Kinematic Comparison of Voluntary Opening and Closing Body-Powered Prostheses

Exoprostheses with prehensor operations are commonly powered by body movement. Body-powered prostheses allow individuals with upper extremity limb loss to control prehensors without external power. Various prehensors can be controlled manually with a harness system through scapular abduction. Voluntary closing (VC) and voluntary opening (VO) devices are two common prehensors used with body-powered prostheses. The purpose of this study was to kinematically compare the use of VC and VO devices in individuals, with unilateral transradial limb loss performing functional movement activities. Movement mechanics between those with limb loss and those without (able-bodied subjects) were also compared to further assess the magnitude of differences. Ten able-bodied subjects and eight subjects with a unilateral transradial amputation who use body-powered prostheses participated. Subjects completed activities and torso, shoulder, and elbow joint kinematics were calculated. While completing the unilateral lifting task with the use of the VO prehensor, subjects performed with similar body mechanics to the able-bodied subjects, incorporating greater torso and elbow movement. During the bilateral lift and cutting task the individuals using the VC prehensor, used similar shoulder and elbow joint trajectories as the able-bodied subjects while the VO prehensor required lower body compensatory movement. Each prehensor was task and user-specific. To avoid additional strain on the body, it is important to discuss the unique function and characteristics of each type of prehensor and to encourage the most optimal movement with each user. This will enable proper prosthetic prescription, improved movement efficiency, and enhanced function for individuals following upper limb loss.