Symptoms

Symptoms of patellar tracking disorder can include:

• A dull ache under, around, and/or at the outer edges of the kneecap, sometimes called patellofemoral pain syndrome. This is often made worse by using the stairs (especially going down stairs), sitting for long periods, and squatting.
• A popping, grinding, slipping, or catching of the kneecap as the knee bends or extends. A grinding or popping sensation may develop before painful symptoms start or may not occur at all. If you have kneecap popping or grinding without pain, see the Prevention section of this topic for stretching and strengthening exercises.
• Swelling of the knee, in some cases.
• The knee buckling or "giving way," as though the knee suddenly won't support your weight.

Knee pain has many causes. If you have knee pain when you are squatting, standing up from a sitting position, going down stairs, or sitting, you may have patellar tracking disorder. But other conditions cause symptoms similar to those of patellar tracking disorder. For more information on other causes of knee symptoms, see the topic Knee Problems and Injuries.

What Happens

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

The kneecap can shift, tilt, or rotate off track (sublux) if:

• The femoral groove is shallow.
• The patella is small or flat.
• The patellar tendon is too long.
• The stabilizing ligaments, tendons, or muscles are too tight or too loose.

And 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:

• Patellofemoral pain syndrome.
• Cartilage damage (chondrosis).
• Osteoarthritis of the knee.

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