Osteoporosis is a loss of bone mass that results in weakening of the bones (Fig. 1). A decrease in estrogens after menopause makes women over age 50 most susceptible to the effects of this disorder. Efforts to prevent osteoporosis include adequate intake of calcium and engaging in weight-bearing exercise. Because of safety concerns, hormone replacement therapy (HRT) is currently being re-evaluated for use in prevention of osteoporosis. Some drugs are available for reducing bone resorption and increasing bone density. Osteoporosis can be diagnosed and monitored using a DEXA (dual-energy x-ray absorptiometry) scan, an imaging technique that measures bone mineral density (BMD).
FIGURE 1. Osteoporosis. A section of the vertebral column showing a loss of bone tissue and a compression fracture of a vertebra (top). (Reprinted with permission from Rubin E, Farber JL. Pathology. 3rd Ed. Philadelphia: Lippincott Williams & Wilkins, 1999.)
Other conditions that can lead to osteoporosis include nutritional deficiencies; disuse, as in paralysis or immobilization in a cast; and excess steroids from the adrenal cortex. Overactivity of the parathyroid glands also leads to osteoporosis because parathyroid hormone releases calcium from bones to raise blood calcium levels. Certain drugs, smoking, lack of exercise, and high intake of alcohol, caffeine, and proteins may also contribute to the development of osteoporosis.
In osteomalacia there is a softening of bone tissue because of lack of formation of calcium salts. Possible causes include deficiency of vitamin D, needed to absorb calcium and phosphorus from the intestine; renal disorders; liver disease; and certain intestinal disorders. When osteomalacia occurs in children, the disease is called rickets (Fig. 2). Rickets is usually caused by a deficiency of vitamin D.
Paget disease (osteitis deformans) is a disorder of aging in which bones become overgrown and thicker, but deformed. The disease results in bowing of the long bones and distortion of the flat bones, such as those of the skull. Paget disease usually involves the bones of the axial skeleton, causing pain, fractures, and hearing loss. With time, there may be neurologic signs, heart failure, and predisposition to cancer of the bones.
FIGURE 2. Rickets. Radiograph of the left knee joint showing widening of the growth regions of the bones (arrows). (Reprinted with permission from Erkonen WE, Smith WL. Radiology 101: Basics and Fundamentals of Imaging. Philadelphia: Lippincott Williams & Wilkins, 1998.)
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