The fancy name for runner’s knee is “patellofemoral pain syndrome.” It it characterized by aching pain under and around the kneecap. As suggested by the common name, it affects runners fairly often. It also affects cyclists, skiers, soccer players and other athletes.
A lot of different theories have been proposed as to the etiology of runner’s knee. Unlike most injuries, runner’s knee doesn’t exhibit any signs or symptoms of structural damage to guide theories about causation. The pain itself seems to be the only sign of runner’s knee, and it may be due to some kind of chronic stimulation of the nerves around the patella.
One popular theory that was widely accepted until recently was that runner’s knee was caused by a problem with the quadriceps muscle. A weak quadriceps muscle was thought to not be able to provide support to the kneecap during motion, and therefore the kneecap could track out of alignment during each step, leading to chronic pain under the kneecap. The theory makes sense intuitively.
Other aspects of the quadriceps theory include an imbalance in strength between the hamstrings and the quadriceps. If the hamstrings are weaker than the quadriceps, a great deal of stress is placed on the knee during jumping and pivoting motions. Women athletes frequently have relatively weak hamstrings in comparison to their quadriceps, and this imbalance is thought to be major contributing factor in the high rate of ACL injuries in women athletes. Women also tend to get runner’s knee at high rates.
However, a recent study of athletes with and without runners knee found no differences between the two groups in how they used their quadriceps muscle during squats. The study found no evidence of quadriceps weakness, malfunction, or improper use in those affected by runner’s knee
One theory that seems to be gaining ground is that weak hip muscles are to blame for many cases of the knee pain. When given a thorough gait analysis, many individuals affected by runner’s knee are found to have weak hip stabilizers. As they run, the gait analysis reveals that the weak hip muscles allow the thigh to rotate internally as the foot hits the ground. The thigh rotation is an unconscious effort by the body to compensate for the weakness. The rest of the body tries to stabilize the pelvis and fails, causing the pelvis to fall towards the swinging leg. This falling motion causes the thigh to fall and it ends up pinching the knee. Repeatedly pinching the knee with each stride may lead to the pain of runner’s knee.
If a gait analysis reveals weak hips, the cure for runner’s knee is to strengthen the muscles on the outside of the thighs. In addition to strengthening these muscles, the runner has to actively re-train the body to use the thigh muscles to stabilize the pelvis during each stride. A Computer Assisted Rehabilitation Environment (CAREN) is the best way to retrain the body to beat runner’s knee. New York Neuromuscular Rehabilitation is the first private clinic to use this system for a civilian demographic.