Transverse rotations of the pelvis, femur, and tibia occur in all normal individuals (Table IV). Inward and outward rotations of the segments are related to weight-bearing. Inward rotation takes place during the phase from minimal weight-bearing to full weight-bearing, and outward rotation occurs during the phase from full weight-bearing to minimal load.

The rotations of the lower extremity appear to be absorbed in the articulations of the foot and their related ligamentous structures.

Restrictions placed upon the normal transverse rotations will, to varying degrees, modify the synchrony and rhythm of walking. The awkwardness and discomfort of a patient, required to wear a leg brace which does not provide for these rotations at the hip, knee, and foot, are no doubt due, in part, to the restriction of these motions.

At the present time no prosthesis for the lower extremity has purposely incorporated mechanisms to provide for transverse rotatory motions, except on an experimental basis. Suppressing this rotation prevents the prosthesis from approaching the behavior of a normal extremity, and thus requires alterations in the normal pattern of movement of the joints proximal to the amputation. Relative motion will take place where the resistance to torque is the least. During weight-bearing in the stance phase, this motion will tend to occur between the stump and the socket, producing a most uncomfortable force on the stump. This is particularly true of the above-the-knee suction-socket limb. In the below-the-knee amputee, in addition to the major rotations that occur between the trunk and the fixed foot position, there is further restriction of rotatory motion at the knee, produced by the side hinge bars connecting the thigh lacer and the shank. In the case of below-the-knee amputees who have adequate stump length and shape, the use of suction sockets and an ankle mechanism may make it possible not only to provide for transverse rotation, but also to do away with side hinge bars and lacers, which tend to restrict the normal action of the knee.

The incorporation of a simple mechanism which provides for transverse rotation of sufficient magnitude, together with a unit for the return of the foot to the normal position, may well constitute a major contribution to both the comfort of the amputee and the improvement of function and synchrony in walking. An experimental mechanism has been used on this project. All amputees who have employed this mechanism have attested to the very marked improvement in comfort. Figure 8 shows reproductions of frames, taken from high-speed motion pictures, of an amputee using the experimental rotatory mechanism. The frames selected for reproduction show the six salient positions of the foot during the stance phase. Attention should be called to changes in the gap (A) between the stops;​ the width of the gap shows the amount of rotation occurring between the leg and the foot. The ultimate incorporation of this device, or modifications of it, in a prosthesis may well become standard practice, and may be advantageous in leg braces.