Anatomical and physiological considerations in below-knee prosthetics.

One of the most difficult problems in the design of prostheses is the development of the best means of attaching the prosthesis to the wearer. In lower-extremity cases, transmission of forces between stump and prosthesis is of primary importance. To effect efficient transmission of forces, a stable connection between stump and prosthesis is necessary. At the same time comfort and freedom of motion must be maintained to as high a degree as possible. All of these goals are affected by anatomical and physiological characteristics of the stump and the next proximal joint, and often of the joint above that. Stability is provided most often by encasing the stump in a socket to a point near the first proximal joint. The soft tissues of the stump are not especially ideal for providing resistance to the torques and moments imposed on them by a socket during use of a prosthesis. If the tissues are compressed in an attempt to provide maximum stability, circulation will be impaired; if the socket is too loose, a false-joint effect is produced resulting in abnormally high unit pressures at proximal and distal points, chafing, and a reduction in ability to control the prosthesis. Thus, extreme care must be exercised in socket design and fabrication if the optimum condition is to be obtained. When weight-bearing can be achieved through the long bones, as in the case of many