A correlation between cartilage degradation and inflammation of the synovial membrane of shoulder joint in a rabbit model of collagenase-induced osteoarthritis

Osteoarthritis is a degenerative disease of articular cartilage. Numerous studies have expanded our understanding of the pathophysiology of the disease, yet there remain controversial questions regarding the relationship between mechanical loads on the joint, inflammation, and biochemical changes in cartilage tissue that lead to its degradation. The question of the primary cause of cartilage tissue damage remains unresolved, as synovitis and contracture may result from cartilage injury, while cartilage degeneration can concurrently arise in the presence of synovitis. Animal models play a key role in studying these changes, as they allow for the identification of the structural basis and characteristics of joint tissue disorders. Our hypothesis is that non-mechanical damage to cartilage tissues, through the introduction of collagenase into the synovial cavity, provokes a slow, progressive development of changes in the capsule and articular cartilage. The aim of the work was to investigate changes in cartilage and capsule of the shoulder joint under the conditions of modeling collagenase-induced joint damage. Collagenase was injected into the shoulder joint and saline was injected into the contralateral joint. After 4 months, the articular cartilage of the humerus head and scapula, the joint capsule, was examined. The morphometric method measured the thickness of the capsule, the condition of the cartilage by scale method and correlated between changes in the studied structures of the joint to establish the relationship between the degeneration of cartilage tissue and fibrous changes in the synovial membrane. The statistical analysis of the results was performed using non-parametric methods. The introduced enzyme induced degenerative changes in the shoulder joint cartilage after 3 months, accompanied by an inflammatory reaction in the synovial membrane and signs of connective tissue remodeling in the capsule. The results suggest that inflammation of the synovial membrane correlates with cartilage degradation (for the humeral head, r=0.74, p=0.02, and for the glenoid cavity, r=0.71, p=0.03), which likely represents an early event in the initiation and progression of articular cartilage damage. Damage to the synovial membrane and capsule thickness showed a direct correlation (r=0.87, p=0.001). Although mechanical damage remains the primary risk factor for osteoarthritis, the slow, “sluggish” progression of cartilage-degrading changes provided new insights into the relationship between changes in the cartilage, synovial membrane, and shoulder joint capsule. The model of osteoarthritis described in this study serves as a valid model for investigating the pathogenesis and treatment of the inflammatory and degenerative changes of the shoulder joint.