A Cadaveric Study Measuring Femoral Nerve Tension During Anterior Total Hip Arthroplasty Approach.

Femoral nerve palsy is a rare but devastating complication of anterior total hip arthroplasty. Its etiology is still unknown, but several studies have suggested that anterior acetabular retractors may place the femoral nerve at increased risk. This study hypothesized that hip extension and traction places tension on the femoral nerve, offering an additional explanation for the development of femoral nerve palsy. A spring device was secured across 6 transected femoral nerves from 5 lower extremity cadavers and the hip was extended and pulled into traction with and without retractor placement. The change in spring length was used to determine femoral nerve tension. The average spring length changed +8.83 mm with hip extension, +3.73 mm with traction, -0.7 mm with traction and placement of the anterior acetabular retractor, and -1.15 mm with extension and placement of the femoral retractor. Femoral nerve tension was greatest with hip extension followed by traction. Acetabular and femoral retractor placement decreased average femoral nerve tension in both traction and hip extension. This may be due to medialization of the femoral nerve by the retractors, reducing the overall distance traveled, and thereby reducing tension. Previous studies have found femoral nerve pressure to be greatest during anterior acetabular retractor placement. It is likely that both pressure and tension contribute to femoral nerve palsy. Careful retractor placement, staying safely on anterior acetabular bone, and efficient femoral preparation to decrease time under hip extension and traction may help to minimize the risk of femoral nerve palsy.