Synovial adhesions are more important than pannus proliferation in the pathogenesis of knee joint contracture after immobilization: An experimental investigation in the rat

Objective. To measure intraarticular pannus proliferation after early and p rolonged joint immobility using an animal model. Methods. Forty rats underwent unilateral immobilization of a knee joint wit h an internal fixator for peri ods of 2, 4, 8, 16, and 32 weeks. Twenty rat s received sham surgery. The knee joints were harvested and processed for h istological examination. The synovial intima length and the subintimal area were measured on standardized sagittal sections with image analysis softwa re. The measurements were recorded with regard to their location (anterior or posterior; superior or inferior). Results. Intra and interrater reliabilities for all measurements were > 87. 9%. The synovial intima length was smaller in immobilized knees than in con trols at all time points. At 4 and 32 weeks, the difference was statistical ly significant (p < 0.05). The differences were marked in the posterior syn ovium, where the intima length of immobilized knees was significantly small er than in controls after 4, 8, 16, and 32 weeks of immobilization (p < 0.0 5). The subintimal area was comparable in immobilized and control knees at all time points. Conclusion. We standardized the quantification of intraarticular pannus in a joint contracture model after immobility of up to 32 weeks' duration. Thi s study revealed a significant decrease in synovial intima length but no ch ange in the subintimal area of immobilized knees compared with controls. Th e decrease in synovial intima length with immobility suggests that adhesion s of synovium villi rather than pannus proliferation are the major pathophy siological changes leading to contracture after immobility.