Osteoporosis, a condition characterized by decreased bone strength, is prevalent among postmenopausal women but also occurs in both women and men as a function of age and with underlying conditions or major risk factors associated with bone demineralization. Its chief clinical manifestations are vertebral and hip fractures, although fractures can occur at almost any skeletal site. Osteoporosis affects >10 million individuals in the United States, but only a small proportion are diagnosed and treated.
Osteoporosis is defined as a reduction in the strength of bone that leads to an increased risk of fractures. Loss of bone tissue is associated with deterioration in skeletal microarchitecture. The World Health Organization (WHO) operationally defines osteoporosis as a bone density that falls 2.5 standard deviations (SD) below the mean for young healthy adults of the same sex and race—also referred to as a T-score of –2.5. Postmenopausal women at the lower end of the young normal range (a T-score <–1.0) are defined as having low bone density and are also at increased risk of osteoporosis. Although risk is lower in this group, >50% of fractures among postmenopausal women, including hip fractures, occur in this group with low bone density. As a consequence, clinical assessment has evolved to include absolute risk of fracture, which incorporates bone mineral density (BMD) with age, gender, and other clinical risk factors to calculate 10-year fracture risk.
Osteoporosis-related fractures are adulthood fractures of any bone that occur in the setting of trauma less than or equal to a fall from standing height, with the exceptions of fingers, toes, face and skull.
In the United States, as many as 8 million women and 2 million men have osteoporosis (BMD T-score <–2.5 at lumbar spine, total hip or femoral neck), and >40 million individuals have bone mass levels that put them at increased risk of developing osteoporosis (e.g. BMD T-score <–1.0). Osteoporosis occurs more frequently with increasing age, as bone tissue is lost progressively. In women, the loss of ovarian function at menopause (typically around age 50) precipitates rapid bone loss so that most women meet the diagnostic criterion for osteoporosis by age 70–80. As the population ages, the number of individuals with osteoporosis and fractures will also increase, despite a recognized reduction in age specific risk. It is estimated that currently about 2 million fractures occur each year in the United States as a consequence of osteoporosis. Many of the fractures defined as related to osteoporosis occur in individuals with low bone mass. Within that population, segregation of those at high risk of facture for treatment has become an important issue in clinical management.
The epidemiology of fractures follows the trend for loss of bone density, with most fractures, especially those of the hip and vertebrae, showing exponential increases with advancing age. (Fig. 404-1). Lifetime osteoporotic fracture risk for a woman who reaches the age of 50 is about 50% and corresponding risk for a 50-year old man is about 20%.
Epidemiology of vertebral, hip, and Colles’ fractures with age. (Adapted from C Cooper, LJ Melton III: Trends Endocrinol Metab 3:224, 1992; with permission.)
About 300,000 hip fractures occur each year in the United States, almost all requiring hospital admission and emergency surgical intervention. The lifetime probability that a 50-year-old white individual will have a hip fracture is 14% for women and 5% for men; the risk for African-Americans is about half of those rates, and the risk for Asians and nonblack Hispanics appears similar to that for Caucasians. Hip fractures are associated with a high incidence of deep-vein thrombosis and pulmonary embolism and a mortality rate between 5 and 20% during the year after surgery, with higher ...