ABC of Rheumatology: OSTEOPOROSIS

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Abstract
Pathophysiology The human skeleton is composed of about 20% trabecular bone and 80% cortical bone. Bone undergoes a continual process of resorption and formation in discrete bone remodelling units. About 10% of the adult skeleton is remodelled each year. This turnover prevents fatigue damage and is important in maintaining calcium homoeostasis. Bone loss results from an imbalance between the rates of resorption and formation. Trabecular bone is more metabolically active, and osteoporotic fractures tend to occur at sites composed of more than 50% trabecular bone. View larger version: In this window In a new window False colour, scanning electron micrographs of normal trabecular bone (left) and trabecular bone affected by osteoporosis (right). Bone loss leads to thinning, and in some cases perforation, of the trabecular plates. Trabecular perforation occurs in situations of increased bone turnover, and the resulting loss of normal architecture leads to a disproportionate loss of strength for the amount of bone lost. Peak bone mass is achieved by age 30. After skeletal maturity, bone is lost in both sexes at about 1% a year. Women experience a phase of accelerated bone loss for five 10 years after the menopause. View larger version: In this window In a new window Association between age and bone mineral density of lumbar spine in women. (Lines show mean (2 SD)).

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