The knee joint is lined by articular cartilage, a specialised lining which allows smooth, painfree motion of the joint. Arthritis is a degeneration or wearing out of this lining which results in the bone ends rubbing on one another rather than the articular cartilage causing pain.
Osteoarthritis: This form of arthritis can be due to normal ageing, or may develop as a result of another condition, past surgery or trauma. Heavy manual labour, obesity and a family history can predispose patients to osteoarthritis. The pain tends to be worse in the mornings and with vigorous activity.
Inflammatory Arthritis: The most common form is rheumatoid arthritis, an immune disorder resulting in inflammation of the synovial lining of the joint which releases chemicals and can subsequently damage the articular surface. This condition can affect any synovial joint in the body and is best treated medically by a rheumatologist. Knee replacement is only required when there is severe damage to the joint.
Osteoarthritis is diagnosed on history, physical examination and X-ray. Physical examination will reveal pain on moving the joint and limitation of movement as well as osteophytes. X-rays will reveal narrowing of the joint space and often deformity of the bones and osteophytes. Blood tests are useful in inflammatory arthritis.