Prosthetic wrist units are designed to serve two basic functions. First attach a terminal device to the forearm of the prosthesis and secondly to permit the amputee to preposition the terminal device prior to operation.

The above-elbow (trans humeral) amputee has lost all ability to supinate and pronate the prosthetic forearm. The trans radial amputee with a short residual forearm (50% or less than the length of the non-amputated forearm) no longer retains active transmissible supination and pronation. Even at the exceptionally long trans radial levels of amputation, the motions of supination and pronation are severely restricted. Consequently, the upper-limb amputee must be provided with a device that permits some form of substitution for active forearm rotation.