Upper limb compensatory strategies across tasks with an ultrasound-controlled prosthesis

Upper-limb amputation often leads to compensatory trunk and shoulder movements, increasing the risk of secondary musculoskeletal complications. This issue is exacerbated by the limited wrist functionality in current prosthetic systems, which restrict natural movement patterns during daily activities. Here, we investigate how limitations in the degrees of freedom (DoF) of the prosthetic wrist influence compensatory upper body motion during functionally relevant tasks. Three transradial amputees, experienced in the use of both body-powered and myoelectric prostheses, were fitted with custom sockets and a prosthetic hand controlled via a 32-channel A-mode ultrasound interface. Eight able-bodied participants served as controls. All participants performed three standardized tasks-drinking, lightbulb insertion, and the Clothespin Relocation Test-while trunk and shoulder kinematics and kinetics were recorded using motion capture and surface electromyography. The results demonstrated task-dependent compensation, with the Clothespin Relocation Test eliciting the greatest trunk flexion and bilateral shoulder involvement. Distinct adaptive patterns emerged between dominant and non-dominant sides, with increased reliance on proximal joints as wrist DoFs were restricted. The findings highlight the need for prosthetic designs and rehabilitation strategies that are tailored to specific tasks and user movement patterns. Quantifying compensatory motion provides a foundation for developing user-centered control systems that enhance function and reduce long-term musculoskeletal strain.