgeries was 3. Thirteen PSOs were performed at L3, and 4 were performed at L2.

Radiographic data were collected from before surgery, in the immediate postoperative period, and at final follow-up. All the radiographs were standing films. Established radiographic parameters were measured: thoracic kyphosis from T5 to T12, lumbar lordosis from L1 to S1, PSO angle (1 level above to 1 level below osteotomy level), sagittal plumb line (from center of C7 body to posterosuperior aspect of S1 body), and coronal plumb line (from center of C7 body to center of S1 body).²

Good clinical outcomes in the treatment of spinal disorders require careful attention to the alignment of the spine in the sagittal plane.^7,8 When evaluating the preoperative radiographs, we measured and documented pelvic parameters. Figure 1A shows how pelvic incidence was determined. We measured this as the angle between a line drawn from the center of the S1 endplate to the center of the femoral head and the perpendicular off the S1 endplate. Figure 1B shows pelvic tilt as determined by the angle between a line drawn from the center of S1 to the femoral head and a vertical line originating from the center of the femoral head. Figure 1C shows the sacral slope, which we measured as the angle between a line drawn parallel to the endplate of S1 and its intersection with a horizontal line.

Surgical Technique

The overall surgical technique for PSO has been well described.^4,5 Here we describe the “outrigger” modification to osteotomy closure (Figures 2, 3).

Most of our 17 cases were revisions. In these cases, new fixation points are first established. All fixation points that will be needed for the final fusion are placed. If a pedicle above or below the osteotomy level is not suitable for a screw, it can be skipped.

Wide decompression of the involved level is performed from pedicle to pedicle, ensuring that the nerve roots are completely decompressed. The dissection is then continued around the lateral wall of the vertebral body. While the neural elements are protected with gentle retraction, the pedicle and a portion of the posterior aspect of the vertebral body are removed with a combination of a rongeur and reverse-angle curettes. Resection of the vertebral body can be facilitated by attaching a short rod to the pedicle screws on either side of the osteotomy level and using it to provide gentle distraction.

Once sufficient bone has been removed to close the osteotomy, short rods are placed in the pedicle screws in the level above and the level below the osteotomy site. These rods are attached with offset connectors that allow the rods to be placed lateral to the screws. Before the surgical procedure is started, the patient is positioned on 2 sets of posts separated by the break in the table. The break in the table allows flexion to accommodate the preoperative kyphosis and allows hyperextension to help close the osteotomy site. Now, with the osteotomy site ready for closure, the table is gradually positioned in extension along with a combination of posterior pressure and compression between the pedicle screws above and below the osteotomy. Once the osteotomy is adequately compressed, the short rods are tightened, holding the osteotomy in good position. With the osteotomy held by the short rods and table positioning, decompression of the neural elements is confirmed and hemostasis obtained.

Final instrumentation is then performed with long rods that can bypass the osteotomized levels, allowing for simpler contouring. If desired, a cross connector can be placed between the long rod of the fusion construct and the short rod holding the osteotomy. The rest of the fusion procedure is completed in standard fashion with at least 1 subfascial drain.

Results

Our 17 patients’ results are summarized in the Table. Mean sagittal plumb line improved from 17.7 cm (range, 5.9 to 29 cm) before surgery to 4.5 cm (range, –0.2 to 12.9 cm) after surgery, for a mean improvement of 13.2 cm. At final follow-up, mean sagittal plumb line was 5.1 cm (range, –1.4 to 10.2 cm).

Mean lumbar lordosis improved from 10° (range, –14° to 34°) before surgery to 49° (range, 36° to 63°) after surgery, for a mean improvement of 39°. Mean PSO angle improved from 3° (range, –36° to 23°) before surgery to 41° (range, 25° to 65°) after surgery, for a mean improvement of 38°. At final follow-up, mean lumbar lordosis remained at 47° (range, 26° to 64°), and mean PSO angle was 39° (range, 24° to 59°).

Mean thoracic kyphosis improved from 18° (range, –8° to 52°) before surgery to 30° (range, 3° to 58°) after surgery, for a mean improvement of 12°. At final follow-up, mean thoracic kyphosis was 31° (range, 2° to 57°).

Fourteen patients did not have complications during the study period. Of the 3 patients with complications, 1 had an early infection, treated effectively with irrigation and débridement and intravenous antibiotics; 1 had a late deep infection, treated with multiple débridements, hardware removal, and, eventually, suppressive antibiotics; and 1 had cauda equina syndrome (caused by extensive scar tissue on the dura, which buckled with restoration of lordosis leading to cord compression), treated with duraplasty, which resulted in full neurologic recovery.

Discussion

In the present series of patients, the described technique for facilitating PSO for correction of sagittal imbalance was effective, and complications were similar to those previously reported.

The benefit of the outrigger construct is that it allows controlled compression of the osteotomy site and can be left in place at time of final instrumentation, locking in compression and correction. Other techniques involve removing the temporary rod and replacing it with final instrumentation^4,5—an extra step that complicates instrumentation of the additional levels of the fusion construct and possibly adds pedicle screw stress and contributes to loosening when the new rod is reduced to the pedicle screw. The final long rod construct can bypass the osteotomy levels and allow for simpler instrumentation.

 Mean age was 58 years in this series versus 52.4 years in the series reported by Bridwell and colleagues.² Given the higher mean age of our patients, though no objective measures of bone quality were available, this technique is likely applicable to patients with poor bone quality.

The complications we have reported are in line with those reported in previous series, and maintenance of radiographic parameters at final follow-up indicates that this osteotomy technique allows for solid fusion constructs.

The outrigger technique for controlling PSO closure is an effective method that simplifies instrumentation during a complex revision case.

Pedicle subtraction osteotomies (PSOs) have been used in the treatment of multiple spinal conditions involving a fixed sagittal imbalance, such as degenerative scoliosis, idiopathic scoliosis, posttraumatic deformities, iatrogenic flatback syndrome, and ankylosing spondylitis. The procedure was first described by Thomasen¹ for the treatment of ankylosing spondylitis. More recently, multiple centers have reported the expanded use and good success of PSO in the treatment of fixed sagittal imbalance of other etiologies.^2,3 According to Bridwell and colleagues,² lumbar lordosis can be increased 34.1°, and sagittal plumb line can be improved 13.5 cm.

PSO is a complex, extensive surgery most often performed in the revision setting. Multiple authors have described the technique for PSO.^4,5 There are significant technical challenges and many complications, including neurologic deficits, pseudarthrosis of adjacent levels, and wound infections.⁶ Short-term challenges include a large loss of blood, 2.4 L on average, according to Bridwell and colleagues.⁶ Time of closure of the osteotomy gap is a crucial point in the surgery. Blood loss, often large, slows only after the gap is closed and stabilized.

In this article, we describe a technique in which an additional rod or pedicle screw construct is used at the periosteotomy levels to close the osteotomy gap during PSO and simplify subsequent instrumentation. In addition, we report our experience with the procedure.

Materials and Methods

Seventeen consecutive patients (mean age, 58 years; range, 12-81 years) with fixed sagittal imbalance were treated with lumbar PSO. The indication in all cases was flatback syndrome after previous spinal surgery. Mean follow-up was 13 months. Mean number of prior surgeries was 3. Thirteen PSOs were performed at L3, and 4 were performed at L2.

Radiographic data were collected from before surgery, in the immediate postoperative period, and at final follow-up. All the radiographs were standing films. Established radiographic parameters were measured: thoracic kyphosis from T5 to T12, lumbar lordosis from L1 to S1, PSO angle (1 level above to 1 level below osteotomy level), sagittal plumb line (from center of C7 body to posterosuperior aspect of S1 body), and coronal plumb line (from center of C7 body to center of S1 body).²

Good clinical outcomes in the treatment of spinal disorders require careful attention to the alignment of the spine in the sagittal plane.^7,8 When evaluating the preoperative radiographs, we measured and documented pelvic parameters. Figure 1A shows how pelvic incidence was determined. We measured this as the angle between a line drawn from the center of the S1 endplate to the center of the femoral head and the perpendicular off the S1 endplate. Figure 1B shows pelvic tilt as determined by the angle between a line drawn from the center of S1 to the femoral head and a vertical line originating from the center of the femoral head. Figure 1C shows the sacral slope, which we measured as the angle between a line drawn parallel to the endplate of S1 and its intersection with a horizontal line.

Surgical Technique

The overall surgical technique for PSO has been well described.^4,5 Here we describe the “outrigger” modification to osteotomy closure (Figures 2, 3).

Most of our 17 cases were revisions. In these cases, new fixation points are first established. All fixation points that will be needed for the final fusion are placed. If a pedicle above or below the osteotomy level is not suitable for a screw, it can be skipped.

Wide decompression of the involved level is performed from pedicle to pedicle, ensuring that the nerve roots are completely decompressed. The dissection is then continued around the lateral wall of the vertebral body. While the neural elements are protected with gentle retraction, the pedicle and a portion of the posterior aspect of the vertebral body are removed with a combination of a rongeur and reverse-angle curettes. Resection of the vertebral body can be facilitated by attaching a short rod to the pedicle screws on either side of the osteotomy level and using it to provide gentle distraction.

Once sufficient bone has been removed to close the osteotomy, short rods are placed in the pedicle screws in the level above and the level below the osteotomy site. These rods are attached with offset connectors that allow the rods to be placed lateral to the screws. Before the surgical procedure is started, the patient is positioned on 2 sets of posts separated by the break in the table. The break in the table allows flexion to accommodate the preoperative kyphosis and allows hyperextension to help close the osteotomy site. Now, with the osteotomy site ready for closure, the table is gradually positioned in extension along with a combination of posterior pressure and compression between the pedicle screws above and below the osteotomy. Once the osteotomy is adequately compressed, the short rods are tightened, holding the osteotomy in good position. With the osteotomy held by the short rods and table positioning, decompression of the neural elements is confirmed and hemostasis obtained.

Final instrumentation is then performed with long rods that can bypass the osteotomized levels, allowing for simpler contouring. If desired, a cross connector can be placed between the long rod of the fusion construct and the short rod holding the osteotomy. The rest of the fusion procedure is completed in standard fashion with at least 1 subfascial drain.

Results

Our 17 patients’ results are summarized in the Table. Mean sagittal plumb line improved from 17.7 cm (range, 5.9 to 29 cm) before surgery to 4.5 cm (range, –0.2 to 12.9 cm) after surgery, for a mean improvement of 13.2 cm. At final follow-up, mean sagittal plumb line was 5.1 cm (range, –1.4 to 10.2 cm).

Mean lumbar lordosis improved from 10° (range, –14° to 34°) before surgery to 49° (range, 36° to 63°) after surgery, for a mean improvement of 39°. Mean PSO angle improved from 3° (range, –36° to 23°) before surgery to 41° (range, 25° to 65°) after surgery, for a mean improvement of 38°. At final follow-up, mean lumbar lordosis remained at 47° (range, 26° to 64°), and mean PSO angle was 39° (range, 24° to 59°).

Mean thoracic kyphosis improved from 18° (range, –8° to 52°) before surgery to 30° (range, 3° to 58°) after surgery, for a mean improvement of 12°. At final follow-up, mean thoracic kyphosis was 31° (range, 2° to 57°).

Fourteen patients did not have complications during the study period. Of the 3 patients with complications, 1 had an early infection, treated effectively with irrigation and débridement and intravenous antibiotics; 1 had a late deep infection, treated with multiple débridements, hardware removal, and, eventually, suppressive antibiotics; and 1 had cauda equina syndrome (caused by extensive scar tissue on the dura, which buckled with restoration of lordosis leading to cord compression), treated with duraplasty, which resulted in full neurologic recovery.

Discussion

In the present series of patients, the described technique for facilitating PSO for correction of sagittal imbalance was effective, and complications were similar to those previously reported.

The benefit of the outrigger construct is that it allows controlled compression of the osteotomy site and can be left in place at time of final instrumentation, locking in compression and correction. Other techniques involve removing the temporary rod and replacing it with final instrumentation^4,5—an extra step that complicates instrumentation of the additional levels of the fusion construct and possibly adds pedicle screw stress and contributes to loosening when the new rod is reduced to the pedicle screw. The final long rod construct can bypass the osteotomy levels and allow for simpler instrumentation.

 Mean age was 58 years in this series versus 52.4 years in the series reported by Bridwell and colleagues.² Given the higher mean age of our patients, though no objective measures of bone quality were available, this technique is likely applicable to patients with poor bone quality.

The complications we have reported are in line with those reported in previous series, and maintenance of radiographic parameters at final follow-up indicates that this osteotomy technique allows for solid fusion constructs.

The outrigger technique for controlling PSO closure is an effective method that simplifies instrumentation during a complex revision case.

In the United States, surgeons perform an estimated 200,000 anterior cruciate ligament reconstructions (ACLRs) each year. Over the past decade, there has been a surge in interest in defining anterior cruciate ligament (ACL) anatomy to guide ACLR. With this renewed interest in the anatomical features of the ACL, particularly the insertion site, many authors have advocated an approach for complete or near-complete “footprint restoration” for anatomical ACLR.^1,2 Some have recommended a double-bundle (DB) technique that completely “fills” the footprint, but it is seldom used. Others have proposed centralizing the femoral tunnel position within the ACL footprint in the hope of capturing the function of both the anteromedial (AM) and posterolateral (PL) bundles.^1,3,4 Indeed, a primary surgical goal of most anatomical ACLR techniques is creation of a femoral tunnel based off the anatomical centrum (center point) of the ACL femoral footprint.^3,5 With a single-bundle technique, the femoral socket is localized in the center of the entire footprint; with a DB technique, sockets are created in the centrums of both the AM and PL bundles.

Because of the complex shape of the native ACL, however, the strategy of restoring the femoral footprint with use of either a central tunnel or a DB approach has been challenged. The femoral footprint is 3.5 times larger than the midsubstance of the ACL.⁶ Detailed anatomical dissections have recently demonstrated that the femoral origin of the ACL has a stout anterior band of fibers with a fanlike extension posteriorly.⁷ As the ACL fibers extend off the bony footprint, they form a flat, ribbonlike structure 9 to 16 mm wide and only 2 to 4 mm thick.^2,8 Within this structure, there is no clear separation of the AM and PL bundles. The presence of this structure makes sense given the anatomical constraints inherent in the notch. Indeed, the space for the native ACL is narrow, as the posterior cruciate ligament (PCL) occupies that largest portion of the notch with the knee in full extension, leaving only a thin, 5-mm slot through which the ACL must pass.⁹ Therefore, filling the femoral footprint with a tubular ACL graft probably does not reproduce the dynamic 3-dimensional morphology of the ACL.

In light of the discrepancy between the sizes of the femoral footprint and the midsubstance of the native ACL, it seems reasonable that optimizing the position of the ACL femoral tunnel may be more complex than simply centralizing the tunnel within the footprint or attempting to maximize footprint coverage. In this article, we amalgamate the lessons of 4 decades of ACL research into 5 points for strategic femoral tunnel positioning, based on anatomical, histologic, isometric, biomechanical, and clinical data. These points are summarized by the acronym I.D.E.A.L., which refers to placing a femoral tunnel in a position that reproduces the Isometry of the native ACL, that covers the fibers of the Direct insertion histologically, that is Eccentrically located in the anterior (high) and proximal (deep) region of the footprint, that is Anatomical (within the footprint), and that replicates the Low tension-flexion pattern of the native ACL throughout the range of flexion and extension.

1. Anatomy Considerations

In response to study results demonstrating that some transtibial ACLRs were associated with nonanatomical placement of the femoral tunnel—resulting in vertical graft placement, PCL impingement, and recurrent rotational instability^10-16—investigators have reexamined both the anatomy of the femoral origin of the native ACL and the ACL graft. Specifically, a large body of research has been devoted to characterizing the osseous landmarks of the femoral origin of the ACL¹⁷ and the dimensions of the femoral footprint.³ In addition, authors have supported the concept that the ACL contains 2 functional bundles, AM and PL.^5,17 Several osseous landmarks have been identified as defining the boundaries of the femoral footprint. The lateral intercondylar ridge is the most anterior aspect of the femoral footprint and was first defined by Clancy.¹⁸ More recently, the lateral bifurcate ridge, which separates the AM and PL bundle insertion sites, was described¹⁹ (Figure 1A).

These osseous ridges delineate the location of the femoral footprint. Studies have shown that ACL fibers attach from the lateral intercondylar ridge on the anterior border of the femoral footprint and extend posteriorly to the cartilage of the lateral femoral condyle (Figure 1B).

ACL fibers from this oblong footprint are organized such that the midsubstance of the ACL is narrower than the femoral footprint. Anatomical dissections have demonstrated that, though the femoral footprint is oval, the native ACL forms a flat, ribbonlike structure 9 to 16 mm wide and only 2 to 4 mm thick as it takes off from the bone.^8,20 There is a resulting discrepancy between the femoral footprint size and shape and the morphology of the native ACL, and placing a tunnel in the center of the footprint or “filling the footprint” with ACL graft may not reproduce the morphology or function of the native ACL. Given this size mismatch, strategic decisions need to be made to place the femoral tunnel in a specific region of the femoral footprint to optimize its function.

2. Histologic Findings

Histologic analysis has further clarified the relationship between the femoral footprint and functional aspects of the native ACL. The femoral origin of the ACL has distinct direct and indirect insertions, as demonstrated by histology and 3-dimensional volume-rendered computed tomography.²¹ The direct insertion consists of dense collagen fibers anterior in the footprint that is attached to a bony depression immediately posterior to the lateral intercondylar ridge.¹⁹ Sasaki and colleagues²² found that these direct fibers extended a mean (SD) of 5.3 (1.1) mm posteriorly but did not continue to the posterior femoral articular cartilage. The indirect insertion consists of more posterior collagen fibers that extend to and blend into the articular cartilage of the posterior aspect of the lateral femoral condyle. Mean (SD) width of this membrane-like tissue, located between the direct insertion and the posterior femoral articular cartilage, was found by Sasaki and colleagues²²  to be 4.4 (0.5) mm anteroposteriorly(Figure 2). This anterior band of ACL tissue with the direct insertion histologically corresponds to the fibers in the anterior, more isometric region of the femoral footprint. Conversely, the more posterior band of fibers with its indirect insertion histologically corresponds to the more anisometric region and is seen macroscopically as a fanlike projection extending to the posterior articular cartilage.⁷

The dense collagen fibers of the direct insertion and the more membrane-like indirect insertion regions of the femoral footprint of the native ACL suggest that these regions have different load-sharing characteristics. The direct fibers of the insertion form a firm, fixed attachment that allows for gradual load distribution into the subchondral bone. From a biomechanical point of view, this attachment is extremely important, a key ligament–bone link transmitting mechanical load to the joint.²³ A recent kinematic analysis revealed that the indirect fibers in the posterior region of the footprint, adjacent to the posterior articular cartilage, contribute minimally to restraint of tibial translation and rotations during stability examination.²⁴ This suggests it may be strategically wise to place a tunnel in the direct insertion region of the footprint—eccentrically anterior (high) in the footprint rather than in the centrum.

3. Isometric Considerations

Forty years ago, Artmann and Wirth²⁵ reported that a nearly isometric region existed in the femur such that there is minimal elongation of the native ACL during knee motion. The biomechanical rationale for choosing an isometric region of an ACL graft is that it will maintain function throughout the range of flexion and extension. A nonisometric graft would be expected to slacken during a large portion of the flexion cycle and not restrain anterior translation of the tibia, or, if fixed at the wrong flexion angle, it could capture the knee and cause graft failure by excessive tension. These 2 theoretical undesirable effects from nonisometric graft placement are supported by many experimental and clinical studies demonstrating that nonisometric femoral tunnel placement at time of surgery can cause recurrent anterior laxity of the knee.^26-28 Multiple studies have further clarified that the isometric characteristics of an ACL graft are largely determined by femoral positioning. The most isometric region of the femoral footprint is consistently shown to be localized eccentrically within the footprint, in a relatively narrow bandlike region that is proximal (deep) and anterior (along the lateral intercondylar ridge within the footprint)^19,29,30 (Figure 3).

A large body of literature has demonstrated that a tunnel placed in the center of the femoral footprint is less isometric than a tunnel in the more anterior region.^25,29,31,32 Indeed, the anterior position (high in the footprint) identified by Hefzy and colleagues²⁹ demonstrated minimal anisometry with 1 to 4 mm of length change through the range of motion. In contrast, a central tunnel would be expected to demonstrate 5 to 7 mm of length change, whereas a lower graft (in the PL region of the footprint) would demonstrate about 1 cm of length change through the range of motion.^31,32 As such, central grafts, or grafts placed in the PL portion of the femoral footprint, would be expected to see high tension or graft forces as the knee is flexed, or to lose tension completely if the graft is fixed at full extension.³²

Importantly, Markolf and colleagues³³ reported that the native ACL does not behave exactly in a so-called isometric fashion during the last 30° of extension. They showed that about 3 mm of retraction of a trial wire into the joint during the last 30° of extension (as measured with an isometer) is reasonable to achieve graft length changes approximating those of the intact ACL. Given this important caveat, a primary goal for ACLR is placement of the femoral tunnel within this isometric region so that the length change in the ACL graft is minimized to 3 mm from 30° to full flexion. In addition, results of a time-zero biomechanical study suggested better rotational control with anatomical femoral tunnel position than with an isometric femoral tunnel³⁴ placed outside the femoral footprint. Therefore, maximizing isometry alone is not the goal; placing the graft in the most isometric region within the anatomical femoral footprint is desired. This isometric region in the footprint is in the histologic region that corresponds to the direct fibers. Again, this region is eccentrically located in the anterior (high) and proximal (deep) portion of the footprint.

4. Biomechanical Considerations

Multiple cadaveric studies have investigated the relationship between femoral tunnel positioning and time-zero stability. These studies often demonstrated superior time-zero control of knee stability, particularly in pivot type maneuvers, with a femoral tunnel placed more centrally in the femoral footprint than with a tunnel placed outside the footprint.^34-37 However, an emerging body of literature is finding no significant difference in time-zero stability between an anteriorly placed femoral tunnel within the anatomical footprint (eccentrically located in the footprint) and a centrally placed graft.^38,39 Returning to the more isometric tunnel position, still within the femoral footprint, would be expected to confer the benefits of an anatomically based graft position with the advantageous profile of improved isometry, as compared with a centrally placed or PL graft. Biomechanical studies⁴⁰ have documented that ACL graft fibers placed posteriorly (low) in the footprint cause high graft forces in extension and, in some cases, graft rupture (Figure 4). Accordingly, the importance of reconstructing the posterior region of the footprint to better control time-zero stability is questioned.⁴¹

In addition to time-zero control of the stability examination, restoring the low tension-flexion pattern in the ACL graft to replicate the tension-flexion behavior of the native ACL is a fundamental biomechanical principle of ACLR.^15,33,42,43 These studies have demonstrated that a femoral tunnel localized anterior (high) and proximal (deep) within the footprint better replicates the tension-flexion behavior of the native ACL, as compared with strategies that attempt to anatomically “fill the footprint.”⁴⁰ Together, these studies have demonstrated that an eccentric position in the footprint, in the anterior (high) and proximal (deep) region, not only maximizes isometry and restores the direct fibers, but provides favorable time-zero stability and a low tension-flexion pattern biomechanically, particularly as compared with a tunnel in the more central or posterior region of the footprint.

5. Clinical Data

Clinical studies of the traditional transtibial ACLR have shown good results.^44,45 However, when the tibial tunnel in the coronal plane was drilled vertical with respect to the medial joint line of the tibia, the transtibially placed femoral tunnel migrated anterior to the anatomical femoral footprint, often on the roof of the notch.^10,14 This nonanatomical, vertical placement of the femoral tunnel led to failed normalization of knee kinematics.^46-50 Indeed, a higher tension-flexion pattern was found in this nonanatomical “roof” position for the femoral tunnel as compared with the native ACL—a pattern that can result in either loss of flexion or recurrent instability.^13,15,51

Clinical results of techniques used to create an anatomical ACLR centrally within the footprint have been mixed. Registry data showed that the revision rate at 4 years was higher with the AM portal technique (5.16%) than with transtibial drilling (3.20%).⁵² This higher rate may be associated with the more central placement of the femoral tunnel with the AM portal technique than with the transtibial technique, as shown in vivo with high-resolution magnetic resonance imaging.¹² Recent reports have documented a higher rate of failure with DB or central ACLR approaches than with traditional transtibial techniques.⁵³ As mentioned, in contrast to a more isometric position, a central femoral tunnel position would be expected to demonstrate 5 to 7 mm of length change, whereas moving the graft more posterior in the footprint (closer to the articular cartilage) would result in more than 1 cm of length change through the range of motion.^31,32 As such, these more central grafts, or grafts placed even lower (more posterior) in the footprint, would be expected to see high tension in extension (if fixed in flexion), or to lose tension completely during flexion (if the graft is fixed at full extension).³² This may be a mechanistic cause of the high failure rate in the more posterior bundles of the DB approach.⁵⁴

Together, these clinical data suggest that the femoral tunnel should be placed within the anatomical footprint of the ACL. However, within the footprint, a more eccentric femoral tunnel position capturing the isometric and direct region of the insertion may be preferable to a more central or posterior (low region) position.

Summary

Anatomical, histologic, isometric, biomechanical, and clinical data from more than 4 decades collectively point to an optimal position for the femoral tunnel within the femoral footprint. This position can be summarized by the acronym I.D.E.A.L., which refers to placing a femoral tunnel in a position that reproduces the Isometry of the native ACL, that covers the fibers of the Direct insertion histologically, that is Eccentrically located in the anterior (high) and proximal (deep) region of the footprint, that is Anatomical (within the footprint), and that replicates the Low tension-flexion pattern of the native ACL throughout the range of flexion and extension (Figure 5).

In vivo and in vitro studies as well as surgical experience suggest a need to avoid both (a) the nonanatomical vertical (roof) femoral tunnel placement that causes PCL impingement, high tension in the ACL graft in flexion, and ultimately graft stretch-out with instability and (b) the femoral tunnel placement in the posterior (lowest) region of the footprint that causes high tension in extension and can result in graft stretch-out with instability.^13,15,39,40 The transtibial and AM portal techniques can both be effective in properly placing the femoral tunnel and restoring motion, stability, and function to the knee. Their effectiveness, however, depends on correct placement of the femoral tunnel. We think coming studies will focus on single-bundle ACLR and will be designed to improve the reliability of the transtibial and AM portal techniques for placing a femoral tunnel in keeping with the principles summarized by the I.D.E.A.L. acronym.

In the United States, surgeons perform an estimated 200,000 anterior cruciate ligament reconstructions (ACLRs) each year. Over the past decade, there has been a surge in interest in defining anterior cruciate ligament (ACL) anatomy to guide ACLR. With this renewed interest in the anatomical features of the ACL, particularly the insertion site, many authors have advocated an approach for complete or near-complete “footprint restoration” for anatomical ACLR.^1,2 Some have recommended a double-bundle (DB) technique that completely “fills” the footprint, but it is seldom used. Others have proposed centralizing the femoral tunnel position within the ACL footprint in the hope of capturing the function of both the anteromedial (AM) and posterolateral (PL) bundles.^1,3,4 Indeed, a primary surgical goal of most anatomical ACLR techniques is creation of a femoral tunnel based off the anatomical centrum (center point) of the ACL femoral footprint.^3,5 With a single-bundle technique, the femoral socket is localized in the center of the entire footprint; with a DB technique, sockets are created in the centrums of both the AM and PL bundles.

Because of the complex shape of the native ACL, however, the strategy of restoring the femoral footprint with use of either a central tunnel or a DB approach has been challenged. The femoral footprint is 3.5 times larger than the midsubstance of the ACL.⁶ Detailed anatomical dissections have recently demonstrated that the femoral origin of the ACL has a stout anterior band of fibers with a fanlike extension posteriorly.⁷ As the ACL fibers extend off the bony footprint, they form a flat, ribbonlike structure 9 to 16 mm wide and only 2 to 4 mm thick.^2,8 Within this structure, there is no clear separation of the AM and PL bundles. The presence of this structure makes sense given the anatomical constraints inherent in the notch. Indeed, the space for the native ACL is narrow, as the posterior cruciate ligament (PCL) occupies that largest portion of the notch with the knee in full extension, leaving only a thin, 5-mm slot through which the ACL must pass.⁹ Therefore, filling the femoral footprint with a tubular ACL graft probably does not reproduce the dynamic 3-dimensional morphology of the ACL.

In light of the discrepancy between the sizes of the femoral footprint and the midsubstance of the native ACL, it seems reasonable that optimizing the position of the ACL femoral tunnel may be more complex than simply centralizing the tunnel within the footprint or attempting to maximize footprint coverage. In this article, we amalgamate the lessons of 4 decades of ACL research into 5 points for strategic femoral tunnel positioning, based on anatomical, histologic, isometric, biomechanical, and clinical data. These points are summarized by the acronym I.D.E.A.L., which refers to placing a femoral tunnel in a position that reproduces the Isometry of the native ACL, that covers the fibers of the Direct insertion histologically, that is Eccentrically located in the anterior (high) and proximal (deep) region of the footprint, that is Anatomical (within the footprint), and that replicates the Low tension-flexion pattern of the native ACL throughout the range of flexion and extension.

1. Anatomy Considerations

In response to study results demonstrating that some transtibial ACLRs were associated with nonanatomical placement of the femoral tunnel—resulting in vertical graft placement, PCL impingement, and recurrent rotational instability^10-16—investigators have reexamined both the anatomy of the femoral origin of the native ACL and the ACL graft. Specifically, a large body of research has been devoted to characterizing the osseous landmarks of the femoral origin of the ACL¹⁷ and the dimensions of the femoral footprint.³ In addition, authors have supported the concept that the ACL contains 2 functional bundles, AM and PL.^5,17 Several osseous landmarks have been identified as defining the boundaries of the femoral footprint. The lateral intercondylar ridge is the most anterior aspect of the femoral footprint and was first defined by Clancy.¹⁸ More recently, the lateral bifurcate ridge, which separates the AM and PL bundle insertion sites, was described¹⁹ (Figure 1A).

These osseous ridges delineate the location of the femoral footprint. Studies have shown that ACL fibers attach from the lateral intercondylar ridge on the anterior border of the femoral footprint and extend posteriorly to the cartilage of the lateral femoral condyle (Figure 1B).

ACL fibers from this oblong footprint are organized such that the midsubstance of the ACL is narrower than the femoral footprint. Anatomical dissections have demonstrated that, though the femoral footprint is oval, the native ACL forms a flat, ribbonlike structure 9 to 16 mm wide and only 2 to 4 mm thick as it takes off from the bone.^8,20 There is a resulting discrepancy between the femoral footprint size and shape and the morphology of the native ACL, and placing a tunnel in the center of the footprint or “filling the footprint” with ACL graft may not reproduce the morphology or function of the native ACL. Given this size mismatch, strategic decisions need to be made to place the femoral tunnel in a specific region of the femoral footprint to optimize its function.

2. Histologic Findings

Histologic analysis has further clarified the relationship between the femoral footprint and functional aspects of the native ACL. The femoral origin of the ACL has distinct direct and indirect insertions, as demonstrated by histology and 3-dimensional volume-rendered computed tomography.²¹ The direct insertion consists of dense collagen fibers anterior in the footprint that is attached to a bony depression immediately posterior to the lateral intercondylar ridge.¹⁹ Sasaki and colleagues²² found that these direct fibers extended a mean (SD) of 5.3 (1.1) mm posteriorly but did not continue to the posterior femoral articular cartilage. The indirect insertion consists of more posterior collagen fibers that extend to and blend into the articular cartilage of the posterior aspect of the lateral femoral condyle. Mean (SD) width of this membrane-like tissue, located between the direct insertion and the posterior femoral articular cartilage, was found by Sasaki and colleagues²²  to be 4.4 (0.5) mm anteroposteriorly(Figure 2). This anterior band of ACL tissue with the direct insertion histologically corresponds to the fibers in the anterior, more isometric region of the femoral footprint. Conversely, the more posterior band of fibers with its indirect insertion histologically corresponds to the more anisometric region and is seen macroscopically as a fanlike projection extending to the posterior articular cartilage.⁷

The dense collagen fibers of the direct insertion and the more membrane-like indirect insertion regions of the femoral footprint of the native ACL suggest that these regions have different load-sharing characteristics. The direct fibers of the insertion form a firm, fixed attachment that allows for gradual load distribution into the subchondral bone. From a biomechanical point of view, this attachment is extremely important, a key ligament–bone link transmitting mechanical load to the joint.²³ A recent kinematic analysis revealed that the indirect fibers in the posterior region of the footprint, adjacent to the posterior articular cartilage, contribute minimally to restraint of tibial translation and rotations during stability examination.²⁴ This suggests it may be strategically wise to place a tunnel in the direct insertion region of the footprint—eccentrically anterior (high) in the footprint rather than in the centrum.

3. Isometric Considerations

Forty years ago, Artmann and Wirth²⁵ reported that a nearly isometric region existed in the femur such that there is minimal elongation of the native ACL during knee motion. The biomechanical rationale for choosing an isometric region of an ACL graft is that it will maintain function throughout the range of flexion and extension. A nonisometric graft would be expected to slacken during a large portion of the flexion cycle and not restrain anterior translation of the tibia, or, if fixed at the wrong flexion angle, it could capture the knee and cause graft failure by excessive tension. These 2 theoretical undesirable effects from nonisometric graft placement are supported by many experimental and clinical studies demonstrating that nonisometric femoral tunnel placement at time of surgery can cause recurrent anterior laxity of the knee.^26-28 Multiple studies have further clarified that the isometric characteristics of an ACL graft are largely determined by femoral positioning. The most isometric region of the femoral footprint is consistently shown to be localized eccentrically within the footprint, in a relatively narrow bandlike region that is proximal (deep) and anterior (along the lateral intercondylar ridge within the footprint)^19,29,30 (Figure 3).

A large body of literature has demonstrated that a tunnel placed in the center of the femoral footprint is less isometric than a tunnel in the more anterior region.^25,29,31,32 Indeed, the anterior position (high in the footprint) identified by Hefzy and colleagues²⁹ demonstrated minimal anisometry with 1 to 4 mm of length change through the range of motion. In contrast, a central tunnel would be expected to demonstrate 5 to 7 mm of length change, whereas a lower graft (in the PL region of the footprint) would demonstrate about 1 cm of length change through the range of motion.^31,32 As such, central grafts, or grafts placed in the PL portion of the femoral footprint, would be expected to see high tension or graft forces as the knee is flexed, or to lose tension completely if the graft is fixed at full extension.³²

Importantly, Markolf and colleagues³³ reported that the native ACL does not behave exactly in a so-called isometric fashion during the last 30° of extension. They showed that about 3 mm of retraction of a trial wire into the joint during the last 30° of extension (as measured with an isometer) is reasonable to achieve graft length changes approximating those of the intact ACL. Given this important caveat, a primary goal for ACLR is placement of the femoral tunnel within this isometric region so that the length change in the ACL graft is minimized to 3 mm from 30° to full flexion. In addition, results of a time-zero biomechanical study suggested better rotational control with anatomical femoral tunnel position than with an isometric femoral tunnel³⁴ placed outside the femoral footprint. Therefore, maximizing isometry alone is not the goal; placing the graft in the most isometric region within the anatomical femoral footprint is desired. This isometric region in the footprint is in the histologic region that corresponds to the direct fibers. Again, this region is eccentrically located in the anterior (high) and proximal (deep) portion of the footprint.

4. Biomechanical Considerations

Multiple cadaveric studies have investigated the relationship between femoral tunnel positioning and time-zero stability. These studies often demonstrated superior time-zero control of knee stability, particularly in pivot type maneuvers, with a femoral tunnel placed more centrally in the femoral footprint than with a tunnel placed outside the footprint.^34-37 However, an emerging body of literature is finding no significant difference in time-zero stability between an anteriorly placed femoral tunnel within the anatomical footprint (eccentrically located in the footprint) and a centrally placed graft.^38,39 Returning to the more isometric tunnel position, still within the femoral footprint, would be expected to confer the benefits of an anatomically based graft position with the advantageous profile of improved isometry, as compared with a centrally placed or PL graft. Biomechanical studies⁴⁰ have documented that ACL graft fibers placed posteriorly (low) in the footprint cause high graft forces in extension and, in some cases, graft rupture (Figure 4). Accordingly, the importance of reconstructing the posterior region of the footprint to better control time-zero stability is questioned.⁴¹

In addition to time-zero control of the stability examination, restoring the low tension-flexion pattern in the ACL graft to replicate the tension-flexion behavior of the native ACL is a fundamental biomechanical principle of ACLR.^15,33,42,43 These studies have demonstrated that a femoral tunnel localized anterior (high) and proximal (deep) within the footprint better replicates the tension-flexion behavior of the native ACL, as compared with strategies that attempt to anatomically “fill the footprint.”⁴⁰ Together, these studies have demonstrated that an eccentric position in the footprint, in the anterior (high) and proximal (deep) region, not only maximizes isometry and restores the direct fibers, but provides favorable time-zero stability and a low tension-flexion pattern biomechanically, particularly as compared with a tunnel in the more central or posterior region of the footprint.

5. Clinical Data

Clinical studies of the traditional transtibial ACLR have shown good results.^44,45 However, when the tibial tunnel in the coronal plane was drilled vertical with respect to the medial joint line of the tibia, the transtibially placed femoral tunnel migrated anterior to the anatomical femoral footprint, often on the roof of the notch.^10,14 This nonanatomical, vertical placement of the femoral tunnel led to failed normalization of knee kinematics.^46-50 Indeed, a higher tension-flexion pattern was found in this nonanatomical “roof” position for the femoral tunnel as compared with the native ACL—a pattern that can result in either loss of flexion or recurrent instability.^13,15,51

Clinical results of techniques used to create an anatomical ACLR centrally within the footprint have been mixed. Registry data showed that the revision rate at 4 years was higher with the AM portal technique (5.16%) than with transtibial drilling (3.20%).⁵² This higher rate may be associated with the more central placement of the femoral tunnel with the AM portal technique than with the transtibial technique, as shown in vivo with high-resolution magnetic resonance imaging.¹² Recent reports have documented a higher rate of failure with DB or central ACLR approaches than with traditional transtibial techniques.⁵³ As mentioned, in contrast to a more isometric position, a central femoral tunnel position would be expected to demonstrate 5 to 7 mm of length change, whereas moving the graft more posterior in the footprint (closer to the articular cartilage) would result in more than 1 cm of length change through the range of motion.^31,32 As such, these more central grafts, or grafts placed even lower (more posterior) in the footprint, would be expected to see high tension in extension (if fixed in flexion), or to lose tension completely during flexion (if the graft is fixed at full extension).³² This may be a mechanistic cause of the high failure rate in the more posterior bundles of the DB approach.⁵⁴

Together, these clinical data suggest that the femoral tunnel should be placed within the anatomical footprint of the ACL. However, within the footprint, a more eccentric femoral tunnel position capturing the isometric and direct region of the insertion may be preferable to a more central or posterior (low region) position.

Summary

Anatomical, histologic, isometric, biomechanical, and clinical data from more than 4 decades collectively point to an optimal position for the femoral tunnel within the femoral footprint. This position can be summarized by the acronym I.D.E.A.L., which refers to placing a femoral tunnel in a position that reproduces the Isometry of the native ACL, that covers the fibers of the Direct insertion histologically, that is Eccentrically located in the anterior (high) and proximal (deep) region of the footprint, that is Anatomical (within the footprint), and that replicates the Low tension-flexion pattern of the native ACL throughout the range of flexion and extension (Figure 5).

In vivo and in vitro studies as well as surgical experience suggest a need to avoid both (a) the nonanatomical vertical (roof) femoral tunnel placement that causes PCL impingement, high tension in the ACL graft in flexion, and ultimately graft stretch-out with instability and (b) the femoral tunnel placement in the posterior (lowest) region of the footprint that causes high tension in extension and can result in graft stretch-out with instability.^13,15,39,40 The transtibial and AM portal techniques can both be effective in properly placing the femoral tunnel and restoring motion, stability, and function to the knee. Their effectiveness, however, depends on correct placement of the femoral tunnel. We think coming studies will focus on single-bundle ACLR and will be designed to improve the reliability of the transtibial and AM portal techniques for placing a femoral tunnel in keeping with the principles summarized by the I.D.E.A.L. acronym.

In the United States, surgeons perform an estimated 200,000 anterior cruciate ligament reconstructions (ACLRs) each year. Over the past decade, there has been a surge in interest in defining anterior cruciate ligament (ACL) anatomy to guide ACLR. With this renewed interest in the anatomical features of the ACL, particularly the insertion site, many authors have advocated an approach for complete or near-complete “footprint restoration” for anatomical ACLR.^1,2 Some have recommended a double-bundle (DB) technique that completely “fills” the footprint, but it is seldom used. Others have proposed centralizing the femoral tunnel position within the ACL footprint in the hope of capturing the function of both the anteromedial (AM) and posterolateral (PL) bundles.^1,3,4 Indeed, a primary surgical goal of most anatomical ACLR techniques is creation of a femoral tunnel based off the anatomical centrum (center point) of the ACL femoral footprint.^3,5 With a single-bundle technique, the femoral socket is localized in the center of the entire footprint; with a DB technique, sockets are created in the centrums of both the AM and PL bundles.

Because of the complex shape of the native ACL, however, the strategy of restoring the femoral footprint with use of either a central tunnel or a DB approach has been challenged. The femoral footprint is 3.5 times larger than the midsubstance of the ACL.⁶ Detailed anatomical dissections have recently demonstrated that the femoral origin of the ACL has a stout anterior band of fibers with a fanlike extension posteriorly.⁷ As the ACL fibers extend off the bony footprint, they form a flat, ribbonlike structure 9 to 16 mm wide and only 2 to 4 mm thick.^2,8 Within this structure, there is no clear separation of the AM and PL bundles. The presence of this structure makes sense given the anatomical constraints inherent in the notch. Indeed, the space for the native ACL is narrow, as the posterior cruciate ligament (PCL) occupies that largest portion of the notch with the knee in full extension, leaving only a thin, 5-mm slot through which the ACL must pass.⁹ Therefore, filling the femoral footprint with a tubular ACL graft probably does not reproduce the dynamic 3-dimensional morphology of the ACL.

In light of the discrepancy between the sizes of the femoral footprint and the midsubstance of the native ACL, it seems reasonable that optimizing the position of the ACL femoral tunnel may be more complex than simply centralizing the tunnel within the footprint or attempting to maximize footprint coverage. In this article, we amalgamate the lessons of 4 decades of ACL research into 5 points for strategic femoral tunnel positioning, based on anatomical, histologic, isometric, biomechanical, and clinical data. These points are summarized by the acronym I.D.E.A.L., which refers to placing a femoral tunnel in a position that reproduces the Isometry of the native ACL, that covers the fibers of the Direct insertion histologically, that is Eccentrically located in the anterior (high) and proximal (deep) region of the footprint, that is Anatomical (within the footprint), and that replicates the Low tension-flexion pattern of the native ACL throughout the range of flexion and extension.

1. Anatomy Considerations

In response to study results demonstrating that some transtibial ACLRs were associated with nonanatomical placement of the femoral tunnel—resulting in vertical graft placement, PCL impingement, and recurrent rotational instability^10-16—investigators have reexamined both the anatomy of the femoral origin of the native ACL and the ACL graft. Specifically, a large body of research has been devoted to characterizing the osseous landmarks of the femoral origin of the ACL¹⁷ and the dimensions of the femoral footprint.³ In addition, authors have supported the concept that the ACL contains 2 functional bundles, AM and PL.^5,17 Several osseous landmarks have been identified as defining the boundaries of the femoral footprint. The lateral intercondylar ridge is the most anterior aspect of the femoral footprint and was first defined by Clancy.¹⁸ More recently, the lateral bifurcate ridge, which separates the AM and PL bundle insertion sites, was described¹⁹ (Figure 1A).

These osseous ridges delineate the location of the femoral footprint. Studies have shown that ACL fibers attach from the lateral intercondylar ridge on the anterior border of the femoral footprint and extend posteriorly to the cartilage of the lateral femoral condyle (Figure 1B).

ACL fibers from this oblong footprint are organized such that the midsubstance of the ACL is narrower than the femoral footprint. Anatomical dissections have demonstrated that, though the femoral footprint is oval, the native ACL forms a flat, ribbonlike structure 9 to 16 mm wide and only 2 to 4 mm thick as it takes off from the bone.^8,20 There is a resulting discrepancy between the femoral footprint size and shape and the morphology of the native ACL, and placing a tunnel in the center of the footprint or “filling the footprint” with ACL graft may not reproduce the morphology or function of the native ACL. Given this size mismatch, strategic decisions need to be made to place the femoral tunnel in a specific region of the femoral footprint to optimize its function.

2. Histologic Findings

Histologic analysis has further clarified the relationship between the femoral footprint and functional aspects of the native ACL. The femoral origin of the ACL has distinct direct and indirect insertions, as demonstrated by histology and 3-dimensional volume-rendered computed tomography.²¹ The direct insertion consists of dense collagen fibers anterior in the footprint that is attached to a bony depression immediately posterior to the lateral intercondylar ridge.¹⁹ Sasaki and colleagues²² found that these direct fibers extended a mean (SD) of 5.3 (1.1) mm posteriorly but did not continue to the posterior femoral articular cartilage. The indirect insertion consists of more posterior collagen fibers that extend to and blend into the articular cartilage of the posterior aspect of the lateral femoral condyle. Mean (SD) width of this membrane-like tissue, located between the direct insertion and the posterior femoral articular cartilage, was found by Sasaki and colleagues²²  to be 4.4 (0.5) mm anteroposteriorly(Figure 2). This anterior band of ACL tissue with the direct insertion histologically corresponds to the fibers in the anterior, more isometric region of the femoral footprint. Conversely, the more posterior band of fibers with its indirect insertion histologically corresponds to the more anisometric region and is seen macroscopically as a fanlike projection extending to the posterior articular cartilage.⁷

The dense collagen fibers of the direct insertion and the more membrane-like indirect insertion regions of the femoral footprint of the native ACL suggest that these regions have different load-sharing characteristics. The direct fibers of the insertion form a firm, fixed attachment that allows for gradual load distribution into the subchondral bone. From a biomechanical point of view, this attachment is extremely important, a key ligament–bone link transmitting mechanical load to the joint.²³ A recent kinematic analysis revealed that the indirect fibers in the posterior region of the footprint, adjacent to the posterior articular cartilage, contribute minimally to restraint of tibial translation and rotations during stability examination.²⁴ This suggests it may be strategically wise to place a tunnel in the direct insertion region of the footprint—eccentrically anterior (high) in the footprint rather than in the centrum.

3. Isometric Considerations

Forty years ago, Artmann and Wirth²⁵ reported that a nearly isometric region existed in the femur such that there is minimal elongation of the native ACL during knee motion. The biomechanical rationale for choosing an isometric region of an ACL graft is that it will maintain function throughout the range of flexion and extension. A nonisometric graft would be expected to slacken during a large portion of the flexion cycle and not restrain anterior translation of the tibia, or, if fixed at the wrong flexion angle, it could capture the knee and cause graft failure by excessive tension. These 2 theoretical undesirable effects from nonisometric graft placement are supported by many experimental and clinical studies demonstrating that nonisometric femoral tunnel placement at time of surgery can cause recurrent anterior laxity of the knee.^26-28 Multiple studies have further clarified that the isometric characteristics of an ACL graft are largely determined by femoral positioning. The most isometric region of the femoral footprint is consistently shown to be localized eccentrically within the footprint, in a relatively narrow bandlike region that is proximal (deep) and anterior (along the lateral intercondylar ridge within the footprint)^19,29,30 (Figure 3).

A large body of literature has demonstrated that a tunnel placed in the center of the femoral footprint is less isometric than a tunnel in the more anterior region.^25,29,31,32 Indeed, the anterior position (high in the footprint) identified by Hefzy and colleagues²⁹ demonstrated minimal anisometry with 1 to 4 mm of length change through the range of motion. In contrast, a central tunnel would be expected to demonstrate 5 to 7 mm of length change, whereas a lower graft (in the PL region of the footprint) would demonstrate about 1 cm of length change through the range of motion.^31,32 As such, central grafts, or grafts placed in the PL portion of the femoral footprint, would be expected to see high tension or graft forces as the knee is flexed, or to lose tension completely if the graft is fixed at full extension.³²

Importantly, Markolf and colleagues³³ reported that the native ACL does not behave exactly in a so-called isometric fashion during the last 30° of extension. They showed that about 3 mm of retraction of a trial wire into the joint during the last 30° of extension (as measured with an isometer) is reasonable to achieve graft length changes approximating those of the intact ACL. Given this important caveat, a primary goal for ACLR is placement of the femoral tunnel within this isometric region so that the length change in the ACL graft is minimized to 3 mm from 30° to full flexion. In addition, results of a time-zero biomechanical study suggested better rotational control with anatomical femoral tunnel position than with an isometric femoral tunnel³⁴ placed outside the femoral footprint. Therefore, maximizing isometry alone is not the goal; placing the graft in the most isometric region within the anatomical femoral footprint is desired. This isometric region in the footprint is in the histologic region that corresponds to the direct fibers. Again, this region is eccentrically located in the anterior (high) and proximal (deep) portion of the footprint.

4. Biomechanical Considerations

Multiple cadaveric studies have investigated the relationship between femoral tunnel positioning and time-zero stability. These studies often demonstrated superior time-zero control of knee stability, particularly in pivot type maneuvers, with a femoral tunnel placed more centrally in the femoral footprint than with a tunnel placed outside the footprint.^34-37 However, an emerging body of literature is finding no significant difference in time-zero stability between an anteriorly placed femoral tunnel within the anatomical footprint (eccentrically located in the footprint) and a centrally placed graft.^38,39 Returning to the more isometric tunnel position, still within the femoral footprint, would be expected to confer the benefits of an anatomically based graft position with the advantageous profile of improved isometry, as compared with a centrally placed or PL graft. Biomechanical studies⁴⁰ have documented that ACL graft fibers placed posteriorly (low) in the footprint cause high graft forces in extension and, in some cases, graft rupture (Figure 4). Accordingly, the importance of reconstructing the posterior region of the footprint to better control time-zero stability is questioned.⁴¹

In addition to time-zero control of the stability examination, restoring the low tension-flexion pattern in the ACL graft to replicate the tension-flexion behavior of the native ACL is a fundamental biomechanical principle of ACLR.^15,33,42,43 These studies have demonstrated that a femoral tunnel localized anterior (high) and proximal (deep) within the footprint better replicates the tension-flexion behavior of the native ACL, as compared with strategies that attempt to anatomically “fill the footprint.”⁴⁰ Together, these studies have demonstrated that an eccentric position in the footprint, in the anterior (high) and proximal (deep) region, not only maximizes isometry and restores the direct fibers, but provides favorable time-zero stability and a low tension-flexion pattern biomechanically, particularly as compared with a tunnel in the more central or posterior region of the footprint.

5. Clinical Data

Clinical studies of the traditional transtibial ACLR have shown good results.^44,45 However, when the tibial tunnel in the coronal plane was drilled vertical with respect to the medial joint line of the tibia, the transtibially placed femoral tunnel migrated anterior to the anatomical femoral footprint, often on the roof of the notch.^10,14 This nonanatomical, vertical placement of the femoral tunnel led to failed normalization of knee kinematics.^46-50 Indeed, a higher tension-flexion pattern was found in this nonanatomical “roof” position for the femoral tunnel as compared with the native ACL—a pattern that can result in either loss of flexion or recurrent instability.^13,15,51

Clinical results of techniques used to create an anatomical ACLR centrally within the footprint have been mixed. Registry data showed that the revision rate at 4 years was higher with the AM portal technique (5.16%) than with transtibial drilling (3.20%).⁵² This higher rate may be associated with the more central placement of the femoral tunnel with the AM portal technique than with the transtibial technique, as shown in vivo with high-resolution magnetic resonance imaging.¹² Recent reports have documented a higher rate of failure with DB or central ACLR approaches than with traditional transtibial techniques.⁵³ As mentioned, in contrast to a more isometric position, a central femoral tunnel position would be expected to demonstrate 5 to 7 mm of length change, whereas moving the graft more posterior in the footprint (closer to the articular cartilage) would result in more than 1 cm of length change through the range of motion.^31,32 As such, these more central grafts, or grafts placed even lower (more posterior) in the footprint, would be expected to see high tension in extension (if fixed in flexion), or to lose tension completely during flexion (if the graft is fixed at full extension).³² This may be a mechanistic cause of the high failure rate in the more posterior bundles of the DB approach.⁵⁴

Together, these clinical data suggest that the femoral tunnel should be placed within the anatomical footprint of the ACL. However, within the footprint, a more eccentric femoral tunnel position capturing the isometric and direct region of the insertion may be preferable to a more central or posterior (low region) position.

Summary

Anatomical, histologic, isometric, biomechanical, and clinical data from more than 4 decades collectively point to an optimal position for the femoral tunnel within the femoral footprint. This position can be summarized by the acronym I.D.E.A.L., which refers to placing a femoral tunnel in a position that reproduces the Isometry of the native ACL, that covers the fibers of the Direct insertion histologically, that is Eccentrically located in the anterior (high) and proximal (deep) region of the footprint, that is Anatomical (within the footprint), and that replicates the Low tension-flexion pattern of the native ACL throughout the range of flexion and extension (Figure 5).

In vivo and in vitro studies as well as surgical experience suggest a need to avoid both (a) the nonanatomical vertical (roof) femoral tunnel placement that causes PCL impingement, high tension in the ACL graft in flexion, and ultimately graft stretch-out with instability and (b) the femoral tunnel placement in the posterior (lowest) region of the footprint that causes high tension in extension and can result in graft stretch-out with instability.^13,15,39,40 The transtibial and AM portal techniques can both be effective in properly placing the femoral tunnel and restoring motion, stability, and function to the knee. Their effectiveness, however, depends on correct placement of the femoral tunnel. We think coming studies will focus on single-bundle ACLR and will be designed to improve the reliability of the transtibial and AM portal techniques for placing a femoral tunnel in keeping with the principles summarized by the I.D.E.A.L. acronym.

Osteoarthritic (OA) knees with varus deformities commonly present with tight, contracted medial collateral ligaments and soft-tissue sleeves.¹ More severe varus deformities require more extensive medial releases on the concave side to optimize flexion-extension gaps. Excessive soft-tissue releases in milder varus deformities can result in medial instability in flexion and extension.^2-4 Misjudgments in soft-tissue release can therefore lead to knee instability, an important cause of early total knee arthroplasty (TKA) failures.^2,5,6 Some authors have reported difficulty in coronal plane balancing in knees with preoperative varus deformity of more than 20°.^4,7

Surgeons often refer to varus as a description of coronal mal­alignment, mainly with the knee in extension. In the surgical setting, however, descriptions are given regarding differential medial soft-tissue tightness in extension and flexion. Balancing the knee in extension may not necessarily balance the knee in flexion. Thus, there is the concept of extension and flexion varus, which has not been well described in the literature. Releases on the anterior medial and posterior medial aspects of the proximal tibia have differential effects on flexion and extension gaps, respectively.²

Intraoperative alignment certainly has a pivotal role in component longevity.⁸ Since its advent in the 1990s, use of computer navigation in TKA has offered new hope for improving component alignment. Some authors routinely use computer navigation for intraoperative soft-tissue releases.⁹ A recent meta-analysis found that computer-navigated surgery is associated with fewer outliers in final component alignment compared with conventional TKA.¹⁰

Increased use of computer navigation in TKA at our institution in recent years has come with the observation that knees with severe extension varus seem to have correspondingly more severe flexion varus. Before computer navigation, coronal alignment of knees in flexion was almost impossible to measure because of the spatial alignment of the knees in that position.

We conducted a study to evaluate the relationship of extension and flexion varus in OA knees and to determine whether severity of fixed flexion deformity (FFD) in the sagittal plane correlates with severity of coronal plane varus deformity. We hypothesized that there would be differential varus in flexion and extension and that increasing knee extension varus would correlate closely with knee flexion varus beyond a certain tibiofemoral angle. We also hypothesized that severity of sagittal plane deformity will correlate with the severity of coronal plane deformity.

Patients and Methods

Data Collection

After this study was approved by our institution’s ethics review committee, we prospectively collected data from 403 consecutive computer-navigated TKAs performed at our institution between November 2008 and August 2011. Dr. Tan, who was not the primary physician, retrospectively analyzed the radiographic and navigation data.

Each patient’s knee varus-valgus angles were captured by Dr. Teo, an adult reconstruction surgeon, in standard fashion from maximal extension to 0º, 30º, 45º, 60º, 90º, and maximal flexion. An example of standard data capture appears in Table 1. With varus-hyperextension defined as –0.5° or less (more negative), neutral as 0°, and valgus-flexion as 0.5° or more, there were 362 varus knees, 41 valgus knees, and no neutral knees.

Study inclusion criteria were OA and varus deformity. Exclusion criteria were rheumatoid arthritis, other types of inflammatory arthritis, neuromuscular disorders, knees with valgus angulation, and incomplete data (Table 2). Figure 1 summarizes the inclusion/exclusion process, which left 317 knees available for study. Cases of incomplete data were likely due to computer errors or to inadvertent movement when navigation data were being acquired during surgery.

In conventional TKA, the main objective is to equalize flexion-extension gaps with knee at 90° flexion and 0° extension. The ability to achieve this often implies the knee will be balanced throughout its range of motion (ROM). From the data for the 317 study knees, 3 sets of values were extracted: varus angles from maximal knee extension (extension varus), varus angles from 90° knee flexion (flexion varus), and maximal knee extension. All knees were able to achieve 90° flexion.

Power Calculation

Our analysis used a correlation coefficient (r) of at least 0.5 at a 5% level of significance and power of 80%. With 317 knees, the study was more than adequately powered for significance.

Surgical and Navigation Technique

All patients underwent either general or regional anesthesia for their surgeries, which were performed by Dr. Teo. Standard medial parapatellar arthrotomy was performed. Navigation pins were then inserted into the femur and tibia outside the knee wound. Anatomical reference points were digitized per routine navigation requirements. (The reference for varus-valgus alignment of the femur is the mechanical femur axis defined by the digitized hip center and knee center, and the reference for varus-valgus alignment of the tibia is the mechanical tibia axis defined by the digitized tibia center and calculated ankle center. The ankle center is calculated by dividing the digitized transmalleolar axis according to a ratio of 56% lateral to 44% medial with the inherent navigation software.) Our institution uses an imageless navigation system (Navigation System II; Stryker Orthopedics, Mahwah, New Jersey).

The leg was then brought from maximal knee extension to maximal knee flexion to assess preoperative ROM, which indicates inherent flexion contracture or hyperextension. Varus-valgus measurements of the knee were then generated as part of the navigation software protocol. These measurements were obtained without additional varus or valgus stress applied to the knee and before any bony resection. The rest of the operation was completed using navigation to guide bony resection and soft-tissue balancing. The final components used were all cemented cruciate-substituting TKA implants. After component insertion, the knee was again brought through ROM from maximal knee extension to maximal knee flexion to assess postoperative ROM before wound closure.

Extension and Flexion Varus

As none of the patients in the flexion varus dataset (range, –0.5° to –19°) had a varus deformity of more than 20° at 90° flexion, we used a cutoff of 10° to divide these patients into 2 subgroups: less than 10° (237 knees) and 10° or more (80 knees). The extension varus dataset ranged from –0.5° to –24°. Incremental values of –0.5° to –24° in this dataset were then analyzed against the 90° flexion varus subgroups using logistic regression. A scatterplot of the relationship between extension and flexion varus is shown in Figure 2. The probability function was then derived and a probability graph plotted.

FFD and Extension and Flexion Varus

Maximal knee extension, obtained from intraoperative navigation measurements, ranged from –9° (hyperextension) to 33° (FFD) and maximal knee flexion ranged from 90° to 146°. Ninety-two knees had slight hyperextension, and 6 were neutral. Of the 317 OA knees with varus deformity, 219 (69%) had FFD. This sagittal plane alignment parameter was analyzed against coronal plane alignment in maximal knee extension and 90° knee flexion to determine if increasing severity of FFD corresponds with increasing extension or flexion varus.

Statistical Analysis

Statistical analysis was performed with Stata 10.1 (Statacorp, College Station, Texas). Significance was set at P < .05.

Results

Extension and Flexion Varus

Patient demographic data are listed in Table 3. Univariate logistic regression analysis revealed that age (P = .110), body mass index (P = .696), and sex (P = .584) did not affect the association between preoperative extension and flexion varus.

Mean (SD) preoperative extension varus was –9.9° (4.80°), and mean (SD) preoperative flexion 90° varus was –7.02° (3.74°). Linear regression of the data showed a significant positive correlation between preoperative extension varus and flexion varus (Pearson correlation coefficient, 0.57; P < .0001). The probability function was determined as follows: Probability of having flexion varus of more than 10° = 1 / (1 + e–z), where z = –4.014 – 0.265 × extension varus. Plotting the probability graph of flexion varus against varus angles at maximal knee extension from the probability formula yielded a sigmoid graph (Figure 3). The most linear part of the graph corresponds to the 10° to 20° of extension varus (solid line), demonstrating an almost linear increase in the probability of having more than 10° flexion varus with increasing extension varus from 10° to 20°. For extension varus of 20° or more, the probability of having flexion varus of more than 10° approaches 1.

FFD and Extension and Flexion Varus

Mean (SD) preoperative maximal knee extension (analogous to FFD) was 4.41° (7.50°), mean (SD) extension varus was –9.9° (4.80°), and mean (SD) 90° flexion varus was –7.02° (3.74°). We did not find any correlation between preoperative FFD and preoperative flexion varus (r = –0.02; P = .6583) or extension varus (r = –0.11; P = .046) (Figure 4).

Postoperative Alignment

Of the 317 OA knees, 18 had incomplete navigation-acquired postoperative alignment data. The postoperative alignment of the other 299 knees at various degrees of knee flexion is illustrated with a box-and-whisker plot (Figure 5).

Knees With Severe Extension Varus

Fourteen of the 15 knees with severe extension varus (>20°) had flexion varus of more than 9° (range, –9° to –17.5°, with only 1 outlier, at –5°). For the 15 patients, maximal knee extension ranged from –9° hyperextension to 27.5° FFD. Six knees had slight hyperextension, and 9 had FFD demonstrating large variability in sagittal alignment. Despite severe preoperative coronal deformity, all 15 knees had satisfactory deformity correction. Preoperative and postoperative knee alignment data for these 15 knees appear in Table 4 and Figure 6, respectively.

Discussion

OA varus knees represent a majority of the cases being managed by orthopedic surgeons. Soft-tissue contractures involving the medial collateral ligament (MCL), posteromedial capsule, pes anserinus, and semimembranosus muscle are commonly encountered. Bone loss may also occur on the tibial and femoral joint surfaces in knees with severe angular deformity. In an OA varus knee, bone loss tends to be mainly on the medial tibial plateau and usually on the posterior aspect of the tibia because flexion contractures often are concomitant with these marked deformities.¹¹ Therefore, a varus deformity is apparent whether the knee is extended or flexed. Our results showed a correlation between extension and flexion varus in OA varus knees. In contrast, for a valgus deformity, as bone loss can occur on both the tibial and femoral surfaces,¹¹ a similar correlation may not be seen. For that reason, and because there were only 41 valgus knees in this study, they were excluded. For FFD, soft-tissue contractures often involve both the posterior capsule and the posterior cruciate ligament (PCL). Posterior osteophytes often cause tenting of the posterior capsule in knees with FFD. Anteriorly, growth of osteophytes at the tibial spine and intercondylar notch of the femur can result in bony causes of restricted knee extension.¹²

One would expect increased coronal plane angular deformity to correspond to more severe FFD in the sagittal plane because the same pathology affects soft tissue or bones in an OA knee in both planes. Interestingly, our study results proved otherwise. FFD did not correlate with degree of extension or flexion varus severity. This phenomenon has not been described in the literature likely because clinical measurements of flexion varus and FFD were difficult to perform because of the spatial alignment of the knee in flexion. In recent years, however, computer navigation technology has made such measurements possible.

Mihalko and colleagues² established that soft-tissue releases on different parts of the proximal tibia have different effects on soft-tissue balancing in flexion and extension. In knees with extension varus, more releases are required on the posterior medial aspect of the tibia (the posterior oblique fibers of the superficial MCL, the posteromedial capsule, and, sometimes, the semimembranosus), whereas knees with flexion varus require more releases on the anterior medial aspect of the tibia (the deep MCL, the anterior fibers of the superficial MCL, and, sometimes, the pes anserinus attachment).¹³ Consequently, soft-tissue stabilizers seem to have different functions in flexion and extension and cannot reliably be released solely in extension or flexion for optimal gap balancing during TKA.² Other authors, in cadaveric studies, have found that a larger amount of coronal deformity correction is achieved with more distal soft-tissue releases from the joint line.^9,14 Surgical techniques for correcting FFD include removal of prominent anterior and posterior osteophytes, posterior capsular releases, sometimes PCL sacrifices, and even gastrocnemius recession.¹²

In our study, all 14 patients with severe extension and correspondingly severe flexion varus needed not only modest posterior medial soft-tissue releases for the severe extension varus, but also modest anterior medial releases for the flexion varus. The respective soft-tissue releases were confirmed in real time with computer navigation sequentially after bony resection and osteophyte removal. With this method, we restored final postoperative alignment to within 3° of the mechanical axis (Figure 6). Our experience here led us to believe that, with these patients, modest anterior medial and posterior medial releases could be performed at the start of surgery, as severe extension varus (>20°) almost certainly equates to severe flexion varus (>10°). Therein lies the clinical relevance of our study. However, not all patients with severe coronal plane deformity have correspondingly severe sagittal plane deformity in the form of FFD, as illustrated in our study. Therefore, not all patients with severe varus knee deformity need aggressive posterior capsular release or PCL recession to correct FFD. Some patients have mild hyperextension, which can be attributed partly to the postanesthesia effects of soft-tissue laxity. It is unclear exactly how much anesthesia contributes to this difference in sagittal alignment, though the majority of our patients had FFD. It is not our intent here to discuss the surgical techniques of soft-tissue balancing or to advocate routine use of computer navigation.

Many factors (eg, medial femoral condyle bone loss, medial tibial plateau bone loss, femur or tibia bowing, medial soft-tissue contracture) can contribute to varus malalignment. Current navigation technology cannot isolate the causes of varus alignment, and we did not intend to investigate them in this study. Our primary aim was to assess for a correlation between overall extension varus alignment and expected flexion varus. We also wanted to analyze the correlation between FFD and the coronal plane alignment, in extension and flexion, contributed by the combined bony and soft-tissue components in OA varus knees.

The strengths of this study are that it was a single-surgeon series with knee data from consecutive patients who had computer-navigated TKA. Patient data were prospectively generated from the navigation software and retrospectively analyzed. All navigation alignment was performed by a single surgeon, thereby eliminating examination bias during the time knee alignment data were being obtained. The study was adequately powered and had a large number of patients for data analysis. The authors believe that this is the first study to analyze alignment in both the coronal and sagittal plane in varus OA knees.

We acknowledge a few limitations in our study. Although several investigators have found that navigation can be used to achieve accurate postoperative alignment,^10,15,16 subtle errors may be inadvertently introduced at different points of alignment measurement. These error points include identification of visually selected anatomical landmarks; kinematic registration of hip, knee, and ankle; and intraoperative changes in the navigation environment (eg, inadvertent movement of pins or rigid bodies). In addition, different surgeons have different techniques for kinematic registration. However, the surgeries in our study were performed by the same surgeon, so this confounding factor was effectively removed. Another limitation was that navigation alignment was obtained during surgery, when patients were under anesthesia and in a supine, non-weight-bearing position, whereas routine clinical weight-bearing radiographs are taken with nonanesthetized patients and this might overestimate the deformities intraoperatively. However, all parameters were measured in the same patient under the same anesthetic effects, so this should not have affected the analyses. Most surgeons would make an intraoperative assessment of the severity of any deformity before the surgery proper anyway. Nevertheless, some authors have found that knee alignment obtained with intraoperative navigation correlated well with alignment obtained with weight-bearing radiographs.^17,18

Conclusion

Our study results showed that, in OA varus knees, extension varus highly correlated with flexion varus. However, there was no correlation between FFD and coronal plane varus deformity.

Osteoarthritic (OA) knees with varus deformities commonly present with tight, contracted medial collateral ligaments and soft-tissue sleeves.¹ More severe varus deformities require more extensive medial releases on the concave side to optimize flexion-extension gaps. Excessive soft-tissue releases in milder varus deformities can result in medial instability in flexion and extension.^2-4 Misjudgments in soft-tissue release can therefore lead to knee instability, an important cause of early total knee arthroplasty (TKA) failures.^2,5,6 Some authors have reported difficulty in coronal plane balancing in knees with preoperative varus deformity of more than 20°.^4,7

Surgeons often refer to varus as a description of coronal mal­alignment, mainly with the knee in extension. In the surgical setting, however, descriptions are given regarding differential medial soft-tissue tightness in extension and flexion. Balancing the knee in extension may not necessarily balance the knee in flexion. Thus, there is the concept of extension and flexion varus, which has not been well described in the literature. Releases on the anterior medial and posterior medial aspects of the proximal tibia have differential effects on flexion and extension gaps, respectively.²

Intraoperative alignment certainly has a pivotal role in component longevity.⁸ Since its advent in the 1990s, use of computer navigation in TKA has offered new hope for improving component alignment. Some authors routinely use computer navigation for intraoperative soft-tissue releases.⁹ A recent meta-analysis found that computer-navigated surgery is associated with fewer outliers in final component alignment compared with conventional TKA.¹⁰

Increased use of computer navigation in TKA at our institution in recent years has come with the observation that knees with severe extension varus seem to have correspondingly more severe flexion varus. Before computer navigation, coronal alignment of knees in flexion was almost impossible to measure because of the spatial alignment of the knees in that position.

We conducted a study to evaluate the relationship of extension and flexion varus in OA knees and to determine whether severity of fixed flexion deformity (FFD) in the sagittal plane correlates with severity of coronal plane varus deformity. We hypothesized that there would be differential varus in flexion and extension and that increasing knee extension varus would correlate closely with knee flexion varus beyond a certain tibiofemoral angle. We also hypothesized that severity of sagittal plane deformity will correlate with the severity of coronal plane deformity.

Patients and Methods

Data Collection

After this study was approved by our institution’s ethics review committee, we prospectively collected data from 403 consecutive computer-navigated TKAs performed at our institution between November 2008 and August 2011. Dr. Tan, who was not the primary physician, retrospectively analyzed the radiographic and navigation data.

Each patient’s knee varus-valgus angles were captured by Dr. Teo, an adult reconstruction surgeon, in standard fashion from maximal extension to 0º, 30º, 45º, 60º, 90º, and maximal flexion. An example of standard data capture appears in Table 1. With varus-hyperextension defined as –0.5° or less (more negative), neutral as 0°, and valgus-flexion as 0.5° or more, there were 362 varus knees, 41 valgus knees, and no neutral knees.

Study inclusion criteria were OA and varus deformity. Exclusion criteria were rheumatoid arthritis, other types of inflammatory arthritis, neuromuscular disorders, knees with valgus angulation, and incomplete data (Table 2). Figure 1 summarizes the inclusion/exclusion process, which left 317 knees available for study. Cases of incomplete data were likely due to computer errors or to inadvertent movement when navigation data were being acquired during surgery.

In conventional TKA, the main objective is to equalize flexion-extension gaps with knee at 90° flexion and 0° extension. The ability to achieve this often implies the knee will be balanced throughout its range of motion (ROM). From the data for the 317 study knees, 3 sets of values were extracted: varus angles from maximal knee extension (extension varus), varus angles from 90° knee flexion (flexion varus), and maximal knee extension. All knees were able to achieve 90° flexion.

Power Calculation

Our analysis used a correlation coefficient (r) of at least 0.5 at a 5% level of significance and power of 80%. With 317 knees, the study was more than adequately powered for significance.

Surgical and Navigation Technique

All patients underwent either general or regional anesthesia for their surgeries, which were performed by Dr. Teo. Standard medial parapatellar arthrotomy was performed. Navigation pins were then inserted into the femur and tibia outside the knee wound. Anatomical reference points were digitized per routine navigation requirements. (The reference for varus-valgus alignment of the femur is the mechanical femur axis defined by the digitized hip center and knee center, and the reference for varus-valgus alignment of the tibia is the mechanical tibia axis defined by the digitized tibia center and calculated ankle center. The ankle center is calculated by dividing the digitized transmalleolar axis according to a ratio of 56% lateral to 44% medial with the inherent navigation software.) Our institution uses an imageless navigation system (Navigation System II; Stryker Orthopedics, Mahwah, New Jersey).

The leg was then brought from maximal knee extension to maximal knee flexion to assess preoperative ROM, which indicates inherent flexion contracture or hyperextension. Varus-valgus measurements of the knee were then generated as part of the navigation software protocol. These measurements were obtained without additional varus or valgus stress applied to the knee and before any bony resection. The rest of the operation was completed using navigation to guide bony resection and soft-tissue balancing. The final components used were all cemented cruciate-substituting TKA implants. After component insertion, the knee was again brought through ROM from maximal knee extension to maximal knee flexion to assess postoperative ROM before wound closure.

Extension and Flexion Varus

As none of the patients in the flexion varus dataset (range, –0.5° to –19°) had a varus deformity of more than 20° at 90° flexion, we used a cutoff of 10° to divide these patients into 2 subgroups: less than 10° (237 knees) and 10° or more (80 knees). The extension varus dataset ranged from –0.5° to –24°. Incremental values of –0.5° to –24° in this dataset were then analyzed against the 90° flexion varus subgroups using logistic regression. A scatterplot of the relationship between extension and flexion varus is shown in Figure 2. The probability function was then derived and a probability graph plotted.

FFD and Extension and Flexion Varus

Maximal knee extension, obtained from intraoperative navigation measurements, ranged from –9° (hyperextension) to 33° (FFD) and maximal knee flexion ranged from 90° to 146°. Ninety-two knees had slight hyperextension, and 6 were neutral. Of the 317 OA knees with varus deformity, 219 (69%) had FFD. This sagittal plane alignment parameter was analyzed against coronal plane alignment in maximal knee extension and 90° knee flexion to determine if increasing severity of FFD corresponds with increasing extension or flexion varus.

Statistical Analysis

Statistical analysis was performed with Stata 10.1 (Statacorp, College Station, Texas). Significance was set at P < .05.

Results

Extension and Flexion Varus

Patient demographic data are listed in Table 3. Univariate logistic regression analysis revealed that age (P = .110), body mass index (P = .696), and sex (P = .584) did not affect the association between preoperative extension and flexion varus.

Mean (SD) preoperative extension varus was –9.9° (4.80°), and mean (SD) preoperative flexion 90° varus was –7.02° (3.74°). Linear regression of the data showed a significant positive correlation between preoperative extension varus and flexion varus (Pearson correlation coefficient, 0.57; P < .0001). The probability function was determined as follows: Probability of having flexion varus of more than 10° = 1 / (1 + e–z), where z = –4.014 – 0.265 × extension varus. Plotting the probability graph of flexion varus against varus angles at maximal knee extension from the probability formula yielded a sigmoid graph (Figure 3). The most linear part of the graph corresponds to the 10° to 20° of extension varus (solid line), demonstrating an almost linear increase in the probability of having more than 10° flexion varus with increasing extension varus from 10° to 20°. For extension varus of 20° or more, the probability of having flexion varus of more than 10° approaches 1.

FFD and Extension and Flexion Varus

Mean (SD) preoperative maximal knee extension (analogous to FFD) was 4.41° (7.50°), mean (SD) extension varus was –9.9° (4.80°), and mean (SD) 90° flexion varus was –7.02° (3.74°). We did not find any correlation between preoperative FFD and preoperative flexion varus (r = –0.02; P = .6583) or extension varus (r = –0.11; P = .046) (Figure 4).

Postoperative Alignment

Of the 317 OA knees, 18 had incomplete navigation-acquired postoperative alignment data. The postoperative alignment of the other 299 knees at various degrees of knee flexion is illustrated with a box-and-whisker plot (Figure 5).

Knees With Severe Extension Varus

Fourteen of the 15 knees with severe extension varus (>20°) had flexion varus of more than 9° (range, –9° to –17.5°, with only 1 outlier, at –5°). For the 15 patients, maximal knee extension ranged from –9° hyperextension to 27.5° FFD. Six knees had slight hyperextension, and 9 had FFD demonstrating large variability in sagittal alignment. Despite severe preoperative coronal deformity, all 15 knees had satisfactory deformity correction. Preoperative and postoperative knee alignment data for these 15 knees appear in Table 4 and Figure 6, respectively.

Discussion

OA varus knees represent a majority of the cases being managed by orthopedic surgeons. Soft-tissue contractures involving the medial collateral ligament (MCL), posteromedial capsule, pes anserinus, and semimembranosus muscle are commonly encountered. Bone loss may also occur on the tibial and femoral joint surfaces in knees with severe angular deformity. In an OA varus knee, bone loss tends to be mainly on the medial tibial plateau and usually on the posterior aspect of the tibia because flexion contractures often are concomitant with these marked deformities.¹¹ Therefore, a varus deformity is apparent whether the knee is extended or flexed. Our results showed a correlation between extension and flexion varus in OA varus knees. In contrast, for a valgus deformity, as bone loss can occur on both the tibial and femoral surfaces,¹¹ a similar correlation may not be seen. For that reason, and because there were only 41 valgus knees in this study, they were excluded. For FFD, soft-tissue contractures often involve both the posterior capsule and the posterior cruciate ligament (PCL). Posterior osteophytes often cause tenting of the posterior capsule in knees with FFD. Anteriorly, growth of osteophytes at the tibial spine and intercondylar notch of the femur can result in bony causes of restricted knee extension.¹²

One would expect increased coronal plane angular deformity to correspond to more severe FFD in the sagittal plane because the same pathology affects soft tissue or bones in an OA knee in both planes. Interestingly, our study results proved otherwise. FFD did not correlate with degree of extension or flexion varus severity. This phenomenon has not been described in the literature likely because clinical measurements of flexion varus and FFD were difficult to perform because of the spatial alignment of the knee in flexion. In recent years, however, computer navigation technology has made such measurements possible.

Mihalko and colleagues² established that soft-tissue releases on different parts of the proximal tibia have different effects on soft-tissue balancing in flexion and extension. In knees with extension varus, more releases are required on the posterior medial aspect of the tibia (the posterior oblique fibers of the superficial MCL, the posteromedial capsule, and, sometimes, the semimembranosus), whereas knees with flexion varus require more releases on the anterior medial aspect of the tibia (the deep MCL, the anterior fibers of the superficial MCL, and, sometimes, the pes anserinus attachment).¹³ Consequently, soft-tissue stabilizers seem to have different functions in flexion and extension and cannot reliably be released solely in extension or flexion for optimal gap balancing during TKA.² Other authors, in cadaveric studies, have found that a larger amount of coronal deformity correction is achieved with more distal soft-tissue releases from the joint line.^9,14 Surgical techniques for correcting FFD include removal of prominent anterior and posterior osteophytes, posterior capsular releases, sometimes PCL sacrifices, and even gastrocnemius recession.¹²

In our study, all 14 patients with severe extension and correspondingly severe flexion varus needed not only modest posterior medial soft-tissue releases for the severe extension varus, but also modest anterior medial releases for the flexion varus. The respective soft-tissue releases were confirmed in real time with computer navigation sequentially after bony resection and osteophyte removal. With this method, we restored final postoperative alignment to within 3° of the mechanical axis (Figure 6). Our experience here led us to believe that, with these patients, modest anterior medial and posterior medial releases could be performed at the start of surgery, as severe extension varus (>20°) almost certainly equates to severe flexion varus (>10°). Therein lies the clinical relevance of our study. However, not all patients with severe coronal plane deformity have correspondingly severe sagittal plane deformity in the form of FFD, as illustrated in our study. Therefore, not all patients with severe varus knee deformity need aggressive posterior capsular release or PCL recession to correct FFD. Some patients have mild hyperextension, which can be attributed partly to the postanesthesia effects of soft-tissue laxity. It is unclear exactly how much anesthesia contributes to this difference in sagittal alignment, though the majority of our patients had FFD. It is not our intent here to discuss the surgical techniques of soft-tissue balancing or to advocate routine use of computer navigation.

Many factors (eg, medial femoral condyle bone loss, medial tibial plateau bone loss, femur or tibia bowing, medial soft-tissue contracture) can contribute to varus malalignment. Current navigation technology cannot isolate the causes of varus alignment, and we did not intend to investigate them in this study. Our primary aim was to assess for a correlation between overall extension varus alignment and expected flexion varus. We also wanted to analyze the correlation between FFD and the coronal plane alignment, in extension and flexion, contributed by the combined bony and soft-tissue components in OA varus knees.

The strengths of this study are that it was a single-surgeon series with knee data from consecutive patients who had computer-navigated TKA. Patient data were prospectively generated from the navigation software and retrospectively analyzed. All navigation alignment was performed by a single surgeon, thereby eliminating examination bias during the time knee alignment data were being obtained. The study was adequately powered and had a large number of patients for data analysis. The authors believe that this is the first study to analyze alignment in both the coronal and sagittal plane in varus OA knees.

We acknowledge a few limitations in our study. Although several investigators have found that navigation can be used to achieve accurate postoperative alignment,^10,15,16 subtle errors may be inadvertently introduced at different points of alignment measurement. These error points include identification of visually selected anatomical landmarks; kinematic registration of hip, knee, and ankle; and intraoperative changes in the navigation environment (eg, inadvertent movement of pins or rigid bodies). In addition, different surgeons have different techniques for kinematic registration. However, the surgeries in our study were performed by the same surgeon, so this confounding factor was effectively removed. Another limitation was that navigation alignment was obtained during surgery, when patients were under anesthesia and in a supine, non-weight-bearing position, whereas routine clinical weight-bearing radiographs are taken with nonanesthetized patients and this might overestimate the deformities intraoperatively. However, all parameters were measured in the same patient under the same anesthetic effects, so this should not have affected the analyses. Most surgeons would make an intraoperative assessment of the severity of any deformity before the surgery proper anyway. Nevertheless, some authors have found that knee alignment obtained with intraoperative navigation correlated well with alignment obtained with weight-bearing radiographs.^17,18

Conclusion

Our study results showed that, in OA varus knees, extension varus highly correlated with flexion varus. However, there was no correlation between FFD and coronal plane varus deformity.

Osteoarthritic (OA) knees with varus deformities commonly present with tight, contracted medial collateral ligaments and soft-tissue sleeves.¹ More severe varus deformities require more extensive medial releases on the concave side to optimize flexion-extension gaps. Excessive soft-tissue releases in milder varus deformities can result in medial instability in flexion and extension.^2-4 Misjudgments in soft-tissue release can therefore lead to knee instability, an important cause of early total knee arthroplasty (TKA) failures.^2,5,6 Some authors have reported difficulty in coronal plane balancing in knees with preoperative varus deformity of more than 20°.^4,7

Surgeons often refer to varus as a description of coronal mal­alignment, mainly with the knee in extension. In the surgical setting, however, descriptions are given regarding differential medial soft-tissue tightness in extension and flexion. Balancing the knee in extension may not necessarily balance the knee in flexion. Thus, there is the concept of extension and flexion varus, which has not been well described in the literature. Releases on the anterior medial and posterior medial aspects of the proximal tibia have differential effects on flexion and extension gaps, respectively.²

Intraoperative alignment certainly has a pivotal role in component longevity.⁸ Since its advent in the 1990s, use of computer navigation in TKA has offered new hope for improving component alignment. Some authors routinely use computer navigation for intraoperative soft-tissue releases.⁹ A recent meta-analysis found that computer-navigated surgery is associated with fewer outliers in final component alignment compared with conventional TKA.¹⁰

Increased use of computer navigation in TKA at our institution in recent years has come with the observation that knees with severe extension varus seem to have correspondingly more severe flexion varus. Before computer navigation, coronal alignment of knees in flexion was almost impossible to measure because of the spatial alignment of the knees in that position.

We conducted a study to evaluate the relationship of extension and flexion varus in OA knees and to determine whether severity of fixed flexion deformity (FFD) in the sagittal plane correlates with severity of coronal plane varus deformity. We hypothesized that there would be differential varus in flexion and extension and that increasing knee extension varus would correlate closely with knee flexion varus beyond a certain tibiofemoral angle. We also hypothesized that severity of sagittal plane deformity will correlate with the severity of coronal plane deformity.

Patients and Methods

Data Collection

After this study was approved by our institution’s ethics review committee, we prospectively collected data from 403 consecutive computer-navigated TKAs performed at our institution between November 2008 and August 2011. Dr. Tan, who was not the primary physician, retrospectively analyzed the radiographic and navigation data.

Each patient’s knee varus-valgus angles were captured by Dr. Teo, an adult reconstruction surgeon, in standard fashion from maximal extension to 0º, 30º, 45º, 60º, 90º, and maximal flexion. An example of standard data capture appears in Table 1. With varus-hyperextension defined as –0.5° or less (more negative), neutral as 0°, and valgus-flexion as 0.5° or more, there were 362 varus knees, 41 valgus knees, and no neutral knees.

Study inclusion criteria were OA and varus deformity. Exclusion criteria were rheumatoid arthritis, other types of inflammatory arthritis, neuromuscular disorders, knees with valgus angulation, and incomplete data (Table 2). Figure 1 summarizes the inclusion/exclusion process, which left 317 knees available for study. Cases of incomplete data were likely due to computer errors or to inadvertent movement when navigation data were being acquired during surgery.

In conventional TKA, the main objective is to equalize flexion-extension gaps with knee at 90° flexion and 0° extension. The ability to achieve this often implies the knee will be balanced throughout its range of motion (ROM). From the data for the 317 study knees, 3 sets of values were extracted: varus angles from maximal knee extension (extension varus), varus angles from 90° knee flexion (flexion varus), and maximal knee extension. All knees were able to achieve 90° flexion.

Power Calculation

Our analysis used a correlation coefficient (r) of at least 0.5 at a 5% level of significance and power of 80%. With 317 knees, the study was more than adequately powered for significance.

Surgical and Navigation Technique

All patients underwent either general or regional anesthesia for their surgeries, which were performed by Dr. Teo. Standard medial parapatellar arthrotomy was performed. Navigation pins were then inserted into the femur and tibia outside the knee wound. Anatomical reference points were digitized per routine navigation requirements. (The reference for varus-valgus alignment of the femur is the mechanical femur axis defined by the digitized hip center and knee center, and the reference for varus-valgus alignment of the tibia is the mechanical tibia axis defined by the digitized tibia center and calculated ankle center. The ankle center is calculated by dividing the digitized transmalleolar axis according to a ratio of 56% lateral to 44% medial with the inherent navigation software.) Our institution uses an imageless navigation system (Navigation System II; Stryker Orthopedics, Mahwah, New Jersey).

The leg was then brought from maximal knee extension to maximal knee flexion to assess preoperative ROM, which indicates inherent flexion contracture or hyperextension. Varus-valgus measurements of the knee were then generated as part of the navigation software protocol. These measurements were obtained without additional varus or valgus stress applied to the knee and before any bony resection. The rest of the operation was completed using navigation to guide bony resection and soft-tissue balancing. The final components used were all cemented cruciate-substituting TKA implants. After component insertion, the knee was again brought through ROM from maximal knee extension to maximal knee flexion to assess postoperative ROM before wound closure.

Extension and Flexion Varus

As none of the patients in the flexion varus dataset (range, –0.5° to –19°) had a varus deformity of more than 20° at 90° flexion, we used a cutoff of 10° to divide these patients into 2 subgroups: less than 10° (237 knees) and 10° or more (80 knees). The extension varus dataset ranged from –0.5° to –24°. Incremental values of –0.5° to –24° in this dataset were then analyzed against the 90° flexion varus subgroups using logistic regression. A scatterplot of the relationship between extension and flexion varus is shown in Figure 2. The probability function was then derived and a probability graph plotted.

FFD and Extension and Flexion Varus

Maximal knee extension, obtained from intraoperative navigation measurements, ranged from –9° (hyperextension) to 33° (FFD) and maximal knee flexion ranged from 90° to 146°. Ninety-two knees had slight hyperextension, and 6 were neutral. Of the 317 OA knees with varus deformity, 219 (69%) had FFD. This sagittal plane alignment parameter was analyzed against coronal plane alignment in maximal knee extension and 90° knee flexion to determine if increasing severity of FFD corresponds with increasing extension or flexion varus.

Statistical Analysis

Statistical analysis was performed with Stata 10.1 (Statacorp, College Station, Texas). Significance was set at P < .05.

Results

Extension and Flexion Varus

Patient demographic data are listed in Table 3. Univariate logistic regression analysis revealed that age (P = .110), body mass index (P = .696), and sex (P = .584) did not affect the association between preoperative extension and flexion varus.

Mean (SD) preoperative extension varus was –9.9° (4.80°), and mean (SD) preoperative flexion 90° varus was –7.02° (3.74°). Linear regression of the data showed a significant positive correlation between preoperative extension varus and flexion varus (Pearson correlation coefficient, 0.57; P < .0001). The probability function was determined as follows: Probability of having flexion varus of more than 10° = 1 / (1 + e–z), where z = –4.014 – 0.265 × extension varus. Plotting the probability graph of flexion varus against varus angles at maximal knee extension from the probability formula yielded a sigmoid graph (Figure 3). The most linear part of the graph corresponds to the 10° to 20° of extension varus (solid line), demonstrating an almost linear increase in the probability of having more than 10° flexion varus with increasing extension varus from 10° to 20°. For extension varus of 20° or more, the probability of having flexion varus of more than 10° approaches 1.

FFD and Extension and Flexion Varus

Mean (SD) preoperative maximal knee extension (analogous to FFD) was 4.41° (7.50°), mean (SD) extension varus was –9.9° (4.80°), and mean (SD) 90° flexion varus was –7.02° (3.74°). We did not find any correlation between preoperative FFD and preoperative flexion varus (r = –0.02; P = .6583) or extension varus (r = –0.11; P = .046) (Figure 4).

Postoperative Alignment

Of the 317 OA knees, 18 had incomplete navigation-acquired postoperative alignment data. The postoperative alignment of the other 299 knees at various degrees of knee flexion is illustrated with a box-and-whisker plot (Figure 5).

Knees With Severe Extension Varus

Fourteen of the 15 knees with severe extension varus (>20°) had flexion varus of more than 9° (range, –9° to –17.5°, with only 1 outlier, at –5°). For the 15 patients, maximal knee extension ranged from –9° hyperextension to 27.5° FFD. Six knees had slight hyperextension, and 9 had FFD demonstrating large variability in sagittal alignment. Despite severe preoperative coronal deformity, all 15 knees had satisfactory deformity correction. Preoperative and postoperative knee alignment data for these 15 knees appear in Table 4 and Figure 6, respectively.

Discussion

OA varus knees represent a majority of the cases being managed by orthopedic surgeons. Soft-tissue contractures involving the medial collateral ligament (MCL), posteromedial capsule, pes anserinus, and semimembranosus muscle are commonly encountered. Bone loss may also occur on the tibial and femoral joint surfaces in knees with severe angular deformity. In an OA varus knee, bone loss tends to be mainly on the medial tibial plateau and usually on the posterior aspect of the tibia because flexion contractures often are concomitant with these marked deformities.¹¹ Therefore, a varus deformity is apparent whether the knee is extended or flexed. Our results showed a correlation between extension and flexion varus in OA varus knees. In contrast, for a valgus deformity, as bone loss can occur on both the tibial and femoral surfaces,¹¹ a similar correlation may not be seen. For that reason, and because there were only 41 valgus knees in this study, they were excluded. For FFD, soft-tissue contractures often involve both the posterior capsule and the posterior cruciate ligament (PCL). Posterior osteophytes often cause tenting of the posterior capsule in knees with FFD. Anteriorly, growth of osteophytes at the tibial spine and intercondylar notch of the femur can result in bony causes of restricted knee extension.¹²

One would expect increased coronal plane angular deformity to correspond to more severe FFD in the sagittal plane because the same pathology affects soft tissue or bones in an OA knee in both planes. Interestingly, our study results proved otherwise. FFD did not correlate with degree of extension or flexion varus severity. This phenomenon has not been described in the literature likely because clinical measurements of flexion varus and FFD were difficult to perform because of the spatial alignment of the knee in flexion. In recent years, however, computer navigation technology has made such measurements possible.

Mihalko and colleagues² established that soft-tissue releases on different parts of the proximal tibia have different effects on soft-tissue balancing in flexion and extension. In knees with extension varus, more releases are required on the posterior medial aspect of the tibia (the posterior oblique fibers of the superficial MCL, the posteromedial capsule, and, sometimes, the semimembranosus), whereas knees with flexion varus require more releases on the anterior medial aspect of the tibia (the deep MCL, the anterior fibers of the superficial MCL, and, sometimes, the pes anserinus attachment).¹³ Consequently, soft-tissue stabilizers seem to have different functions in flexion and extension and cannot reliably be released solely in extension or flexion for optimal gap balancing during TKA.² Other authors, in cadaveric studies, have found that a larger amount of coronal deformity correction is achieved with more distal soft-tissue releases from the joint line.^9,14 Surgical techniques for correcting FFD include removal of prominent anterior and posterior osteophytes, posterior capsular releases, sometimes PCL sacrifices, and even gastrocnemius recession.¹²

In our study, all 14 patients with severe extension and correspondingly severe flexion varus needed not only modest posterior medial soft-tissue releases for the severe extension varus, but also modest anterior medial releases for the flexion varus. The respective soft-tissue releases were confirmed in real time with computer navigation sequentially after bony resection and osteophyte removal. With this method, we restored final postoperative alignment to within 3° of the mechanical axis (Figure 6). Our experience here led us to believe that, with these patients, modest anterior medial and posterior medial releases could be performed at the start of surgery, as severe extension varus (>20°) almost certainly equates to severe flexion varus (>10°). Therein lies the clinical relevance of our study. However, not all patients with severe coronal plane deformity have correspondingly severe sagittal plane deformity in the form of FFD, as illustrated in our study. Therefore, not all patients with severe varus knee deformity need aggressive posterior capsular release or PCL recession to correct FFD. Some patients have mild hyperextension, which can be attributed partly to the postanesthesia effects of soft-tissue laxity. It is unclear exactly how much anesthesia contributes to this difference in sagittal alignment, though the majority of our patients had FFD. It is not our intent here to discuss the surgical techniques of soft-tissue balancing or to advocate routine use of computer navigation.

Many factors (eg, medial femoral condyle bone loss, medial tibial plateau bone loss, femur or tibia bowing, medial soft-tissue contracture) can contribute to varus malalignment. Current navigation technology cannot isolate the causes of varus alignment, and we did not intend to investigate them in this study. Our primary aim was to assess for a correlation between overall extension varus alignment and expected flexion varus. We also wanted to analyze the correlation between FFD and the coronal plane alignment, in extension and flexion, contributed by the combined bony and soft-tissue components in OA varus knees.

The strengths of this study are that it was a single-surgeon series with knee data from consecutive patients who had computer-navigated TKA. Patient data were prospectively generated from the navigation software and retrospectively analyzed. All navigation alignment was performed by a single surgeon, thereby eliminating examination bias during the time knee alignment data were being obtained. The study was adequately powered and had a large number of patients for data analysis. The authors believe that this is the first study to analyze alignment in both the coronal and sagittal plane in varus OA knees.

We acknowledge a few limitations in our study. Although several investigators have found that navigation can be used to achieve accurate postoperative alignment,^10,15,16 subtle errors may be inadvertently introduced at different points of alignment measurement. These error points include identification of visually selected anatomical landmarks; kinematic registration of hip, knee, and ankle; and intraoperative changes in the navigation environment (eg, inadvertent movement of pins or rigid bodies). In addition, different surgeons have different techniques for kinematic registration. However, the surgeries in our study were performed by the same surgeon, so this confounding factor was effectively removed. Another limitation was that navigation alignment was obtained during surgery, when patients were under anesthesia and in a supine, non-weight-bearing position, whereas routine clinical weight-bearing radiographs are taken with nonanesthetized patients and this might overestimate the deformities intraoperatively. However, all parameters were measured in the same patient under the same anesthetic effects, so this should not have affected the analyses. Most surgeons would make an intraoperative assessment of the severity of any deformity before the surgery proper anyway. Nevertheless, some authors have found that knee alignment obtained with intraoperative navigation correlated well with alignment obtained with weight-bearing radiographs.^17,18

Conclusion

Our study results showed that, in OA varus knees, extension varus highly correlated with flexion varus. However, there was no correlation between FFD and coronal plane varus deformity.

Postoperative dislocation remains a common complication of primary total hip arthroplasties (THAs), affecting less than 1% to more than 10% in reported series.^1,2 In large datasets for modern implants, the incidence of dislocation is 2% to 4%.^3,4 Given that more than 200,000 THAs are performed in the United States each year,⁵ these low percentages represent a large number of patients. The multiplex patient variables that affect THA stability include age, sex, body mass index (BMI), and comorbid conditions.^6-8 Surgical approach, restoration of leg length and femoral offset, femoral head size, and component positioning are also important surgical factors that can increase or decrease the incidence of dislocation.^3,8,9 In particular, appropriate acetabular component orientation is crucial; surgeons can control this factor and thereby limit the occurrence of dislocation.¹⁰ Furthermore, acetabular malpositioning can increase the risk of liner fractures and accelerate bearing-surface wear.^11-14

To minimize the risk of postoperative dislocation, surgeons traditionally have targeted the Lewinnek safe zone, with its mean (SD) inclination of 40° (10°) and mean (SD) anteversion of 15° (10°), for acetabular component orientation.¹⁵ However, the applicability of this target zone to preventing hip instability using modern implant designs, components, and surgical techniques remains unknown. Achieving acetabular orientation based on maximizing range of motion (ROM) before impingement may be optimal, with anteversion from 20° to 30° and inclination from 40° to 45°.^16,17 Furthermore, mean (SD) native acetabular anteversion ranges from 21.3° (6.2°) for men to 24.6° (6.6°) for women.¹⁸ Placing THA acetabular components near the native range for anteversion may best provide impingement-free ROM and thus optimize THA stability,^16,19 but this has not been proved in a clinical study.

Early dislocation is typically classified as occurring within 6 months after surgery,⁹ with almost 80% of dislocations occurring within 3 months after surgery.¹⁰ Surgeon-specific factors, such as acetabular component positioning, are thought to have a predominant effect on dislocations in the early postoperative period.¹⁰ Computer-assisted surgery (CAS), such as imageless navigation, is more accurate than conventional methods for acetabular component placement,^20-23 but the clinical relevance of improving accuracy for acetabular component placement has not been shown with respect to altering patient outcomes.²³

We conducted a study in a large single-surgeon patient cohort to determine the incidence of early postoperative dislocation with target anteversion increased to 25°, approximating mean native acetabular anteversion.^16,19 In addition, we sought to determine the accuracy of imageless navigation in achieving target acetabular component placement.

Materials and Methods

After obtaining institutional review board approval for this retrospective clinical study, we reviewed 671 consecutive cases of primary THA performed by a single surgeon using an imageless CAS system (AchieveCAS; Smith & Nephew, Memphis, Tennessee) between July 2006 and October 2012. THAs were excluded if a metal-on-metal bearing surface was used, if an adequate 6-week postoperative supine anteroposterior (AP) pelvis radiograph was unavailable, or if 6-month clinical follow-up findings were not available (Figure 1). The quality of AP radiographs was deemed poor if they were not centered on the symphysis pubis and if the sacrococcygeal joint was not centered over the symphysis pubis. After exclusion criteria were applied, 553 arthroplasties (479 patients) with a mean (SD) follow-up of 2.4 (1.4) years remained. Perioperative demographic data and component sizes are listed in Table 1.

During surgery, the anterior pelvic plane, defined by the anterior-superior iliac spines and pubic tubercle, was registered with the CAS system with the patient in the supine position. THA was performed with the patient in the lateral decubitus position using a posterolateral technique. For all patients, the surgeon used a hemispherical acetabular component (R3 Acetabular System; Smith & Nephew); bearings that were either metal on highly cross-linked polyethylene (XLPE) or Oxinium (Smith & Nephew) on XLPE; and neutral XLPE acetabular inserts. The goals for acetabular inclination and anteversion were 40° and 25°, respectively, with ±10° each for the target zone. The CAS system was used to adjust target anteversion for sagittal pelvic tilt.²⁴ Uncemented femoral components were used for all patients, and the goal for femoral component anteversion was 15°. Transosseous repair of the posterior capsule and short external rotators was performed after component implantation.²⁵

On each 6-week postoperative radiograph, acetabular orientation was measured with Ein-Bild-Röntgen-Analyse (EBRA; University of Innsbruck, Austria) software, which provides a validated method for measuring acetabular inclination and anteversion on supine AP pelvis radiographs.^10,26 Pelvic boundaries were delineated with grid lines defining pelvic position. Reference points around the projections of the prosthetic femoral head, the hemispherical cup, and the rim of the cup were marked (Figure 2). EBRA calculated radiographic inclination and anteversion of the acetabular component based on the spatial position of the cup center in relation to the plane of the radiograph and the pelvic position.²⁶

Charts were reviewed to identify patients with early postoperative dislocations, as well as dislocation timing, recurrence, and other characteristics. We defined early dislocation as instability occurring within 6 months after surgery. Revision surgery for instability was also identified.

For the statistical analysis, orientation error was defined as the absolute value of the difference between target orientation (40° inclination, 25° anteversion) and radiographic measurements. Repeated-measures multiple regression with the generalized estimating equations approach was used to identify baseline patient characteristics (age, sex, BMI, primary diagnosis, laterality) associated with component positioning outside of our targeted ranges for inclination and anteversion. Fisher exact tests were used to examine the relationship between dislocation and component placement in either the Lewinnek safe zone or our targeted zone. All tests were 2-sided with a significance level of .05. All analyses were performed with SAS for Windows 9.3 (SAS Institute, Cary, North Carolina).

Results

Mean (SD) acetabular inclination was 42.2° (4.9°) (range, 27.6°-65.0°), with a mean (SD) orientation error of 4.2° (3.4°) (Figure 3A). Mean (SD) anteversion was 23.9° (6.5°) (range, 6.2°-48.0°), with a mean (SD) orientation error of 5.2° (4.1°) (Figure 3B). Components were placed outside the Lewinnek safe zone for inclination or anteversion in 46.5% of cases and outside the target zone in 17.7% of cases (Figure 4). Variation in acetabular anteversion alone accounted for 67.3% of target zone outliers (Table 2). Only 0.9% of components were placed outside the target ranges for both inclination and anteversion.

Regression analysis was performed separately for inclination and anteversion to determine the risk factors for placing the acetabular component outside the target orientation ranges. Only higher BMI was associated with malposition with respect to inclination (hazard ratio [HR], 1.059; 95% confidence interval [CI], 1.011-1.111; P = .017). Of obese patients with inclination outside the target range, 90.9% had an inclination angle of more than 50°. Associations between inclination outside the target range and age (P = .769), sex (P = .217), preoperative diagnosis (P > .99), and laterality (P = .106) were statistically insignificant. Only female sex was associated with position of the acetabular component outside the target range for anteversion (HR, 1.871; 95% CI, 1.061-3.299; P = .030). Of female patients with anteversion outside the target range, 70.0% had anteversion of less than 15°. Associations between anteversion outside the target range and age (P = .762), BMI (P = .583), preoperative diagnosis (P > .99), and laterality (P = .235) were statistically insignificant.

Six THAs (1.1%) in 6 patients experienced dislocation within 6 months after surgery (Table 3); mean (SD) time of dislocation was 58.3 (13.8) days after surgery. There was no relationship between dislocation incidence and component placement in the Lewinnek zone (P = .224) or our target zone (P = .287). Of the dislocation cases, 50% involved female patients, and 50% involved right hips. Mean (SD) age of these patients was 53.3 (7.6) years. Mean (SD) BMI was 25.4 (0.9) kg/m². Osteoarthritis was the primary diagnosis for all patients with early dislocation; 32- or 36-mm femoral heads were used in these cases. Two patients had acetabular components placed outside of our target zone. One patient, who had abnormal pelvic obliquity and sagittal tilt from scoliosis (Figures 5A, 5B), had an acetabular component placed outside both the target zone and the Lewinnek safe zone. Mean (SD) acetabular inclination was 39.8° (3.6°), and mean (SD) anteversion was 21.8° (7.3°) (Figure 5C). Two dislocations resulted from trauma, 1 dislocation was related to hyperlaxity, 1 patient had cerebral palsy, and 1 patient had no evident predisposing risk factors. Three patients (0.54%) had multiple episodes of instability requiring revision during the follow-up period.

Discussion

To our knowledge, this study represents the largest cohort of primary THAs performed with an imageless navigation system. Our results showed that increasing targeted acetabular anteversion to 25° using a posterolateral surgical approach and modern implants resulted in a 1.1% incidence of early dislocation and a 0.54% incidence of recurrent instability requiring reoperation. Of the patients with a dislocation, only 1 did not experience trauma and did not have a risk factor for dislocation. Only 1 patient with a dislocation had acetabular components positioned outside both the target zone and the Lewinnek safe zone. The acetabular component was placed within the target zone in 82.3% of cases in which the imageless navigation system was used. In our cohort, BMI was the only risk factor for placement of the acetabular component outside our target range for inclination, and sex was associated with components outside the target range for anteversion.

Early dislocation after THA is often related to improper implant orientation, inadequate restoration of offset and myofascial tension, and decreased femoral head–neck ratio.⁸ Although dislocation rates in the literature vary widely,^1,2 Medicare data suggest that the rate for the first 6 months after surgery can be as high as 4.21%.^3,4 Although use of femoral heads with a diameter of 32 mm or larger may decrease this rate to 2.14%,³ accurate acetabular component orientation helps prevent postoperative dislocation.¹⁰ Using an imageless navigation system to target 25° of anteversion and 40° of inclination resulted in an early-dislocation rate about 49% less than the rate in a Medicare population treated with similar, modern implants.³

Callanan and colleagues¹¹ found that freehand techniques were inaccurate for acetabular positioning in up to 50% of cases, and several studies have demonstrated that imageless navigation systems were more accurate than conventional guides.^20,21,27-29 Higher BMI has been implicated as a risk factor for acetabular malpositioning in several studies of the accuracy of freehand techniques¹¹ and imageless navigation techniques.^23,30 Soft-tissue impediment to the component insertion handle poses a risk of increased inclination and inadequate anteversion, regardless of method used (conventional, CAS). When the acetabular component is placed freehand in obese patients, it is difficult to judge the position of the pelvis on the operating room table. For imageless navigation, a larger amount of adipose tissue over bony landmarks may limit the accuracy of anterior pelvic plane registration.³⁰ Sex typically is not cited as a risk factor for inaccurate acetabular component positioning. We speculate that omitted-variable bias may explain the observed association between female sex and anteversion. For example, changes in postoperative pelvic tilt alter apparent anteversion on plain radiographs,^31-34 but preoperative and postoperative sagittal pelvic tilt was not recorded in this study.

The proper position of the acetabular component has been debated.^15,16,35,36 Although it is generally agreed that inclination of 40° ± 10° balances ROM, stability, and bearing-surface wear,^12,13,15,16 proposed targets for anteversion vary widely, from 0° to 40°.^35,36 Patel and colleagues¹⁶ formulated computer models based on cadaveric specimens to determine that THA impingement was minimized when the acetabular component was placed to match the native anteversion of the acetabulum.In their study model, 20° of anteversion paralleled native acetabular orientation. Tohtz and colleagues¹⁸ reviewed computed tomography scans of 144 female hips and 192 male hips and found that mean (SD) anteversion was 24.6° (6.6°) for women and 21.3° (6.2°) for men. Whether native anatomy is a valid reference for acetabular anteversion is controversial,¹⁹ and definitive recommendations for target anteversion cannot be made, as the effect of acetabular anteversion on the wear of various bearing materials is unknown.¹⁴ Yet, as with inclination, ideal anteversion is likely a compromise between maximizing impingement-free ROM and minimizing wear.

The present study had several limitations. A single-surgeon patient series was reviewed retrospectively, and there was no control group. We determined the incidence only of early dislocation, and 5.3% of THAs that were not metal-on-metal were either lost to follow-up or had inadequate radiographs. However, of the patients excluded for inadequate radiographs, none had an early dislocation. The effects of our surgical techniques on long-term outcomes, bearing wear, and dislocation are unknown. We were not able to comment on the direction of dislocation for any of the 6 patients with early dislocation, as all dislocations were reduced at facilities other than our hospital. Therefore, we cannot determine whether increasing acetabular anteversion resulted in a larger number of anterior versus posterior dislocations.¹⁵

We did not use CAS to place any of the femoral components. Therefore, we could not accurately target combined anteversion, defined as the sum of acetabular and femoral version, which may be an important determinant of THA stability.²⁸ Although restoration of femoral offset and leg length is important in preventing THA dislocation,⁸ the CAS techniques used did not influence these parameters, and they were not measured.

As an imageless navigation system was used, there were no preoperative axial images, which could have been used to assess native acetabular orientation. This limited our assessment with respect to matching each patient’s natural anteversion. Imageless navigation, which references only the anterior pelvic plane, may not be reliable in patients with excessive sagittal pelvic tilt.³⁷ Furthermore, changes in the functional position of the pelvis from supine to sitting to standing were not accounted for, and changes in sagittal tilt between these positions can be significant.³⁸ Changes in sagittal pelvic tilt affect measurement of acetabular anteversion on plain radiographs, with anterior tilt reducing apparent anteversion and posterior tilt increasing it.^32,34 Although postoperative computed tomography is the gold standard for assessing acetabular component orientation, EBRA significantly reduces errors of measurement on plain radiographs.¹⁰ Some variability in measured anteversion may be explained by our surgical technique. In particular, if the cup was uncovered anteriorly, additional anteversion was usually accepted during surgery to minimize anterior impingement and limit the risk of iliopsoas tendonitis.^16,39

Our study results suggested that increasing target acetabular anteversion to 25° may reduce the incidence of early postoperative instability relative to rates reported in the literature. Despite the higher accuracy of component placement with an imageless navigation system, dislocations occurred in patients with acetabular components positioned in our target zone and in the historical safe zone. These dislocations support the notion that there likely is no absolute safe range for acetabular component positioning, as THA stability depends on many factors. Ideal targets for implant orientation for acetabulum and femur may be patient-specific.^16,19 Investigators should prospectively evaluate patient-specific THA component positioning and determine its effect on postoperative dislocation and bearing-surface wear. As specific implant targets are further defined, tools that are more precise and accurate than conventional techniques will be needed to achieve goal component positioning. Our study results confirmed that imageless navigation is an accurate method for achieving acetabular orientation targets.

Postoperative dislocation remains a common complication of primary total hip arthroplasties (THAs), affecting less than 1% to more than 10% in reported series.^1,2 In large datasets for modern implants, the incidence of dislocation is 2% to 4%.^3,4 Given that more than 200,000 THAs are performed in the United States each year,⁵ these low percentages represent a large number of patients. The multiplex patient variables that affect THA stability include age, sex, body mass index (BMI), and comorbid conditions.^6-8 Surgical approach, restoration of leg length and femoral offset, femoral head size, and component positioning are also important surgical factors that can increase or decrease the incidence of dislocation.^3,8,9 In particular, appropriate acetabular component orientation is crucial; surgeons can control this factor and thereby limit the occurrence of dislocation.¹⁰ Furthermore, acetabular malpositioning can increase the risk of liner fractures and accelerate bearing-surface wear.^11-14

To minimize the risk of postoperative dislocation, surgeons traditionally have targeted the Lewinnek safe zone, with its mean (SD) inclination of 40° (10°) and mean (SD) anteversion of 15° (10°), for acetabular component orientation.¹⁵ However, the applicability of this target zone to preventing hip instability using modern implant designs, components, and surgical techniques remains unknown. Achieving acetabular orientation based on maximizing range of motion (ROM) before impingement may be optimal, with anteversion from 20° to 30° and inclination from 40° to 45°.^16,17 Furthermore, mean (SD) native acetabular anteversion ranges from 21.3° (6.2°) for men to 24.6° (6.6°) for women.¹⁸ Placing THA acetabular components near the native range for anteversion may best provide impingement-free ROM and thus optimize THA stability,^16,19 but this has not been proved in a clinical study.

Early dislocation is typically classified as occurring within 6 months after surgery,⁹ with almost 80% of dislocations occurring within 3 months after surgery.¹⁰ Surgeon-specific factors, such as acetabular component positioning, are thought to have a predominant effect on dislocations in the early postoperative period.¹⁰ Computer-assisted surgery (CAS), such as imageless navigation, is more accurate than conventional methods for acetabular component placement,^20-23 but the clinical relevance of improving accuracy for acetabular component placement has not been shown with respect to altering patient outcomes.²³

We conducted a study in a large single-surgeon patient cohort to determine the incidence of early postoperative dislocation with target anteversion increased to 25°, approximating mean native acetabular anteversion.^16,19 In addition, we sought to determine the accuracy of imageless navigation in achieving target acetabular component placement.

Materials and Methods

After obtaining institutional review board approval for this retrospective clinical study, we reviewed 671 consecutive cases of primary THA performed by a single surgeon using an imageless CAS system (AchieveCAS; Smith & Nephew, Memphis, Tennessee) between July 2006 and October 2012. THAs were excluded if a metal-on-metal bearing surface was used, if an adequate 6-week postoperative supine anteroposterior (AP) pelvis radiograph was unavailable, or if 6-month clinical follow-up findings were not available (Figure 1). The quality of AP radiographs was deemed poor if they were not centered on the symphysis pubis and if the sacrococcygeal joint was not centered over the symphysis pubis. After exclusion criteria were applied, 553 arthroplasties (479 patients) with a mean (SD) follow-up of 2.4 (1.4) years remained. Perioperative demographic data and component sizes are listed in Table 1.

During surgery, the anterior pelvic plane, defined by the anterior-superior iliac spines and pubic tubercle, was registered with the CAS system with the patient in the supine position. THA was performed with the patient in the lateral decubitus position using a posterolateral technique. For all patients, the surgeon used a hemispherical acetabular component (R3 Acetabular System; Smith & Nephew); bearings that were either metal on highly cross-linked polyethylene (XLPE) or Oxinium (Smith & Nephew) on XLPE; and neutral XLPE acetabular inserts. The goals for acetabular inclination and anteversion were 40° and 25°, respectively, with ±10° each for the target zone. The CAS system was used to adjust target anteversion for sagittal pelvic tilt.²⁴ Uncemented femoral components were used for all patients, and the goal for femoral component anteversion was 15°. Transosseous repair of the posterior capsule and short external rotators was performed after component implantation.²⁵

On each 6-week postoperative radiograph, acetabular orientation was measured with Ein-Bild-Röntgen-Analyse (EBRA; University of Innsbruck, Austria) software, which provides a validated method for measuring acetabular inclination and anteversion on supine AP pelvis radiographs.^10,26 Pelvic boundaries were delineated with grid lines defining pelvic position. Reference points around the projections of the prosthetic femoral head, the hemispherical cup, and the rim of the cup were marked (Figure 2). EBRA calculated radiographic inclination and anteversion of the acetabular component based on the spatial position of the cup center in relation to the plane of the radiograph and the pelvic position.²⁶

Charts were reviewed to identify patients with early postoperative dislocations, as well as dislocation timing, recurrence, and other characteristics. We defined early dislocation as instability occurring within 6 months after surgery. Revision surgery for instability was also identified.

For the statistical analysis, orientation error was defined as the absolute value of the difference between target orientation (40° inclination, 25° anteversion) and radiographic measurements. Repeated-measures multiple regression with the generalized estimating equations approach was used to identify baseline patient characteristics (age, sex, BMI, primary diagnosis, laterality) associated with component positioning outside of our targeted ranges for inclination and anteversion. Fisher exact tests were used to examine the relationship between dislocation and component placement in either the Lewinnek safe zone or our targeted zone. All tests were 2-sided with a significance level of .05. All analyses were performed with SAS for Windows 9.3 (SAS Institute, Cary, North Carolina).

Results

Mean (SD) acetabular inclination was 42.2° (4.9°) (range, 27.6°-65.0°), with a mean (SD) orientation error of 4.2° (3.4°) (Figure 3A). Mean (SD) anteversion was 23.9° (6.5°) (range, 6.2°-48.0°), with a mean (SD) orientation error of 5.2° (4.1°) (Figure 3B). Components were placed outside the Lewinnek safe zone for inclination or anteversion in 46.5% of cases and outside the target zone in 17.7% of cases (Figure 4). Variation in acetabular anteversion alone accounted for 67.3% of target zone outliers (Table 2). Only 0.9% of components were placed outside the target ranges for both inclination and anteversion.

Regression analysis was performed separately for inclination and anteversion to determine the risk factors for placing the acetabular component outside the target orientation ranges. Only higher BMI was associated with malposition with respect to inclination (hazard ratio [HR], 1.059; 95% confidence interval [CI], 1.011-1.111; P = .017). Of obese patients with inclination outside the target range, 90.9% had an inclination angle of more than 50°. Associations between inclination outside the target range and age (P = .769), sex (P = .217), preoperative diagnosis (P > .99), and laterality (P = .106) were statistically insignificant. Only female sex was associated with position of the acetabular component outside the target range for anteversion (HR, 1.871; 95% CI, 1.061-3.299; P = .030). Of female patients with anteversion outside the target range, 70.0% had anteversion of less than 15°. Associations between anteversion outside the target range and age (P = .762), BMI (P = .583), preoperative diagnosis (P > .99), and laterality (P = .235) were statistically insignificant.

Six THAs (1.1%) in 6 patients experienced dislocation within 6 months after surgery (Table 3); mean (SD) time of dislocation was 58.3 (13.8) days after surgery. There was no relationship between dislocation incidence and component placement in the Lewinnek zone (P = .224) or our target zone (P = .287). Of the dislocation cases, 50% involved female patients, and 50% involved right hips. Mean (SD) age of these patients was 53.3 (7.6) years. Mean (SD) BMI was 25.4 (0.9) kg/m². Osteoarthritis was the primary diagnosis for all patients with early dislocation; 32- or 36-mm femoral heads were used in these cases. Two patients had acetabular components placed outside of our target zone. One patient, who had abnormal pelvic obliquity and sagittal tilt from scoliosis (Figures 5A, 5B), had an acetabular component placed outside both the target zone and the Lewinnek safe zone. Mean (SD) acetabular inclination was 39.8° (3.6°), and mean (SD) anteversion was 21.8° (7.3°) (Figure 5C). Two dislocations resulted from trauma, 1 dislocation was related to hyperlaxity, 1 patient had cerebral palsy, and 1 patient had no evident predisposing risk factors. Three patients (0.54%) had multiple episodes of instability requiring revision during the follow-up period.

Discussion

To our knowledge, this study represents the largest cohort of primary THAs performed with an imageless navigation system. Our results showed that increasing targeted acetabular anteversion to 25° using a posterolateral surgical approach and modern implants resulted in a 1.1% incidence of early dislocation and a 0.54% incidence of recurrent instability requiring reoperation. Of the patients with a dislocation, only 1 did not experience trauma and did not have a risk factor for dislocation. Only 1 patient with a dislocation had acetabular components positioned outside both the target zone and the Lewinnek safe zone. The acetabular component was placed within the target zone in 82.3% of cases in which the imageless navigation system was used. In our cohort, BMI was the only risk factor for placement of the acetabular component outside our target range for inclination, and sex was associated with components outside the target range for anteversion.

Early dislocation after THA is often related to improper implant orientation, inadequate restoration of offset and myofascial tension, and decreased femoral head–neck ratio.⁸ Although dislocation rates in the literature vary widely,^1,2 Medicare data suggest that the rate for the first 6 months after surgery can be as high as 4.21%.^3,4 Although use of femoral heads with a diameter of 32 mm or larger may decrease this rate to 2.14%,³ accurate acetabular component orientation helps prevent postoperative dislocation.¹⁰ Using an imageless navigation system to target 25° of anteversion and 40° of inclination resulted in an early-dislocation rate about 49% less than the rate in a Medicare population treated with similar, modern implants.³

Callanan and colleagues¹¹ found that freehand techniques were inaccurate for acetabular positioning in up to 50% of cases, and several studies have demonstrated that imageless navigation systems were more accurate than conventional guides.^20,21,27-29 Higher BMI has been implicated as a risk factor for acetabular malpositioning in several studies of the accuracy of freehand techniques¹¹ and imageless navigation techniques.^23,30 Soft-tissue impediment to the component insertion handle poses a risk of increased inclination and inadequate anteversion, regardless of method used (conventional, CAS). When the acetabular component is placed freehand in obese patients, it is difficult to judge the position of the pelvis on the operating room table. For imageless navigation, a larger amount of adipose tissue over bony landmarks may limit the accuracy of anterior pelvic plane registration.³⁰ Sex typically is not cited as a risk factor for inaccurate acetabular component positioning. We speculate that omitted-variable bias may explain the observed association between female sex and anteversion. For example, changes in postoperative pelvic tilt alter apparent anteversion on plain radiographs,^31-34 but preoperative and postoperative sagittal pelvic tilt was not recorded in this study.

The proper position of the acetabular component has been debated.^15,16,35,36 Although it is generally agreed that inclination of 40° ± 10° balances ROM, stability, and bearing-surface wear,^12,13,15,16 proposed targets for anteversion vary widely, from 0° to 40°.^35,36 Patel and colleagues¹⁶ formulated computer models based on cadaveric specimens to determine that THA impingement was minimized when the acetabular component was placed to match the native anteversion of the acetabulum.In their study model, 20° of anteversion paralleled native acetabular orientation. Tohtz and colleagues¹⁸ reviewed computed tomography scans of 144 female hips and 192 male hips and found that mean (SD) anteversion was 24.6° (6.6°) for women and 21.3° (6.2°) for men. Whether native anatomy is a valid reference for acetabular anteversion is controversial,¹⁹ and definitive recommendations for target anteversion cannot be made, as the effect of acetabular anteversion on the wear of various bearing materials is unknown.¹⁴ Yet, as with inclination, ideal anteversion is likely a compromise between maximizing impingement-free ROM and minimizing wear.

The present study had several limitations. A single-surgeon patient series was reviewed retrospectively, and there was no control group. We determined the incidence only of early dislocation, and 5.3% of THAs that were not metal-on-metal were either lost to follow-up or had inadequate radiographs. However, of the patients excluded for inadequate radiographs, none had an early dislocation. The effects of our surgical techniques on long-term outcomes, bearing wear, and dislocation are unknown. We were not able to comment on the direction of dislocation for any of the 6 patients with early dislocation, as all dislocations were reduced at facilities other than our hospital. Therefore, we cannot determine whether increasing acetabular anteversion resulted in a larger number of anterior versus posterior dislocations.¹⁵

We did not use CAS to place any of the femoral components. Therefore, we could not accurately target combined anteversion, defined as the sum of acetabular and femoral version, which may be an important determinant of THA stability.²⁸ Although restoration of femoral offset and leg length is important in preventing THA dislocation,⁸ the CAS techniques used did not influence these parameters, and they were not measured.

As an imageless navigation system was used, there were no preoperative axial images, which could have been used to assess native acetabular orientation. This limited our assessment with respect to matching each patient’s natural anteversion. Imageless navigation, which references only the anterior pelvic plane, may not be reliable in patients with excessive sagittal pelvic tilt.³⁷ Furthermore, changes in the functional position of the pelvis from supine to sitting to standing were not accounted for, and changes in sagittal tilt between these positions can be significant.³⁸ Changes in sagittal pelvic tilt affect measurement of acetabular anteversion on plain radiographs, with anterior tilt reducing apparent anteversion and posterior tilt increasing it.^32,34 Although postoperative computed tomography is the gold standard for assessing acetabular component orientation, EBRA significantly reduces errors of measurement on plain radiographs.¹⁰ Some variability in measured anteversion may be explained by our surgical technique. In particular, if the cup was uncovered anteriorly, additional anteversion was usually accepted during surgery to minimize anterior impingement and limit the risk of iliopsoas tendonitis.^16,39

Our study results suggested that increasing target acetabular anteversion to 25° may reduce the incidence of early postoperative instability relative to rates reported in the literature. Despite the higher accuracy of component placement with an imageless navigation system, dislocations occurred in patients with acetabular components positioned in our target zone and in the historical safe zone. These dislocations support the notion that there likely is no absolute safe range for acetabular component positioning, as THA stability depends on many factors. Ideal targets for implant orientation for acetabulum and femur may be patient-specific.^16,19 Investigators should prospectively evaluate patient-specific THA component positioning and determine its effect on postoperative dislocation and bearing-surface wear. As specific implant targets are further defined, tools that are more precise and accurate than conventional techniques will be needed to achieve goal component positioning. Our study results confirmed that imageless navigation is an accurate method for achieving acetabular orientation targets.

Postoperative dislocation remains a common complication of primary total hip arthroplasties (THAs), affecting less than 1% to more than 10% in reported series.^1,2 In large datasets for modern implants, the incidence of dislocation is 2% to 4%.^3,4 Given that more than 200,000 THAs are performed in the United States each year,⁵ these low percentages represent a large number of patients. The multiplex patient variables that affect THA stability include age, sex, body mass index (BMI), and comorbid conditions.^6-8 Surgical approach, restoration of leg length and femoral offset, femoral head size, and component positioning are also important surgical factors that can increase or decrease the incidence of dislocation.^3,8,9 In particular, appropriate acetabular component orientation is crucial; surgeons can control this factor and thereby limit the occurrence of dislocation.¹⁰ Furthermore, acetabular malpositioning can increase the risk of liner fractures and accelerate bearing-surface wear.^11-14

To minimize the risk of postoperative dislocation, surgeons traditionally have targeted the Lewinnek safe zone, with its mean (SD) inclination of 40° (10°) and mean (SD) anteversion of 15° (10°), for acetabular component orientation.¹⁵ However, the applicability of this target zone to preventing hip instability using modern implant designs, components, and surgical techniques remains unknown. Achieving acetabular orientation based on maximizing range of motion (ROM) before impingement may be optimal, with anteversion from 20° to 30° and inclination from 40° to 45°.^16,17 Furthermore, mean (SD) native acetabular anteversion ranges from 21.3° (6.2°) for men to 24.6° (6.6°) for women.¹⁸ Placing THA acetabular components near the native range for anteversion may best provide impingement-free ROM and thus optimize THA stability,^16,19 but this has not been proved in a clinical study.

Early dislocation is typically classified as occurring within 6 months after surgery,⁹ with almost 80% of dislocations occurring within 3 months after surgery.¹⁰ Surgeon-specific factors, such as acetabular component positioning, are thought to have a predominant effect on dislocations in the early postoperative period.¹⁰ Computer-assisted surgery (CAS), such as imageless navigation, is more accurate than conventional methods for acetabular component placement,^20-23 but the clinical relevance of improving accuracy for acetabular component placement has not been shown with respect to altering patient outcomes.²³

We conducted a study in a large single-surgeon patient cohort to determine the incidence of early postoperative dislocation with target anteversion increased to 25°, approximating mean native acetabular anteversion.^16,19 In addition, we sought to determine the accuracy of imageless navigation in achieving target acetabular component placement.

Materials and Methods

After obtaining institutional review board approval for this retrospective clinical study, we reviewed 671 consecutive cases of primary THA performed by a single surgeon using an imageless CAS system (AchieveCAS; Smith & Nephew, Memphis, Tennessee) between July 2006 and October 2012. THAs were excluded if a metal-on-metal bearing surface was used, if an adequate 6-week postoperative supine anteroposterior (AP) pelvis radiograph was unavailable, or if 6-month clinical follow-up findings were not available (Figure 1). The quality of AP radiographs was deemed poor if they were not centered on the symphysis pubis and if the sacrococcygeal joint was not centered over the symphysis pubis. After exclusion criteria were applied, 553 arthroplasties (479 patients) with a mean (SD) follow-up of 2.4 (1.4) years remained. Perioperative demographic data and component sizes are listed in Table 1.

During surgery, the anterior pelvic plane, defined by the anterior-superior iliac spines and pubic tubercle, was registered with the CAS system with the patient in the supine position. THA was performed with the patient in the lateral decubitus position using a posterolateral technique. For all patients, the surgeon used a hemispherical acetabular component (R3 Acetabular System; Smith & Nephew); bearings that were either metal on highly cross-linked polyethylene (XLPE) or Oxinium (Smith & Nephew) on XLPE; and neutral XLPE acetabular inserts. The goals for acetabular inclination and anteversion were 40° and 25°, respectively, with ±10° each for the target zone. The CAS system was used to adjust target anteversion for sagittal pelvic tilt.²⁴ Uncemented femoral components were used for all patients, and the goal for femoral component anteversion was 15°. Transosseous repair of the posterior capsule and short external rotators was performed after component implantation.²⁵

On each 6-week postoperative radiograph, acetabular orientation was measured with Ein-Bild-Röntgen-Analyse (EBRA; University of Innsbruck, Austria) software, which provides a validated method for measuring acetabular inclination and anteversion on supine AP pelvis radiographs.^10,26 Pelvic boundaries were delineated with grid lines defining pelvic position. Reference points around the projections of the prosthetic femoral head, the hemispherical cup, and the rim of the cup were marked (Figure 2). EBRA calculated radiographic inclination and anteversion of the acetabular component based on the spatial position of the cup center in relation to the plane of the radiograph and the pelvic position.²⁶

Charts were reviewed to identify patients with early postoperative dislocations, as well as dislocation timing, recurrence, and other characteristics. We defined early dislocation as instability occurring within 6 months after surgery. Revision surgery for instability was also identified.

For the statistical analysis, orientation error was defined as the absolute value of the difference between target orientation (40° inclination, 25° anteversion) and radiographic measurements. Repeated-measures multiple regression with the generalized estimating equations approach was used to identify baseline patient characteristics (age, sex, BMI, primary diagnosis, laterality) associated with component positioning outside of our targeted ranges for inclination and anteversion. Fisher exact tests were used to examine the relationship between dislocation and component placement in either the Lewinnek safe zone or our targeted zone. All tests were 2-sided with a significance level of .05. All analyses were performed with SAS for Windows 9.3 (SAS Institute, Cary, North Carolina).

Results

Mean (SD) acetabular inclination was 42.2° (4.9°) (range, 27.6°-65.0°), with a mean (SD) orientation error of 4.2° (3.4°) (Figure 3A). Mean (SD) anteversion was 23.9° (6.5°) (range, 6.2°-48.0°), with a mean (SD) orientation error of 5.2° (4.1°) (Figure 3B). Components were placed outside the Lewinnek safe zone for inclination or anteversion in 46.5% of cases and outside the target zone in 17.7% of cases (Figure 4). Variation in acetabular anteversion alone accounted for 67.3% of target zone outliers (Table 2). Only 0.9% of components were placed outside the target ranges for both inclination and anteversion.

Regression analysis was performed separately for inclination and anteversion to determine the risk factors for placing the acetabular component outside the target orientation ranges. Only higher BMI was associated with malposition with respect to inclination (hazard ratio [HR], 1.059; 95% confidence interval [CI], 1.011-1.111; P = .017). Of obese patients with inclination outside the target range, 90.9% had an inclination angle of more than 50°. Associations between inclination outside the target range and age (P = .769), sex (P = .217), preoperative diagnosis (P > .99), and laterality (P = .106) were statistically insignificant. Only female sex was associated with position of the acetabular component outside the target range for anteversion (HR, 1.871; 95% CI, 1.061-3.299; P = .030). Of female patients with anteversion outside the target range, 70.0% had anteversion of less than 15°. Associations between anteversion outside the target range and age (P = .762), BMI (P = .583), preoperative diagnosis (P > .99), and laterality (P = .235) were statistically insignificant.

Six THAs (1.1%) in 6 patients experienced dislocation within 6 months after surgery (Table 3); mean (SD) time of dislocation was 58.3 (13.8) days after surgery. There was no relationship between dislocation incidence and component placement in the Lewinnek zone (P = .224) or our target zone (P = .287). Of the dislocation cases, 50% involved female patients, and 50% involved right hips. Mean (SD) age of these patients was 53.3 (7.6) years. Mean (SD) BMI was 25.4 (0.9) kg/m². Osteoarthritis was the primary diagnosis for all patients with early dislocation; 32- or 36-mm femoral heads were used in these cases. Two patients had acetabular components placed outside of our target zone. One patient, who had abnormal pelvic obliquity and sagittal tilt from scoliosis (Figures 5A, 5B), had an acetabular component placed outside both the target zone and the Lewinnek safe zone. Mean (SD) acetabular inclination was 39.8° (3.6°), and mean (SD) anteversion was 21.8° (7.3°) (Figure 5C). Two dislocations resulted from trauma, 1 dislocation was related to hyperlaxity, 1 patient had cerebral palsy, and 1 patient had no evident predisposing risk factors. Three patients (0.54%) had multiple episodes of instability requiring revision during the follow-up period.

Discussion

To our knowledge, this study represents the largest cohort of primary THAs performed with an imageless navigation system. Our results showed that increasing targeted acetabular anteversion to 25° using a posterolateral surgical approach and modern implants resulted in a 1.1% incidence of early dislocation and a 0.54% incidence of recurrent instability requiring reoperation. Of the patients with a dislocation, only 1 did not experience trauma and did not have a risk factor for dislocation. Only 1 patient with a dislocation had acetabular components positioned outside both the target zone and the Lewinnek safe zone. The acetabular component was placed within the target zone in 82.3% of cases in which the imageless navigation system was used. In our cohort, BMI was the only risk factor for placement of the acetabular component outside our target range for inclination, and sex was associated with components outside the target range for anteversion.

Early dislocation after THA is often related to improper implant orientation, inadequate restoration of offset and myofascial tension, and decreased femoral head–neck ratio.⁸ Although dislocation rates in the literature vary widely,^1,2 Medicare data suggest that the rate for the first 6 months after surgery can be as high as 4.21%.^3,4 Although use of femoral heads with a diameter of 32 mm or larger may decrease this rate to 2.14%,³ accurate acetabular component orientation helps prevent postoperative dislocation.¹⁰ Using an imageless navigation system to target 25° of anteversion and 40° of inclination resulted in an early-dislocation rate about 49% less than the rate in a Medicare population treated with similar, modern implants.³

Callanan and colleagues¹¹ found that freehand techniques were inaccurate for acetabular positioning in up to 50% of cases, and several studies have demonstrated that imageless navigation systems were more accurate than conventional guides.^20,21,27-29 Higher BMI has been implicated as a risk factor for acetabular malpositioning in several studies of the accuracy of freehand techniques¹¹ and imageless navigation techniques.^23,30 Soft-tissue impediment to the component insertion handle poses a risk of increased inclination and inadequate anteversion, regardless of method used (conventional, CAS). When the acetabular component is placed freehand in obese patients, it is difficult to judge the position of the pelvis on the operating room table. For imageless navigation, a larger amount of adipose tissue over bony landmarks may limit the accuracy of anterior pelvic plane registration.³⁰ Sex typically is not cited as a risk factor for inaccurate acetabular component positioning. We speculate that omitted-variable bias may explain the observed association between female sex and anteversion. For example, changes in postoperative pelvic tilt alter apparent anteversion on plain radiographs,^31-34 but preoperative and postoperative sagittal pelvic tilt was not recorded in this study.

The proper position of the acetabular component has been debated.^15,16,35,36 Although it is generally agreed that inclination of 40° ± 10° balances ROM, stability, and bearing-surface wear,^12,13,15,16 proposed targets for anteversion vary widely, from 0° to 40°.^35,36 Patel and colleagues¹⁶ formulated computer models based on cadaveric specimens to determine that THA impingement was minimized when the acetabular component was placed to match the native anteversion of the acetabulum.In their study model, 20° of anteversion paralleled native acetabular orientation. Tohtz and colleagues¹⁸ reviewed computed tomography scans of 144 female hips and 192 male hips and found that mean (SD) anteversion was 24.6° (6.6°) for women and 21.3° (6.2°) for men. Whether native anatomy is a valid reference for acetabular anteversion is controversial,¹⁹ and definitive recommendations for target anteversion cannot be made, as the effect of acetabular anteversion on the wear of various bearing materials is unknown.¹⁴ Yet, as with inclination, ideal anteversion is likely a compromise between maximizing impingement-free ROM and minimizing wear.

The present study had several limitations. A single-surgeon patient series was reviewed retrospectively, and there was no control group. We determined the incidence only of early dislocation, and 5.3% of THAs that were not metal-on-metal were either lost to follow-up or had inadequate radiographs. However, of the patients excluded for inadequate radiographs, none had an early dislocation. The effects of our surgical techniques on long-term outcomes, bearing wear, and dislocation are unknown. We were not able to comment on the direction of dislocation for any of the 6 patients with early dislocation, as all dislocations were reduced at facilities other than our hospital. Therefore, we cannot determine whether increasing acetabular anteversion resulted in a larger number of anterior versus posterior dislocations.¹⁵

We did not use CAS to place any of the femoral components. Therefore, we could not accurately target combined anteversion, defined as the sum of acetabular and femoral version, which may be an important determinant of THA stability.²⁸ Although restoration of femoral offset and leg length is important in preventing THA dislocation,⁸ the CAS techniques used did not influence these parameters, and they were not measured.

As an imageless navigation system was used, there were no preoperative axial images, which could have been used to assess native acetabular orientation. This limited our assessment with respect to matching each patient’s natural anteversion. Imageless navigation, which references only the anterior pelvic plane, may not be reliable in patients with excessive sagittal pelvic tilt.³⁷ Furthermore, changes in the functional position of the pelvis from supine to sitting to standing were not accounted for, and changes in sagittal tilt between these positions can be significant.³⁸ Changes in sagittal pelvic tilt affect measurement of acetabular anteversion on plain radiographs, with anterior tilt reducing apparent anteversion and posterior tilt increasing it.^32,34 Although postoperative computed tomography is the gold standard for assessing acetabular component orientation, EBRA significantly reduces errors of measurement on plain radiographs.¹⁰ Some variability in measured anteversion may be explained by our surgical technique. In particular, if the cup was uncovered anteriorly, additional anteversion was usually accepted during surgery to minimize anterior impingement and limit the risk of iliopsoas tendonitis.^16,39

Our study results suggested that increasing target acetabular anteversion to 25° may reduce the incidence of early postoperative instability relative to rates reported in the literature. Despite the higher accuracy of component placement with an imageless navigation system, dislocations occurred in patients with acetabular components positioned in our target zone and in the historical safe zone. These dislocations support the notion that there likely is no absolute safe range for acetabular component positioning, as THA stability depends on many factors. Ideal targets for implant orientation for acetabulum and femur may be patient-specific.^16,19 Investigators should prospectively evaluate patient-specific THA component positioning and determine its effect on postoperative dislocation and bearing-surface wear. As specific implant targets are further defined, tools that are more precise and accurate than conventional techniques will be needed to achieve goal component positioning. Our study results confirmed that imageless navigation is an accurate method for achieving acetabular orientation targets.

Anorexia nervosa can affect a number of systems of the body, including the otolaryngologic presentation of autophonia^1,2—a rare hyperperception of an abnormally intense hearing of one’s own voice and respiratory sounds.² The most common cause of autophonia in patients with anorexia is a patulous (patent) eusta­chian tube, which can be caused by extreme weight loss.^2,3

Significant reduction in the quantity of fat tissue at the location of the eustachian tube can cause patency.³ This creates an abnor­mal connection between the nasopharynx and tympanic membrane, in which sounds are transmitted directly from the oral cavity to the middle ear, causing autophonia, tin­nitus, or sound distortion.⁴
What are the symptoms?Patients often report hearing their own voice more loudly in the affected ear. This can be distressing, and they might become preoccupied with the sound of their voice—thus affecting quality of life.^2,4

The intensity of symptoms varies: from a mild sensation of a clogged ear to extremely bothersome discomfort much like a middle-ear infection.^2,4 Autophonia, however, cannot be relieved by conven­tional therapies for those conditions.^2,3

A patulous eustachian tube is difficult to detect and can be misdiagnosed as another condition. Pregnancy, stress, fatigue, radia­tion therapy, hormonal therapy, and dra­matic weight loss also can cause a patulous eustachian tube.²
How is the diagnosis made?The diagnosis of autophonia is clinical and begins with a detailed history. Symptoms often appear within the time frame of rapid weight loss and without evidence of infection or other illness.^2,3 The clinical examination is otherwise unremarkable.^2,4
Is there treatment?To improve the patient’s comfort and qual­ity of life, intervention is required, best provided by an integrated team of medi­cal specialists. Weight gain, of course, is the treatment goal in anorexia, but this is a complex process often marked by relapse; a detailed discussion of treatment strate­gies is beyond the scope of this “Pearl.” Symptoms usually diminish as fatty tissue is restored upon successful treatment of anorexia, which closes the abnormal eusta­chian tube opening.^2,3
 

Disclosures
The authors report no financial relationships with any company whose products are mentioned in this article or with manufacturers of competing products.

Anorexia nervosa can affect a number of systems of the body, including the otolaryngologic presentation of autophonia^1,2—a rare hyperperception of an abnormally intense hearing of one’s own voice and respiratory sounds.² The most common cause of autophonia in patients with anorexia is a patulous (patent) eusta­chian tube, which can be caused by extreme weight loss.^2,3

Significant reduction in the quantity of fat tissue at the location of the eustachian tube can cause patency.³ This creates an abnor­mal connection between the nasopharynx and tympanic membrane, in which sounds are transmitted directly from the oral cavity to the middle ear, causing autophonia, tin­nitus, or sound distortion.⁴
What are the symptoms?Patients often report hearing their own voice more loudly in the affected ear. This can be distressing, and they might become preoccupied with the sound of their voice—thus affecting quality of life.^2,4

The intensity of symptoms varies: from a mild sensation of a clogged ear to extremely bothersome discomfort much like a middle-ear infection.^2,4 Autophonia, however, cannot be relieved by conven­tional therapies for those conditions.^2,3

A patulous eustachian tube is difficult to detect and can be misdiagnosed as another condition. Pregnancy, stress, fatigue, radia­tion therapy, hormonal therapy, and dra­matic weight loss also can cause a patulous eustachian tube.²
How is the diagnosis made?The diagnosis of autophonia is clinical and begins with a detailed history. Symptoms often appear within the time frame of rapid weight loss and without evidence of infection or other illness.^2,3 The clinical examination is otherwise unremarkable.^2,4
Is there treatment?To improve the patient’s comfort and qual­ity of life, intervention is required, best provided by an integrated team of medi­cal specialists. Weight gain, of course, is the treatment goal in anorexia, but this is a complex process often marked by relapse; a detailed discussion of treatment strate­gies is beyond the scope of this “Pearl.” Symptoms usually diminish as fatty tissue is restored upon successful treatment of anorexia, which closes the abnormal eusta­chian tube opening.^2,3
 

Disclosures
The authors report no financial relationships with any company whose products are mentioned in this article or with manufacturers of competing products.

Anorexia nervosa can affect a number of systems of the body, including the otolaryngologic presentation of autophonia^1,2—a rare hyperperception of an abnormally intense hearing of one’s own voice and respiratory sounds.² The most common cause of autophonia in patients with anorexia is a patulous (patent) eusta­chian tube, which can be caused by extreme weight loss.^2,3

Significant reduction in the quantity of fat tissue at the location of the eustachian tube can cause patency.³ This creates an abnor­mal connection between the nasopharynx and tympanic membrane, in which sounds are transmitted directly from the oral cavity to the middle ear, causing autophonia, tin­nitus, or sound distortion.⁴
What are the symptoms?Patients often report hearing their own voice more loudly in the affected ear. This can be distressing, and they might become preoccupied with the sound of their voice—thus affecting quality of life.^2,4

The intensity of symptoms varies: from a mild sensation of a clogged ear to extremely bothersome discomfort much like a middle-ear infection.^2,4 Autophonia, however, cannot be relieved by conven­tional therapies for those conditions.^2,3

A patulous eustachian tube is difficult to detect and can be misdiagnosed as another condition. Pregnancy, stress, fatigue, radia­tion therapy, hormonal therapy, and dra­matic weight loss also can cause a patulous eustachian tube.²
How is the diagnosis made?The diagnosis of autophonia is clinical and begins with a detailed history. Symptoms often appear within the time frame of rapid weight loss and without evidence of infection or other illness.^2,3 The clinical examination is otherwise unremarkable.^2,4
Is there treatment?To improve the patient’s comfort and qual­ity of life, intervention is required, best provided by an integrated team of medi­cal specialists. Weight gain, of course, is the treatment goal in anorexia, but this is a complex process often marked by relapse; a detailed discussion of treatment strate­gies is beyond the scope of this “Pearl.” Symptoms usually diminish as fatty tissue is restored upon successful treatment of anorexia, which closes the abnormal eusta­chian tube opening.^2,3
 

Disclosures
The authors report no financial relationships with any company whose products are mentioned in this article or with manufacturers of competing products.

Total hip arthroplasty (THA) effectively provides adequate pain relief and favorable outcomes in patients with hip osteoarthritis (OA). However, leg-length discrepancy (LLD) is still a significant cause of morbidity,¹ including nerve damage,^2,3 low back pain,^2,4,5 and abnormal gait.^2,6,7 Although most of the LLD values reported in the literature fall under the acceptable threshold of 10 mm,⁸ some patients report dissatisfaction,⁹ leading to litigation against orthopedic surgeons.² However, lower extremity lengthening is sometimes needed to achieve adequate hip joint stability and prevent dislocations.^2,10

Several methods have been developed to help surgeons estimate the change in leg length during surgery in an attempt to improve clinical outcomes. Use of guide pins as a reference on the pelvis decreased LLD and improved outcomes in some published studies.^11,12 Preoperative templating of implant size, cup position, and level of femoral neck cut is very important in helping minimize clinically significant LLD after THA.^2,13,14 Computer-assisted THA has also been introduced to try to improve component positioning, restoration of hip center of rotation, and minimizing of LLD.^15-17 However, cost and increased operative time have prevented widespread adoption of computer-assisted surgery in THA.

Proponents of different surgical approaches have argued about the superiority of one approach over another. The posterior approach is the gold standard in THA because it is safe, easy to perform, and, if needed, extensile.¹¹ However, exact determination of the intraoperative 3-dimensional (3-D) orientation of the pelvis, and subsequently of LLD, is challenging when the patient lies in the lateral position. The anterior approach has gained in popularity because of its advantages in accelerating postoperative rehabilitation and decreasing hospital length of stay.¹⁸ Placing the patient supine is advantageous because it allows leveling of the pelvis and estimation of LLD (by comparing the positions of the lower extremities).¹⁹ The anterior approach also allows for radiographic measurements on the operating table.^19,20 However, this approach has a high learning curve²¹ and is not extensile.²¹ To date, no study has shown superiority of the anterior approach over either the conventional posterior approach or the robot-assisted posterior approach in minimizing LLD after THA.

We conducted a study to compare LLD in patients who underwent THA performed with a robot-assisted posterior approach (RTHA), a fluoroscopy-guided anterior approach (ATHA), or a conventional posterior approach (PTHA). We hypothesized that, compared with PTHA, both RTHA and ATHA would result in reduced LLD.

Materials and Methods

We reviewed all RTHAs, ATHAs, and PTHAs performed by Dr. Domb between September 2008 and December 2012. Study inclusion criteria were a diagnosis of hip OA and the availability of postoperative supine anteroposterior pelvis radiographs. Exclusion criteria were a diagnosis other than hip OA, missing or improper postoperative radiographs (radiographs with rotated or tilted pelvis),²² and radiographs on which at least one of the lesser trochanters was difficult to define. Of the 155 cases included in the study, 67 were RTHAs, 29 were ATHAs, and 59 were PTHAs.

All patients scheduled for THA underwent preoperative planning; plain radiographs were used to determine component size and position, level of neck cut, and amount of leg lengthening or shortening needed. In all RTHA cases, computed tomography of the involved hip was performed before surgery. The MAKO system (MAKO Surgical Corporation, Davie, Florida) was used to develop a patient-specific 3-D model of the pelvis and proximal femur, and this model was used to guide THA execution. The system was then used to detect patient-specific landmarks during surgery, to register the femur and the acetabulum, and to help determine the position of the pelvis and proximal femur during surgery. This system, which uses a haptic robotic arm that guides acetabular reaming and cup placement, provides feedback regarding cup placement, stem version, leg length, and global offset. Pelvic tilt and rotation were accounted for by the MAKO software, and all provided measurements were made on the coronal (functional) plane of the body, as described by Murray.²³ ATHA was performed with the patient in the supine position on a Hana table (Mizuho OSI, Union City, California) with fluoroscopic guidance. PTHA was performed in the conventional way, with the patient in the lateral position.

Radiographic measurements of LLD were made with TraumaCad software (Build 2.2.535.0; Voyant Health, Petah-Tikva, Israel). The accuracy of this software has been studied and reported in the literature.^24-26 Radiographs were calibrated using the known size of each femoral head as a marker. The reference on the pelvis was the interobturator line (line tangent to inferior border of obturator foramina), and the reference on the femurs was the most superior and medial aspect of each lesser trochanter. Two lines were drawn, each perpendicular to the interobturator line, starting from the previously defined reference point on each lesser trochanter. The difference in length between these 2 lines was recorded as the LLD. Values were recorded relative to the operative extremity. For example, if the operative extremity was longer than the nonoperative extremity, the LLD was given a positive value.

To eliminate bias and increase measurement accuracy, the study had each of 2 observers collect the LLD data twice, 2 months apart. These observers were blinded to each other’s results and to the type of surgery performed. (Neither observer was Dr. Domb, the senior surgeon.) IBM SPSS Statistics software (Version 20; IBM, Armonk, New York) was used for statistical analysis. Each patient’s 4 measurements were averaged into a single number for LLD, and the absolute LLD values were used in all statistical analyses. Means, standard deviations (SDs), and 95% confidence intervals (CIs) were calculated for LLD in each of the 3 groups. Pearson correlation coefficient was used to determine interobserver and intraobserver reliability. One-way analysis of variance (ANOVA) was used to compare group means for age, body mass index (BMI), and LLD. In each group, number of outliers was determined with outliers set at LLDs of more than 3 mm and more than 5 mm. Fischer exact test was used to compare number of outliers in each group. P < .05 was considered statistically significant.

Results

Table 1 lists the demographic data, including age, sex, and BMI, and compares the means. There were strong interobserver and intraobserver correlations for all LLD measurements (r > 0.9; P < .001). Mean (SD) LLD was 2.7 (1.8) mm (95% CI, 2.3-3.2) in the RTHA group, 1.8 (1.6) mm (95% CI, 1.2-2.4) in the ATHA group, and 1.9 (1.6) mm (95% CI, 1.5-2.4) in the PTHA group (P = .01). When LLD of more than 3 mm was set as an outlier, percentage of outliers was 37.3% (RTHA), 17.2% (ATHA), and 22% (PTHA) (P = .06-.78). When LLD of more than 5 mm was set as an outlier, percentage of outliers was 10.4% (RTHA), 6.9% (ATHA), and 8.5% (PTHA) (P = .72 to >.99). No patient in any group had LLD of 10 mm or more (Figure). Table 2 lists percentages of patients’ operated extremities that were longer, shorter, or the same size as their contralateral extremities. Six (9.0%) of the 67 RTHA patients, 4 (13.8%) of the 29 ATHA patients, and 3 (5.1%) of the 59 PTHA patients had a contralateral THA.

Discussion

Our study results showed that RTHA, ATHA, and PTHA were equally effective in minimizing LLD. There was a statistically significant difference in mean LLD among the 3 groups studied. The RTHA group had the largest mean (SD) LLD: 2.7 (1.8) mm. However, statistically significant differences do not always indicate clinical significance.²⁷ Therefore, comparison of the 3 groups’ means is not enough for drawing significant conclusions. The more important point to consider is the number of cases of LLD of 10 mm or more—a discrepancy that would be perceptible to patients and thus become a source of dissatisfaction with painless THA.²⁸ Patients perceive LLD when shortening exceeds 10 mm and lengthening exceeds 6 mm,²⁹ or when LLD is more than 10 mm.^16,19,20 Despite significant differences in means, all our cases came in under the 10-mm threshold. When the threshold was decreased to 5 mm (and to 3 mm), there was no statistically significant difference among the groups in the number of cases above the threshold.

LLD remains a source of significant post-THA comorbidity and patient dissatisfaction.^1-7,19 Despite surgeons’ efforts to minimize LLD, some patients can detect even a subtle LLD after surgery.^1,8,29 Most LLD values reported in the literature fall under the 10-mm threshold.^16,19,20 In some cases, however, postoperative LLD is more than 1 cm, enough to prompt litigation against orthopedic surgeons.² Surgeons have tried to improve LLD with use of multiple techniques, including use of intraoperative measuring devices,³⁰ patient positioning during surgery,²⁰ use of computer-assisted surgery,¹⁹ and use of intraoperative fluoroscopy.²⁰

Proponents of computer-assisted THA have argued that this technique improves accuracy in placing the acetabular cup in the safe zone,³¹ minimizes LLD, and restores femoral offset.^32,33 Manzotti and colleagues¹⁶ reported on 48 cases of computer-assisted THA matched to 48 cases of conventional THA using the posterior approach. Mean (SD) LLD was 5.06 (2.99) mm in the computer-assisted group and 7.64 (4.36) mm in the conventional group; there was a statistically significant difference in favor of the computer-assisted group (P = .04). However, 5 patients in the computer-assisted group and 13 in the conventional group had LLD of more than 10 mm, and the difference was statistically significant.¹⁶ Moreover, the study population was heterogeneous, with 12 patients in both groups having developmental dysplasia as a primary diagnosis.¹⁶ All the cases in our study had a diagnosis of OA, and no case had LLD of 10 mm or more.

Several advantages have been proposed for the anterior approach. The supine position (with direct comparison of leg lengths) and the use of fluoroscopy have been described as advantageous in minimizing LLD.^20,21 In their study of 494 primary THAs performed with the anterior approach, Matta and colleagues²⁰ reported mean (SD) postoperative LLD of 3 (2) mm (range, 0-26 mm) and concluded that the anterior approach was effective in restoring leg lengths and ensuring proper cup placement while not increasing the dislocation rate. However, they did not compare this approach with others or with computer-assisted THA with respect to LLD.

In another study, Nam and colleagues¹⁹ compared LLD after THA performed with 3 different approaches (anterior, conventional posterior, posterior-navigated) and found no statistically significant difference in LLD among the groups. However, LLD was more than 10 mm in 2.2% of anterior cases, 4.4% of conventional posterior cases, and 4.4% of posterior-navigated cases. When 5 mm was used as a cutoff, percentage of patients who were outliers was 31.1% (anterior), 20% (conventional posterior), and 23.3% (navigated-posterior). Our data showed superior results in using 5 mm as a cutoff, with percentage of outliers of 6.9% with ATHA, 8.5% with PTHA, and 10.4% with RTHA. However, Nam and colleagues¹⁹ used a larger patient cohort and different techniques for measuring LLD on anteroposterior pelvis radiographs.

The most likely reason that the groups in our study were comparable in terms of LLD accuracy and lack of outliers over the 10-mm cutoff was Dr. Domb’s high accuracy in minimizing LLD using each of the 3 techniques. For ATHA, mean (SD) LLD was 1.8 (1.6) mm (no LLD of ≥10 mm), better than the 3 (2) mm (0.9% with LLD of >10 mm) reported by Matta and colleagues²⁰ and the 3.8 (3.9) mm (2.2% with LLD of >10 mm) reported by Nam and colleagues.¹⁹ For PTHA, mean (SD) LLD was 1.9 (1.6) mm (no LLD of ≥10 mm), comparable to some of the best results reported in the literature—for example, the 1 mm (3% with LLD of >10 mm) reported by Woolson and colleagues.³⁴ For RTHA, mean (SD) LLD was 2.7 (1.8) mm (no LLD of ≥10 mm), superior to the 3.9 (2.7) mm (4.4% with LLD of >10 mm) reported by Nam and colleagues¹⁹ for posterior-navigated THA and the 5.06 (2.99) mm (10.4% with LLD of >10 mm) reported by Manzotti and colleagues¹⁶ for computer-assisted THA.

This study had several notable strengths. All patients had a diagnosis of hip OA and were operated on by a single surgeon. Radiographs were calibrated using the size of the implanted femoral head. Radiographic data were measured using the same technique in all cases and were collected twice by 2 observers (not the senior surgeon) to decrease bias and determine interobserver and intraobserver reliability. In addition, surgeon experience might have played an important role in minimizing LLD regardless of technique and approach used for THA.

Study limitations were different number of cases in each group, lack of matching, lack of clinical follow-up, and lack of long-term assessment of clinical outcomes and complications.

Conclusion

As performed by an experienced surgeon, RTHA, ATHA, and PTHA did not differ in obtaining minimal LLD. All 3 groups had a low frequency of outliers, using thresholds of 3 mm and 5 mm, and no patient in any group had LLD of 10 mm or more. All 3 techniques are effective in achieving accuracy in LLD.

Total hip arthroplasty (THA) effectively provides adequate pain relief and favorable outcomes in patients with hip osteoarthritis (OA). However, leg-length discrepancy (LLD) is still a significant cause of morbidity,¹ including nerve damage,^2,3 low back pain,^2,4,5 and abnormal gait.^2,6,7 Although most of the LLD values reported in the literature fall under the acceptable threshold of 10 mm,⁸ some patients report dissatisfaction,⁹ leading to litigation against orthopedic surgeons.² However, lower extremity lengthening is sometimes needed to achieve adequate hip joint stability and prevent dislocations.^2,10

Several methods have been developed to help surgeons estimate the change in leg length during surgery in an attempt to improve clinical outcomes. Use of guide pins as a reference on the pelvis decreased LLD and improved outcomes in some published studies.^11,12 Preoperative templating of implant size, cup position, and level of femoral neck cut is very important in helping minimize clinically significant LLD after THA.^2,13,14 Computer-assisted THA has also been introduced to try to improve component positioning, restoration of hip center of rotation, and minimizing of LLD.^15-17 However, cost and increased operative time have prevented widespread adoption of computer-assisted surgery in THA.

Proponents of different surgical approaches have argued about the superiority of one approach over another. The posterior approach is the gold standard in THA because it is safe, easy to perform, and, if needed, extensile.¹¹ However, exact determination of the intraoperative 3-dimensional (3-D) orientation of the pelvis, and subsequently of LLD, is challenging when the patient lies in the lateral position. The anterior approach has gained in popularity because of its advantages in accelerating postoperative rehabilitation and decreasing hospital length of stay.¹⁸ Placing the patient supine is advantageous because it allows leveling of the pelvis and estimation of LLD (by comparing the positions of the lower extremities).¹⁹ The anterior approach also allows for radiographic measurements on the operating table.^19,20 However, this approach has a high learning curve²¹ and is not extensile.²¹ To date, no study has shown superiority of the anterior approach over either the conventional posterior approach or the robot-assisted posterior approach in minimizing LLD after THA.

We conducted a study to compare LLD in patients who underwent THA performed with a robot-assisted posterior approach (RTHA), a fluoroscopy-guided anterior approach (ATHA), or a conventional posterior approach (PTHA). We hypothesized that, compared with PTHA, both RTHA and ATHA would result in reduced LLD.

Materials and Methods

We reviewed all RTHAs, ATHAs, and PTHAs performed by Dr. Domb between September 2008 and December 2012. Study inclusion criteria were a diagnosis of hip OA and the availability of postoperative supine anteroposterior pelvis radiographs. Exclusion criteria were a diagnosis other than hip OA, missing or improper postoperative radiographs (radiographs with rotated or tilted pelvis),²² and radiographs on which at least one of the lesser trochanters was difficult to define. Of the 155 cases included in the study, 67 were RTHAs, 29 were ATHAs, and 59 were PTHAs.

All patients scheduled for THA underwent preoperative planning; plain radiographs were used to determine component size and position, level of neck cut, and amount of leg lengthening or shortening needed. In all RTHA cases, computed tomography of the involved hip was performed before surgery. The MAKO system (MAKO Surgical Corporation, Davie, Florida) was used to develop a patient-specific 3-D model of the pelvis and proximal femur, and this model was used to guide THA execution. The system was then used to detect patient-specific landmarks during surgery, to register the femur and the acetabulum, and to help determine the position of the pelvis and proximal femur during surgery. This system, which uses a haptic robotic arm that guides acetabular reaming and cup placement, provides feedback regarding cup placement, stem version, leg length, and global offset. Pelvic tilt and rotation were accounted for by the MAKO software, and all provided measurements were made on the coronal (functional) plane of the body, as described by Murray.²³ ATHA was performed with the patient in the supine position on a Hana table (Mizuho OSI, Union City, California) with fluoroscopic guidance. PTHA was performed in the conventional way, with the patient in the lateral position.

Radiographic measurements of LLD were made with TraumaCad software (Build 2.2.535.0; Voyant Health, Petah-Tikva, Israel). The accuracy of this software has been studied and reported in the literature.^24-26 Radiographs were calibrated using the known size of each femoral head as a marker. The reference on the pelvis was the interobturator line (line tangent to inferior border of obturator foramina), and the reference on the femurs was the most superior and medial aspect of each lesser trochanter. Two lines were drawn, each perpendicular to the interobturator line, starting from the previously defined reference point on each lesser trochanter. The difference in length between these 2 lines was recorded as the LLD. Values were recorded relative to the operative extremity. For example, if the operative extremity was longer than the nonoperative extremity, the LLD was given a positive value.

To eliminate bias and increase measurement accuracy, the study had each of 2 observers collect the LLD data twice, 2 months apart. These observers were blinded to each other’s results and to the type of surgery performed. (Neither observer was Dr. Domb, the senior surgeon.) IBM SPSS Statistics software (Version 20; IBM, Armonk, New York) was used for statistical analysis. Each patient’s 4 measurements were averaged into a single number for LLD, and the absolute LLD values were used in all statistical analyses. Means, standard deviations (SDs), and 95% confidence intervals (CIs) were calculated for LLD in each of the 3 groups. Pearson correlation coefficient was used to determine interobserver and intraobserver reliability. One-way analysis of variance (ANOVA) was used to compare group means for age, body mass index (BMI), and LLD. In each group, number of outliers was determined with outliers set at LLDs of more than 3 mm and more than 5 mm. Fischer exact test was used to compare number of outliers in each group. P < .05 was considered statistically significant.

Results

Table 1 lists the demographic data, including age, sex, and BMI, and compares the means. There were strong interobserver and intraobserver correlations for all LLD measurements (r > 0.9; P < .001). Mean (SD) LLD was 2.7 (1.8) mm (95% CI, 2.3-3.2) in the RTHA group, 1.8 (1.6) mm (95% CI, 1.2-2.4) in the ATHA group, and 1.9 (1.6) mm (95% CI, 1.5-2.4) in the PTHA group (P = .01). When LLD of more than 3 mm was set as an outlier, percentage of outliers was 37.3% (RTHA), 17.2% (ATHA), and 22% (PTHA) (P = .06-.78). When LLD of more than 5 mm was set as an outlier, percentage of outliers was 10.4% (RTHA), 6.9% (ATHA), and 8.5% (PTHA) (P = .72 to >.99). No patient in any group had LLD of 10 mm or more (Figure). Table 2 lists percentages of patients’ operated extremities that were longer, shorter, or the same size as their contralateral extremities. Six (9.0%) of the 67 RTHA patients, 4 (13.8%) of the 29 ATHA patients, and 3 (5.1%) of the 59 PTHA patients had a contralateral THA.

Discussion

Our study results showed that RTHA, ATHA, and PTHA were equally effective in minimizing LLD. There was a statistically significant difference in mean LLD among the 3 groups studied. The RTHA group had the largest mean (SD) LLD: 2.7 (1.8) mm. However, statistically significant differences do not always indicate clinical significance.²⁷ Therefore, comparison of the 3 groups’ means is not enough for drawing significant conclusions. The more important point to consider is the number of cases of LLD of 10 mm or more—a discrepancy that would be perceptible to patients and thus become a source of dissatisfaction with painless THA.²⁸ Patients perceive LLD when shortening exceeds 10 mm and lengthening exceeds 6 mm,²⁹ or when LLD is more than 10 mm.^16,19,20 Despite significant differences in means, all our cases came in under the 10-mm threshold. When the threshold was decreased to 5 mm (and to 3 mm), there was no statistically significant difference among the groups in the number of cases above the threshold.

LLD remains a source of significant post-THA comorbidity and patient dissatisfaction.^1-7,19 Despite surgeons’ efforts to minimize LLD, some patients can detect even a subtle LLD after surgery.^1,8,29 Most LLD values reported in the literature fall under the 10-mm threshold.^16,19,20 In some cases, however, postoperative LLD is more than 1 cm, enough to prompt litigation against orthopedic surgeons.² Surgeons have tried to improve LLD with use of multiple techniques, including use of intraoperative measuring devices,³⁰ patient positioning during surgery,²⁰ use of computer-assisted surgery,¹⁹ and use of intraoperative fluoroscopy.²⁰

Proponents of computer-assisted THA have argued that this technique improves accuracy in placing the acetabular cup in the safe zone,³¹ minimizes LLD, and restores femoral offset.^32,33 Manzotti and colleagues¹⁶ reported on 48 cases of computer-assisted THA matched to 48 cases of conventional THA using the posterior approach. Mean (SD) LLD was 5.06 (2.99) mm in the computer-assisted group and 7.64 (4.36) mm in the conventional group; there was a statistically significant difference in favor of the computer-assisted group (P = .04). However, 5 patients in the computer-assisted group and 13 in the conventional group had LLD of more than 10 mm, and the difference was statistically significant.¹⁶ Moreover, the study population was heterogeneous, with 12 patients in both groups having developmental dysplasia as a primary diagnosis.¹⁶ All the cases in our study had a diagnosis of OA, and no case had LLD of 10 mm or more.

Several advantages have been proposed for the anterior approach. The supine position (with direct comparison of leg lengths) and the use of fluoroscopy have been described as advantageous in minimizing LLD.^20,21 In their study of 494 primary THAs performed with the anterior approach, Matta and colleagues²⁰ reported mean (SD) postoperative LLD of 3 (2) mm (range, 0-26 mm) and concluded that the anterior approach was effective in restoring leg lengths and ensuring proper cup placement while not increasing the dislocation rate. However, they did not compare this approach with others or with computer-assisted THA with respect to LLD.

In another study, Nam and colleagues¹⁹ compared LLD after THA performed with 3 different approaches (anterior, conventional posterior, posterior-navigated) and found no statistically significant difference in LLD among the groups. However, LLD was more than 10 mm in 2.2% of anterior cases, 4.4% of conventional posterior cases, and 4.4% of posterior-navigated cases. When 5 mm was used as a cutoff, percentage of patients who were outliers was 31.1% (anterior), 20% (conventional posterior), and 23.3% (navigated-posterior). Our data showed superior results in using 5 mm as a cutoff, with percentage of outliers of 6.9% with ATHA, 8.5% with PTHA, and 10.4% with RTHA. However, Nam and colleagues¹⁹ used a larger patient cohort and different techniques for measuring LLD on anteroposterior pelvis radiographs.

The most likely reason that the groups in our study were comparable in terms of LLD accuracy and lack of outliers over the 10-mm cutoff was Dr. Domb’s high accuracy in minimizing LLD using each of the 3 techniques. For ATHA, mean (SD) LLD was 1.8 (1.6) mm (no LLD of ≥10 mm), better than the 3 (2) mm (0.9% with LLD of >10 mm) reported by Matta and colleagues²⁰ and the 3.8 (3.9) mm (2.2% with LLD of >10 mm) reported by Nam and colleagues.¹⁹ For PTHA, mean (SD) LLD was 1.9 (1.6) mm (no LLD of ≥10 mm), comparable to some of the best results reported in the literature—for example, the 1 mm (3% with LLD of >10 mm) reported by Woolson and colleagues.³⁴ For RTHA, mean (SD) LLD was 2.7 (1.8) mm (no LLD of ≥10 mm), superior to the 3.9 (2.7) mm (4.4% with LLD of >10 mm) reported by Nam and colleagues¹⁹ for posterior-navigated THA and the 5.06 (2.99) mm (10.4% with LLD of >10 mm) reported by Manzotti and colleagues¹⁶ for computer-assisted THA.

This study had several notable strengths. All patients had a diagnosis of hip OA and were operated on by a single surgeon. Radiographs were calibrated using the size of the implanted femoral head. Radiographic data were measured using the same technique in all cases and were collected twice by 2 observers (not the senior surgeon) to decrease bias and determine interobserver and intraobserver reliability. In addition, surgeon experience might have played an important role in minimizing LLD regardless of technique and approach used for THA.

Study limitations were different number of cases in each group, lack of matching, lack of clinical follow-up, and lack of long-term assessment of clinical outcomes and complications.

Conclusion

As performed by an experienced surgeon, RTHA, ATHA, and PTHA did not differ in obtaining minimal LLD. All 3 groups had a low frequency of outliers, using thresholds of 3 mm and 5 mm, and no patient in any group had LLD of 10 mm or more. All 3 techniques are effective in achieving accuracy in LLD.

Total hip arthroplasty (THA) effectively provides adequate pain relief and favorable outcomes in patients with hip osteoarthritis (OA). However, leg-length discrepancy (LLD) is still a significant cause of morbidity,¹ including nerve damage,^2,3 low back pain,^2,4,5 and abnormal gait.^2,6,7 Although most of the LLD values reported in the literature fall under the acceptable threshold of 10 mm,⁸ some patients report dissatisfaction,⁹ leading to litigation against orthopedic surgeons.² However, lower extremity lengthening is sometimes needed to achieve adequate hip joint stability and prevent dislocations.^2,10

Several methods have been developed to help surgeons estimate the change in leg length during surgery in an attempt to improve clinical outcomes. Use of guide pins as a reference on the pelvis decreased LLD and improved outcomes in some published studies.^11,12 Preoperative templating of implant size, cup position, and level of femoral neck cut is very important in helping minimize clinically significant LLD after THA.^2,13,14 Computer-assisted THA has also been introduced to try to improve component positioning, restoration of hip center of rotation, and minimizing of LLD.^15-17 However, cost and increased operative time have prevented widespread adoption of computer-assisted surgery in THA.

Proponents of different surgical approaches have argued about the superiority of one approach over another. The posterior approach is the gold standard in THA because it is safe, easy to perform, and, if needed, extensile.¹¹ However, exact determination of the intraoperative 3-dimensional (3-D) orientation of the pelvis, and subsequently of LLD, is challenging when the patient lies in the lateral position. The anterior approach has gained in popularity because of its advantages in accelerating postoperative rehabilitation and decreasing hospital length of stay.¹⁸ Placing the patient supine is advantageous because it allows leveling of the pelvis and estimation of LLD (by comparing the positions of the lower extremities).¹⁹ The anterior approach also allows for radiographic measurements on the operating table.^19,20 However, this approach has a high learning curve²¹ and is not extensile.²¹ To date, no study has shown superiority of the anterior approach over either the conventional posterior approach or the robot-assisted posterior approach in minimizing LLD after THA.

We conducted a study to compare LLD in patients who underwent THA performed with a robot-assisted posterior approach (RTHA), a fluoroscopy-guided anterior approach (ATHA), or a conventional posterior approach (PTHA). We hypothesized that, compared with PTHA, both RTHA and ATHA would result in reduced LLD.

Materials and Methods

We reviewed all RTHAs, ATHAs, and PTHAs performed by Dr. Domb between September 2008 and December 2012. Study inclusion criteria were a diagnosis of hip OA and the availability of postoperative supine anteroposterior pelvis radiographs. Exclusion criteria were a diagnosis other than hip OA, missing or improper postoperative radiographs (radiographs with rotated or tilted pelvis),²² and radiographs on which at least one of the lesser trochanters was difficult to define. Of the 155 cases included in the study, 67 were RTHAs, 29 were ATHAs, and 59 were PTHAs.

All patients scheduled for THA underwent preoperative planning; plain radiographs were used to determine component size and position, level of neck cut, and amount of leg lengthening or shortening needed. In all RTHA cases, computed tomography of the involved hip was performed before surgery. The MAKO system (MAKO Surgical Corporation, Davie, Florida) was used to develop a patient-specific 3-D model of the pelvis and proximal femur, and this model was used to guide THA execution. The system was then used to detect patient-specific landmarks during surgery, to register the femur and the acetabulum, and to help determine the position of the pelvis and proximal femur during surgery. This system, which uses a haptic robotic arm that guides acetabular reaming and cup placement, provides feedback regarding cup placement, stem version, leg length, and global offset. Pelvic tilt and rotation were accounted for by the MAKO software, and all provided measurements were made on the coronal (functional) plane of the body, as described by Murray.²³ ATHA was performed with the patient in the supine position on a Hana table (Mizuho OSI, Union City, California) with fluoroscopic guidance. PTHA was performed in the conventional way, with the patient in the lateral position.

Radiographic measurements of LLD were made with TraumaCad software (Build 2.2.535.0; Voyant Health, Petah-Tikva, Israel). The accuracy of this software has been studied and reported in the literature.^24-26 Radiographs were calibrated using the known size of each femoral head as a marker. The reference on the pelvis was the interobturator line (line tangent to inferior border of obturator foramina), and the reference on the femurs was the most superior and medial aspect of each lesser trochanter. Two lines were drawn, each perpendicular to the interobturator line, starting from the previously defined reference point on each lesser trochanter. The difference in length between these 2 lines was recorded as the LLD. Values were recorded relative to the operative extremity. For example, if the operative extremity was longer than the nonoperative extremity, the LLD was given a positive value.

To eliminate bias and increase measurement accuracy, the study had each of 2 observers collect the LLD data twice, 2 months apart. These observers were blinded to each other’s results and to the type of surgery performed. (Neither observer was Dr. Domb, the senior surgeon.) IBM SPSS Statistics software (Version 20; IBM, Armonk, New York) was used for statistical analysis. Each patient’s 4 measurements were averaged into a single number for LLD, and the absolute LLD values were used in all statistical analyses. Means, standard deviations (SDs), and 95% confidence intervals (CIs) were calculated for LLD in each of the 3 groups. Pearson correlation coefficient was used to determine interobserver and intraobserver reliability. One-way analysis of variance (ANOVA) was used to compare group means for age, body mass index (BMI), and LLD. In each group, number of outliers was determined with outliers set at LLDs of more than 3 mm and more than 5 mm. Fischer exact test was used to compare number of outliers in each group. P < .05 was considered statistically significant.

Results

Table 1 lists the demographic data, including age, sex, and BMI, and compares the means. There were strong interobserver and intraobserver correlations for all LLD measurements (r > 0.9; P < .001). Mean (SD) LLD was 2.7 (1.8) mm (95% CI, 2.3-3.2) in the RTHA group, 1.8 (1.6) mm (95% CI, 1.2-2.4) in the ATHA group, and 1.9 (1.6) mm (95% CI, 1.5-2.4) in the PTHA group (P = .01). When LLD of more than 3 mm was set as an outlier, percentage of outliers was 37.3% (RTHA), 17.2% (ATHA), and 22% (PTHA) (P = .06-.78). When LLD of more than 5 mm was set as an outlier, percentage of outliers was 10.4% (RTHA), 6.9% (ATHA), and 8.5% (PTHA) (P = .72 to >.99). No patient in any group had LLD of 10 mm or more (Figure). Table 2 lists percentages of patients’ operated extremities that were longer, shorter, or the same size as their contralateral extremities. Six (9.0%) of the 67 RTHA patients, 4 (13.8%) of the 29 ATHA patients, and 3 (5.1%) of the 59 PTHA patients had a contralateral THA.

Discussion

Our study results showed that RTHA, ATHA, and PTHA were equally effective in minimizing LLD. There was a statistically significant difference in mean LLD among the 3 groups studied. The RTHA group had the largest mean (SD) LLD: 2.7 (1.8) mm. However, statistically significant differences do not always indicate clinical significance.²⁷ Therefore, comparison of the 3 groups’ means is not enough for drawing significant conclusions. The more important point to consider is the number of cases of LLD of 10 mm or more—a discrepancy that would be perceptible to patients and thus become a source of dissatisfaction with painless THA.²⁸ Patients perceive LLD when shortening exceeds 10 mm and lengthening exceeds 6 mm,²⁹ or when LLD is more than 10 mm.^16,19,20 Despite significant differences in means, all our cases came in under the 10-mm threshold. When the threshold was decreased to 5 mm (and to 3 mm), there was no statistically significant difference among the groups in the number of cases above the threshold.

LLD remains a source of significant post-THA comorbidity and patient dissatisfaction.^1-7,19 Despite surgeons’ efforts to minimize LLD, some patients can detect even a subtle LLD after surgery.^1,8,29 Most LLD values reported in the literature fall under the 10-mm threshold.^16,19,20 In some cases, however, postoperative LLD is more than 1 cm, enough to prompt litigation against orthopedic surgeons.² Surgeons have tried to improve LLD with use of multiple techniques, including use of intraoperative measuring devices,³⁰ patient positioning during surgery,²⁰ use of computer-assisted surgery,¹⁹ and use of intraoperative fluoroscopy.²⁰

Proponents of computer-assisted THA have argued that this technique improves accuracy in placing the acetabular cup in the safe zone,³¹ minimizes LLD, and restores femoral offset.^32,33 Manzotti and colleagues¹⁶ reported on 48 cases of computer-assisted THA matched to 48 cases of conventional THA using the posterior approach. Mean (SD) LLD was 5.06 (2.99) mm in the computer-assisted group and 7.64 (4.36) mm in the conventional group; there was a statistically significant difference in favor of the computer-assisted group (P = .04). However, 5 patients in the computer-assisted group and 13 in the conventional group had LLD of more than 10 mm, and the difference was statistically significant.¹⁶ Moreover, the study population was heterogeneous, with 12 patients in both groups having developmental dysplasia as a primary diagnosis.¹⁶ All the cases in our study had a diagnosis of OA, and no case had LLD of 10 mm or more.

Several advantages have been proposed for the anterior approach. The supine position (with direct comparison of leg lengths) and the use of fluoroscopy have been described as advantageous in minimizing LLD.^20,21 In their study of 494 primary THAs performed with the anterior approach, Matta and colleagues²⁰ reported mean (SD) postoperative LLD of 3 (2) mm (range, 0-26 mm) and concluded that the anterior approach was effective in restoring leg lengths and ensuring proper cup placement while not increasing the dislocation rate. However, they did not compare this approach with others or with computer-assisted THA with respect to LLD.

In another study, Nam and colleagues¹⁹ compared LLD after THA performed with 3 different approaches (anterior, conventional posterior, posterior-navigated) and found no statistically significant difference in LLD among the groups. However, LLD was more than 10 mm in 2.2% of anterior cases, 4.4% of conventional posterior cases, and 4.4% of posterior-navigated cases. When 5 mm was used as a cutoff, percentage of patients who were outliers was 31.1% (anterior), 20% (conventional posterior), and 23.3% (navigated-posterior). Our data showed superior results in using 5 mm as a cutoff, with percentage of outliers of 6.9% with ATHA, 8.5% with PTHA, and 10.4% with RTHA. However, Nam and colleagues¹⁹ used a larger patient cohort and different techniques for measuring LLD on anteroposterior pelvis radiographs.

The most likely reason that the groups in our study were comparable in terms of LLD accuracy and lack of outliers over the 10-mm cutoff was Dr. Domb’s high accuracy in minimizing LLD using each of the 3 techniques. For ATHA, mean (SD) LLD was 1.8 (1.6) mm (no LLD of ≥10 mm), better than the 3 (2) mm (0.9% with LLD of >10 mm) reported by Matta and colleagues²⁰ and the 3.8 (3.9) mm (2.2% with LLD of >10 mm) reported by Nam and colleagues.¹⁹ For PTHA, mean (SD) LLD was 1.9 (1.6) mm (no LLD of ≥10 mm), comparable to some of the best results reported in the literature—for example, the 1 mm (3% with LLD of >10 mm) reported by Woolson and colleagues.³⁴ For RTHA, mean (SD) LLD was 2.7 (1.8) mm (no LLD of ≥10 mm), superior to the 3.9 (2.7) mm (4.4% with LLD of >10 mm) reported by Nam and colleagues¹⁹ for posterior-navigated THA and the 5.06 (2.99) mm (10.4% with LLD of >10 mm) reported by Manzotti and colleagues¹⁶ for computer-assisted THA.

This study had several notable strengths. All patients had a diagnosis of hip OA and were operated on by a single surgeon. Radiographs were calibrated using the size of the implanted femoral head. Radiographic data were measured using the same technique in all cases and were collected twice by 2 observers (not the senior surgeon) to decrease bias and determine interobserver and intraobserver reliability. In addition, surgeon experience might have played an important role in minimizing LLD regardless of technique and approach used for THA.

Study limitations were different number of cases in each group, lack of matching, lack of clinical follow-up, and lack of long-term assessment of clinical outcomes and complications.

Conclusion

As performed by an experienced surgeon, RTHA, ATHA, and PTHA did not differ in obtaining minimal LLD. All 3 groups had a low frequency of outliers, using thresholds of 3 mm and 5 mm, and no patient in any group had LLD of 10 mm or more. All 3 techniques are effective in achieving accuracy in LLD.

Psychiatrists often serve as risk-management consultants for our medical colleagues. As part of this role, psychiatrists working with trainees— including resident physicians, medical students, and physician assistant students— have an opportunity to emphasize the impor­tance of professional boundaries.¹ Discussing appropriate professional boundaries and describing what might represent a violation of these boundaries is meaningful because a good understanding of these concepts pro­motes high-quality treatment and minimizes professional liability.²

Physical boundaries
Psychiatric patients might be agitated or display potentially dangerous behaviors; discussing the importance of body language and contact between physicians and their patients is, therefore, first and foremost, a matter of safety. Students who can recognize the signs and symptoms of agitation and maintain a safe distance between themselves and their patients are less likely to be injured.

Addressing romantic and sexual rela­tionships between patients and their health care providers also is necessary. One study reported that 21% of medical students sur­veyed might not regard sexual contact with a patient as inappropriate.³ An adequate discus­sion of this topic is necessary to protect train­ees and patients from a catastrophic misstep.

Emotional boundaries
Maintaining appropriate emotional bound­aries is necessary in psychiatry. Given the prevalence of mental illness and substance abuse, many trainees have personal experi­ence with psychiatric illness outside of their training. Discussing issues of transference and countertransference with students will prepare them for intense emotional reac­tions they will experience while working in psychiatry. Students who feel comfortable recognizing their own countertransference feelings and discussing them in supervision with their attending psychiatrist will be more successful in addressing the complex inter­personal challenges that their patients face.

Personal and informational boundaries
Discussing personal and informational boundaries can protect trainees from uncom­fortable experiences in their non-clinical lives. Although, in previous decades, we needed to discourage students only from sharing their home address and telephone number with patients, the Internet and social media have made it easier for patients to discover personal information about their treatment team. Addressing issues related to social networks and instructing students on how to appropriately address and decline requests for personal information can pre­vent unwanted boundary crossings.

Psychiatrists are well suited to discuss these issues with trainees. In doing so, we can help them become knowledgeable health care providers—no matter which medical discipline they specialize in.

Disclosure
The author reports no financial relationships with any company whose products are mentioned in this article or with manufacturers of competing products.

Psychiatrists often serve as risk-management consultants for our medical colleagues. As part of this role, psychiatrists working with trainees— including resident physicians, medical students, and physician assistant students— have an opportunity to emphasize the impor­tance of professional boundaries.¹ Discussing appropriate professional boundaries and describing what might represent a violation of these boundaries is meaningful because a good understanding of these concepts pro­motes high-quality treatment and minimizes professional liability.²

Physical boundaries
Psychiatric patients might be agitated or display potentially dangerous behaviors; discussing the importance of body language and contact between physicians and their patients is, therefore, first and foremost, a matter of safety. Students who can recognize the signs and symptoms of agitation and maintain a safe distance between themselves and their patients are less likely to be injured.

Addressing romantic and sexual rela­tionships between patients and their health care providers also is necessary. One study reported that 21% of medical students sur­veyed might not regard sexual contact with a patient as inappropriate.³ An adequate discus­sion of this topic is necessary to protect train­ees and patients from a catastrophic misstep.

Emotional boundaries
Maintaining appropriate emotional bound­aries is necessary in psychiatry. Given the prevalence of mental illness and substance abuse, many trainees have personal experi­ence with psychiatric illness outside of their training. Discussing issues of transference and countertransference with students will prepare them for intense emotional reac­tions they will experience while working in psychiatry. Students who feel comfortable recognizing their own countertransference feelings and discussing them in supervision with their attending psychiatrist will be more successful in addressing the complex inter­personal challenges that their patients face.

Personal and informational boundaries
Discussing personal and informational boundaries can protect trainees from uncom­fortable experiences in their non-clinical lives. Although, in previous decades, we needed to discourage students only from sharing their home address and telephone number with patients, the Internet and social media have made it easier for patients to discover personal information about their treatment team. Addressing issues related to social networks and instructing students on how to appropriately address and decline requests for personal information can pre­vent unwanted boundary crossings.

Psychiatrists are well suited to discuss these issues with trainees. In doing so, we can help them become knowledgeable health care providers—no matter which medical discipline they specialize in.

Disclosure
The author reports no financial relationships with any company whose products are mentioned in this article or with manufacturers of competing products.

Psychiatrists often serve as risk-management consultants for our medical colleagues. As part of this role, psychiatrists working with trainees— including resident physicians, medical students, and physician assistant students— have an opportunity to emphasize the impor­tance of professional boundaries.¹ Discussing appropriate professional boundaries and describing what might represent a violation of these boundaries is meaningful because a good understanding of these concepts pro­motes high-quality treatment and minimizes professional liability.²

Physical boundaries
Psychiatric patients might be agitated or display potentially dangerous behaviors; discussing the importance of body language and contact between physicians and their patients is, therefore, first and foremost, a matter of safety. Students who can recognize the signs and symptoms of agitation and maintain a safe distance between themselves and their patients are less likely to be injured.

Addressing romantic and sexual rela­tionships between patients and their health care providers also is necessary. One study reported that 21% of medical students sur­veyed might not regard sexual contact with a patient as inappropriate.³ An adequate discus­sion of this topic is necessary to protect train­ees and patients from a catastrophic misstep.

Emotional boundaries
Maintaining appropriate emotional bound­aries is necessary in psychiatry. Given the prevalence of mental illness and substance abuse, many trainees have personal experi­ence with psychiatric illness outside of their training. Discussing issues of transference and countertransference with students will prepare them for intense emotional reac­tions they will experience while working in psychiatry. Students who feel comfortable recognizing their own countertransference feelings and discussing them in supervision with their attending psychiatrist will be more successful in addressing the complex inter­personal challenges that their patients face.

Personal and informational boundaries
Discussing personal and informational boundaries can protect trainees from uncom­fortable experiences in their non-clinical lives. Although, in previous decades, we needed to discourage students only from sharing their home address and telephone number with patients, the Internet and social media have made it easier for patients to discover personal information about their treatment team. Addressing issues related to social networks and instructing students on how to appropriately address and decline requests for personal information can pre­vent unwanted boundary crossings.

Psychiatrists are well suited to discuss these issues with trainees. In doing so, we can help them become knowledgeable health care providers—no matter which medical discipline they specialize in.

Disclosure
The author reports no financial relationships with any company whose products are mentioned in this article or with manufacturers of competing products.