Possible Causes Of Osteoarthritis - Osteoarthritis: Arthritis

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Possible causes of osteoarthritis

Doctors may categorize osteoarthritis as primary, meaning the principal cause is unknown. However, excess weight and genetics also contribute to predisposition. Or the disease may be categorized as secondary, originating from trauma, such as a blow or injury, or a recognizable disease process, such as hemophilia. Some scientists believe primary osteoarthritis begins with repeated minor injuries. The cartilage is able to repair itself for a time, but eventually this effort fails.

Excess weight

By now, everyone has heard that carrying excess body fat can lead to problems with the heart and other organs. Here's another reason to slim down: Overweight people are much more likely to develop osteoarthritis of the knee. These weight-bearing joints just don't hold up well under the continued strain of extra pounds — and extra pounding.

An ongoing study of people living in Framingham, Mass., found that overweight young adults were more likely to develop knee osteoarthritis in their 30s and 40s than were their slimmer counterparts. Women who were the heaviest were twice as likely as thinner women to get osteoarthritis and had three times the risk for severe knee osteoarthritis. Losing weight can reduce risk. Researchers who analyzed the Framingham data found that women who lost 11 pounds cut their risk of developing osteoarthritis of the knee by half.

Genetic factors

Consensus is growing that genetic factors likely control the manifestations and progression of osteoarthritis. Studies in identical twins — who share the same genes and thus offer insight into the relative importance of genetic and environmental factors — have shown that roughly half the risk of developing osteoarthritis can be attributed to genetic factors. Multiple genes are thought to be involved, and to complicate matters further, the genes may have different effects depending on the joint affected and whether someone is male or female.

Genetic studies of a disease like osteoarthritis are hampered by several factors. First, the sheer number of people with the disorder makes it impossible to discount the influence of external factors. Second, scientists must establish that a certain gene is present in most people with the disease, but is absent in those who are healthy.

Hormones

Osteoarthritis is common among postmenopausal women. One study found that women who were taking estrogen replacement therapy appeared to have a lower risk of developing the disease, suggesting that estrogen may have a protective effect on cartilage in much the same way that it protects bones from osteoporosis. However, these findings remain controversial: Estrogen has many, and in some cases conflicting, effects on connective tissue and bone, making the association between estrogen and arthritis difficult to sort out.

Postmenopausal women tend to have either osteoarthritis or osteoporosis, but not both. This may be because the bones of thinner people are less dense and more susceptible to osteoporosis; heavier people, who have higher bone density, are less prone to osteoporosis but more susceptible to arthritis from greater stress on joints.

Joint injury

Injury to a joint, either because of repeated use or trauma, may also cause osteoarthritis. As many athletes know, severe knee trauma disrupts the normal mechanics of joint function. Nearly all tissues heal by scarring, leaving irregularities on their surfaces. Because bones, joints, or muscles that are damaged rarely heal perfectly, joint injuries can create unusual mechanical stresses that lead to abnormal wear. People in certain occupations are prone to develop osteoarthritis in those joints subjected to the most stress. For example, osteoarthritis may affect the hips, ankles, and feet of ballet dancers, the knees of soccer players, the hips of farmers, the elbows of riveters, and the hands and wrists of pneumatic tool operators. The cause is thought to be repetitive stress leading to bone fatigue, microscopic fractures, and eventually cartilage breakdown.

Even those who are sedentary can develop occupational osteoarthritis when repetitive stress is sustained for several hours a day. Perhaps surprisingly, people who spend a lot of time using a keyboard aren't more likely to develop osteoarthritis of the hands, because typing puts very little mechanical stress on the joints.

Other diseases

Osteoarthritis can also develop in a joint damaged by a related disease, such as rheumatoid arthritis, infectious arthritis, or gout. Or osteoarthritis may develop because of hemophilia, growth abnormalities, or hereditary metabolic diseases. Hemophilia can produce osteoarthritis as a result of bleeding in the joint.

Growth abnormalities that can lead to osteoarthritis include acromegaly and slipped femoral epiphysis. Acromegaly is characterized by the irregular overgrowth of bone and cartilage due to abnormal production of growth hormone. Slipped femoral epiphysis involves displacement of the growth plate at the end of the femur, the bone that extends from hip to knee. Osteoarthritis can also arise from hereditary metabolic diseases, such as hemochromatosis (the harmful accumulation of iron in tissues).

Last updated:	September 05, 2008