Patellar instability

Causes 

There are two general ways that kneecap dislocation occurs: 

• The kneecap dislocates during an accident: If your child gets into an accident during sports or another physical activity, the kneecap may slide out of place quickly and painfully. It will usually go back into place on its own immediately after it slides out.
  
  After this, your child may feel a lot of pain and experience swelling in the front of his knee, whether he’s sitting or standing. If he tries to walk, he may feel the kneecap catch or slip, and have trouble supporting his weight.
   
• The kneecap dislocates by itself: If your child’s kneecap slides in and out of place on its own, he should see a doctor within the first few weeks of experiencing symptoms, and should not play through pain.
  
  Whether his kneecap dislocates once in a while or very often, dislocation can damage the kneecap and the end of the thighbone. Sometimes the injury can become even more painful, and lead to arthritis later in life. 

Signs and symptoms 

If your child’s knee is bothering him because it buckles, slips off to the side or catches during movement, he may have kneecap dislocation. 

Other symptoms include:

• Pain in the front of his knee that gets worse with activity
• Pain when he’s sitting down
• Stiffness in the knee
• Creaking sounds
• Swelling