Relationship of pelvic and thigh motions during unilateral and bilateral hip flexion.

We filmed the hip flexion movement with a 16-mm motion picture camera to determine if a synergistic relationship between the pelvis and thigh existed. Seventeen young subjects, whose pelvises and thighs were marked with tape, underwent active and passive, unilateral and bilateral hip flexion while in the supine position. Analysis of the film revealed that the hip flexion movement is composed of two components--pelvic rotation and flexion of the thigh on the pelvis. Between one fourth and one third of the hip flexion movement was the consequence of pelvic rotation. This rotation always occurred within the first 8 degrees of the hip flexion movement. When therapists evaluate and treat patients with disorders of the thigh, pelvis, or lumbar spine, they should be aware that these structures normally move in synergy with one another. We suggest that the pelvifemoral relationship be examined further in studies with a wide range of healthy subjects and patients with a variety of clinical disorders.