The biomechanics of the Syme prosthesis.

The purpose of any limb prosthesis is to replace, to the reasonable satisfaction of the wearer, as much as possible of the normal form and function lost through amputation. To provide a suitable prosthesis in any particular case, therefore, the several cooperating professional persons—physicians, prosthetists, therapists, others as appropriate—must have an intimate knowledge of just what losses have been incurred and just what new circumstances, if any, have accrued as a result of the losses. Among these are the losses of structural elements, of joint motion, and of muscle function; the decrease in proprioceptive sense as well as in sensory perception; the development of persistent or recurrent pain in one form or •another; the impairment of circulation; and the losses of what in the normal would be the weight-bearing areas; not to mention numerous other matters purely medical and not necessarily associated with the amputation. Any one of these factors, or any combination of them, may influence the way in which an amputee will use a given type of limb prosthesis—that is, a device intended as a limb substitute. In the case of the Syme amputee, where the patient has suffered loss of the foot and ankle while retaining essentially the full length of the shank and more or less of the typical weightbearing characteristics of the normal heel, the obvious problem is to restore foot and ankle function (or to supply the equivalent of footankle function), to extend the stump so as to accommodate the loss of the tarsus and of the calcaneus, to furnish adequate support for the body during standing and during the stance phase of walking, to provide suitable suspension for the prosthesis during the swing phase, and to do all these things in such a way that the final result is acceptable to the wearer under both static and dynamic conditions. As with prostheses for other levels of amputation in the lower extremity, determination of the requirements of the Syme prosthesis takes its departure from a review of the normal pattern of locomotion and proceeds toward assessment of the means through which such a pattern may best be reproduced by application of inanimate devices. Discussion is here limited to the pertinent features of straight and level walking in the normal person and to the corresponding circumstances in a Syme amputee enjoying good general health, using a prosthesis, and having a stump itself free from any inherent medical complications such as excessive scar tissue, or neuromas, or skin disorders, or sensitive joints, or other conditions ordinarily beyond control of the limb designer.