As with all the joints in the lower limb, knee pain is often caused by problems elsewhere, usually the low back, hip or foot.
It can commonly be caused by arthritis and is also one of the most common sporting injuries. Knee pain patients often struggle to walk especially on stairs (and very often worse going down the stairs!). Some swelling may occur around the knee, which may indicate inflammation within the joint.
A torn cartilage can often be the cause of knee pain and can be associated with a locking or clicking of the joint. However, it is the other soft tissues around the knee which are the problem. Ligaments, tendons and muscles all work very hard to keep the knee stable, and they can be injured if loaded badly.
Knee arthritis is caused by wear of the cartilage in the knee and can occasionally get so severe that a knee replacement is necessary.