The most common long-term running injury is runners knee, pain behind the knee cap during running. You probably have runner’s knee if your knee cap hurts when you walk or run, particularly when you walk down stairs; and it hurts a lot when you push the kneecap against the bone behind it. It usually does not hurt to pedal a bicycle.
The back of the kneecap is shaped like a triangle with the point fitting in a grove in the lower part of the bone behind it. During running, the knee cap is supposed to move up and down and not side to side. If it moves from side to side, the back of the kneecap will rub against the front bottom of the femur, the long bone of the upper leg, causing pain.
Treatment is to stop the kneecap from touching the bone behind it, which is usually caused by the knee cap being pulled toward the outside laterally while the lower leg twists the bone behind it inward medially. When you run, you land on the lateral bottom of your foot and roll inward, causing the lower leg to twist inward. At the same time, three of the four quad muscles attached to the kneecap pull the kneecap outward and cause the knee cap to rub against the bone behind it. You can keep the knee cap from rubbing by wearing orthotics, special insets in your shoes, doing exercises to strengthen the muscle that pulls your knee cap inward. Surgery is rarely necessary.
A study from Long Beach VA Hospital in California shows why runners are far more likely to suffer knee pain than cyclists. When you run, you land on the outside bottom of your foot and roll inward toward the big toe side of your foot, called pronation. This study shows that the amount of inner twisting of the lower leg during running is related to how straight your knee is. Bending your knee decreases inner twisting and rubbing of the knee cap against the bone behind it. So people with runner’s knee can pedal a bicycle with their seats set lower than normal to prevent their knees from straightening, they can wear special inserts in their shoes that restrict pronation, and they can do special exercises that strengthen the vastus medialis muscle above the kneecap that pulls the knee cap inward when you run or pedal.
1)The effects of tibial rotation on the patellofemoral joint: Assessment of the changes in in situ strain in the peripatellar retinaculum and the patellofemoral contact pressures and areas. Journal of Rehabilitation Research and Development, 2001, Vol 38, Iss 5, pp 463-469. TQ Lee, BY Yang, MD Sandusky, PJ McMahon. Lee TQ, VA Long Beach Healthcare Syst 09 151, Orthoped Biomech Lab, 5901 E 7th St, Long Beach,CA 90822 USA
2) TW Flynn, RW Soutaslittle. Patellofemoral joint compressive forces in forward and backward running. Journal of Orthopaedic & Sports Physical Therapy 21: 5(MAY 1995):277-282. The results suggest that backward running at a self-selected speed may reduce patellofemoral joint compressive forces and, coupled with the quadriceps strengthening that has previously been reported, may be beneficial in the rehabilitation of patellofemoral pain syndrome in runners.
3) J Karlsson, R Thomee, L Sward. Eleven year follow-up of patello-femoral pain syndrome. Clinical Journal of Sport Medicine 6: 1 (JAN 1996):22-26. Patients with patello-femoral pain syndrome should be managed nonsurgically as the natural course is benign in most cases. Surgical intervention should be used only if correction of anatomical malalignment is necessary.