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HealthInfo Canterbury

Dislocated kneecap (dislocated patella)

The patella is the bone at the front of your knee. You probably call it your kneecap. 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 quite a 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 is 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 is important to see a doctor for treatment.

How is a dislocated kneecap treated?

woman wearing a patella knee braceIf your kneecap has not slipped back into place by itself, then it will need to be pushed 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 will have an X-ray to check if it is broken (fractured) anywhere. If this is the first time your kneecap has dislocated you probably won't need surgery, unless a piece of bone needs to be taken out or if your knee has another injury.

Usually, you will be fitted with a brace to stabilise your kneecap. You will 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 are healing. It may feel wobbly, and you may have some discomfort. Walking and standing are fine, as long as it's not too painful. If it is very painful stop, and see your doctor.

However, your doctor may tell you not to put any weight at all on your leg until you have 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.

What to expect after treatment

You will have an appointment with the Orthopaedics Outpatient Department one to two weeks after your injury. A physiotherapist 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 at the bottom of this page on 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.

Once your kneecap has dislocated once, 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. However, you might need surgery to stabilise your kneecap. If you need surgery, you will be able to talk to an orthopaedic surgeon about it.

If you have any questions or concerns after your last appointment with the Orthopaedics Outpatient Department, please see your GP.

Written by HealthInfo clinical advisers. Endorsed by orthopaedic surgeon, Canterbury DHB. February 2017.

Sources

Page reference: 148656

Review key: HIHIL-240273