Overview of Osteoporosis

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Osteoporosis is a progressive skeletal disease characterized by low bone density, bone fragility, and susceptibility to hip, spine, and wrist fractures. This condition develops without warning signs. Most people with osteoporosis do not realize they have the disease until a minor fall results in a broken hip, wrist or vertebra.

Bone Remodeling

Calcium, phosphate, and collagen are the primary components of bone. Bone tissue is constantly changing. Cells called osteoclasts break down and remove bone tissue in a process called resorption. Osteoblasts form new bone in a process called formation. Hormones (i.e., cortisol, estrogen, progesterone, parathyroid hormone, calcitonin, insulin) regulate the entire sequence, which is called remodeling.

Two types of bone are affected by osteoporosis:

  • Cortical bone—the compact outer layer of the bone shaft
  • Trabecular bone—a meshlike inner structure

Trabecular bone, which is found in high percentages in the hip, spine, and wrist, is more vulnerable because it has a higher turnover rate.

During childhood and early adulthood, bone formation exceeds bone resorption. By age 35, men and women reach and maintain maximum bone density and strength, called peak bone mass. After the age of 40 or so, resorption exceeds formation, and gradual bone loss begins.

In menopausal women in their fifties, bone loss increases rapidly. During menopause, estrogen production decreases, which increases the rate of bone resorption. Some women experience a rate of trabecular bone loss that is 4 times greater than before menopause. During menopause, trabecular bone in the spine is especially at risk. After menopause, the rate of resorption slows. In severe cases, accrued bone loss can be up to 50 percent.

Incidence and Prevalence of Osteoporosis

An estimated 10 million Americans have osteoporosis and another 18 million are likely to develop it. Eighty percent of those who have or will have osteoporosis are women. In the United States, osteoporosis causes 1.5 million fractures each year and is the leading cause of hip fractures. According to the National Institutes of Health (NIH), the number of people hospitalized for osteoporosis-related bone fractures and other injuries has increased substantially in recent years and more than 254,000 of these serious injuries were reported in 2006.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 31 Mar 2001

Last Modified: 29 Sep 2015