The most common form of arthritis is osteoarthritis, also referred to as degenerative joint disease (DJD). It is mainly seen in older animals where the articular cartilage wears away eventually exposing the underlying (subchondral) bone. The joint space becomes narrowed and new bone is deposited around the outer edges of the joint. This is not an inflammatory condition so the joint lining (synovial membrane) is not effected and joint fluid is normal. DJD can be primary (cause unknown), or secondary to injury or abnormal movement resulting from conditions such as hip dysplasia.

Early signs of DJD may be mild lameness after prolonged exercise, or reduced ability to exercise to previous levels. As the condition progresses lameness and stiffness is most pronounced when first moving after resting, and is often worse in cold weather.

Treatment of DJD utilizes anti-inflammatory drugs, moderate exercise programs, and more recently drugs which stimulate repair of the articular cartilage. Corticosteroids were widely used in the past of control of pain and inflammation in arthritis. There is some evidence however that they may accelerate the rate of joint degeneration. Non-steroidal anti-inflammatory / analgesics have generally replaced the use of corticosteroids. Older drugs include aspirin and phenylbutazone which although effective suffer from the side effect of gastric (stomach) ulceration. Some of the drugs developed for humans including naproxen, indomethacin, and ibuprophen can also cause ulceration. Ketoprofen, flunixin and metacam are veterinary preparations which produce less of the ulcerative side effects. Pentosan is a new drug which stimulates the repair of worn articular cartilage and is proving to be very effective in the long term treatment of DJD.

Inflammatory arthritis refers to damage or wear to the joint secondary to inflammatory conditions. These can be infectious causes such as bacteria or viruses and noninfectious immune-mediated causes such as rheumatoid arthritis and systemic lupus erythematosus. In all of these conditions there is inflammation of the synovial membrane and synovial fluid. Systemic (whole body) signs are also common.

Treatment of inflammatory arthritis requires identification and therapy for the underlying cause in conjunction with anti-inflammatory treatment of the arthritis