Patellar tracking disorder is a condition that disrupts the normal function of the knee.

Normal kneecap function

As your knee straightens and bends, the kneecap (patella) glides up and down the femoral groove at the front end of the thighbone (femur). At the same time, the patella tilts and rotates slightly, held in check by ligaments on the sides and tendons on the top and bottom.

See a picture of the knee joint.

Kneecap instability

If the femoral groove is shallow, the patellar tendon is excessively long, or the stabilizing ligaments, tendons, or muscles are too tight or loose, the kneecap can shift, tilt, or rotate off track (sublux). As you bend your knee to a 90-degree angle, a misaligned kneecap will have increasing abnormal contact with the thighbone, creating painful pressure.

In extreme cases, the kneecap can dislocate. After a kneecap has been dislocated once, it may dislocate more easily in the future. Any resulting damage to the kneecap or supportive tissue can lead to ongoing patellar tracking problems.

Untreated patellar tracking disorder can lead to:

• Cartilage damage (chondrosis).
• Osteoarthritis of the knee.

A blow to the middle or inside of a structurally sound kneecap can also dislocate the kneecap.