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Dislocated kneecap (dislocated patella)

Popoki pakoki

woman wearing a patella knee braceYour kneecap (patella) is the bone at the front of your knee. It sits in a shallow groove at the end of your thigh bone (femur).

Dislocation means your kneecap slips out of this groove. It usually slips sideways and outwards, tearing the ligament on the other side.

A dislocated kneecap is a quite common sports injury and mostly happens in young active people. Usually, it happens when you twist awkwardly or if something directly hits your knee when it's bent. People often say they can feel a popping sensation as their kneecap slips out of its groove.

Sometimes, the kneecap slips back into place by itself. And sometimes a small piece of bone breaks off. If that happens your knee will usually swell up very quickly.

Even if your kneecap slips back into place, it's important to see a doctor for treatment.

Treating a dislocated kneecap

If your kneecap has not slipped back into place by itself, it will need to be put back. A doctor or paramedic can do this and can give you gas (also called laughing gas or nitrous oxide) for pain relief when they do. It can be done before you have an X-ray. Your knee will probably feel much more comfortable when your kneecap is back in place.

Once your kneecap is back in place, you'll have an X-ray to check if it's broken anywhere. If this is the first time your kneecap has dislocated, you probably will not need surgery unless a piece of bone needs to be taken out or if your knee has another injury.

Self-care for a dislocated kneecap

Usually, you'll be fitted with a brace to stabilise your kneecap. You'll need to wear this most of the time for three to six weeks. For the first few days, raise your leg on a pillow and apply ice for 10 to 15 minutes four times every day. (Wrap the ice in a tea towel first – never apply ice directly to your skin.)

Most people can walk on their leg and bend their knee while they're healing. It may feel wobbly, and you may have some discomfort. Walking and standing are fine as long as it is not too painful. If it's very painful, stop and see your doctor.

Your doctor may tell you not to put any weight at all on your leg until you've had further investigations such as an MRI. If this is the case for you, a nurse or physiotherapist will be able to show you how to use crutches and keep weight off your leg.

Once your kneecap has dislocated, it may become unstable and dislocate more easily in the future. This can cause problems when playing sport. You can use a neoprene knee brace or strapping to help your knee feel more stable when playing sport. But you might need surgery to stabilise your kneecap.

Getting help for a dislocated kneecap

You should see a physiotherapist who will give you some exercises to strengthen your thigh (quadriceps) muscles, core (tummy muscles) and hip abductor muscles.

You can find some of these exercises here (follow the link then scroll down to Exercises for patellar dislocation). The aim is to prevent your kneecap dislocating again by stopping your knee from aligning badly (called knee valgus) and get you back to your normal activity level.

The Orthopaedics Outpatient Department will usually see you one to two weeks after your injury.

If you need surgery, you'll be able to talk to an orthopaedic surgeon about it.

If you have any questions or concerns, especially if your kneecap feels unstable, please see your general practice team. They may need to refer you back to the Orthopaedics Outpatient Department, especially if there is concern that you may need surgery.

ACC may be able to help you after your injury.

Written by HealthInfo clinical advisers. Last reviewed July 2022.


Page reference: 148656

Review key: HIHIL-240273