OSTEOPOROSIS AND BISPHOSPHONATES☆

Abstract

A large number of orthopaedic patients have osteoporosis. They are typically elderly women (usually older than sixty) or older men with back pain and fractures of the hip, spine, wrist, or other bones. Osteoporosis is the primary risk factor for fractures in the elderly, who can be treated to effectively reduce fracture risk. Osteoporosis is defined as a reduction in bone mass and a deterioration in bone microarchitecture resulting in increased bone fragility and fracture risk. It is diagnosed noninvasively by measuring bone density, often with the use of dual-energy x-ray absorptiometry (DXA). This brief review summarizes the pathophysiology and epidemiology of osteoporosis and focuses on bisphosphonates, the most effective therapy available today 1. To carry out the skeletal functions of calcium homeostasis and mechanical support, microscopic bone units are continuously remodeled, resorbed by osteoclasts, and then rebuilt by osteoblasts. Cancellous bone is remodeled at a rate of ~30%/yr and cortical bone, at a rate of ~3%/yr. Peak bone mass is reached in the mid-thirties, after which resorption exceeds formation, causing gradual, continuous bone loss in most individuals. Comparisons of identical and nonidentical twins and of mothers and daughters indicate that genetics strongly influences bone mass 2,3. Estrogen deficiency following menopause substantially increases osteoclast number and osteoclastic bone resorption, most likely via elevated levels of cytokines (interleukins, tumor necrosis factor-alpha [TNF-α], etc.). Women can lose spinal bone at a rate of 2% to 4%/yr immediately after menopause. Hyperparathyroidism, hyperthyroidism, and corticosteroid treatment are other common causes of accelerated bone loss. Ex vivo studies have shown that bone mass is the major determinant of bone strength, accounting for ~75% of the variance. Extensive cross-sectional epidemiological studies and more recent prospective studies have shown a close correlation between low bone mineral density and increased fracture risk 4, …