Histologic study of synovitis induced by trauma to the rat temporomandibular joint

Abstract Objective. The purpose of this study was to establish and histologically examine the time course of synovitis induced by trauma to the rat temporomandibular joint. Study design. Synovitis of the temporomandibular joints of 8-week-old male Wister rats was induced by forced condylar hypermobility, which was administered 10 times successively once a day for 10 days. Pathologic changes were observed microscopically at 2 and 5 days and 2, 4, 6, 8, 10, and 20 weeks after treatment. Results. Histologic findings from the 5th day to the 6th week after treatment were characterized by multiple layers of synovial cells, an increase of dilated vasculature, fibrin deposits, and synovial adhesion. These findings were in good agreement with those reported for the human temporomandibular joint. The pathologic changes decreased with advancing time, and synovitis was not observed at 20 weeks after treatment. Conclusion. The present procedure for inducing synovitis of the temporomandibular joint in rats will be useful in understanding the pathogenesis of synovitis in human temporomandibular joints.