Compositional and metabolic changes in damaged cartilage are peak-stress, stress-rate, and loading-duration dependent

The first objective of this study was to determine if the cumulative effect s of impact or smoothly arising compression would damage the matrix of arti cular cartilage. Canine cartilage explants were subjected to repeated impac ts or to smoothly arising compressions of as much as 20 MPa at 0.3 Hz for a s long as 120 minutes. An increase in the water content of the loaded core compared with the surrounding ring was considered indicative of matrix dama ge. The results showed that damage to cartilage required repeated impacts w ith a peak stress of at least 2.5 MPa and a stress rate of at least 30 MPa/ sec for 2 minutes or longer. This suggested that impact damage is cumulativ e and stress-rate dependent. The second objective was to identify biosynthe tic and compositional changes in impact-damaged cartilage over a period of time after loading. Accordingly, canine cartilage explants were subjected t o repetitive impacts of 5 MPa at 0.3 Hz for 2, 20, and 120 minutes. The loa ded explants were then cultured for as long as 10 days. The increase in wat er content (1.9-3.8%) in the core region relative to the surrounding ring p ersisted during the 10-day culture. A significant increase in fibronectin s ynthesis (22-47%) was found in the core region of impact-damaged cartilage. Proteoglycan synthesis was increased by 41-104%. An increase in denatured collagens (11-70%) in the loaded cores substantiated damage to the collagen network. Denatured collagens stained with COL2-3/4m monoclonal antibody we re consistent with the compositional findings and were mainly located near the articular surface and in the deep zone. These changes were consistent w ith early osteoarthritis and suggested the induction of the initial stages of osteoarthritis in the impact-damaged cartilage.