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  • Fracture propensity of spine, hip, pelvis, and wrist from depletion of bone matrix with subsequent demineralization.

  • Asymptomatic until a fracture has occurred.

  • Serum PTH, calcium, phosphorus, and alkaline phosphatase usually normal.

  • Serum 25-hydroxyvitamin D levels often low as a comorbid condition.


Osteoporosis is a skeletal disorder characterized by a loss of bone osteoid that reduces bone integrity and bone strength, predisposing to an increased risk of fracture. In the United States, osteoporosis causes over 1.5 million fractures annually, most commonly vertebral fractures, followed by hip fractures (300,000 annually) and pelvic fractures. In the United States, at least 20% of men and women over age 50 years have one or more fractured vertebrae. White women age 50 years and older (who do not receive estrogen replacement) have a 46% risk of sustaining an osteoporotic fracture during the remainder of their lives. Vertebral fractures are the most common fracture; they are associated with increased mortality, pain, and spinal kyphosis, although they are usually diagnosed incidentally on radiographs or CT scanning. Hip fractures are also associated with increased mortality, pain, reduced independence, and diminished quality of life.

The frequency of fragility fractures varies with ethnicity, sex, and age. The lifetime risk of hip fracture in the United States is 15.8% in white women and 6.0% in white men, 8.5% in Hispanic women and 3.8% in Hispanic men, and 2.4% in Chinese women and 1.9% in Chinese men. Blacks also have a lower risk for fracture due to higher bone mineral density and hip morphology that is less fracture-prone. There is much less ethnic variability for vertebral fractures. The prevalence of vertebral fractures in women older than 65 years is 70% for white women, 68% for Japanese women, 55% for Mexican women, and 50% in African American women.

Osteoporosis is caused by a reduction and disarray of bone’s microarchitectural organic collagenous matrix, which normally accounts for about 40% of bone mass and provides bone’s tensile strength. Inorganic calcium and phosphate compounds, largely calcium hydroxyapatite, mineralize the available collagenous bone matrix and normally provide about 60% of bone mass and most of bone’s compressive strength.

Osteoporosis can be caused by a variety of factors (Table 26–9). The most common causes include aging, sex hormone deficiency, alcoholism, smoking, long-term proton pump inhibitor therapy, and high-dose corticosteroid administration. Hypogonadal men frequently develop osteoporosis. Anti-androgen therapy for prostate cancer can cause osteoporosis, and such men should be monitored with bone densitometry.

Table 26–9.Causes of osteoporosis.1

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