Changes in the anatomical positions of the femoral nerve and artery in the lateral and supine positions: a multicenter retrospective study

Introduction Femoral nerve palsy and femoral artery injury are serious complications of total hip arthroplasty. However, few studies have compared the anatomical positions of these structures in different patient positions. This study aimed to compare the anatomical positions of the femoral nerve and artery in the lateral and supine positions.
Materials and methods This multicenter retrospective study included 111 patients who underwent lateral and supine computed tomography (CT) from 2016 to 2023. CT images were reconstructed in the anterior pelvic plane. The horizontal distance from the anterior margin of the acetabulum to the femoral nerve (Distance N) and femoral artery (Distance A) was measured. The difference in Distance N between the two positions (ΔLateral–supine Distance N) was calculated by subtracting the supine value from the lateral value.
Results The average Distance N was 26.5 ± 5.1 mm in the lateral position and 21.1 ± 4.4 mm in the supine position, with the nerve located significantly closer to the acetabulum in the supine position (P < 0.001). Similarly, the average Distance A was 26.8 ± 5.4 mm in the lateral position and 20.4 ± 4.9 mm in the supine position (P < 0.001). Multiple regression analysis showed that Distance N in the lateral position was significantly shorter in female patients and those with low body weight. In addition, low body weight correlated with a smaller ΔLateral–supine Distance N.
Conclusions The femoral nerve and artery are located closer to the anterior margin of the acetabulum in the supine position than in the lateral position. Low body weight was an independent predictor of shorter Distance N in both positions and a smaller ΔLateral–supine Distance N. These findings underscore the importance of considering patient positioning during total hip arthroplasty, particularly in patients with low body weight, to reduce neurovascular risks.