Principal Investigators: V. Rodney Hentz, MD and Felix E. Zajac, PhD Project Staff: Wendy M. Murray, PhD; M. Elise Johanson, MS, PT; Joseph D. Towles, MS; and Niels Smaby, MS Project Category: Spinal Cord Injury - 2001 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 is being tested. 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. A collaboration with the Cleveland VA FES Center of Excellence has been established to evaluate the relationship between quantiative measures of hand impairment and the ability to perform a task. 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. Expected Outcome: Our laboratory data suggest that increasing the ability to produce pinch force at narrow grasp openings may be critical for improving functional grasping after quadriplegia. The anatomical and computer modeling studies will investigate different surgical approaches to accomplish this aim, as well as evaluating different surgical techniques that could alter the orientation of the pinch force. Funding Source: VA RR&D Merit Review Funding Status: Funded |
