Dislocated Kneecap

Overview

A dislocated kneecap (doctors call it patellar dislocation) happens when the small, round bone at the front of your knee slips out of its usual groove and moves to one side — usually the outside of your knee. The kneecap sits in a shallow channel at the end of your thigh bone and slides up and down as you bend and straighten your leg. If it slips out, the knee can look bent or twisted, it hurts a lot, and it swells quickly. In many cases the kneecap pops back into place on its own, but sometimes a doctor needs to guide it back.

Yes, it is a fairly common knee injury. It is one of the most common reasons young people go to an emergency department with a knee problem. Many people who dislocate a kneecap once never have it happen again, though some people get repeated dislocations.

It can affect anyone at any age, but it is most common in teenagers and young adults between about 13 and 25. It is slightly more common in girls and women, in people who are very flexible, and in people who play sports that involve twisting, jumping or sudden changes of direction, such as football, netball, basketball, gymnastics and skiing. People who have had one dislocation are more likely to have another.

Symptoms

Common symptoms

• A sudden, sharp pain in the front of the knee at the moment it happens
• The knee giving way, or a feeling that something has 'popped' out of place
• The kneecap looking out of position, or sitting to one side of the knee
• Rapid swelling around the knee within a few hours
• Difficulty bending or straightening the knee, or not wanting to put weight on it
• A feeling of the knee being unstable or 'untrustworthy' afterwards
• Bruising around the knee in the days that follow

Symptoms in children

• Young children may simply cry and refuse to walk or stand on the leg
• They may hold the leg still and resist having the knee touched or moved
• Swelling can appear quickly and the knee may look puffy
• Sometimes a child describes a 'click' or a strange feeling rather than severe pain
• Some children have naturally looser joints and a kneecap that slips partly out and back without a big injury — this still deserves a check-up

Symptoms in older adults

• Dislocation is less common in older adults but can happen after a fall or a twisting injury
• There may be more swelling and bruising, and recovery can take longer
• Existing knee arthritis can make the knee feel more painful and stiff afterwards
• Older adults may be more at risk of falls, so balance and strength work matters

Causes

Main causes

• A twisting injury, such as planting your foot and turning your body while playing sport
• A direct blow or fall onto the front or side of the knee
• Landing awkwardly from a jump
• For some people, very little force is needed because the knee joint is naturally lax (loose) or the kneecap sits high or shallow in its groove
• Sometimes it happens without any injury at all, during ordinary movement

Risk factors

• Being a teenager or young adult, when bones and muscles are still developing
• Being female
• Naturally flexible or 'double-jointed' joints (hypermobility)
• Weak thigh muscles, especially the inner thigh muscle that helps hold the kneecap in place
• Flat feet or knees that roll inwards when you walk or run
• A previous kneecap dislocation or a previous knee injury
• A family history of kneecap problems
• Playing sports with lots of jumping, pivoting or sudden stops

When to see a doctor

See a doctor urgently if:

• You think your kneecap has dislocated and it has not popped back into place
• You cannot put any weight on the leg, or the knee is locked and cannot be straightened
• There is numbness, tingling, or the foot looks pale or cold
• The knee is extremely swollen or very painful
• You are unsure whether it is a dislocation or a break — an X-ray may be needed

Book a routine appointment if:

• The kneecap has gone back in but the knee still feels unstable or painful after a few days
• You have had more than one dislocation, or the knee regularly feels like it might slip
• Swelling or stiffness is not improving with rest and gentle movement
• You want advice on exercises to build strength and reduce the risk of it happening again
• You are worried about getting back to sport or to work

Diagnosis

A doctor or nurse will usually diagnose a dislocated kneecap by talking to you about what happened and examining your knee. They will look at the shape of the knee, check how it moves, feel for tenderness and swelling, and check the strength and feeling in your leg, foot and ankle. If the kneecap is still out of place, they may gently guide it back — often with pain relief and relaxation first. Imaging tests help confirm the diagnosis and check for other injuries.

Tests that may be done

• Physical examination of the knee, hip and leg
• An X-ray to confirm the diagnosis and rule out a broken bone or loose piece of bone
• Sometimes an MRI scan, especially if the knee stays unstable or surgery is being considered — this shows cartilage and ligament damage
• Occasionally a CT scan if the shape of the bones needs to be looked at more closely

What to expect at your appointment

The examination can be uncomfortable, but it is usually quick. If your kneecap needs guiding back into place, the medical team will explain what they are doing and use pain relief to make it as comfortable as possible. You may be given a brace or a splint and crutches, and told how to care for the knee at home. You will usually be referred to a physiotherapist, and you may be asked to come back for a review.

Treatment

The aim of treatment is to get the kneecap back into place comfortably, settle the pain and swelling, and then build up the muscles that hold the kneecap steady so it is less likely to slip again. Most people do not need surgery. The first few days focus on rest and reducing swelling; the following weeks focus on gentle movement and then strengthening. Progress is usually gradual, and it is normal for the knee to take a few weeks to a few months to feel close to normal.

Self-care at home

• Rest the knee and avoid the activity that caused it for a short while
• Use ice packs wrapped in a cloth for about 15 to 20 minutes, several times a day, to ease pain and swelling
• Elevate the leg on cushions when resting to help swelling drain away
• Use a compression bandage or brace if your clinician advises it
• Take ordinary pain relief recommended by your doctor or pharmacist if you need it
• Follow the physiotherapy exercises you are given, even on days when the knee feels fine
• Return to sport gradually, and only when your clinician or physiotherapist says it is safe
• Use crutches for as long as you have been advised to, then wean off them steadily

Medical treatments

Treatment usually starts with putting the kneecap back in place if it is still out — this is called reduction and is done by a trained clinician. You may be given pain relief and something to help you relax beforehand. After that, the knee is often supported with a brace, splint or bandage for a short period, and you may be given crutches. Physiotherapy is the mainstay of treatment: a physiotherapist will teach you exercises to strengthen the thigh and hip muscles, improve your balance and help you move confidently again. They may also use taping or a knee brace during sport. Your clinician will discuss pain relief options with you and review how the knee is healing.

When is surgery considered?

Surgery is not needed for most people. It may be discussed if the kneecap keeps dislocating, if there is damage to the cartilage or to the ligament that holds the kneecap in place, if a piece of bone has broken off, or if the shape of your bones makes dislocation very likely. Surgery is usually keyhole (arthroscopic) or a small open operation to repair or tighten the supporting tissues, and sometimes to adjust the pull of the tissues around the kneecap. Your specialist team would explain the benefits and risks in detail before you decide.

Living with this condition

In the first week or two you may need to take it easier, keep the leg raised and use crutches for longer walks. Everyday things like stairs, getting in and out of a car, or kneeling can feel awkward for a while. Build activity back gradually — short walks first, then longer ones. Many people find a brace gives extra confidence when they first return to sport or uneven ground. Keep doing your exercises; they are the single most useful thing you can do for your knee.

Lifestyle tips

• Warm up properly before exercise and cool down afterwards
• Build strength in your thighs, hips and bottom muscles with regular, progressive exercise
• Include balance and control work, such as standing on one leg, once your knee allows
• Wear supportive, well-fitting footwear
• If you play sport, consider a knee brace or taping during play, as advised by your physiotherapist
• Keep to a healthy weight to reduce the load on your knees
• Avoid suddenly increasing how much you train — build up steadily

Diet and exercise

There is no special diet for a dislocated kneecap, but eating a balanced diet with enough protein, calcium and vitamin D supports bone and muscle health. Exercise is a core part of recovery. Start with gentle movement such as straightening and bending the knee, then short walks, then strengthening work. Swimming and cycling are often comfortable ways to rebuild fitness. Avoid pivoting or contact sports until your clinician or physiotherapist is happy for you to return. It is normal for the knee to ache after exercise at first — reduce the amount and build up again if it swells or hurts more than a little.

Mental health and emotional wellbeing

It is very common to feel anxious about your knee after a dislocation, especially the fear of it happening again during sport or in public. You may feel frustrated by having to slow down, or worried about missing school, work or training. These feelings are normal and usually settle as your strength and confidence return. Talking to your physiotherapist about your worries can help a lot. If low mood, worry or hopelessness is affecting your daily life, please reach out to a healthcare professional. If you ever feel you are in crisis or having thoughts of harming yourself, contact your local emergency number or a crisis support service straight away.

Prevention

You cannot always prevent a first dislocation, but you can lower the chance of it happening again. The most effective step is a regular strengthening programme for the thigh, hip and bottom muscles, plus balance and landing practice. Warming up before sport, building up training gradually, using good footwear and, where advised, taping or bracing during sport all help.

Complications

If left untreated

• The knee may keep feeling unstable, and the kneecap may slip again — repeated dislocations become more likely after the first one
• Damage to the smooth cartilage on the back of the kneecap or in the joint, which can lead to pain and, in the long term, earlier wear-and-tear arthritis
• A small piece of bone or cartilage can break off and stay loose in the joint
• Ongoing pain, swelling or stiffness, making sport and everyday activities harder
• Loss of confidence in the knee, which can lead to avoiding activity and losing strength

Long-term outlook

The outlook is generally good. Most people who dislocate a kneecap recover well with physiotherapy and get back to their usual activities, including sport. Some people do have further episodes, and a small number need surgery, but even then the results are usually positive. The key is to keep up your strengthening work and to return to activity gradually — with patience, most people end up with a knee they can trust again.

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