Skeletal osteoporosis.

Osteoporosis is characterized by decreased bone mass and increased susceptibility to fractures. The clinical consequences of osteoporosis are fracture, most commonly seen at the wrist, the spine, and the hip. The prevalence of osteoporotic fracture is extremely high with 30%-40% of 70-year-old women having had at least one osteoporotic fracture. The prevalence in men is lower but may constitute a larger problem than expected. Osteoporotic fracture is, therefore, a significant cause of morbidity and mortality and represents a major problem of health care. Bone is the site of substantial metabolic exchanges, with bone resorption and formation continuing throughout life. The turnover processes are carried out by osteoclasts and osteoblasts in specialized cellular units. After cessation of growth, the skeleton probably consolidates to reach the peak bone mass at the age of 35-40 years. The relatively slow subsequent age-related bone loss occurs in both men and women, but women are additionally exposed to accelerated bone losses after the menopause. Estrogen deficiency is the dominating pathogenetic factor for osteoporosis in women. The role of disturbances in the calcium-regulating hormones and vitamin D deficiency is less sure. The pathophysiologic mechanisms of osteoporosis in men are not well investigated. Those who are endowed with a low peak bone mass and/or are exposed to a large bone loss are at particular risk of developing symptomatic osteoporosis. Several risk factors have been recognized but are insufficiently sensitive and specific to predict an individual's overall risk of developing osteoporosis.