MSK: anatomy, function, pathology and challenges Bone: from cortical bone to osteoporosis

(1) Clinical Significance Bone strength governs fracture risk and reflects the integration of two main features: bone mass or density and bone quality. Bone mineral density (BMD) is expressed as grams of mineral per area or volume and in any given individual is determined by peak bone mass and amount of bone loss. Bone quality refers to trabecular bone architecture, turnover, damage accumulation (e.g., microfractures), cortical bone thickness, macro-architecture, osteon density, for both trabecular and cortical bone – mineralization, and other factors such as cell viability and osteocyte density as previously defined by the NIH Consensus Development Panel in 2001 (1). Among these bone quality parameters trabecular and cortical bone architecture are most accessible with non-invasive imaging techniques and multiple studies have shown that architecture gives additional information to BMD in assessing bone strength and discriminating patients with and without osteoporotic fractures (2-13). Today it is widely recognized that bone structure assessment improves our knowledge of the pathophysiology of osteoporosis, may improve fracture prediction and may give us more information on therapeutic effects of osteoporosis specific medications on bone. Recently also MR based measures of bone marrow function, such as spectroscopy and perfusion have been introduced to study bone metabolism (14-16).