Simulation of Tendon Transfer Surgery in The Arm

Abstract

Restoring functional wrist movements, particularly extension and supination, in patients with upper limb impairments such as cerebral palsy often requires tendon transfer surgery. Although the Flexor Carpi Ulnaris (FCU) to Extensor Carpi Radialis Brevis (ECRB) transfer is a well-established technique, no clear consensus exists on the optimal routing path to maximise outcomes. This study used musculoskeletal simulation in OpenSim software to evaluate three routing strategies: Straight Path, Radial Volar Wrap, and Ulna Dorsal Wrap to determine which configuration provides the most significant biomechanical advantage for restoring wrist extension and supination. The Ulna Dorsal Wrap produced the largest supination and extension moment arms, attributed to its greater perpendicular distance from the rotational axes and more favourable tendon line of action. To refine this route, seven tendon slack lengths were tested. A slack length of 0.2825 m was identified as optimal, aligning FCU fibres closest to their physiological operating length and maximising active force generation. This configuration also demonstrated the best overall tendon force performance, reflecting the combined contributions of active fibre force and passive force, which, together with the improved moment arm, produced the greatest supination and extension moments of all tested strategies. Importantly, flexion and pronation were preserved, helping to maintain overall wrist function. These findings directly address the research question: "What is the best routing to optimise supination moment?" Confirming that the Ulna Dorsal Wrap with a 0.2825 m slack length is the most biomechanically advantageous configuration for restoring functional wrist extension and supination.