Patellar instability

Patellar instability

Your patella (knee cap) is a small triangular bone that sits in a groove at the bottom end of your thigh bone (femur). As you bend and straighten your knee, your patella slides up and down in this groove, controlled by ligaments and muscles.

In patellar instability, the patella slips out of the groove. If it partially slides out, it’s known as subluxation. If the patella is completely pushed out of the groove, it’s called a dislocation. A dislocation often occurs as a result of trauma.

Unfortunately, the more times your knee cap dislocates, the more loose and stretched the supporting ligaments become which makes the chances of another dislocation much more likely to happen in future.If it continually comes out of the groove, it can damage the underlying ligament or muscles that hold the knee in place.

Patella subluxation typically affects teenagers, during sport or dance. It can be a particular problem for adolescents who are highly flexible or bendy because the ligaments can be looser.


Pain when standing up from a sitting position
feeling that the knee is weak or loose and may buckle or give way.
When the kneecap slips partially or completely you may have severe pain, swelling, bruising, visible deformity and loss of function of the knee. You may also have changes in sensation such as numbness or even partial paralysis below the dislocation because of pressure on the nerves and blood vessels.


Clinical examination and diagnostic tests such as X-rays, MRI, and CT scan may be ordered to determine the cause of your knee pain and to rule out other conditions.


Non operative

  • If only partially dislocation -pain medications, rest, ice, knee-bracing.
  • If the kneecap has been completely dislocated, the kneecap may need to be repositioned back in its proper place in the groove. This process is called closed reduction.
  • A physiotherapy regime to strengthen the knee to hold it in place.


Surgery is sometimes necessary. Options include arthroscopy, ligament reconstructions, osteotomy and realignment procedures for patellar tracking.