Kneecap (patella) instability

The kneecap (patella) is in the V-shaped groove at the bottom of the thigh bone. The knee joint is stabilised and supported by ligaments, which are thick bands of rubbery tissue connecting bones at the knee joint. The main ligament that stabilises the knee is the medial patella-femoral ligament (MPFL). If this is torn, it can mean the kneecap is more likely to dislocate in the future which is very painful and can also damage the surrounding tissues, leading to cartilage injuries.

What causes kneecap (patella) instability?

Knee instability is caused by damage to the ligaments in the knee. Each time the kneecap moves out of place, or dislocates, it stretches the ligaments, which can cause ligament injuries.

Factors that increase the risk of kneecap instability include:

  • Having an internally twisted or rotated thigh bone and/or loose ligaments surrounding the knee (this is more common in adolescent girls)
  • Taking part in sports that involve twisting the knee such as skiing, football, netball, hockey, tennis or rugby
  • Knee injuries: during an injury to the knee, the MPFL can rupture (tear) and cause the kneecap to dislocate. If this happens, you’re more at risk of having further dislocations in the future

What are the symptoms of kneecap (patella) instability?

The symptoms include:

  • Dislocation of the knee – which can happen repeatedly
  • Severe pain, swelling and difficulty in walking
  • ‘Popping’ or ‘cracking’ and stiffness in the joint
  • The knee giving way or buckling

Left untreated, it can also cause cartilage injuries and lead to arthritis in the future.

How is kneecap (patella) instability diagnosed?

Adrian will discuss your symptoms with you and examine your knee to check for tenderness, stiffness, swelling and check your range of movement. In most cases, he will arrange for you to have an X-ray to confirm the diagnosis. He may also arrange for you to have a magnetic resonance imaging (MRI) scan to examine any damage to the cartilage.

How is kneecap (patella) instability treated?

In most cases, Adrian will advise you to have MPFL reconstruction surgery to stabilise the kneecap. You may also need additional ligament surgery.

If the instability is caused by a bone deformity, this can be corrected during knee realignment (osteotomy) surgery. In some cases, you may also be offered adipose tissue therapy.


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