Localized and adaptive synoviocyte proliferation characteristics in rat knee joint contractures secondary to immobility

Objective: To investigate the proliferative activity of synoviocytes in joint contracture. Design: Experimental controlled trial. Setting: Laboratory in vivo study. Animals: Adult male Sprague-Dawley rats (avg weight, 340g). Interventions: Not applicable. Main Outcome Measures: We immobilized the knee joints of 24 rats, in 135degrees of flexion, for up to 32 weeks. Controls were 24 sham-operated and 5 unoperated rats. On sagittal sections, synoviocytes that stained with a proliferating cell nuclear antigen antibody were counted over the anterior and posterior synovial intima. The length of the synovial intima was also measured. Results: The absolute number of proliferating synoviocytes decreased markedly in the posterior capsule of knee joints immobilized for more than 2 weeks (2.4+/-1.0 vs 22.7+/-7.1 at week 16, P<.05), and so did the synovial intima length (1.4+/-0. 1mm vs 8.6+/-0.5mm at week 16, P<.05). No change occurred anteriorly. Conclusion: A decreased number of proliferating synoviocytes and increased intima adhesion in the posterior capsule characterized joint contractures. The data further suggest that the synovial intima adapted to the new position of the joint. Phenomena of mechanotransduction could explain the fact that adaptations were restricted to the posterior synovial intima.