Fig. 1

Magnetic resonance (MR) images showing measurements of the distance (white double-headed arrow) between the femoral nerve (FN) (solid line) and anterior acetabulum (AA), and the cross-sectional area (CSA) of the iliopsoas muscle (dotted line). a Measurement levels: (1) top of the anterior inferior iliac spine (AIIS), (2) bottom of the AIIS, (3) tip of the greater trochanter. b Axial T1-weighted image of the left acetabulum at level (1). The measurement point was defined as the intersection of the cortex and midline of the AIIS (white dot). The ambiguous FN was identified using the “nerve-sheath signal increased with inked rest-tissue rare imaging” (3D-NerveVIEW image. c Axial 3D-NerveVIEW image of the left acetabulum at the same level of B). The FN was clearly visualized in white (outline arrow). d Axial T1-weighted image of the left acetabulum at level (2). The measurement point on the acetabulum was defined as the head of the bony AA rim. The minimum FN to AA distance was measured from the lateral edge of the FN to the head of the acetabulum. e Axial T1-weighted image of the left acetabulum at level (3). The measurement point on the acetabulum was defined as the head of the bony AA rim. The minimum distance was measured from the medial edge of the FN to the head of the acetabulum