Osteoarthritis is a chronic disease causing deterioration of the joint cartilage (the softer parts of bones, which cushion their connections to each other) and the formation of new bone (bone spurs) at the margins of the joints.

For most people, the cause of osteoarthritis is unknown, but metabolic, genetic, chemical, and mechanical factors play a role in its development. It is associated with the aging process and is the most common form of arthritis.

It may first appear without symptoms between 30 and 40 years of age and is present in almost everyone by the age of 70. Symptoms generally appear in middle age. Before the age of 55 it occurs equally in both sexes. However, after 55 the incidence is higher in women.

The cartilage of the affected joint is roughened and becomes worn down. As the disease progresses, the cartilage becomes completely worn down and the bone rubs on bone. Bony spurs usually develop around the joint.

Systemic symptoms, sometimes associated with other arthritic conditions, are not associated with osteoarthritis. The joints of the hands and fingers, hips, knees, big toe, and cervical and lumbar spine are commonly affected.

The degeneration of the joint may begin as a result of trauma to the joint, occupational overuse, obesity, or mal-alignment of the joints (for example being bow-legged or knock-kneed).