Osteoporosis, a condition characterized by decreased bone strength, is prevalent among postmenopausal women but also occurs in men and women 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 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—also referred to as a T-score of –2.5. Postmenopausal women who fall 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. More than 50% of fractures among postmenopausal women, including hip fractures, occur in this group with low bone density.
In the United States, as many as 8 million women and 2 million men have osteoporosis (T-score <–2.5), and an additional 18 million individuals have bone mass levels that put them at increased risk of developing osteoporosis (e.g., bone mass 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 about age 50) precipitates rapid bone loss so that most women meet the diagnostic criterion for osteoporosis by age 70–80.
The epidemiology of fractures follows the trend for loss of bone density. Fractures of the distal radius increase in frequency before age 50 and plateau by age 60, with only a modest age-related increase thereafter. In contrast, incidence rates for hip fractures double every 5 years after age 70 (Fig. 354-1). This distinct epidemiology may be related to the way people fall as they age, with fewer falls on an outstretched hand and more falls directly on the hip. At least 1.5 million fractures occur each year in the United States as a consequence of osteoporosis. As the population continues to age, the total number of fractures will continue to escalate.
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, most of which require hospital admission and surgical intervention. The probability that a 50-year-old white individual will have a hip fracture during his or her lifetime is 14% for women and 5% for men; the risk for blacks is lower (about one-half those rates). Hip fractures are associated with a high incidence of deep vein thrombosis and pulmonary embolism (20–50%) and a mortality rate between 5 and 20% during the year after surgery.
There are about 700,000 vertebral crush fractures per year in the United States. Only a fraction of them are recognized clinically, since many are relatively asymptomatic and are identified incidentally during radiography for other purposes (Fig. 354-2). Vertebral fractures rarely require hospitalization but are associated with long-term morbidity and a slight increase in mortality rates, primarily related to pulmonary disease. Multiple vertebral fractures lead to height loss (often of several inches), kyphosis, and secondary pain and discomfort related to altered biomechanics of the back. Thoracic fractures can be associated with restrictive lung disease, whereas lumbar fractures are associated with abdominal symptoms that include distention, early satiety, and constipation.
Lateral spine x-ray showing severe osteopenia and a severe wedge-type deformity (severe anterior compression).
Approximately 250,000 wrist fractures occur in the United States each year. Fractures of other bones (estimated to be ˜300,000 per year) also occur with osteoporosis; this is not surprising in light of the fact that bone loss is a systemic phenomenon. Fractures of the pelvis and proximal humerus clearly are associated with osteoporosis. Although some fractures result from major trauma, the threshold for fracture is reduced for an osteoporotic bone (Fig. 354-3). In addition to bone density, there are a number of risk factors for fracture; the common ones are summarized in Table 354-1. Age, prior fractures, a family history of osteoporosis-related fractures, low body weight, cigarette consumption, and excessive alcohol use are all independent predictors of fracture. Chronic diseases with inflammatory components that increase skeletal remodeling such as rheumatoid arthritis, increase the risk of osteoporosis, as do diseases associated with malabsorption. Chronic diseases that increase the risk of falling or frailty, including dementia, Parkinson's disease, and multiple sclerosis, also increase fracture risk.
Factors leading to osteoporotic fractures.
Table 354-1 Risk Factors for Osteoporosis Fracture
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Table 354-1 Risk Factors for Osteoporosis Fracture
|Personal history of fracture as an adult||Early menopause (<45 years) or bilateral ovariectomy|
|History of fracture in first-degree relative||Prolonged premenstrual amenorrhea (>1 year)|
|Female sex||Low calcium intake|
|White race||Impaired eyesight despite adequate correction|
|Potentially modifiable||Inadequate physical activity|
|Current cigarette smoking||Poor health/frailty|
|Low body weight [<58 kg (127 lb)]|
In the United States and Europe, osteoporosis-related fractures are more common among women than men, presumably due to a lower peak bone mass as well as postmenopausal bone loss in women. However, this sex difference in bone density and age-related increase in hip fractures is not as apparent in some other cultures, possibly due to genetics, physical activity level, or diet.
Fractures are themselves risk factors for future fractures (Table 354-1). Vertebral fractures increase the risk of other vertebral fractures as well as fractures of the peripheral skeleton such as the hip and wrist. Wrist fractures also increase the risk of vertebral and hip fractures. Consequently, among individuals over age 50, any fracture should be considered as potentially related to osteoporosis regardless of the circumstances of the fracture. Osteoporotic bone is ...