Definition

Osteoporosis is a skeletal disorder characterized by compromised bone strength predisposing a person to an increased risk for fracture. Bone strength primarily reflects the integration of bone density and bone quality. Bone quality refers to factors such as microarchitectural changes, bone turnover, collagen structure, damage accumulation (e.g., microfractures), and degree of mineralization [1].

Osteoporosis can also be defined according to the World Health Organization criteria on the basis of bone mineral density and bone mineral content measurements (see section on diagnostic studies).

Osteoporosis is the most common metabolic bone disease. The National Osteoporosis Foundation estimates that at least 10 million Americans have osteoporosis and another 34 million have decreased bone mass, putting them at increased risk for osteoporosis and fractures. Of the 10 million, 8 million are women and 2 million are men. Annually in the United States, more than 1.5 million fractures attributable to osteoporosis occur, including approximately 750,000 vertebral, 300,000 hip, and 250,000 wrist fractures. The annual cost of caring for osteoporosis-related fractures in the United States is in excess of $16 billion. In addition, there is a 15% to 25% excess mortality within the first year after a hip fracture. In recent years, the hip fracture rate has been reported to be declining [2].

Symptoms

Osteoporosis is a silent disease until a fracture occurs. Pain and deformity are usually present at the site of fracture. Vertebral fractures often occur with little trauma, such as coughing, lifting, or bending over. Acute back pain may be related to a vertebral compression fracture, with pain localized to the fracture site or in a radicular distribution. New back pain or chronic back pain in a patient with osteoporosis and prior vertebral fractures may be related to new fractures, muscle spasm, or other causes.

With vertebral fractures, even if they are asymptomatic, there may be a gradual loss of height and the development of a kyphosis. Breathing may be difficult, and early satiety and bloating—a sensation of fullness and dyspepsia—may develop because of less room in the abdominal cavity.

Physical Examination

In evaluating patients with osteoporosis, it is important to diagnose treatable and reversible causes and to assess the risk factors for development of osteoporosis and osteoporotic fractures. Table 140.1 lists common causes of osteoporosis. Table 140.2 lists risk factors for osteoporosis.

The physical examination focuses on findings suggestive of secondary causes of osteoporosis (e.g., hyperthyroidism and Cushing syndrome). One should also examine areas previously involved with fractures (e.g., back, hip, and wrist) to assess for deformity and limitation of function. A baseline measurement of height should be obtained and reevaluated at subsequent visits. Localized vertebral tenderness may be present from fracture, paravertebral muscle spasm, or exaggerated thoracic kyphosis. The findings of the neurologic examination looking for any deficits due to vertebral fracture are usually normal.

Functional Limitations

Functional limitations are related to the type of fracture and its long-term consequences. With vertebral fractures, the functional limitation may initially be related to the acute pain and inability to move. The chronic limitations may be related to loss of height, chronic back pain, difficulty in moving, abdominal distention, and difficulty in breathing.

The functional limitations after a hip fracture are related to the decreased functional mobility, often the need for long-term use of assistive devices, the lack of independence, and the long-term need for assistive care. An assistive device will be needed permanently for ambulation by 50% of people with a hip fracture, and two thirds will lose some of their ability to perform ordinary daily activities.

Wrist fractures usually heal completely, but some people have chronic pain, deformity, and functional limitations.

Diagnostic Studies

Bone density measurements are the standard for assessment of risk, diagnosis, and long-term management of patients with osteoporosis. Bone density measurement is often essential to make management decisions. Available techniques include single-photon absorptiometry, dual-energy x-ray absorptiometry, quantitative computed tomography, and quantitative ultrasonography. Dual-energy x-ray absorptiometry, although it is not as sensitive as quantitative computed tomography for detection of early trabecular bone loss, is the method of choice for measurement of bone mineral density because of its good precision, low radiation dose, and fast examination time.

Bone mineral density testing should be based on an individual’s fracture risk profile and skeletal health assessment. It should be performed only if the results will influence a treatment decision.

Bone mineral density testing should be considered on the basis of the National Osteoporosis Foundation guidelines, as follows [3]:

• Women age 65 and older and men age 70 and older, regardless of clinical risk factors

• Younger postmenopausal women and men age 50-69 about whom you have concern based on their clinical risk factor profile

• Adults who have a fracture after age 50

• Adults with a condition (e.g., rheumatoid arthritis) or taking a medication (e.g., glucocorticoids in a daily dose of 5 mg or more for > 3 months) associated with low bone mass or bone loss

• Anyone being considered for pharmacologic therapy for osteoporosis

• Anyone being treated for osteoporosis, to monitor treatment effect

• Anyone not receiving therapy in whom evidence of bone loss would lead to treatment

• Postmenopausal women discontinuing estrogen

Bone mineral density is reported by T and Z scores (Table 140.3). The T score compares an individual’s bone mineral density with the mean value for young normal individuals expressed as a standard deviation (SD); the Z score compares the values to age- and sex-matched adults.

• Normal: a T score value for bone mineral density or bone mineral content that is not more than 1 SD below the young adult mean value.

• Low bone mass (osteopenia): a T score value for bone mineral density or bone mineral content that lies between1.0 and 2.5 SDs below the young adult mean value.

• Osteoporosis: a T score value for bone mineral density or bone mineral content that is 2.5 SDs or more below the young adult mean value.

The lower the T score, the higher the risk for subsequent fractures. However, the score will not predict who will fracture because other factors come into play (e.g., fall velocity, type of fall, direction of fall, and protective padding). A low Z score may suggest excessive bone loss due to secondary causes of osteoporosis.

Specific laboratory tests are obtained to help in the differential diagnosis of osteoporosis and to rule out osteomalacia. The general laboratory tests include a complete blood count, chemistry profile including calcium and phosphorus, liver and kidney tests, serum and urine protein electrophoresis, and thyroid-stimulating hormone concentration. A 24-hour collection of urine for calcium and creatinine measurement is also helpful. Because of the high prevalence of vitamin D deficiency in the adult population, especially elderly individuals, a serum 25-hydroxyvitamin D level should be obtained. A parathyroid hormone level should be determined in suspected cases of primary or secondary hyperparathyroidism. Blood and urine test results are usually normal in uncomplicated cases of osteoporosis. After a fracture, the alkaline phosphatase activity may be elevated. Biochemical markers of bone turnover, including urine N-telopeptide and serum C-telopeptide, may be helpful in selective patients to assess for bone turnover and whether someone is responding to treatment.

The initial approach to the prevention and treatment of osteoporosis involves nonpharmacologic interventions and, in appropriate patients, the use of various pharmacologic agents (Table 140.4). Prevention and treatment guidelines are presented in Tables 140.5 and 140.6.