Kneecap (patella) dislocation

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What is kneecap (patella) dislocation?

A dislocated kneecap occurs when the patella (kneecap) that sits over the front of the knee comes out of its groove at the end of the thigh bone (femur), coming to rest on the outside of the knee joint. This can cause stretching or tearing to the supporting ligaments and tendons. Normally, the kneecap glides smoothly over a groove in the joint when you bend or straighten your leg but if the kneecap is dislocated you may be unable to bend or straighten your leg. A dislocated kneecap is a common injury that can take around 6 weeks to heal. If you have dislocated your kneecap once it is far more likely to dislocate in the future.

Kneecap dislocation is not the same as knee dislocation.

“Our hopes are that George will make a full recovery and carry on playing rugby to an elite level. So far the signs are incredible.”

What causes a dislocated kneecap?

A dislocated kneecap can be caused by:

  • A blow to the knee, for example if the knee joint collides with another person or object with great force.
  • A sudden change of direction while the leg is still planted firmly on the ground, such as during sports or dancing.
  • Weak leg muscles which puts pressure on the knee joint.
  • A misaligned or elevated kneecap.

Being tall and/or being overweight increases the risk of dislocation and women are also more at risk.

After a dislocated kneecap, the medial patellofemoral ligament may become torn. This is the ligament that secures the kneecap to the inside (medial) of the knee. Once it is torn it may not heal with the same level of tension as before. This can lead to recurrent dislocation of the kneecap.

What are the symptoms of a dislocated kneecap?

If you have dislocated your kneecap you may experience:

  • Obvious distortion of the kneecap, which may look out of place or appear to be at an odd angle.
  • Severe pain in the knee and sudden swelling and bruising.
  • Inability to bend or straighten your leg.
  • Being unable to walk.
  • A painful popping sensation in your knee.

You should never try and relocate a dislocated kneecap by yourself as you may cause further damage.

How is a dislocated kneecap diagnosed?

A dislocated kneecap can sometimes correct itself. However you should always seek urgent medical help even if it has gone back into position as a dislocation can cause damage to surrounding ligaments and tendons. If you are unable to walk you should call an ambulance.

You will be treated as a medical emergency. Your consultant will manipulate your kneecap back into place normally under anaesthetic. Once the kneecap is back in position you may be given an X-ray to check that the bones are correctly aligned and to rule out further damage.

How is a dislocated kneecap treated?

A dislocated kneecap will be quickly put back into position (referred to as “reduction”) by the consultant. This may need to be performed under local or general anaesthetic. Once the kneecap has been put back into place, you will need to rest the knee and use ice, compression and elevation to control swelling. You will normally need crutches or a knee brace while your knee is healing. Patients are generally offered physiotherapy to help them to strengthen the muscles and regain movement in the knee.

If you experience recurrent kneecap dislocation, you may be offered surgery to tighten the muscles or reconstruct the inside ligaments. In rare circumstances you may need to have the bone cut and repositioned.

Some surgeons are starting to recommend preventative surgery to repair the medial patellofemoral ligament (MPFL) after the first kneecap dislocation. This is because repeated dislocations can damage cartilage, leading to an increased risk of arthritis.