Dislocated Kneecap (Patella Dislocation)

What is a dislocated kneecap (patella dislocation)?

A patella dislocation occurs when your kneecap (patella) slides out of the groove at your knee joint. Your knee joint is a meeting of three bones: your thighbone (femur), shinbone (tibia) and patella in the middle. Normally, when you bend and straighten your leg, your kneecap slides up and down inside a vertical groove (the trochlear groove) between the bottom end of your femur and the upper end of your tibia. A network of tendons and ligaments secure your kneecap within the groove, flexing as it moves.

When your patella dislocates, it’s forced outside of the trochlear groove and can no longer move up and down. This locks your knee and pulls the ligaments out of place, often tearing them. Most frequently, your kneecap pops out laterally (to the side of the groove). Like any dislocation, a dislocated kneecap is painful and debilitating until you correct it. But a dislocated patella will sometimes correct itself.

A patella dislocation is different than a knee dislocation, a much more serious injury that involves your femur and tibia. It’s also different than a patella subluxation, in which your kneecap only partially dislocates.

Types of patella dislocation

There are two main types of patella dislocations:

• Acute patella dislocation. Most of the time, a kneecap dislocation is an acute (sudden) injury caused by force. It’s a common injury, since your kneecap takes less force to dislocate than other joints.
• Congenital patella dislocation. Rarely, a dislocated patella happens developmentally. Also called trochlear dysplasia, it occurs when your patella develops outside of the trochlear groove.

How can you tell if your kneecap is dislocated?

Patellar dislocation symptoms may include:

• An audible pop
• Buckling of your knee
• Intense knee pain
• Effusion
• Bruising at your knee
• Locking of your knee
• Inability to walk
• The kneecap is visually out of place

What are the complications and side effects of knee dislocation?

Long-term complications may include a less stable knee joint and deteriorated cartilage, which can contribute to knee osteoarthritis later in life.

In addition, up to 45% of people who’ve experienced a patella dislocation will dislocate their knee again. This recurrence can happen from weeks to years later.

What causes kneecap dislocation?

Force — either from a direct impact or a bad step that uses your own body weight against you — causes acute patellar dislocation. A heavy fall or collision can knock your kneecap out of place. But it doesn’t always take that much. Something as simple as a sudden turn that twists your knee while your lower leg is still firmly planted can cause it. This commonly happens to athletes and dancers, who are prone to quick pivots.

Some people have patellar instability, which means that the tendons and ligaments that hold your kneecap in place are already loose and unstable. An unstable kneecap will dislocate more easily.

People with congenital patellar dislocation (trochlear dysplasia) are born with the condition. It’s often, but not always, related to other developmental abnormalities.

What are the risk factors for a patella dislocation?

Anyone can dislocate their patellas through injury. But certain people are more at risk, including:

• Athletes, especially in high-impact sports that cause sports injuries
• Dancers, who are prone to quick pivots
• Teenagers, whose joints and ligaments are looser from constant growth
• Women, whose wider hips and looser ligaments put more lateral stress on their knees
• Big and tall men, whose joints are under more pressure

Researchers don’t know what causes congenital patella dislocation, but a higher incidence among biological family members suggests a genetic link. Certain other congenital conditions are also associated with it, including:

• Larson syndrome
• Arthrogryposis
• Diastrophic dysplasia
• Nail-patella syndrome
• Down syndrome
• Ellis-Van Creveld syndrome

How is a patella dislocation diagnosed?

A healthcare provider can usually diagnose a dislocated kneecap by physically examining your knee and asking you questions about the injury. In addition, they’ll order imaging tests to check for any related injuries, like torn ligaments, cartilage injuries or fractures. Imaging tests may include:

• Knee X-ray
• MRI scan
• CT scan

If your dislocated patella corrected itself, you might not realize that it was dislocated. A dislocation that corrects itself is called “transient.” Afterward, your knee will still be sore and swollen, but it may look like many other more common knee injuries. In this case, imaging tests can show evidence after the fact that there was a dislocation, along with secondary injuries.

How is a patella dislocation treated?

Patellar dislocation treatment starts by resting your knee. Don’t try to walk on it or perform any of your usual physical activities. You may also want to use an ice pack and take pain relievers (NSAIDs) to help with the pain and swelling. Your healthcare provider may treat the kneecap dislocation using several different methods:

• Reduction. Your provider will gently push your kneecap back into place using a procedure called closed reduction. You may receive a minor pain reliever or sedative.
• Bracing and crutches. You’ll wear a brace or splint for a few weeks to stabilize your kneecap. Your provider will probably recommend crutches to keep weight off your knee.
• Surgery. If there’s significant damage to the bone or cartilage and tendons of your knee, or you’ve had more than one dislocation, your provider may recommend surgery to repair it.
• Rehabiliation. Physical therapy is very important to restrengthen your muscles while limiting your range of motion until your joint restabilizes.

Can I fix a dislocated patella myself?

Possibly. The kneecap has been known to pop back into place on its own when the leg is carefully extended. If it’s too painful to extend the leg, your healthcare provider can give you medication to make it easier. If you do fix it yourself, see your healthcare provider after. They’ll want to check for fractures and for damage done to the cartilage and ligaments.

When should I see my healthcare provider?

If you think you may have dislocated your kneecap, you should see your provider. Look for signs including:

• Unstable feeling in your kneecap
• Difficulty lifting your leg
• Pain or swelling
• Knee catching and locking

What questions should I ask my healthcare provider?

Questions you may want to ask your provider include:

• What treatment do you recommend?
• What’s the recovery process like?
• How long do I need to stay off my knee?
• How can I prevent this from happening again?

How can I prevent patella dislocation from recurring?

All dislocations stretch your ligaments and deteriorate the cartilage of your joints to some extent. Once you dislocate your patella, it’s more likely to happen again if you reinjure it in a similar way. Accidents are hard to prevent, but sometimes there are contributing factors that you can try to reduce. Depending on what made your patella dislocate in the first place, you may want to take one or several of these preventive measures:

• Diligent rehabilitation. Recover fully from a dislocation by following through with physical therapy as prescribed and not using your leg too much, too soon.
• Leg muscle conditioning. Stretch and strengthen each of the different muscle groups that stabilize your knee to help ensure that no single muscle group is carrying too much stress.
• Proper athletic form. If you’re an athlete, you might want to have a specialist analyze the way you practice certain movements and exercises and make sure that your form is correct.
• Reconstructive surgery. If your knee ligaments and tendons are especially loose, it might be worth considering surgery to help strengthen your knee. Consult your healthcare provider.

What’s the recovery time for a dislocated kneecap?

Recovery time for a dislocated kneecap depends on the severity of your injury and method of treatment.

If this is your first patella dislocation and there’s no major damage, your prognosis (outlook) is good. Most people will be able to get back to their normal, daily activities within six to eight weeks. You can usually participate in sports after three to four months.

If you have recurring dislocations or major damage that requires surgery, your recovery time will take longer. It may be more than a year before you’re back to playing sports.

How painful is a dislocated kneecap?

Dislocations are often very painful, but there’s a range. It depends on the extent of the injury. It’ll always be painful to move the dislocated joint or bear weight on it. You won’t be able to use the limb normally until you correct the joint.

If your dislocated patella corrects itself, your pain and mobility may improve. But you should still see your healthcare provider. They’ll check for secondary injuries to your ligaments and guide you through the longer rehabilitation process.

Can you walk with a dislocated patella?

No. Your knee will either be locked and unable to straighten or bend, or it’ll catch and pop when you try to bend it. The joint will be unstable and buckle when you try to bear weight on it. It will also be painful to move it. If you can walk, you may only have a patella subluxation.

If your dislocated patella pops back into place, you may be able to walk afterward. But the knee will still be swollen and painful from the trauma. You shouldn’t try to walk if it’s too painful. Always see your healthcare provider anyway to check for any secondary injuries. They’ll likely recommend crutches and a brace when you begin to walk again.