Wrist Range of Motion Depends on Elbow Position after the BR-ECRB Tendon Transfer

Wendy M. Murray, PhD; Anne M. Bryden; Kevin L. Kilgore, PhD; Michael W. Keith

Objectives: The overall purpose of this project is to improve outcomes of surgical interventions that restore hand and wrist function to individuals with tetraplegia. We hypothesize that the wrist’s active range of motion depends on elbow position after the brachioradialis (Br) to ECRB tendon transfer. The objectives of this study are: (i) to quantify active range of motion of the wrist at different elbow positions in individuals with Br-ECRB transfers, and (ii) to simulate how surgical tensioning of the Br-ECRB transfer influences the relationship between elbow posture and wrist range of motion using a biomechanical model.

Methods: Active range of motion of the wrist was evaluated in seven individuals (nine wrists) with Br-ECRB tendon transfers. The subjects had C5 or C6 level injuries, and were an average of 50 months (range=7-76 months) post-op. The human subjects protocol was approved by the Institutional Review Board of MetroHealth Medical Center (Cleveland, OH). All subjects provided informed consent. We simulated the active range of motion of the wrist after the Br-ECRB tendon transfer in different elbow positions using a biomechanical model of the upper extremity. To do so, we developed a model of the Br-ECRB transfer’s anatomical path and force-generating capability. We compared the active and passive moment-generating capacities of the transfer under different surgical tensioning conditions with the passive properties of the wrist joint to estimate restored range of motion.

Results: The maximum position of wrist extension that could be maintained against gravity decreased substantially in five of nine wrists when the elbow was flexed. In eight wrists, the wrist rested in a more flexed posture at 120° elbow flexion compared to full elbow extension. The biomechanical model indicates that surgical tensioning influences both active wrist extension and the rest position of the wrist against gravity. Elbow flexion compromised active wrist extension when the transfer was tensioned to operate at shorter muscle fiber lengths. Tensioning the transfer to operate at longer lengths improved wrist extension when the elbow was flexed but limited passive wrist flexion at full extension.

Conclusions: After cervical spinal cord injury, the inability to maintain a given wrist posture in different elbow positions could influence grasp strength and could limit an individual’s ability to acquire, hold, or release objects over the full range of elbow motion. The biomechanical model suggests that surgical tensioning of the transfer can be optimized to maximize active wrist extension over the full range of elbow motion. However, optimizing wrist extension may sacrifice passive wrist flexion when the elbow is fully extended.

Funding acknowledgments: Research support provided by the Spinal Cord Research Foundation of the PVA (SCRF #2047), NIH Neural Prosthesis Program (N01-NS-2-2344), and the Rehabilitation Research and Development Service of the Department of Veteran’s Affairs (B898-3RA).