Immobilization is often associated with decreased muscle elasticity. This condition is known as muscle contracture; however, the mechanism remains unclear. The purpose of this study was to clarify the mechanism governing muscle contracture in rat soleus muscle by identifying changes in ankle joint mobility, insoluble collagen concentration and type I and type III collagen isoforms following 1- and 3-week immobilizations. Following a 1-week immobilization, range of motion (ROM) of dorsiflexion declined to 90% of the control value; additionally, ROM dropped to 67.5% of the control value after a 3-week immobilization. This finding suggested that ankle joint mobility decreases in conjunction with extended periods of immobilization. Insoluble collagen concentration in soleus muscles, which was unchanged after 1 week of immobilization, increased 3 weeks after immobilization. These results may be indicative of collagen fibers with strong intermolecular cross-links contained in the muscle was made increased relatively by 3 weeks of immobilization. Therefore, the change in intermolecular cross-links may be significant in terms of progress of muscle contracture with longer periods of immobilization. On the other hand, the ratio of type III to type I collagen isoforms in muscular tissue increased following a 1-week immobilization; moreover, this ratio remained constant after 3 weeks of immobilization. These data suggested that muscle immobilization may induce type III collagen isoform expression. The increase in the ratio of type III to type I collagen isoforms do not change in parallel with the increase in the limitation in ROM; however, this phenomenon probably is not closely related to the progress of muscle contracture. The change of collagen isoform in immobilized muscle may be involved in the mechanism governing the progression of muscle fibrosis.

[Purpose] The purpose of our study was to clarify temporal effects on restrictions to range of motion and the histopathological changes of joint components after joint immobilization in a rat knee-contracture model. [Subjects] Fifty-four male Wistar rats were randomly divided into two groups: a fixation group, and a control group. [Methods] In the fixation group, unilateral knee joints were immobilized at full flexion using a plaster cast for 4 weeks. At four weeks the animals were randomly divided into six subgroups, corresponding to the time of examination after cast removal: 0, 4, 8, 16, 24, and 32 weeks. For comparison, control group animals of corresponding age were also examined. [Results] Although movement restrictions of the knee joint had completely recovered 6 weeks after the cast removal, cartilage and synovial membrane structures did not completely recover. [Conclusion] These findings have not previously been reported, and as they form an addition to the fundamental scientific foundations of physical therapy, further research must examine these findings from a variety of perspectives.

Abstract. [Purpose] We examined the histopathological changes in the joint capsule that occurred due to long-term immobilization of the joint, and compared them with those seen in aged rats.[Subjects] A total of 26 male Wistar rats were used in this study.[Methods] The right knee joints of the experimental group rats were immobilized for periods of 2, 4, 8, 16, or 32 weeks, and three 13-week-old "adult" rats and three 70-week-old "aged" rats were used as control groups. At the end of each immobilization period, the right knee joints of the rats were used as samples for histological examination.[Results] We observed histopathological changes in the joint capsules occurring due to joint immobilization. Increase in the thickness of the joint capsule had occurred by 4 weeks of immobilization and developed with prolongation of the immobilization period. An increase in the thickness was also observed in the joint capsule of aged rats. Further, the areas of elastic fibers in aged rats and those immobilized for 32 weeks were decreased compared to adult rats.[Conclusion] The joint capsules after immobility and aging showed similar changes, suggesting that some kind of identical mechanism causes the two conditions.

Abstract.[Purpose] The aim of this study was to investigate the histopathological effects of mobilization on joint components using a rat knee joint contracture model. [Method] Twenty-two male Wistar rats (aged 9 weeks) were randomly divided into an experimental group (n = 18) and a control group (n = 4). The experimental group had the right posterior limb knee joint immobilized for 8 weeks to induce contracture after which this group was subdivided into three subgroups-immobilized, treatment, and non-treatment groups. In the immobilized group (n = 6), knee joint specimens were collected immediately after immobilization. The non-treatment group (n = 6) was bred normally for 8 weeks, while the treatment group (n = 6) underwent mobilization during the same 8 weeks. After breeding, we prepared tissue specimens of the knee joint for observation in the sagittal plane and examined them using a light microscope. [Results] Compared to the non-treatment group, the treatment group showed an increase in the number of fat cells in the synovial subintima and a reduction in the density of collagen fiber bundles in the posterior joint capsule.[Conclusion] Joint mobilization appears to effectively improve joint function.