Histopathological Changes of Joint Capsule after Joint Immobility Compared with Aging in Rats

[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.