Three human cadavera were utilized for the study of the effects of varying axes of rotation upon flexion of the thigh. The investigation was carried out in an attempt to determine the optimum functional position of the external hip joint in the above-the-knee prosthesis with pelvic suspension. Variations in the angles formed between the axes of rotation and the frontal and transverse planes of the anterior superior iliac spines were facilitated by an adjustable ball-and-socket joint; this was placed opposite the hip joint of the cadaver, and a rod was passed through it into the center of the head of the femur.

Flexion to 54 degrees was carried out from starting positions—characterized by various combinations of flexion, abduction, and external rotation of the thigh—which simulated the postural deviations observed clinically in amputation stumps.

The results indicate that, for straight-forward flexion to occur, the external joint should be placed from one and one-quarter to one and three-quarters inches anterior to the middle of the greater trochanter.

An axis which passed through the greater trochanter was conducive to considerable abduction, as the thigh was moved forward in flexion. Conversely, when the external joint was placed too far anteriorly, adduction was associated with flexion.

Considerable adjustment in the position of the external joint, within rather narrow limits, is necessary to compensate for varying degrees of flexion, abduction, and external rotation of the thigh.