Tendon Transfer Surgery Increases Passive Tension of Muscle, Muscle Fiber Bundles, and Muscle Fibers

Introduction: Muscles can adapt to altered length change by increasing or decreasing serial sarcomere number [1]. The functional result of this adaptation is for the muscle to work on or around optimal sarcomere length. If this finding applies to muscles after tendon transfer surgery, this would be desirable, as intraoperative measurements reveal that transferred muscles may be overstretched to the point where they produce less than 30% of their maximum active tension [2]. This dramatic structural reorganization in response to stretch may alter muscle passive tension, which can also influence function. However, passive tension after tendon transfer has not been thoroughly studied. Since muscle tension can be regulated at the fiber, fiber bundle or even whole muscle level, it is important to know which (if any) of these scales is affected. Therefore, the purpose of this study was to measure the passive tension of the entire muscle, fiber bundle and single fiber after stretched tendon transfer surgery that resulted in increased sarcomere number.