Osteoarthritis of the knee is a chronic condition that typically affects people over the age of 55, though it can occasionally affect younger people, too. It occurs when cartilage surrounding the knee joint begins to wear away, becoming inflamed, torn, and uneven, decreasing the protective cushioning between bones. This can eventually cause bone to rub against bone, resulting in highly painful growths known as osteophytes, or bone spurs.

Symptoms of osteoarthritis of the knee include painfully stiff or swollen joints, which often make it difficult to bend and straighten the leg. This pain begins slowly and worsens over time, and can increase during vigorous physical activity or other activities that place a lot of pressure on the knee (such as climbing stairs, squatting, sitting cross-legged, jumping, etc.). This regularly causes weakness, locking, or buckling in the affected knee, and can also result in swelling of the surrounding tissue, or an uncomfortable grating sensation known as crepitus.

When examining a patient to determine if they have osteoarthritis of the knee, a doctor will perform a physical examination, and may also use imaging tests or blood tests to confirm the diagnosis.