Markers of Bone and Cartilage Turnover

Over the past few decades, scientists have been trying to identify tissue-specific markers that would help to better understand the pathogenesis of bone and cartilage diseases and could be used clinically for the screening, diagnosis and followup of bone or joint diseases. Historically, only a few components known to be involved in bone, mineral or cartilage turnover were available for this purpose (e.g., urine hydroxyproline, serum and urine calcium and phosphate levels). However, since most if not all of these substances have wider biological functions beyond bone, mineral and cartilage metabolism, their clinical value as tissue-specific markers was limited. Hence, there was a need to identify more specific indices of bone and cartilage metabolism. Since the 1980s, a number of collagenous and non-collagenous breakdown products as well as cell-specific enzymes have been discovered and developed into markers of musculoskeletal tissue metabolism. This review describes their chemical and biological function, available analytical methods and possible clinical applications.