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Background: Femoral neurovascular injury is a serious complication in a direct anterior approach (DAA) total hip arthroplasty. However, dynamic neurovascular bundle location changes during the approach were not examined. Thus, this study aimed to analyze the effects of leg position on the femoral neurovascular bundle location using magnetic resonance imaging (MRI). Methods: This study scanned 30 healthy volunteers (15 males and 15 females) with 3.0T MRI in a supine and 30-degree hip extension position with the left leg in a neutral rotation position and the right leg in a 45-degree external extension position. The minimum distance from the edge of the anterior acetabulum to the femoral nerve (dFN), artery, and vein were measured on axial T1-weighted images at the hip center level, as well as the angle to the horizontal line of the femoral nerve (aFN), artery (aFA), and vein from the anterior acetabulum. Results: The dFN in the supine position with external rotation was significantly larger than supine with neutral and extension with external rotation position (20.7, 19.5, and 19.0; p = 0.031 and 0.012, respectively). The aFA in supine with external rotation was significantly larger than in other postures (52.4°, 34.2°, and 36.2°, p < 0.001, respectively). The aFV in supine with external rotation was significantly larger than in supine with a neutral position (52.3° versus 47.7°, p = 0.037). The aFN in supine and external rotation was significantly larger than other postures (54.6, 38.2, and 33.0, p < 0.001, respectively). Conclusions: This radiographic study revealed that the leg position affected the neurovascular bundle location. These movements can be the risk of direct neurovascular injury or traction. [ABSTRACT FROM AUTHOR]

Background. Osteoarthritis (OA) is the most common disease of the hip in adults, and its etiology is divided into two groups: primary and secondary. Although acetabular dysplasia is the most frequent reason for total hip arthroplasty (THA) in Japan, primary OA has increased recently. Although there are two types of femoral head migration in primary OA: superior and medial, there are some patients with prominent femoral head lateralization. This study aimed at evaluating the relationship between femoral head lateralization and bone morphology of the acetabulum and proximal femur using radiographic factors in primary OA of the hip. Methods. A retrospective study was conducted between 2008 and 2017 to assess 1308 hips with OA who underwent primary THAs at our institute. The diagnostic criteria for primary OA were Crowe type 1, Sharp's angle <45°, and center-edge (CE) angle >25°. We classified patients with primary OA into two groups based on femoral head lateralization: group L with lateralization or group N without. Radiographic factors included Sharp's angle, CE angle, acetabular inclination, acetabular depth ratio (ADR), acetabular head index (AHI), and femoral neck-shaft angle (FNA), all examined on an anteroposterior pelvic radiograph. Femoral neck anteversion was calculated using computerized axial tomography. Results. Primary OA was diagnosed in 210/1308 hips (16.1%) (group L: 112 hips (8.6%); group N: 98 (7.5%)). Patient demographics were not significantly different. Radiographic factors with observed significant differences between group L and group N were the average CE angle (33.0° vs. 35.1°, respectively, p = 0.009), ADR (251.6 vs. 273.4, p < 0.001), AHI (77.2 vs. 80.4, p < 0.001), and FNA (136.9° vs. 134.8°, p = 0.012). Conclusions. This investigation suggests that primary OA with femoral head lateralization demonstrated specific identifiable radiographic characteristics in the acetabulum and proximal femur that might contribute to hip joint instability such as the dysplastic hip. [ABSTRACT FROM AUTHOR]