Using the body kinematics to assess the utilization of transhumeral prostheses

Abstract

There is a gap between the technical capability of upper limb prostheses, and the control strategy (commonly sequential myoelectric control) used to actuate the motorized joints. Surprisingly, the control method is the same for prosthetic hands and hand/wrist/elbow systems, which leads to a complex utilization. Research groups are investigating new control strategies to make the prosthetic control easier. Most studies are focusing on the task achievement, but it is nonetheless essential to assess the achievement method, especially since high-level amputees are prone to develop compensation-related musculoskeletal disorders. The study aims to show that body kinematics can be used to compare different control strategies, or prosthetic equipments. Transhumeral amputees performed a reaching task with different prosthetic parameters (different sockets, different control strategies). They performed the task with a prosthesis prototype that could be adapted to any socket, and implemented with any control strategy. They were equipped with motion capture sensors in order to record their body kinematics. The body motion analysis included the trunk and shoulder displacements, as well as the weight deviation. We could observe that each transhumeral amputee had a unique utilization of their prosthesis, and that they had their own residual capabilities. All the participants performed the task with the two tested control strategies successfully. However, the kinematic analysis showed differences between the control strategies in terms of coordination restauration, that the participants described but that the task assessment (success or not) could not provide. Differences could be highlighted between control strategies that the standard assessment method could not show. Hence the whole body kinematics can be a substantial source of information, especially given the potential severity of compensatory strategies in upper limb prosthesis utilization.