Principal Investigators: Vincent R. Hentz, MD and Felix E. Zajac, PhD Project Staff: Wendy M. Murray, PhD; M. Elise. Johanson, MS, PT; Joe Towles, MS; and Niels Smaby, MS Project Category: Spinal Cord Injury Objective: Our overall objective is to improve functional grasping for individuals with quadriplegia by improving their biomechanical ability to grasp and secure objects. Reconstructive surgeries, including tendon transfers, are commonly performed to restore partial grasp or pinch function. Uncertainty in the outcome of new or modified surgical procedures hinders our ability to expand rehabilitation options for quadriplegic individuals. We propose to identify surgical musculoskeletal reconstructive interventions for improving pinch by quantifying pinch deficits in individuals with quadriplegia and evaluating the biomechanical basis of these deficits via computer modeling and anatomical studies of the thumb. Research Plan: Hand impairment in individuals with quadriplegia is being evaluated using clinical and laboratory protocols that measure lateral pinch force in different grasp openings and arm postures. A new clinical assessment device, which measures magnitude and direction of force in different grasp openings and subject-determined arm postures was developed and implemented in our lab. We have quantified the minimum pinch force required to accomplish selected functional tasks using a six-axis force-torque sensor mounted on a robotic arm. These threshold forces define a "virtual task" protocol, which tests an individual's ability to produce the force necessary to complete a given task. Computer modeling and cadaveric studies are being used to quantify the force produced at the thumbtip by individual muscles, and evaluate how surgical modifications (e.g., joint fusions) influence endpoint force production. Work Accomplished: We have completed an evaluation of the minimum pinch force required to accomplish five simple tasks, including opening and closing a zipper, stabbing food with a fork, pressing a remote control button, inserting and removing a plug from a socket, and inserting and removing a key from a lock. These activities require a range of forces. However, many of the tasks require a narrow grasp opening. Our data shows that lateral pinch force is substantially lower with a narrow grasp opening in quadriplegia. Lateral pinch force produced during maximum effort by individuals with quadriplegia is more mis-directed than the force produced by able-bodied individuals. The model simulations and cadaveric studies illustrate that joint posture and common surgical modifications to the thumb alter both the magnitude and orientation of the endpoint force produced by individual muscles of the thumb. Summary: This project met its stated goals: we successfully quantified pinch deficits in 18 individuals with quadriplegia, and identified novel aspects of hand impairment following cervical spinal cord injury. In particular, our work documented changes in pinch force that occur in different hand postures (i.e., grasp opening) and the mis-direction of pinch forces in subjects with tetraplegia. We focused computer modeling and anatomical studies to elucidate the biomechanical basis of these deficits in order to provide information useful for the refinement of surgical procedures. Funding Source: VA RR&D Merit Review Funding Status: Completed |
