The patient with a fracture
Osteoporosis is usually unrecognized until the patient has a fracture. A prior low-trauma (non-vehicular) fracture by history or on spine x-ray is the most powerful risk factor for another fracture, increasing the risk of another fracture three- to fivefold, even when bone mineral density is not very low. A history of a non-vehicular fracture before menopause (ages 20 – 50) doubles the risk of a postmenopausal fracture.
Surgical treatment of the first fracture will not prevent the next fracture. When a woman has a low-trauma fracture after age 45, she should be presumed to have osteoporosis and should be considered for treatment with a bone-specific medication. Further evaluation is necessary only to exclude other pathology. Treatment with a bone-specific agent may also improve the outcome after hip replacement. Unfortunately, less than half of women receive medical treatment for osteoporosis after surgery for hip fracture.
The patient without a fracture
The two strongest risk factors for osteoporosis are age and low body weight. A family history of osteoporosis or hip fracture (mother, father or sibling) doubles the risk. Osteoporosis is more likely if the patient has been a cigarette smoker, consumed a diet low in dairy products, has a history of intentional or unintentional weight loss, immobilization, rheumatoid arthritis, or hyperthyroidism, or has chronically used thyroid hormone, cortisone, or anticonvulsants. (Use of sex hormones or diuretics is associated with better bone density.) Women of African descent generally have better bone density and fewer fractures, and Asian women tend to have poorer bone density but not necessarily more fractures than women of northern European origin.
Very thin women are at increased risk of low bone density and fractures. Weight loss, intentional or not, is associated with bone loss. Height and weight should be measured at each visit, and compared with previously measured or reported young adult height and weight. A height loss of more than 3 cm strongly suggests one or more vertebral fractures, which can be confirmed by lateral spine radiographs. Kyphosis with onset in late menopause (the dowager’s hump) does not necessarily mean the patient has osteoporotic spine fractures and is often associated with osteoarthritis.
Because one-third of bone must be lost before osteoporosis is obvious on roentgenogram, a “normal x-ray” does not rule out osteoporosis. Lateral spine films are useful if a vertebral fracture is suspected, but most bone pain is not due to a fracture and most spine fractures do not cause pain.
Blood and urine tests can provide information on bone turnover. They are not recommended for diagnosis but, because changes are seen much earlier, they are superior to bone density for determining response to treatment and may be available routinely in the future.
The gold standard for the diagnosis of osteoporosis is a bone density test of the hip or spine using dual energy x-ray absorptiometry (DEXA), technology with a high degree of precision. Ideally both hip and spine should be evaluated because women with osteoporosis at the spine may not show low bone density at the hip or vice versa. If only one site is scanned, the hip is the preferred site for the evaluation of older postmenopausal women because vertebral osteophytes often mask low bone density in the lumbar spine. Bone density of the lumbar spine is preferred for younger women (who do not usually have osteophytes), because bone loss progresses more rapidly and is visible earlier at the spine than the hip.
Dual energy x-ray absorptiometry of the hip or spine requires a large, expensive piece of equipment, limiting its use to specialty clinics. Low bone density at the distal wrist, forearm, or heel (which can be measured with much smaller, less expensive devices) predicts future fracture risk reasonably well. Broader use of these less expensive instruments should improve the ability to diagnose osteoporosis in general practice.
Whether and when to measure bone density is controversial. In the USA, a bone density test is recommended for all women aged 65 and older, but other countries usually require additional risk factors before recommending a bone density test. Experts recommend bone mineral density measurements for relatively young postmenopausal women who have had an early menopause or other risk factors such as family history, excessive thinness, and cigarette smoking. Bone density has also been used to motivate women to accept therapy and to monitor response to therapy. Bone density is a better motivator than monitor, because bone density changes slowly, and relates poorly to change in fracture risk. A repeat bone scan to monitor treatment should be postponed until at least 2 years have passed since therapy was initiated.
Interpretation of bone density
The Z-score is the number of standard deviations above or below the average bone mineral density value for a woman of the same age. A T-score is the number of standard deviations above or below the average bone mineral density for healthy young white women. The World Health Organization defines osteoporosis as a T-score at least 2.5 standard deviations below the mean T-score for a young adult reference sample. Every standard deviation of reduction in bone mineral density doubles the risk of fracture, that is, approximately -1 T-score or -1 Z-score. This is true whether central or peripheral bones are assessed.
Bone density is used to diagnose osteoporosis. To predict future fracture risk, bone density must be considered together with clinical risk factors, including the patient’s years postmenopause, frailty, and propensity to fall.
A fracture risk of 5% in the next year warrants bone-specific drug therapy. This level of risk is observed in elderly women who have had a vertebral fracture, women on high-dose corticosteroids, and in some women who have very low bone mineral density plus several clinical risk factors (Table lists diseases and drugs associated with osteoporosis risk). Targeting women 65+ years of age who have multiple risk factors or who show clinical evidence of osteoporosis (height loss, fracture) makes more efficient use of limited medical resources by reducing the number needed to treat to prevent one fracture.
|Table Risk factors for falls|
|Table Diseases and drugs associated with risk of osteoporosis in adults|