Safe zone for anterior retractor placement in total hip arthroplasty: A cadaveric study

Aim: Femoral nerve entrapment during placement of anterior retractors for total hip replacement results in considerable morbidity, although it is uncommon. The aim of this study is to describe a safe zone for placement of anterior retractors during total hip arthroplasty by studying anatomy in cadavers. Materials and Methods: Ten hips from 6 cadavers were dissected and studied. The clock face anatomy of the acetabulum was used as pins were placed at various clock positions before proceeding with the sectioning of the surrounding muscles. For the left hip 6, 5, 3, 1, and 12'o clock positions and for the right hip 6, 7, 9, 11, and 12'o clock positions were pinned along the anterior acetabular wall. The limbs were dissected axially, beginning from the inferior aspect of the acetabulum and proceeding in a proximal sequence with an interval of 1 cm. The plane of the first section passed through the distal end of the acetabulum and was named plane A. The subsequent proximal planes were named planes B, C, and D, respectively. The distance between the femoral nerve and the anterior acetabular wall was measured. Results: The distance from the anterior acetabular rim to the femoral nerve was closest at plane C, measuring 10.76 ± 2.58 mm (which coincides with the 3'o clock position in the left hip and the 9'o clock position in the right hip). The anteroposterior diameter of Iliacus muscle was maximum at plane A, measuring 17.56 ± 3.90 mm (which coincides with the 6'o clock position in both the right and left hips), and mediolateral diameter of iliopsoas was maximum at plane D, measuring 28.50 ± 3.74 mm (which coincides with the 11'o clock position in the right hip and the 1'o clock position in the left hip). Conclusions: The femoral nerve is closest to the anterior acetabular rim at plane C (9'o clock position of the right hip/3'o clock position of the left hip). Hence, the Hohmann retractor should not be placed on this plane. Anterior retractors can be safely placed adjacent the acetabular rim at planes A, B, and D.