musculoskeletal and connective tissue disorders
Osteoporosis
Pathophysiology of Osteoporosis
Bone is continually being formed and resorbed. Normally, bone formation and resorption are closely balanced. Osteoblasts (cells that make the organic matrix of bone and then mineralize bone) and osteoclasts (cells that resorb bone) are regulated byparathyroid hormone(PTH),calcitonin,estrogen,vitamin D, various cytokines, and other local factors such as prostaglandins. Peak bone mass in men and women occurs around age 30. Men have higher bone mass than women. (Previous data suggesting people with African ancestry achieve higher peak bone mass are currently being questioned.) After achieving its peak, bone mass plateaus for about 10 years, during which time bone formation approximately equals bone resorption. Beginning with menopause, bone loss accelerates in women to approximately 2% a year for about 10 years and then the rate of loss decelerates ( Pathophysiology reference ). Osteoporotic bone loss affects cortical and trabecular (cancellous) bone. Cortical thickness and the number and size of trabeculae decrease, resulting in increased porosity. Trabeculae may be disrupted or entirely absent. Trabecular bone loss occurs more rapidly than cortical bone loss because trabecular bone is more porous and bone turnover is higher. However, loss of both types contributes to skeletal fragility. A fragility fracture is one that occurs after less trauma than might be expected to fracture a normal bone. Fractures resulting from falls from a standing height or less, including falls out of bed, are typically considered fragility fractures. The most common sites for fragility fractures are the following: Spine ( Vertebral Compression Fractures —the most common osteoporosis-related fracture) Hip Fractures None Hip Fractures None Distal Radius Fractures None Other sites may include the Proximal Humeral Fractures and Fractures at sites such as the nose, Rib Fracture , 1.Finkelstein JS, Brockwell SE, Mehta V, et al: Bone mineral density changes during the menopause transition in a multiethnic cohort of women.J Clin Endocrinol Metab93(3):861-868, 2008. doi:10.1210/jc.2007-1876 