Fig. 3

Orientation measurements of the gluteus minimus and joint capsule in the FADIR-positive group. Analysis process of ultrasound images in the FADIR-positive group. The following are shown in order from the top row: the grayscale image of the region of interest shown in Fig. 1 (upper row), the corresponding binary image, the power spectrum picture after two-dimensional Fourier transform of the binary image, and the orientation distribution denoted by the angle and mean amplitude (polar coordinate graph) and its elliptic approximation. The ratio of the major and minor axes of the ellipse can be regarded as the orientation intensity. Images and their analysis process at 20° and 10° external rotations (ER 20° and 10°), 0° external/internal rotation (ER/IR 0°), and 10° internal rotation (IR 10°) in 90° hip flexion, in order from left to right, are shown. FADIR = flexion adduction internal rotation