Histopathological Changes in Synovium after Two-week Knee Joint Immobility in Rats

Objective: To clarify the histopathologic findings of the contracture mechanism, we conducted experiments to observe the histopathological changes in the synovium after knee joint immobility in rats. Methods: Three adult male Wistar rats had their right knee joints immobilized with a casting fixator for 2 weeks, and constituted the fixation group. Their left knee joints represented the control group. The excised knee joints were fixed in formalin, decalcified and embedded in paraffin. They were stained with hematoxylin and eosin, and the synovium was examined with a light microscope. Results: Atrophy of synoviocytes, fibrosis of the layer underlying the synovium, dilatation and congestion of the microvasculature were observed in the fixation group. Conclusion: Changes in the synovium of joint contracture observed in this study was considered as a secondary disorder caused by the cast fixation. This suggests that the concept of disuse atrophy would be applieable to the synovium of articular structures.