The role of bone metabolism in osteoarthritis.

Bone is not structurally normal in osteoarthritis (OA). Periarticular bone in OA has increased turnover, decreased bone mineral content and stiffness, and decreased trabecular numbers. The increased turnover of collagen, in particular, may affect the biomechanical competence of bone and is driven by a number of processes, including osteoblast phenotypic expression, chondrocyte apoptosis, matrix metalloproteinases, and growth factors. This turnover is reflected in alterations in biomarkers and bone mineral density (BMD). High BMD at non-joint sites is associated with an increased risk of OA; however, low BMD and high bone turnover appears to be associated with more rapid progression. These alterations in bone turnover offer new therapeutic opportunities.