Runner's Knee

Runner's knee (patellofemoral stress syndrome) is a condition in which the kneecap (patella) rubs roughly against the end of the thighbone (femur) when the knee moves.

The kneecap is a circular bone that is attached to ligaments and tendons around the knee. The kneecap normally moves up or down slightly without touching the thighbone during running.

See the figure Runner's Knee.

Runner's knee may be caused by a structural defect, such as a kneecap located too high or too low in the knee joint, off-center insertion of the muscles into the kneecap, tight hamstrings, tight Achilles tendons, and weak thigh muscles--which normally help stabilize the knee. Weak thigh muscles are the most common treatable cause of runner's knee; these weak muscles allow the kneecap to move sideways and rub against the thigh bone. A second common treatable cause is rolling of the feet onto the outside (pronation) excessively when walking or running while the front thigh muscles (quadriceps) pull the kneecap outward. Together, these forces cause the kneecap to rub against the end of the thighbone.

Pain and sometimes swelling usually start during running and are concentrated on the undersurface of the kneecap. At first, only running downhill is painful, but later any running and eventually even other leg movements, particularly walking down steps, are painful.

Refraining from running until it can be done without pain is important. Other exercises, such as riding a bicycle (if not painful), rowing, and swimming, can be continued to maintain physical fitness. Exercises to stretch the muscles in the back (hamstrings) and front (quadriceps) of the thigh and to strengthen the vastus medialis, an inner thigh muscle that pulls the kneecap inward, are helpful. Commercially available arch supports placed in both exercise and street shoes may help. Sometimes, shoe inserts have to be custom-made.

See the sidebar Strengthening the Vastus Medialis (Inner Thigh) Muscle.