Osteoarthritis Health Article

Definition

Osteoarthritis is a degenerative joint disease characterized by the breakdown of the joint's cartilage.

Description

Osteoarthritis is one of the oldest and most common types of arthritis. With the breakdown of cartilage, the part of the joint that cushions the ends of bones, bones rub against each other, causing pain and loss of movement. Often called "wear-and-tear arthritis" or "old person's arthritis," many factors can cause osteoarthritis.

The biologic causes of the disorder are currently unknown. It does not appear to be caused by aging itself, although osteoarthritis generally accompanies aging. Osteoarthritic cartilage is chemically different from normal aged cartilage.

In many cases, certain conditions seem to trigger osteoarthritis. People with joint injuries from sports, work-related activity, or accidents may be at increased risk, and obesity may lead to osteoarthritis of the knees. Individuals with mismatched surfaces on the joints that could be damaged over time by abnormal stress may be prone to osteoarthritis. One study reported that wearing shoes with 2.5 in (6.3 cm) heels or higher may also be a contributing factor. High heels force women to alter the way they normally maintain balance, putting strain on the areas between the kneecap and thigh bone and on the inside of the knee joint.

Demographics

Osteoarthritis is estimated to affect more than 20 million Americans, mostly after age 45. Women are more commonly affected than men.

In the United States about 6% of adults over 30 have osteoarthritis of the knee and about 3% have osteoarthritis of the hip. Prevalence of osteoarthritis in most joints is higher in men than women before age 50, but after this age, more women are affected by osteoarthritis. The occurrence of the disease increases with age. In men, the hip is affected more often while in women, the hands, fingers, and knees are more problematic.

Some forms of osteoarthritis are more prevalent in African-American men and women than in Caucasians, possibly because they have a higher bone mineral density. In the case of knee osteoarthritis, it may be related to occupational and physical demands. Black women also have a higher risk of developing bilateral knee osteoarthritis and hip osteoarthritis compared to women of other races. This difference may be because black women generally have a higher body mass index than the white women, which puts more stress on the joints.

Osteoarthritis is common worldwide, although risk of osteoarthritis varies among ethnic groups. Caucasians have a higher risk than Asians, and the risk of osteoarthritis in the hips is lower in Asia and some Middle East countries than in the United States. Asians appear to have a higher incidence of osteoarthritis in the knee than Caucasians, however, and an equal risk in the spine. Location of affected joints and inherited forms of the disorder can influence age of onset.

Genetic profile

Genetics plays a role in the development of osteoarthritis, particularly in the hands and hips. One study found that heredity may be involved in 30% of people with osteoarthritic hands and 65% of those with osteoarthritic knees. Another study found a higher correlation of osteoarthritis between parents and children and between siblings than between spouses. Other research has shown that a genetic abnormality may promote a breakdown in the protective structure of cartilage.

Abnormal collagen genes have been identified in some families with osteoarthritis. One recent study found that the type IX collagen gene COL9A1 (6q12-q13) may be a susceptibility locus for female hip osteoarthritis. Other research has suggested that mutations in the COL2A1 gene may be associated with osteoarthritis.

Some evidence also suggests that a female-specific susceptibility gene for idiopathic osteoarthritis is located on 11q. There is some evidence of genetic abnormality at the IL1R1 marker on gene 2q12 in individuals with severe osteoarthritis and Heberden nodes (bony lumps on the end joint of fingers).