The response of elderly human articular cartilage to mechanical stimuli in vitro.

OBJECTIVE To investigate the biosynthetic response of elderly human femoral head articular cartilage to mechanical stimulation in vitro and its variation with site. METHOD Full-depth cartilage biopsies of articular cartilage were removed from defined sites on 10 femoral heads from patients aged 68-95 years. Cartilage explants were subjected to either static or cyclic (2s on/2s off) loading in unconfined compression at a stress of 1MPa for 24h, or no load. Metabolic activity was assessed by adding medium containing (35)S-sulphate and (3)H-leucine during the last 4h of loading and measuring the incorporated radioisotope. Matrix composition was measured in terms of the amounts of collagen, sulphated glycosaminoglycans (GAG) and water content. RESULTS Loading of elderly human articular cartilage at 1MPa significantly inhibited incorporation of (35)S-sulphate (P=0.023) into cartilage explants. Pairwise comparisons showed that the difference in incorporation was only for static loading (43% decrease compared to unloaded) (P<0.05). (3)H-leucine incorporation appeared to follow the same trends but neither static nor cyclic load was significantly different from control (P=0.31). Significant topographical variation was found for % GAG wet and GAG:collagen but not water content, % GAG dry or collagen. Isotope incorporation rates were in the order anterior>superior>posterior. CONCLUSION Static loading inhibits matrix biosynthesis in elderly human cartilage, and cyclic loading is not stimulatory. This is in contrast to previous studies on young bovine tissue where cyclic loading is stimulatory.