Objective: To develop methods to quantify intraarticular connective tissue proliferation after immobility and to report results in an animal model of joint contracture.
Methods: Six rats had their right knee joints immobilized with an internal fixator for 3 weeks. The joints were harvested and sectioned. We measured the length of synovial intima and the subintimal area with image analysis software. Proliferating synoviocytes were identified by immunohistochemistry using the "proliferating cell nuclear antigen" antibody and were counted under optical microscopy on whole joint sections. Two outcomes were analyzed: the subintimal area and a synoviocyte proliferation index (number of proliferating synoviocytes/synovial intima length). Both were obtained for posterior and anterior aspects of the knee.
Results: Intra and interobserver reliabilities over 87% were found with these measurement techniques. Subintimal area means were not statistically different between immobilized and contralateral knees. In all subjects, the synoviocyte proliferation index (SPI) posteriorly was higher in immobilized than in contralateral knees (p<0.05), due to an increase in proliferating cells (p<0.05) rather than a change in synovial intima length (p>0.05). The SPI anteriorly was comparable in immobilized and contralateral knees (p>0.05).
Conclusion: We developed methods to measure intraarticular connective tissue proliferation in a contracture model in vivo. Proliferative changes in the posterior aspect of the knee suggest local mediation of connective tissue proliferation in the contracture process. These methods and preliminary results will benefit investigators assessing interventions in similar models.