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Runner's Knee

Clinical Overview

Reviewed by Joseph Maloney, M.D.

Three bones meet in the knee: the thighbone (femur), the shinbone (tibia), and the kneecap (patella). When the leg moves, the kneecap slides along a shallow groove at the end of the femur known as the trochlear groove. The joint is cushioned and made smooth by articular cartilage, which wraps around the ends of all the bones in the joint.

Repeated stress of the joint, whether due to age, injury, overuse, abnormal alignment, or muscle weakness, can weaken and soften the articular cartilage. This phenomenon goes by many names: anterior knee pain syndrome, runner's knee, patellofemoral pain syndrome, or chondromalacia patellae. Doctors estimate that about one-half of all non-injury knee pain complaints are due to this disorder.

When afflicted with the condition, the patient's knee rubs against the trochlear groove, instead of gliding smoothly across it. The damage may range from a slight abnormality of the surface of the cartilage to a surface that has been worn away completely to the bone. Anterior knee pain can present a diagnostic challenge because of the complex anatomy of the knee.


  • Overuse
  • Chronic Injury
  • Muscle weakness (of the vastus medialis)
  • Anatomic variation in certain individuals

    Risk Factors
    Risk factors include participation in high-impact sports like running, skiing, soccer, and high-impact aerobics, and trauma. The Q-Angle, the angle formed by the thighbone and the patellar tendon (the misnamed ligament that stretches from the kneecap to the shinbone) is also a major factor in the development of anterior knee pain syndrome. Quickly-growing teenage women most often have a more acute Q-angle than others, and are thus at the highest risk group for developing the condition. Old age and a knock-kneed or bow-legged stance also increase the risk for developing anterior knee pain syndrome.

    Last updated: Apr-11-07

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