CAPTURING SHOULDER MOTION AS AN INPUT FOR EXTERNALLY-POWERED, SHOULDER DISARTICULATION PROSTHESES

Individuals with shoulder disarticulation amputations present major challenges for functional prosthetic restoration. Conventionally controlled, cable-driven prostheses for shoulder disarticulation and humeral neck amputations require the use of scapular or bi-scapular protraction. This requires that the individual have good shoulder and torso posture and maintain adequate range of motion within the prosthetic socket(s). The absence of scapulo-thoracic and sterno-clavicular motion in intra-scapulo-thoracic level amputations make individuals with said amputations inappropriate for the device being considered in this study. It is well know that 2 inches of excursion is required to fully open an adult, voluntary-opening, split-hook terminal device while another 2 ½ inches of excursion is required to fully flex a mechanical elbow (provided the elbow flexion attachment is placed in the original, “starting position”). Mechanical analysis of these systems can easily prove that changes to reduce the necessary excursion are possible by moving the location of the actuation lever or elbow flexion attachment; however, these changes are minimal and require a trade-off of increased force requirements. Components such as excursion amplifiers have traditionally been used to enable the users of such body-powered prostheses to have the necessary excursion to control the prosthesis with these aforementioned increases in force. This being said, unless highly motivated, many individuals with these higher levels of amputation will discard their body-powered prostheses due to the limited tangible benefits of the device. Scapular protraction is being used to activate elbow flexion and/or terminal device operation. This gross body movement does not physiologically translate into the actions being performed by the prosthesis and compounds the drawback of increased force requirements. Although the motions used in this study are not completely physiological; they have closer ties to the functions for which the users intends the prosthesis to perform.