prosthesis(redirected from externally powered prosthesis)
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a mechanical device that replaces missing segments of extremities or other parts of the body and compensates for the defect cosmetically and functionally.
There are several types of prostheses. Temporary prostheses, which are used after amputation, are intended for shaping the stump and teaching the patient to walk. Intermediate prostheses, used for therapy and training, are more elaborate and compare in design and biomechanical characteristics with permanent prostheses; they are made from standard semifinished products and can therefore be assembled differently for each individual. Lower-extremity prostheses of this type have a foot and hinges at the ankle and knee. Their length is adjustable, and sockets made of various materials can be joined to them. Definitive (permanent) prostheses are used after the final shaping of the stump.
Prostheses for the upper extremities may replace the hand, forearm, or shoulder or may be fitted following disarticulation of the shoulder; those for the lower extremities may replace the foot, crus, or thigh, or they may be fitted following disarticulation of the thigh. The prostheses are made of standardized semifinished products, and the stump is individually fitted with socket-sleeves. The material used provides a classification for the prosthesis: wood, metal, plastic, or a combination of leather and fabric-reinforced rubber. These prostheses are usually cosmetic and functional (active) prostheses, since they compensate to some extent for the function of the missing extremity. In particular, some types of foot prostheses have been designed with shock absorption and additional lateral movements. There are also crus prostheses without a thigh sleeve that are deeply set onto the lateral condyles of the femur and the kneecap and gently held in place by a harness; these prostheses eliminate undesirable piston-like movements of the stump. Such prostheses compensate for the cosmetic defect.
Among the artificial aids with bioelectric control, the most widely used are forearm prostheses with artificial fingers that flex and extend, allowing the hand to grip and open. Prostheses with bioelectric control have the following advantages: the control system is similar to the natural regulation of movements; the healthy muscles do not have to make unnatural control movements; control is effected without great expenditure of muscle energy; and delicate regulation of finger movements is possible. Forearm prostheses may feature two pairs of movements (gripping and opening of the hand and rotation of the forearm), a feedback device, a multifunctional hand that executes three types of gripping movements using a single actuation mechanism (contraction into a fist, lateral movement, and pinching), or one or three pairs of movements (gripping and opening of the hand, rotation of the forearm, and bending at the elbow hinge).
Bioelectric prostheses are prescribed on an individual basis because of the strict indications and contraindications that govern their use. Prostheses with terminal devices useful in the patient’s occupation are used mostly after amputation of the upper extremities. They are intended to perform tasks corresponding to the patient’s occupational skills. Such prostheses consist of a shoulder or forearm sleeve and, instead of a hand, a special device for holding tools.
Breast prostheses fitted after amputation are made of foam rubber, or they may consist of a shell filled with liquid. They are held in place by a special brassiere. Ocular prostheses compensate for the cosmetic defect created by the removal of an eye. They are made of special types of glass or plastic. An implant prosthesis developed in the 1960’s is sewn to the eye muscles and is thus able to move. Dental prostheses are artificial objects used to compensate for defects in the crowns of teeth or to replace some or all missing teeth. Dental prostheses may be fixed, that is, attached to natural teeth, such as inlays, artificial crowns, or bridges, or removable, such as dental plates and partial dentures. Dental prostheses may also be worn by children to prevent deformation of the face and jaws. Prostheses have also been developed for the nose, ears, and other parts of the face.
N. I. KONDRASHIN and V. G. SANIN