OPTIMAL FIXED WRIST ALIGNMENT FOR BELOW-ELBOW, POWERED, PROSTHETIC HANDS

Abstract

Generally, a prosthetic wrist has one degree of freedom in a supination/pronation sense. Some do allow bending of the wrist [1-4], however, due to the complexity of integration and operation, they are not as commonly used. The restricted motion of the prosthetic wrist is compensated for by additional motion of the shoulder and elbow. Not only can this additional motion appear awkward making the person self-conscious [5], but it may also increase the risk of joint injury [6]. In an attempt to balance function, cosmesis, and “dynamic cosmesis” (minimal compensatory motion), the prosthetist aligns the wrist with the forearm in some combination of flexion/extension and ulnar/radial deviation. Changing the alignment once it is fixed requires significant effort. Therefore, having a sense of the optimal alignment would be very beneficial. Guidelines for wrist alignment do exist [7 and 8], but while some consider them “very applicable”[9], others feel “there is a need for updated text materials” [10]. These guidelines were written over thirty years ago (1958 and 1971 respectively) and this lag of standards behind technology has left prosthetists to develop their own alignment procedures that sometimes contradict those of their colleagues. Where one prosthetist aligns a wrist at 10 degrees extension, another uses slight ulnar deviation and flexion [11-13]. While the experienced prosthetist has a practical knowledge from which to decide on an individual wrist alignment, the novice practitioner requires guidelines on which to base decisions. Our goal was to determine which, if any, of the wrist alignment angles commonly used allows elbow and shoulder motions to be closest to “normal”, resulting in optimal dynamic cosmesis.