The change in position of the sciatic nerve during the posterior approach to the hip

Abstract

The aim of this cadaver study was to identify the change in position of the sciatic nerve during arthroplasty using the posterior surgical approach to the hip. We investigated the position of the nerve during this procedure by dissecting 11 formalin-treated cadavers (22 hips: 12 male, ten female). The distance between the sciatic nerve and the femoral neck was measured before and after dislocation of the hip, and in positions used during the preparation of the femur. The nerve moves closer to the femoral neck when the hip is flexed to > 30° and internally rotated to 90° (90° IR). The mean distance between the nerve and femoral neck was 43.1 mm (standard deviation (sd) 8.7) with the hip at 0° of flexion and 90° IR; this significantly decreased to a mean of 36.1 mm (sd 9.5), 28.8 mm (sd 9.8) and 19.1 mm (sd 9.7) at 30°, 60° and 90° of hip flexion respectively (p < 0.001). In two hips the nerve was in contact with the femoral neck when the hip was flexed to 90°. This study demonstrates that the sciatic nerve becomes closer to the operative field during hip arthroplasty using the posterior approach with progressive flexion of the hip.

Position of the sciatic nerve and effect of gluteus maximus release during hip arthroplasty

“…2 Our previous study had several weaknesses, including the use of formalin-embalmed specimens and the need for gluteus maximus release to facilitate dislocation due to increased stiffness of the cadaveric joints. 1 We have repeated our findings in this study using Thiel embalming which has tissue properties closer to live patients than specimens embalmed in formalin. Thiel embalming results in soft and flexible cadavers with almost natural colours 3 (Figs.…”

“…6 In our previous study we demonstrated that the sciatic nerve becomes closer to the femoral neck with internal rotation and progressive hip flexion as performed during hip arthroplasty using the posterior approach. 1 It is not unknown whether the described hip flexion intra-operatively predisposes to an increased risk of nerve injury, however we believe that this positioning may be part of the cause for patients with sciatic nerve palsy after THA with no clear etiology. 2 Our previous study had several weaknesses, including the use of formalin-embalmed specimens and the need for gluteus maximus release to facilitate dislocation due to increased stiffness of the cadaveric joints.…”

“…Our previous study showed that during the posterior approach to the hip, following hip dislocation and femoral neck osteotomy, the sciatic nerve moves significantly closer to the femoral neck with progressively increasing hip flexion. 1 The use of formalin-embalmed cadavers, with stiffness requiring gluteus maximus tendon release to facilitate hip dislocation, may have had an uncertain impact on these results. It is not known whether the relationship demonstrated between the femoral neck and the sciatic nerve predisposes to an increased risk of nerve injury.…”

The effect of gluteus maximus tenotomy in primary total hip arthroplasty with posterior approach: Kinematic analysis of hip extensor strength

“…With internal rotation and flexion of the hip, the sciatic nerve becomes closer to the femoral neck, while the gluteal sling begins to compress the nerve distally. 3,7 Nerve damage may vary depending on the amount and duration of the pressure applied. A pressure increase of as little as 20 mmHg may result in venous stasis, which may lead to extraneural edema, whereas a 80 mmHg pressure increase stops all intraneural blood flow.…”

“…7 Tenotomy also prevents the GMT from compressing the sciatic nerve during internal rotation and flexion of the hip. 3 Theoretically, weakness of gluteus maximus in a healthy subject without hip osteoarthritis may lead to deterioration in rapid acceleration of the body upward and forward from a position of hip flexion, such as when pushing off into a sprint, arising from a deep squat, or climbing a steep hill. 8 However, no clinical studies reporting any possible disadvantage of the tenotomy or its association with gluteal muscle insufficiency in hip arthroplasty have been found in the literature.…”