Biochemical and mechanical properties of subchondral bone in osteoarthritis

摘要

The subchondral bone has long been known to thicken in osteoaithiitis However, recent evidence has demonstrated that the turnover of the bone is increased several fold, and further suggests that the thickening occurs prior to degradation of the articular cartilage, indicating that it plays a role in the pathogenesis of osteoarthiitis. The mechanical and biochemical properties of the subchondral bone are therefore of particular interest In any attempt to determine the nature of the factors initiating osteoaithiitis.We have shown that the subchondral bone collagen of the femoral head possessed a 20-fold increase in turnover, as assessed by procollagen rate of synthesis and metalloproteinase degradation, and a 25% decrease in mineralisation. This increased metabolism and high lysyl hydioxylation leads to narrower and weaker fibres Additionally the phenotypic expression of the osteoblasts is modified to produce increasing proportions of type I hbmotrimer in addition to the normal type I heteiotrimer, which further reduces the mechanical strength of the bone Overall, the narrow immature collagen fibres, the reduction in pyrrole cioss-linking, decreased mineralisation, and increased amounts of type I homotiimer, all contribute to a weakening of the mechanical properties of the subchondial bone.