The patellar-tendon-bearing socket is made of laminated or molded plastic that provides an intimate fit over the entire area of the amputated portion of the limb, including the distal end. The anterior wall of the socket is high enough to encompass the distal half of the patella while the posterior wall rises slightly higher than the apex of the in- ward bulge of the socket at the level of the patellar tendon. The medial and lateral walls are slightly higher than the anterior wall to control mediolateral forces applied to the stump, thereby enhancing stability, in this plane. The basic PTB socket also incorporates a soft insert liner Provide: The PTB socket provides total contact with the stump. This feature helps to prevent edema, provides some additional support area (although the end of the stump cannot tolerate much pressure), and probably provides better sensory feedback to the wearer because of the greater area of contact between the amputated limb and the socket Air cushion Socket One of the designs, the PTB air-cushion socket, consists of an elastic inner sleeve (stockinette impregnated with silicone rubber) within a rigid outer shell and cap. A sealed chamber between these two walls contains air at atmospheric pressure. Distal support is provided by the tension of the sleeve itself and by compression of the air sealed in the chamber. The advantages of the air-cushion socket are that is offers a possibility for higher distal loading, Maintains distal contact even when limb volume changes slightly, Lessens skin damage due to stretching of skin against an unyielding surface. The increased distal loading may enhance circulation by decreasing the need for more constrictive proximal loading. Two major difficulties are that it is complicated to fabricate and, once completed, modifications are very difficult. Other Socket Variations In addition to the variations-described above, which relate primarily to weight-bearing characteristics. Other variations of the basic PTB socket involve the upward extension of the anterior, medial, and lateral walls to provide al- ternate means of suspension. Since these designs relate to suspension, they are described in the section that follows. Supracondylar Suprapetellar System The basic PTB prosthesis is suspended by means of a supracondylar cuff ,which is attached to the socket in the posteromedial and posterolateral areas, and encircles the thigh just above the femoral epicondyles and patella . The supracondylar cuff serves-primarily to retain the prosthesis on the stump. It provides only slight assistance for mediolateral stability but does resist forces that tend to force the knee into hyperextension. Most amputees, with the possible exception of those with very-short or painful stumps, find the stump-socket pressures well within their tolerance with this type of suspension. The supracondylar/suprapatellar (SC/SP) suspension system has similarly high medial and lateral.