Arthritis in dogs can take several forms. Osteoarthritis is the most common type of arthritis that afflicts dogs. This condition is also known as degenerative joint disease. Some forms of arthritis are hereditary and more common in certain breeds than others. Dogs can also suffer form other forms of arthritis, including auto-immune arthritis (also known as rheumatoid arthritis), hypertrophic arthritis, acute traumatic arthritis, and infectious arthritis.

Osteoarthritis causes various parts of the dog's joints, usually the cartilage, to break down. This breakdown means there is less available cartilage to absorb the movements of the joints, causing the dog’s bones begin to grind against one another. This leads to painful inflammation, as well as reduced flexibility and mobility. The disease generally progresses slowly as the damage to the cartilage increases.

Auto-immune is also known as rheumatoid arthritis, and has no known cause. The disease causes the dog's immune system to attack the joints. The result is painful movement and decreased mobility.

Hypertrophic arthritis is caused by bone spurs, or growths that form on the joint itself. These growths can be the result of either osteoarthritis or trauma. The growths cause pain and decreased mobility by preventing smooth operation of the joint.

Acute traumatic arthritis is brought on by specific trauma to the joints. The onset is usually very sudden, with swelling and lameness resulting quickly from this type of arthritis. In cases of acute traumatic arthritis, immediate surgery is often needed to prevent continued damage, the most likely of which is permanent osteoarthritis.

Infectious arthritis is often caused by a secondary infection due to trauma. Antibiotics are generally effective at treating infectious arthritis.

In most cases, dogs suffering from arthritis show a gradual lameness that may be confined to a single limb or may affect more than one limb. Dogs often display more stiffness or lameness in the early parts of the day, gradually improving as their movement increases throughout the day. Some dogs may have visibly swollen joints as a result of arthritis. A notable exception to this pattern is cases of acute traumatic arthritis.

The type of arthritis as well as the cause can dictate the best course of treatment of arthritis in dogs. Many dogs, especially older dogs, develop arthritis as a result of being overweight or obese. In this case, weight control is the first order of business. If the arthritis is caused by a trauma, surgical intervention may be necessary to repair any damage from the trauma and, just as important, prevent any further damage to the joints. Some dogs benefit from anti-inflammatory medications, which can be helpful to reduce swelling and minimize pain caused by arthritis. Many holistic treatments such as herbal remedies may also be very helpful. Acupuncture has also been found to be an effective, non-medicating way to minimize the symptoms of arthritis in dogs.