Abstract
The hip flexion movement includes movement of the femurs, which is correspondent with the pelvis, and posterior tilt of the pelvis. The pelvifemoral rhythm (rhythm of movement of the femur, which is correspondent with the pelvis) and movement of the sacroiliac joint were analyzed during passive unilateral hip flexion movement with the knee flexed in supine position by high-performance noninvasive magnetic resonance imaging (MRI) in 10 healthy adult women (mean age, 20.3 years). The rates of angles of posterior tilt of the pelvis in the angles of flexion of the right hip joint varied with the increase in angle of the flexion; approximately 1/28 (0.52°/14.8°), 1/20 (1.5°/29.9°), 1/19 (2.4°/45.0°), 1/16 (3.9°/60.7°), and 1/11 (11.4°/127.6°). The pelvis contralateral to that on the flexion side also showed posterior tilt of the same extent as that on the flexion side, when the flexion side was 45° or less. The extent of posterior tilt on the flexion side increased at 60°, and the difference in the extent between the flexion side and the contralateral side incleased at the maximum angle of flexion. At the end of flexion of the right hip joint was maximum, the sacral bone showed nutation in relation to the right ilium bone. From these observations, movement of the sacroiliac joint was confirmed to be involved in the flexion movement.
