Osteoarthritis: Causes and Risk Factors

Until recently, doctors blamed OA on “wear and tear,” implying that simple overuse causes the cartilage to wear away. It’s a logical theory, but it’s wrong. Time and mechanical stress do contribute to OA, but the process is really much more complex. In fact, scientists still don’t understand all the mechanisms involved, but they have identified the major OA risk factors, including:

1. 
   Age. Time takes a toll on the whole body, and joints are no exception. In fact, age is the strongest risk factor for OA. Although the disease can sometimes start in the 30s, it usually surfaces between the ages of 50 and 65, becoming more prevalent (and more prominent) with each passing year. Advancing age does mean more cumulative wear and tear, but age-related changes in the body’s metabolism, circulation, and elastic tissue may be even more important.



2. Heredity. OA tends to run in families. Heredity is particularly important in early-onset OA, in OA of the hands (shown in the figure below) or hips, and in an uncommon form of the disease that strikes many joints at once.



3. Obesity. It’s an important risk factor, and it’s one of the few that’s correctable. Extra weight makes joints work harder; every 10 pounds of excess weight, for example, produces about 40 pounds of extra stress on the knee with each step. A study of young men suggested that each 18 pounds of extra weight increases the lifetime risk of painful knee OA by 70%.



4. Mechanical abnormalities. Neurological or orthopedic problems that produce faulty body mechanics, such as an abnormal gait, increase the stress on joints. The joints that bear the brunt of such stress are the most likely to develop OA.



5. Injury. It’s the reason retired football players appear in advertisements for arthritis medication. A joint injury can seem to heal completely, but residual damage can slowly progress to produce OA later in life. A study of 1,321 Johns Hopkins Medical School graduates proves the point. Nearly 14% of doctors who suffered hip injuries during their student years developed hip OA by age 65, while only 6% of those without hip injuries developed OA. A knee injury in youth was even more significant, producing a fivefold increase in the risk of OA of the knee in maturity.



6. Occupation and sports. Does running cause arthritis of the knees and hips? Most nonrunners would answer yes, but most studies of runners say no. Repetitive use, such as long-distance running, has been linked to a slight increase in x-ray abnormalities but not to an increase in clinical OA (unless a significant injury has occurred along the way). Contrary to expectations, long-distance runners have fewer musculoskeletal complaints over the years than sedentary folks. But occupations that involve frequent knee bending increase the risk of knee OA, and those that require frequent lifting appear linked to hip OA.



7. Nutritional factors. Diet affects the metabolism of many tissues. The Framingham Knee Osteoarthritis Study linked low levels of vitamins C and D to an increased risk of OA. Unfortunately, there is no evidence that vitamin supplements can relieve the symptoms of OA or slow its progression. Still, a good diet is important for health, and weight control is particularly important for OA.

courtesy of Harvard Health Publications