What Is Osteoporosis?
Causes and Risk Factors
Diagnosis
Prevention
Treatment
Fragility Fractures

What Is Osteoporosis?
Osteoporosis is characterized by progressive bone loss and an increased risk of fracture. It literally means “porous bone.” Because the changes in bone are at the microscopic level and the disease initially produces no pain or other outward symptoms, osteoporosis often goes unnoticed for years. As a person ages, it causes loss of height and, in some cases, a dowager’s hump, or rounded back. Osteoporosis affects some 28 million Americans. The term, bone mineral density or BMD, is used to describe bone strength. The lower the BMD, the more porous and weaker the bone.

Causes and Risk Factors
Although the exact cause of osteoporosis is not known, a number of factors do increase the risk. There is clear evidence of a genetic predisposition to osteoporosis. For women, excessive loss of bone occurs when certain hormones essential for bone formation and maintenance decrease substantially following menopause. If the body does not receive enough dietary calcium to meet its needs, it takes calcium from the bones to make up the difference. In premenopausal women, the sex hormone estrogen protects bones from being robbed of calcium by other demands of the body and helps produce and maintain collagen, an important component of bone. Once estrogen levels are depleted, it can no longer play this protective role. Another hormone, calcitonin, may facilitate the uptake of calcium from the blood into the bone and, at the same time, inhibit the loss of calcium from the bone. Other known risk factors include being underweight, tobacco use, excessive alcohol use, and certain medications.

On the basis of criteria set forth by World Health Organization (WHO) expert panel, 54 percent of postmenopausal white women in northern parts of the United States have osteopenia, or low bone mass, and an additional 30 percent have osteoporosis in at least one skeletal site. Osteoporosis occurs in all racial groups. For example, 13-16 percent of Hispanic women have osteoporosis; as many as 49 percent of Mexican-American women age 50 and older have low bone density; about 10 percent of African-American women over age 50 have osteoporosis; and an additional 30 percent have low bone density. Between 80 and 95 percent of all fractures experienced by African-American women over age 64 are related to osteoporosis.

Diagnosis
Osteoporosis is diagnosed on the basis of a medical history and physical examination, skeletal X-rays, bone densitometry, and laboratory tests. Bone densitometry is an X-ray technique that compares a patient’s BMD to the BMD that someone of the patient’s sex and ethnicity should have reached at about age 20-25, when bone density is at its highest. Doctors use several types of bone densitometry to detect bone loss in different areas of the body. Some of the equipment can provide a ten year fracture analysis. Dual beam x-ray absorptiometry (DEXA) is one of the most accurate methods, but other techniques can also identify osteoporosis. These include single photon absorptiometry, quantitative computed tomography (CT), and ultrasound.

WHO has defined osteoporosis  as bone mineral density measuring two and one-half standard deviations or more below the young adult mean. The test is often performed in women at the time of menopause. Bone densitometry is used not only to diagnose osteoporosis but also to monitor the effects of treatment.

Prevention
Once bone mass is lost, it is difficult or impossible to replace. For this reason, preventing osteoporosis is vital. It is important to do everything you can to build peak bone mass by age 25 and then to ensure that the inevitable loss of bone occurs as slowly as possible. Prevention entails a variety of measures. Find out more about prevention.
  
Treatment
Controlled trials involving thousands of women have shown that a number of medications are effective in reducing bone fracture risk in women with osteoporosis. Treatment is often a team effort involving a family physician or internist, an orthopaedic surgeon, a gynecologist, and an endocrinologist 
 
Hormone replacement therapy (HRT) was often recommended to prevent bone loss and reduce fracture risk in postmenopausal women in the past. This therapy consisted of estrogen alone (ERT) or estrogen plus progestin. Such therapy can be effective; for example, a study done as part of the Women’s Health Initiative (WHI) showed a 34 percent reduction in hip fracture risk among women taking estrogen plus progestin compared with women of a similar age who were not taking this drug. Because there also was an increased incidence of breast cancer and various types of circulatory problems found in women in the WHI study, hormone therapy (HT) is no longer the agent of choice for prevention of osteoporotic fractures in women over age 50. If you had been taking HT and stopped or are at menopause and do not intend to start HT, you need to talk with your doctor about alternatives to prevent bone loss.
 
New antiestrogens known as specific estrogen receptor modulators (SERMs) have been introduced. A three-year trial of the SERM, raloxefine,  showed that it was associated with a 2-4  percent increase in spine and hip bone mineral density, a 30 percent reduction in the incidence of new vertebral fractures in women with existing vertebral fractures, and a 50 percent decrease in new vertebral fractures in women without pre-existing fractures. 
 
Bisphosphonates are currently the drugs of choice to prevent bone loss after fracture. These products, called antiresorptive drugs, slow the rate of bone loss and increase bone density. They include alendronate, risedronate, and etidronate. Etidronate was among the first bisphosphonates to be developed. Although it increases bone mineral density slightly and reduces vertebral fracture risk somewhat, it may actually impair bone mineralization over the long term. For this reason, it is not a first-line agent for treatment of fragility fractures. Alendronate and risedronate have both shown convincing evidence of effectiveness. Women in clinical trials with these two medications have shown BMD increases of 3-10 percent and a reduced risk of vertebral fracture of up to 50 percent. In addition, these are the only two therapies that have been shown to reduce hip fracture risk.The older bisphosphonates are taken once a week. The U.S. Food and Drug Administration (FDA) has recently approved another bisphosphonate, ibandronate, which can be taken in a single, monthly dose. Ibandronate has been shown to reduce spinal fracture risk by up to 50 percent and increase bone density at all sites, but no hip fracture data are yet available. 
 
The only FDA-approved product that builds new bone, as opposed to slowing the rate of bone loss by limiting bone breakdown, is teriparatide, which is given as an injection to patients with a history of fractures or at high risk for them.  
 
Calcitonin, available in oral or nasal spray form, is an older medication used to decrease bone loss. Taken alone, calcitonin is not nearly as effective as bisphosphonates, SERMs, or hormone therapy. 
 
In the last decade new procedures have been developed for stabilization of vertebral fractures. These procedures can be performed on an outpatient basis. 
 
Fragility Fractures
Osteoporosis is often called a silent disease because it has no symptoms in its early stage. In fact, bone fracture is often the first indication of osteoporosis. Fractures caused by osteoporosis are typically called fragility fractures—fractures that occur as a result of a relatively minor injury or blow, such as falling from standing height or less. The most common sites of fragility fractures are the vertebrae, hip, wrist and shoulder. Osteoporosis is a contributing factor in as many as 1.5 million fractures each year. Find out more about fragility fractures and how to "fall proof" your surroundings.

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