Principal Investigators: Wendy M. Murray, PhD and Felix E. Zajac, PhD Project Category: Bone & Joint and Spinal Cord Injury Objective: The specific aim of this research project is to improve the functional outcome of the brachioradialis to extensor carpi radialis brevis (Br-ECRB) tendon transfer, an orthopaedic surgical procedure that is commonly used to restore voluntary wrist extension in individuals with tetraplegia. Research Plan: This project utilized biomechanical simulations to predict wrist range of motion following brachioradialis tendon transfer. Based on these simulations, quantitative assessments of wrist range of motion, elbow extension strength, and wrist extension strength were designed to evaluate the importance of biomechanical factors for function following brachioradialis tendon transfer. Work Accomplished: Three main conclusions have resulted from this study. First, this study identified that active range of motion depends on elbow position following Br-ECRB tendon transfer. We found that wrist extension decreased and passive flexion increased when the elbow was flexed. Surgical simulation of the tendon transfer identified two potential sources of compromised wrist extension with elbow flexion: muscle force-length properties or general muscle weakness. The computer simulations suggest that surgical tensioning of the transfer could improve outcomes. Second, our work suggests that the subjects in this study generally had insufficient extension strength to actively maintain an extended elbow postures. Even during maximum effort, six of eight subjects could not voluntarily produce an extension moment greater than the moment we estimated was required to stabilize the elbow at 30° elbow flexion. In contrast, at 120° flexion, the data suggests that weak elbow extensors are not a factor in stabilizing the elbow during wrist extension. This was a surprising result given that we previously observed that these subjects achieve greater wrist extension when the elbow is extended compared to when it is flexed. Our results suggest that improving elbow extension in these subjects would tend to further improve their ability to use their wrist in extended elbow postures, but would not address the deficit in wrist extension that occurs when the elbow is flexed. Third, measurements of active wrist extension strength suggest that the reduction in wrist extension observed with elbow flexion is not due to a reduction in active wrist extension strength with elbow flexion, as is commonly assumed. Specifically, while a significant decrease in wrist extension was observed with the elbow flexed, the most substantial difference in wrist extension strength that was observed in different wrist and elbow postures was an increase in the active moment produced when the elbow was flexed. This result suggests overall muscle weakness is likely to be the factor causing the deficit in wrist extension in flexed elbow postures. Summary: Our computer simulations identified two potential sources of compromised wrist extension with elbow flexion; muscle force-length properties or general muscle weakness. Our experimental data suggest that general muscle weakness is more likely to be the source of compromised wrist extension with elbow flexion for the subjects in this study. Funding Source: PVA SCRF Funding Status: Completed |
