Anatomical Implications Regarding Femoral Nerve Palsy During a Direct Anterior Approach to Total Hip Arthroplasty: A Cadaveric Study.

BACKGROUND: Femoral nerve palsy is a serious neurological complication following total hip arthroplasty (THA) via a direct anterior approach. One hypothesis is that the nerve injury is caused by malpositioning of retractors over the anterior wall of the acetabulum. The purpose of this cadaveric study was to clarify the anatomical features of the femoral nerve around the anterior acetabular rim and the potential risk of nerve injury during a direct anterior approach to THA.

METHODS: We dissected 84 cadaveric hips from 44 formalin-embalmed cadavers. When the cadavers were supine, the iliopsoas muscle and the femoral nerve were exposed and the anterior joint capsule and labrum were resected. The measurement points were determined along the acetabular rim every 30°, and a reference line was drawn from the anterior superior iliac spine to the center of the acetabulum, with the intersection of the rim at 0°. The minimum distance to the femoral nerve margin was measured from 0° to 150° (6 points). Other anatomical structures were measured to determine their association with the distance of the shortest measurement points.

RESULTS: The mean minimum distances to the femoral nerve were 33.2 mm at 0°, 24.4 mm at 30°, 18.4 mm at 60°, 16.6 mm at 90°, 17.9 mm at 120°, and 23.2 mm at 150°, showing that the distance at 90° was the shortest (p < 0.001). The thickness of the iliopsoas muscle and the femoral length were positively associated with the distance to the femoral nerve at 90°.

CONCLUSIONS: In this cadaveric study, the femoral nerve was within 16.6 to 33.2 mm of the acetabular rim at points from 0° to 150° of a line drawn from the anterior superior iliac spine. The nerve was closest to the rim at 90°, indicating that this is an area of high risk during retractor placement.

CLINICAL RELEVANCE: Retractor placement at 90° to the anterior acetabular rim should be avoided to reduce the risk of femoral nerve injury.