Course of the sciatic nerve on magnetic resonance imaging in patients with osteoarthritis of the hip

Sciatic nerve palsy is a serious complication after total hip arthroplasty (THA). This is the first study to report the relationship between the sciatic nerve and the acetabulum on magnetic resonance imaging (MRI) before THA.

235 patients underwent 261 elective, primary THAs via the mini-incision posterolateral approach. We measured the horizontal distance (mm) and vertical distance (mm) from the posterior edge of the acetabulum to the sciatic nerve by T1-weighted imaging on an axial section of the centre of the femoral head. We defined the Dysplastic Group as having a posterior acetabular sector angle (PASA) <90° and the Non-dysplastic Group as having a PASA ⩾ 90°. We compared anatomical distances and angles between the 2 groups.

The horizontal and vertical distances were (mean ± SD) 8.0 ± 9.2 mm and 14 ± 5.0 mm from the posterior edge of the acetabulum to the lateral edge of the sciatic nerve, respectively. The acetabular anteversion (AA), anterior acetabular sector angle (AASA), and PASA were (mean ± SD) 19 ± 6.7°, 49 ± 8.4°, and 87 ± 8.6°, respectively. The horizontal and vertical distances were positively correlated (p < 0.0001). AA and PASA were positively correlated with the horizontal distances (p < 0.0001) as well as with the vertical distances (p = 0.0017 and p = 0.0438, respectively). The horizontal and vertical distances were significantly shorter in the Dysplastic Group than in the Non-dysplastic Group (p < 0.0001 and p = 0.021, respectively).

In cases of posterior acetabular dysplasia we have to be mindful of the course of the sciatic nerve.