Risk Factors
Why some people will remain free of osteoarthritis and others will develop the condition cannot be fully explained. Osteoarthritis appears to depend on many contributing factors and takes various forms in different individuals. The contributions of risk factors differ from joint to joint.
Age: Of all factors contributing to osteoarthritis, age is the most important one. Exactly how the aging process contributes to the risk of osteoarthritis is not known. By age 65, more than 80% of Americans have some signs of osteoarthritis on x rays, but only about one-half of these people experience symptoms.
Gender: Overall, osteoarthritis is more common in women than in men. Until about 55 years of age, the rate of developing osteoarthritis is about equal in women and men. After the age of 55, many more women than men are affected by osteoarthritis. This same trend is apparent for knee osteoarthritis, osteoarthritis that affects several joints at the same time, and especially osteoarthritis of the hand.
Women have a considerably higher risk of osteoarthritis of the knee, a difference that may be due to wearing high-heeled shoes. Men have more frequent osteoarthritis of the hip joint.
Overweight and obesity: Excess body weight that is not due to muscle is a modifiable risk factor that appears to increase the risk of osteoarthritis through mechanical stress and metabolic changes associated with excess fat. The exact nature of the metabolic changes is still being investigated.
- Overweight men and women increase the risk of developing osteoarthritis of the knee—often of both knees.
- Being overweight also increases the risk of osteoarthritis of the knee increasing in severity, once it has developed.
- Excess weight may increase the risk of osteoarthritis of the hand joints.
Muscle strength: The strength of the quadriceps (the large, frontal thigh muscle) is a strong predictor of the risk of the development and progression of knee osteoarthritis, even if no weakness is visible from the outside.
Physical activity: Heavy physical activity has been found to increase the risk of osteoarthritis of the knee. This risk was greater in overweight and obese people.
But the normal use of muscles, tendons, and joints is important to keep joints healthy. This includes doing light-to-moderate physical work and exercise or even recreational, long-distance running. Light and moderate activities, such as walking or climbing stairs, do not increase your risk of getting osteoarthritis. People who exercise regularly develop impairments of muscle and joint function less often and experience less muscle and joint pain as they age than people who exercise less.
Occupation: Frequent or very heavy exercise or physical activity at work increases the risk of osteoarthritis in the knee and possibly the hip. For example, activities that require frequent bending of the knee can increase the risk of osteoarthritis in the knee. This increase in risk appears mostly in people who are over the age of 50 or obese.
Certain jobs, such as farm or shipyard work, increase the risk of osteoarthritis of the hip, and jobs that require much knee-bending increase the risk of osteoarthritis of the knee.
Mechanical stress: Injury to a joint or repeated use of the joint in a way that stresses it beyond its capacity to heal may start a chain of events that leads to osteoarthritis.
Genetics: People with a family history of osteoarthritis are a bit more likely to develop osteoarthritis themselves. This may be because of heritable abnormalities of the joints that make them more vulnerable. Osteoarthritis of the hand, knee, and possibly of other joints tends to run in families through, it is believed, genetic transmission. For example, osteoarthritis of the joints at the fingertips occurs about three times more often among sisters than in the general population, and mutations of a gene that is associated with a severe form of osteoarthritis run in families.
Injuries and diseases: A major injury or operation on a joint increases the risk of developing osteoarthritis at that joint. While normal physical activity and exercise are good for joints, hard, repetitive activity may injure joints.
Diseases that involve abnormalities of joints also can lead to osteoarthritis in later life. For example, Perthes' disease of the hips is an abnormality with which some people are born and which greatly increases their risk of osteoarthritis.
Women who have a high risk of osteoporosis have a lower risk of getting osteoarthritis. And, women who have a low risk of osteoarthritis tend to have lower bone density and, therefore, a higher risk of problems related to osteoporosis.
Race and ethnicity: Ethnic and racial groups have patterns of risk of osteoarthritis that vary depending on the joint. For example, Asians generally have a lower risk of osteoarthritis of most joints, except for knee joints, than do Caucasians. Asians have a higher risk of osteoarthritis of the knee joint than do Caucasians.
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