Comparison of quadricep motor evoked potentials between different surgical positions during total hip arthroplasty

The influence of intraoperative position on femoral nerve palsy after total hip arthroplasty (THA) remains unclear. Therefore, we evaluated the effect of intraoperative position on quadricep motor-evoked potential monitoring in patients undergoing THA using an anterolateral approach. We included patients who underwent primary THA using the anterolateral approach at our hospital between June 2021 and January 2024 with available data on intraoperative quadricep using transcranial electrical stimulation motor-evoked potential. Patient characteristics were compared between the supine and lateral position groups. Intraoperative quadricep MEP were evaluated at the beginning of surgery, after anterior acetabular retractor placement, after acetabular retractor placement, and before wound closure. The MEP amplitude at surgery start was set to 100%, and the change in amplitude at each time point was compared between positions. Ten patients were placed in the supine and lateral positions. Patient background did not differ significantly between the groups, and no postoperative paralysis was observed. The residual rates of quadriceps MEP were significantly lower in the supine position than the lateral position at all three time points (p < 0.05). Intraoperative quadricep motor-evoked potential monitoring in primary THA using the anterolateral approach showed significantly lower MEP amplitude in the supine position than in the lateral position at all three time points. Therefore, the lateral position may decrease femoral nerve palsy risk after THA.