Meniscus injury is one of the causes of secondary osteoarthritis (OA). Cartilage oligomeric matrix protein (COMP) is a major component of the extracellular matrix of the musculoskeletal system. This study was undertaken to evaluate the changes occurring in meniscus from the knees of anterior cruciate ligament (ACL) transected rabbits during the early stages of OA development, especially regarding COMP changes. Ten skeletally mature white New Zealand male rabbits underwent ACL transaction of the right knee joint. Left knee joints were used as controls. Animals were sacrificed at 4 and 12 weeks post-surgery. Meniscal tissues were processed for histology and immunohistochemistry. The number of cells and positive cells were counted per high-power field (HPF). Anti-COMP antiserum was obtained according to Hauser et al. with minor modifications. Monoclonal Ki67 antibody was used to find out cells undergoing active division. TUNEL reaction was used for the study of apoptosis. Alcian blue staining was used to study glycosaminoglycans. At 4 weeks post-ACL section 2/5 of the medial menisci presented with incomplete vertical posterior tears, while all lateral menisci were no altered. At 12 weeks post-ACL section 5/5 of the medial menisci and 2/5 of lateral menisci presented tears. At 4 weeks postsurgery menisci showed: a weak increase of cells with a significant increase of cells undergoing active division; an increase in the number of apoptotic cells; glycosaminoglycans staining was increased and COMP staining was weakly increased. At 12 weeks postsurgery cells per HPF reverted to normal number; the number of cells undergoing active division decrease below normal; whereas the number of apoptotic cells was still elevated; glycosaminoglycans staining was more elevated than at 4 weeks postsurgery and COMP staining of extracellular matrix remain elevated. Areas of large and abundant cell clusters were seen post-ACL around menisci tears. We concluded that after ACL transaction, extracellular matrix changes and altered cell distribution occur early in the meniscus. Cellular division as well as apoptosis occur early too. Elevated concentrations of COMP after ACL transection might indicate meniscus changes early in osteoarthritis process.
