Association between clinical signs and histopathologic changes in the synovium of the tarsocrural joint of horses with osteochondritis dissecans of the tibia

Objective—To develop a scoring system for histopathologic changes in the synovium of tarsocrural joints (TCJs) of horses with osteochondritis dissecans (OCD) and to test for association between histopathologic changes and joint effusion or lameness. Animals—93 horses with OCD of the intermediate ridge of the tibia of 1 or both TCJs (134 joints) and 38 control horses without disease of TCJs (38 joints). Procedures—For OCD-affected horses, pretreatment lameness, TCJ effusion, and results of pelvic limb flexion test were scored. Synovial biopsy specimens were obtained from TCJs of OCD-affected horses during arthroscopy, and similar postmortem tissue specimens were obtained from control horses through a small arthrotomy. Histologic signs of synovitis in 172 biopsy specimens were scored by 2 pathologists (A and B) by use of 2 criteria: synoviocyte proliferation and cellular infiltration. Results—Analysis of scoring revealed good to very good intraobserver agreement within pathologist A (weighted kappa [WK], 0.76 to 0.81), and moderate to good agreement within pathologist B (WK, 0.56 to 0.63). Interobserver agreement for synoviocyte proliferation (WK, 0.34 to 0.52) and cellular infiltration (WK, 0.38 to 0.48) scores was fair to moderate. Joint effusion and synoviocyte proliferation were significantly associated, as were joint effusion and cellular infiltration. There was no association between histopathologic changes and the other clinical signs evaluated. Conclusions and Clinical Relevance—The scoring system was helpful for evaluating synovial inflammation caused by OCD of the intermediate ridge of the tibia in horses. Histopathologic signs of synovial inflammation were associated with effusion but not with lameness.