Knee pain can be a result of injury or disease of the knee joint. Injury can affect any of the ligaments, bursae, or tendons surrounding the knee joint. Injury can also affect the ligaments, cartilage, menisci (plural for meniscus), and bones within the joint. The complexity of the design of the knee joint and the fact that it is an active weight-bearing joint are factors in making the knee one of the most commonly injured joints.
Pain can also occur in the knee from diseases or conditions that involve the knee joint, the soft tissues and bones surrounding the knee, or the nerves that supply sensation to the knee area. In fact, the knee joint is one of the most commonly involved joints in rheumatic diseases, including rheumatoid arthritis, reactive arthritis, systemic lupus erythematosus, as well as osteoarthritis. Overuse injury to the knee can lead to inflammation of the tendon below the kneecap (runner's knee or jumper's knee with infrapatellar tendinitis) and bursitis. Diseases that cause knee pain can lead to symptoms and sign such as
- joint redness,
- warmth of the knee,
- weakness of the knee,
- joint instability,
- joint tenderness,
- stiffness of the joint.
Many of the symptoms of knee pain can be a result of an excess of fluid forming in the joint.