Osteoporosis is a highly prevalent disease that predisposes patients to fragility fractures. These fractures carry serious risks, including increased mortality and the potential loss of functional independence. Effective treatments for osteoporosis are available, but these should be initiated before a fragility fracture actually occurs; to do so, osteoporosis must be diagnosed while it is still asymptomatic. The gold standard screening test used to detect low bone mass is dual-energy x-ray absorptiometry (DXA). Despite its clinical importance, the DXA report is sometimes neglected by radiologists—as though it were somehow less significant in diagnosis than our other modalities. If musculoskeletal radiologists are to help, rather than to hurt, we must raise the profile of this critical test with evidence-based utilization and coherent reporting: detailed recommendations for doing so are available from professional organizations such as the International Society for Clinical Densitometry and the National Osteoporosis Foundation. This brief survey will seek to remind the radiologist that a good densitometry report requires more than just copying numbers from a scanner.
Osteoporosis is the structural weakening of bones—whether from age, disease, or medication. Although the full structural physiology of bones is complex, a major source of their strength is derived from their calcified matrix . Thus, the bone mineral density (BMD), a measure that serves as a surrogate for the quantity of calcium in a bone, has a strong inverse correlation with the risk of osteoporotic fractures . As we will see, this association forms the basis of screening for osteoporosis.
Why does osteoporosis matter? It is a prevalent and highly morbid disease. Nearly half of all postmenopausal women will have an osteoporotic fracture in their lifetimes, with absolute rates increasing with the aging population . For example, in a large prospective study of 14,000 Europeans, the incidence of vertebral fractures in women per 1000 person-years increased exponentially with age: 3.6 (ages 50–54 years), 5.5 (ages 55–59 years), 9.5 (ages 60–64 years), 12.3 (ages 65–69 years), 17.9 (ages 70–74 years), and 29.3 (ages 75–79 years) . The cost of treatment of these fractures is high, with the incremental cost of care after an osteoporotic hip fracture being $11,241 in the first year: together, the direct and indirect costs of osteoporosis amount to billions of dollars annually . What is more, when patients have a fragility fracture, their mortality rate increases dramatically: in one epidemiologic sample, such a fracture decreased 5-year survival from 76% to 61% . Even if patients survive, the fracture and its aftermath can precipitate the loss of their functional independence .
Treatment of osteoporosis
Despite these numbers, osteoporosis is treatable. Nearly anyone benefits from adhering to the daily allowances of calcium and vitamin D, in addition to sensible lifestyle recommendations such as exercise, smoking cessation, and the moderation of alcohol . Yet, when these recommendations are insufficient, various pharmacologic therapies are available, the mainstays of which are the bisphosphonates; alendronate therapy has been proven to decrease the risk of fractures in osteoporotic women and men . The efficacy of the bisphosphonates is also reasonable, with a meta-analysis indicating that only about 50–67 osteoporotic women would need to be treated for 1–3 years to prevent one hip fracture among them (the “number needed to treat”); moreover, perhaps, as few as 30 osteoporotic men might need to be treated to prevent a single vertebral fracture .
Nevertheless, the drugs used to treat osteoporosis are not entirely innocuous. Mild gastrointestinal symptoms from bisphosphonate therapy are quite common, affecting between one-tenth and a half of all patients . Fortunately, the more severe complications are exceedingly rare: for example, osteonecrosis of the jaw tends to occur only in the unusual setting of intravenous bisphosphonate therapy in the oncologic population . Moreover, the counterintuitive association of bisphosphonates with atypical subtrochanteric femoral fractures occurs in only 1 of every 1000 to 50,000 patients . Comparing the average of this estimate to the average number needed to treat for osteoporotic women suggests that bisphosphonate therapy would prevent about 400 hip fractures for every one subtrochanteric fracture that it caused.
Despite these favorable statistics, the use of bisphosphonates requires some judgment. Even from a purely economic perspective, foregoing screening and universally treating everyone at risk for developing osteoporosis might not be feasible: the cost of treating most of the elderly population could be just as expensive as managing just their fractures . That is, when pharmacotherapy is used, its initiation and choice must be individualized, with the future risk of a fragility fracture contributing to the treatment decisions.
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Dual-energy x-ray absorptiometry
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Controversy and confusion in DXA reporting
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Does bone densitometry actually change management?
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Does screening bone densitometry lead to overdiagnosis?
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Conclusions
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