Role of matrix metalloproteinases 2 and 9 in the development of frozen shoulder: human data and experimental analysis in a rat contracture model

BACKGROUND: Although frozen shoulder (FS) is a common shoulder disorder, its pathogenesis is not yet determined. The function of matrix metalloproteinases (MMPs) is related to extracellular matrix remodeling. The purposes of this study were to investigate the pattern of sequential expression of MMPs in a rat model of shoulder contracture and to compare the expression of MMPs in the joint capsule between patients with FS and a control group. METHODS: We obtained joint capsules from rats immobilized by molding plaster (a shoulder contracture model) at baseline, 3 days, 1 week, and 3 weeks (4 rats per time point; 16 rats in total). The expression of the inflammatory cytokine interleukin 6 (IL-6), MMP-2, and MMP-9 was examined by immunohistochemistry. We also obtained joint capsules from 21 patients with FS and 13 control patients with instability to quantify the expression levels of MMP-2 and MMP-9 by immunohistochemistry. RESULTS: In the rat model, IL-6 and MMP-9 tended to be overexpressed in the joint capsule at 3 days and 1 week and MMP-2 at 3 days, 1 week, and 3 weeks. MMP-2 and MMP-9 were significantly overexpressed in the joint capsules of the patients with FS compared with those of control patients. CONCLUSION: The results from both human and animal studies suggest the involvement of MMP-2 and MMP-9 in the development of FS. Animal study showed that the sequential expression of IL-6 and MMPs may be associated with fibrosis of the joint capsule.