Unique Biology of Shoulder Cartilage in Comparison to the Cartilage Obtained from the Knee and Ankle Joints

OBJECTIVES: Glenohumeral joint (GHJ) arthritis in relatively young active patients presents a considerable clinical challenge. Little is known regarding the biology and reparative capacity of GHJ articular cartilage and how it compares to other diarthrodial joints. The objectives of the current study were to 1) describe the histological and morphological appearance of human normal GHJ cartilage; and 2) investigate cellular responses of GHJ cartilage to interleukin-1β (IL-1β), in comparison to cartilage obtained from the knee and ankle of the same donors. METHODS: GHJ, knee (femoral condyle) and ankle (talus) cartilage was obtained through the Gift of Hope Organ and Tissue Donor Network (Itasca, IL) from nine human donors with no documented history of joint diseases (58-75 yo, both genders). Gross morphology of each joint was assessed using Collins grading on a scale 0 to 4. Cartilage explants (3 mm diameter) were removed from each joint, cultured for 48 hours with or without interleukin-1β (IL-1β; 0.1ng/ml or 10ng/ml), and processed for histology with Safranin O, proteoglycan (PG) synthesis/content, and PCR for key extracellular matrix (ECM) genes: Col2, Agg, and SOX9. Results were compared between uncultured and cultured controls and across all three included joints. RESULTS: Unlike grossly normal (Collins grades 0-1) knee and ankle cartilage, grossly normal GHJ cartilage with an intact surface displayed signs of subtle structural changes: loss of Safranin O in the upper layer and in the ECM and increased staining around chondrocytes suggesting elevated metabolic activity. Differences became more apparent with higher Collins grades or in the presence of IL-1β. Treatment with IL-1β (both doses) resulted in more than 2-fold inhibition of PG synthesis in GHJ cartilage (p<0.05), while only high dose IL-1β had the same effect on the knee or ankle cartilage. At the control level, expression of Col2 and Sox9 was comparable between all types of cartilages; Agg expression was the highest in the ankle cartilage. IL-1β increased Agg expression in humeral cartilage and Agg and Col2 genes in glenoid cartilage. CONCLUSION: GHJ cartilage appears to be more susceptible to catabolic processes than cartilage in the knee or ankle. Elevated expression of key ECM genes in the presence of pro-inflammatory mediator IL-1β may suggest an attempted, but failing repair. This study provides new insight into the histological and biochemical characteristics of GHJ cartilage, both of which may contribute to challenges associated with its reconstruction.