Rat Model of Quadriceps Contracture by Joint Immobilization

SIMPLE SUMMARY: Muscle contracture can occur in the quadriceps muscle. At the time of diagnosis, the muscle contracture condition is typically advanced, and treatment prognosis is poor. Therefore, to investigate the pathophysiology, early diagnostic method, treatment efficacy, and physical therapy efficacy in future research, we evaluated an easily performed animal model that can allow prolonged knee joint immobilization with minimal trauma to the experimental animals. We created a contracture model using the quadriceps muscle, a relatively large muscle that generates muscle contracture and facilitates future evaluation and approach. We compared previously reported methods of modeling muscle contracture: casts, Velcro hook-and-loop fasteners, and steel wires. After two weeks of immobilization, the range of joint motion, muscle weight, and histological changes in muscle fiber were evaluated. The results showed that the spiral steel wire method was the superior immobilization method. ABSTRACT: Muscle contracture is an abnormal pathologic process resulting in fibrosis and muscle atrophy, which can lead to limitation of joint motion. To establish a diagnostic method to detect muscle contracture and a method to control its progression, we investigated an appropriate method to create an animal model of quadriceps contracture using rats. Eighteen Wistar rats were divided into three groups, and bilateral hindlimbs were immobilized with either a cast (Group I), a Velcro hook-and-loop fastener (Group V), or steel wire (Group S) with the knee and ankle joints in extension position for two weeks. Five rats in a control group (Group C) were not immobilized. After two weeks, the progression of quadriceps contracture was assessed by measuring the range of joint motion and pathohistological changes. Muscle atrophy and fibrosis were observed in all immobilization groups. The knee joint range of motion, quadriceps muscle weight, and muscle fiber size decreased only in Group S compared to the other immobilization groups. Stress on rats due to immobilization was less in Group S. These results indicate that Group S is the superior quadriceps contracture model. This model aids research investigating diagnostic and therapeutic methods for muscle contracture in humans and animals.