Rheumatoid arthritis is most often seen in younger people, particularly women. This disease usually involves the deterioration of many joint surfaces causing patients to complain of similar symptoms in their hands, feet, shoulders, hips, and knees. Other symptoms include anemia, weight loss, and repeated bouts of swelling in the affected joint along with the pain, stiffness, and instability normally associated with arthritis.

Traumatic arthritis results from severe injury which damages the joint surface and may be accompanied by torn ligaments, tendons, and muscles causing the knee to become grossly unstable. Aseptic necrosis can occur after some knee fractures even after they have healed. While some causes for this interruption in the blood supply to some part of the knee may be attributed to sickle cell disease or a reaction to medication, often there is no identifiable cause.

Infectious arthritis occurs when an infection in some other part of the body travels through the bloodstream and lodges in the knee joint. The invading bacteria and the body's response can rapidly destroy the joint cartilage within a matter of days. Open wounds into the knee joint can also cause an infectious arthritis to develop. Most patients with knee arthritis are successfully treated with prescribed medication, physical therapy, and by limiting those activities that over-stress the knee joint.

Arthrodesis is an operation that renders the knee permanently stiff and is primarily used for patients with infectious arthritis or severe post-traumatic arthritis.