SWELLING AND FIBRONECTIN ACCUMULATION IN ARTICULAR-CARTILAGE EXPLANTSAFTER CYCLICAL IMPACT

The objective of this study was to determine if repeated impact could damage living cartilage and lead to osteoarthritis-like changes in its biology. Canine cartilage explants were subjected to impacts of as mu ch as 50 MPa once every 5 seconds for 30 minutes. On each impact cycle , the loading rate was 100 MPa/sec to the assigned peak stress, which was held for 1 second. After impact testing, the cartilage was kept in defined culture for as long as 10 days. Radiosulfate incorporation in the region that received direct impact varied with load 0-4 hours aft er impact, but it did not vary with load at 20-24 hours after impact. Even so, most explants were visibly damaged by 20 or 50 MPa, and there was subtle evidence of damage from impacts of 5 or 10 MPa, For exampl e, ion-induced swelling in 0.01 M NaCl was increased, suggesting that the physical integrity of the matrix was reduced relative to controls. Self-diffusion of water, measured by proton magnetic resonance imagin g, was also increased in the deeper zones of the explant, consistent w ith changes in structure at the molecular level. Ten days after impact , the water content and the fibronectin content of the loaded region o f the explant were both increased. In combination. these osteoarthriti s-like changes suggested that the physical strength of normal cartilag e limits its ability to withstand cyclical impact.