Passive Mechanical Properties of Muscle in Hamstring Contractures of Children with Spastic Cerebral Palsy

INTRODUCTION: Children with spastic cerebral palsy (CP) often develop hamstring contractures, however, the mechanism of contracture formation is not known. Contractures represent a resistance of muscle to increased length. The structural elements responsible for this increased stiffness are also not known [1]. Previous work showed that single fibers from “contractured” muscle tissue has increased passive stiffness that could lead to the overall increased stiffness of the muscle [2]. Interestingly, the opposite result was observed when scaled to bundles of muscle fibers, as bundles from typically developing (TD) children were stiffer than contractured bundles [3]. Unfortunately, these samples were compared across a variety of muscles which may confound the results. To avoid potential complications associated with comparing among different muscles, the purpose of the current study was to investigate passive mechanical properties of two specific hamstring muscles involved in gait—gracilis (GR) and semitendinosus (ST). Hamstring contractures limit knee extension and are suggested as a contributing factor of crouch gait in patients with CP [4]. Despite new therapies, current best practices are unable to prevent contractures. Further understanding of the mechanism of contracture and the elements responsible for them could lead to new therapies to prevent contracture development and improve muscle function.