3-D Evaluation of Abnormal Upper Extremity Joint Coupling Post-Stroke

Stroke-induced abnormal upper extremity (UE) joint coupling limits independent joint control and impairs functional arm use. While previous studies have predominantly evaluated UE joint coupling within the plane of motion (in-plane) and its effect on functional task performance, minimizing unnecessary joint movements outside the plane of motion (out-of-plane) across all UE degrees of freedom (DOFs) is essential for coordinated movements. To address this limitation, we developed an experimental procedure leveraging 3D motion capture to evaluate in- and out-of-plane joint coupling for seven UE DOFs during isolated shoulder, elbow, and wrist joint movements, and functional task performance during an object transfer task. We introduce a method to calculate the in- and out-of-plane joint coupling ratio (JCR) for seven UE DOFs. We investigated the contribution of stroke-induced abnormal in- and out-of-plane joint coupling to explain deficits in functional task performance using hierarchical regression analysis. In 18 individuals post-stroke, joint coupling was abnormal in- and out-of-plane for seven UE DOFs, evident by significantly higher JCR values for the paretic arm compared to the non-paretic arm. The regression model using both in- and out-of-plane joint coupling explained significantly higher variance, up to 33.8%, in stroke-induced deficits in movement duration, hand trajectory smoothness, trunk displacement, hand movement extent, and peak velocity time compared to models only using either in-plane or out-of-plane joint coupling. Our work advances post-stroke abnormal joint coupling evaluation methods across all UE DOFs, required to more comprehensively understand stroke-induced impairments in independent UE joint control and their effect on functional task performance.