Impact of limb positioning on femoral nerve tension during minimally-invasive anterolateral approach in total hip arthroplasty: a cadaveric study

Abstract

Background:

Excessive traction stress on the femoral nerve during total hip arthroplasty (THA) may cause femoral nerve palsy. This study aimed to evaluate the tension changes on the femoral nerve during the surgical processes in the modified Watson-Jones approach using spring devices.

Methods:

We examined 11 lower extremities from 7 fresh cadavers. The femoral nerve was identified in the ilioinguinal approach and partially replaced with a tension spring (free length, 18.7 mm). Then, a modified Watson-Jones approach was employed in the lateral decubitus position. To assess the tension on the femoral nerve, the spring length was measured in the following settings: (1) limb in neutral position with no retractor after capsule incision; (2) hip joint completely dislocated with extension, adduction, and external rotation after femoral head resection; (3) femur elevated using retractors to expose the cutting surface; and (4) return to a neutral position. The differences in spring lengths were compared.

Results:

Median spring lengths in the first, second, third, and fourth settings were 19.1 mm, 21.0 mm, 23.6 mm, and 18.8 mm, respectively. Significant differences were found between the first and second and the second and third settings, but not between the first and fourth settings. The extension of the springs from the first to the third setting was more than 1.7-fold higher than that from the first to the second setting for all but one spring.

Conclusions:

The changes in spring length indicated that the femoral nerve tension progressively increased by more than 70% from hip dislocation to femur elevation with retractors. We directly demonstrated that tension on the femoral nerve increased in the modified Watson-Jones approach. These findings may contribute to recommendations regarding the surgical procedure.