What is a dislocated kneecap?

Mr Tim Spalding Mr Tim Spalding Consultant Orthopaedic Surgeon
A dislocated kneecap is a common injury, so it’s good to know what to do if you experience it. Tim Spalding, Specialist Knee Surgeon, explains how to tell if you’ve got a dislocated kneecap, why you might get one, and how to treat it.

What causes a dislocated kneecap?

The kneecap (patella) normally sits in a groove at the front of your thighbone (femur), allowing your leg to straighten and bend. However, certain injuries can cause it to jump out of place, to the outer side of your knee.

A dislocated kneecap is often caused by a direct blow to the knee, or a twisting injury due to a sudden change in direction when your leg is planted on the ground. Often this happens during sports, but it can also occur in dancing or jumping activities.

It usually takes a lot of force to dislocate the kneecap. However, some knees grow in such a way that the patella is more susceptible to dislocation, for example if you have a shallower groove where the kneecap sits. Also, statistics show that dislocation is more common in women.


The most obvious symptom of a dislocated kneecap is pain, particularly when you stand up or straighten your knee. You may also experience a popping sensation or sudden swelling.

Another symptom is that your kneecap will be out of place or wobbly.

What does a dislocated knee look like?

When your kneecap moves to the outer side of your knee, it leaves an odd-shaped lump where the exposed femur is, and another on the outer side, made by the dislocated kneecap itself.

Treatment for dislocated kneecap

Sometimes your kneecap may pop back in place by itself. If not, a doctor will need to manipulate it into position by pulling your leg straight, and you may be under sedation so that you're relaxed. 

Once your kneecap is back in its normal position, the pain will soon fade. And to make sure your kneecap stays in place, you can wear a protective knee brace or sleeve.

Recovering from a dislocated kneecap

To recover from a dislocated kneecap, it’s important to follow a course of physiotherapy. This will strengthen your leg and reduce the chance of your kneecap dislocating again.

Related conditions

Usually it’s obvious when your kneecap dislocates and needs to be manipulated back into place, but there are conditions with similar symptoms:

  • Patella subluxation: This is where the kneecap semi-dislocates and pops itself back into place repeatedly – you should get this assessed by a doctor as continued dislocation can damage the delicate joint surfaces, leading to arthritis
  • Anterior cruciate ligament (ACL) tear: If your knee gives way with a popping sensation similar to kneecap dislocation, it may be an ACL tear, which you should also see your doctor about.

Is a dislocated kneecap serious?

A dislocated kneecap isn’t usually serious and by following a programme of physiotherapy, 80% of patients will never have another problem with their knee.

You can also help protect your knees by losing weight, strengthening them through exercise, and eating healthily. For more information, read our article on How to protect and strengthen your hips and knees.

Last updated Wednesday 16 February 2022

First published on Tuesday 28 January 2020