Nerve Paralysis

Femoral nerve palsy, which manifests as quadriceps weakness with or without sensory loss, has been reported as one of the intraoperative complications following total hip arthroplasty (THA). It has a negative impact on the postoperative rehabilitation of patients and results in reduced patient satisfaction [1, 2]. The incidence of femoral nerve palsy following THA was reported to be 0.64% for anterolateral approach THA, 0.40% for anterior approach THA, 0.045% for posterior approach THA, and 0.026% for lateral approach THA among 17,350 patients who underwent initial THA [3]. In a study using magnetic resonance imaging, the distance between the femoral nerve and the acetabular rim was significantly shorter in the supine approach than in the lateral approach [4]. Therefore, more attention must be paid to femoral nerve palsy following THA with the supine approach than with the lateral supine approach.Several reports have highlighted the anterior retractor, which is placed in the osseous wall of the anterior acetabulum to pull the iliopsoas muscle, to gain an adequate view of the anterior margin of the acetabulum [2, 5–8] (Fig. 87.1). In particular, a report validated the effect of the anterior retractor on the femoral nerve using a motor-evoked potential (Neuromaster G1, Nihon Kohden), which enables intraoperative measurement of nerve potentials. Compared with the amplitude of the femoral nerve preoperatively, the amplitude of the femoral nerve after the placement of the anterior retraction on the acetabulum was reduced significantly in 17 of 22 patients (77%) who underwent an anterior approach THA and in 29 of 32 patients (93%) who underwent an anterolateral approach THA [5, 6]. The reduced amplitude of the femoral nerve improved significantly after THA, and there were no cases of paralysis. Therefore, the cause could be the anterior retractor itself compressing the femoral nerve through the iliopsoas muscle bulk [5, 6].In a cadaveric study, the shortest distance between the acetabular rim and femoral nerve was reported as an average of 16.6 mm at the acetabular rim at 90°anteriorly, based on the line connecting the superior anterior iliac spine and the center of the acetabulum [7]. In other words, the anterior retractor should be properly positioned on the acetabular rim at 90°anteriorly to avoid femoral nerve palsy. Furthermore, there have been reports of a positive correlation between the thickness of the iliopsoas muscle and the distance from the acetabular rim to the femoral nerve [7]. In patients with small iliopsoas muscles, anterolateral and anterior THA approaches may lead to femoral nerve palsy. As a result, an intermittent release of the anterior retractor and slight flexion of the hip joint may be useful in reducing pressure on the femoral nerve in these patients [9, 10]. Furthermore, preoperative physical therapy using an ergometer may be useful to increase the thickness of the iliopsoas muscle [11].