Tendon transfers commonly are used to restore arm and hand function after injury to the main motor nerves or after spinal cord injury. Surgeons traditionally use passive tension to determine the length at which a muscle should be attached during tendon transfer. The principles used to choose the length at which the transferred muscle should be attached still are relatively vague and have not been examined thoroughly. Misunderstanding of the sarcomere lengthpassive tension relationship can result in severe overstretch of the muscle and poor function. Upper extremity muscles have operating ranges that vary between synergists and antagonists, and recent architectural and biochemical data suggest that upper extremity muscles are designed to provide optimal control of joint position and stability. It is hypothesized that a significant functional improvement will be realized when muscles are reattached during tendon transfer procedures at the appropriate length and tension.

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