Causes of Osteoarthritis

The exact cause of osteoarthritis (OA), also known as degenerative arthritis or “wear and tear” arthritis, remains elusive. We do know that certain circumstances and conditions, so-called risk factors, increase the likelihood that a person will develop it. It’s important to note that when physicians refer to a patient as having OA, they usually mean the patient has symptoms of OA. Although many people can have findings of OA on x-rays, they may not have symptoms. Unfortunately, we don’t understand why some people have symptoms and others do not.

Your Age The most common risk factor is age. OA most commonly affects people over 55. The theory of how age affects OA is that the constant use of a joint over decades results in a wearing out of its lining, and the body replaces this lining with bone. However, this doesn’t mean that everyone over age 55 will develop OA. This also doesn’t mean that people under 55 cannot develop OA. In fact, population studies show that men develop OA more frequently than women up until the age of 45. Beyond age 45 OA is more common in women.

Your Weight Being overweight is another common risk factor. This is primarily true for the hips and knees — the so-called “ weight bearing joints”. Such OA is felt to be due to the increased pressure applied to the hips and knees which causes a constant rubbing of bone and joint. Similar to age related OA, this results in a wearing of the lining of the joint followed by formation of bone. Your Activity Repetitive use of heavy machinery can increase the risk for developing OA. This is not only a common risk factor in developing OA, but it also often results in disability. Examples are drill press operators, construction workers, and machinists. Again, it is believed that the continuous impact against a joint results in wearing of the lining of the joint followed by formation of bone. Your Joints Unstable joints (joints that are loose and do not support gravitational forces) can sometimes result in an increase in the risk of developing OA. Such unstable joints result in the bumping of bone against the joint lining. This in turn leads to wearing out of the lining and subsequent bone formation. Old Injuries Prior injuries to joints can cause them to become unstable. Most commonly, fractures that didn’t heal normally can lead to OA several years later. Also, injuries to the ligaments in the knees and shoulders can lead to unstable joints. This is why athletes often develop OA early. Some women have a disease called Hyper mobility Joint Syndrome. These women have very loose and unstable joints usually resulting from a combination of reasons, including lack of exercise and genetic factors. A few studies have shown that these women develop OA earlier than expected. Muscle weakness can also cause joints to be unstable. For example, patients with Polymyositis (a deteriorating muscle disease) can develop OA in the knees faster due to thigh muscle weakness. In conclusion, although the most common risk factor for developing OA is age, there are many other possible factors, many of which are preventable.