While this condition probably begins in the early teen years, it does not become symptomatic until a person reaches their 40’s.
Osteoarthritis affects cartilage, the slippery elastic tissue that covers the ends of long bones. Cartilage functions to absorb shock from movement and also to provide a gliding surface for the joints. With OA, the cartilage begins to wear away and the underlying bones begin to rub against each other. This leads to pain. As OS progresses, it causes swelling and loss of motion. Bone spurs develop and the joint starts to deform. Microscopic particles of cartilage and bone flake off and cause irritation of the joint lining leading to more inflammation which leads to pain and more damage.

Symptoms of OA include pain or stiffness in a joint particularly after getting out of bed or after sitting for a prolonged period of time. Some people have “flares" of their symptoms with weather changes. Stiffness and pain in the joints with movement may occur as may “crunchiness".

Some people report no symptoms. One study done at the National Institutes of Health showed that one third of patients with osteoarthritis on x-ray had no symptoms.

While any joint may be affected, the most common areas of involvement are weight-bearing parts of the skeleton such as the neck, low back, hips, and knees. The great toe and the base of the thumb are also common locations. In older women the last row of finger joints and the next to last row of finger joints may be affected. Less common sites are the shoulders, elbows, ankles, and jaws.

Many factors including the way people use their joints. Occupational experiences also play a role. For instance, miners and dockworkers may develop knee OA while farmers have a higher incidence of OA of the hip. Ballet dancers can also develop OA in the feet, ankles, and hips. Athletes also fall into a high risk category with women soccer players being more likely to develop knee OA as a result of prior injury. Other athletic activities which cause joint trauma also can be a trigger for the development of OA.
Obesity is a major risk factor for OA of the hips and knees. The famous Framingham study showed that obese women had the most severe OA.

People with other types of arthritis such as rheumatoid arthritis or gout are at increased risk for developing OA also.
Probably the most significant risk factor is genetic. Patients with a strong family history of OA are at high risk themselves for developing OA. This is most likely a result of defects in cartilage metabolism which hastens wear and tear.