Knee Dislocation

What Is Knee Dislocation?

A dislocated knee is when the three bones of your knee are out of place and aren’t aligned the way they should be. It can happen if the structures in your knee are abnormal. Some people are born with a knee dislocation (congenital dislocation of the knee). Most of the time, knee dislocations happen when a traumatic event thrusts the bones in your knee joint out of place with great force. It’s an emergency, and it's very painful.

If your knee is dislocated, your thigh and shin bones may be completely or partially out of place. A dislocated knee is different from a dislocated kneecap. That’s when your kneecap (patella) slips out of place. Doctors sometimes call this a patellar subluxation.

Dislocated knees are rare, but serious. Other parts of your knee might also have been damaged at the same time. You need to see a doctor right away.

Knee Dislocation Symptoms

When you dislocate your knee, you may hear a popping sound. Common symptoms include:

  • It hurts a lot. Your knee is in so much pain that you can’t move or straighten it.
  • Your knee feels unstable.
  • It’s swollen and severely bruised.
  • Parts of the knee look like they’ve been knocked out of place.
  • You aren’t able to do activities or sports you normally do.

Knee Dislocation Causes

If it’s not something you were born with (congenital dislocation), knee dislocation happens as the result of serious trauma such as:

  • Car accidents. If you bang your knee against a hard surface like your dashboard, the force of the blow may be strong enough to dislocate your knee.
  • Sports injuries. This is less common than car accidents, but it’s possible to dislocate your knee if you collide with great force with another player or with the ground when your knee is bent, or if you overextend your knee (bend it backward farther than it’s supposed to go).
  • Hard falls. It may happen to skiers or runners who lose control and fall on a bent or overextended knee. You may even dislocate your knee if you fall after stepping into a hole in the ground by mistake.

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Knee Dislocation Diagnosis

You should go to your doctor at once so they can see your knee from many angles to confirm the injury.

Examination. Your doctor will look at your knee, and they’ll want to hear how you injured it. They’ll note whether or not your knee is misshapen and swollen, and whether or not you can move it.

Your doctor may push on different parts of your leg to see if you’ve also damaged any ligaments, which are bands of tissue that help to hold the knee in place. It’s common to tear ligaments when you dislocate your knee.

They’ll also note what your skin looks and feels like below your knee, all the way to your foot. Dislocating your knee may cause damage to nerves or blood vessels, which may change the color and temperature of your skin. This could affect blood flow or your sense of touch below the knee. In extreme cases, you could lose your limb (amputation) if these severe complications aren’t addressed.

Ankle-brachial index test. To look for changes in blood flow, they may do this test. It compares your blood pressure measured at your ankle to your blood pressure measured at the usual place on your arm. If your ankle-brachial index number is low, it may mean the dislocation has caused a problem with the blood flow to your legs.

Electromyography. Your doctor may use this procedure to check your muscles and nerves. They’ll insert a needle into your muscle to record electrical activity. Electrodes on the surface can measure the speed and strength of signals from your nerves.

Imaging. Your doctor likely will want to see what’s going on inside your knee.

An X-ray can confirm that your bone has been knocked out of the joint. It can also show if there are broken bones from your accident.

An MRI can show whether any of the ligaments or other soft tissues in the knee have been damaged. It can also help a surgeon prepare to rebuild your knee. An MRI or ultrasound also can show whether there’s nerve injury.

Your doctor may order an arteriogram, an X-ray outlining blood flow in your arteries and veins. It’s another way to see if the knee dislocation damaged blood vessels.

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Knee Dislocation Treatment

Your treatment will depend on how badly you’ve been injured.

No-surgery option. If the damage to your knee isn’t too severe, your doctor may try to pop your bone back into place by pressing and moving your leg in certain ways. This will be very painful, probably. Your doctor will offer to give you medicine so that you won’t feel what’s happening. After your bone is back in the joint, you’ll likely need to wear a splint for a few weeks to allow your knee to heal without moving or bearing any weight.

Surgery. Your doctor may need to do surgery to correct the dislocation and other damage from your injury, including:

  • Broken bones
  • Torn ligaments
  • Damaged nerves
  • Damaged blood vessels

You might not have surgery until 1 to 3 weeks after you’re hurt, to allow time for the swelling to go down. While you wait, you’ll need to wear a splint, keep your leg raised, and put ice on the injury.

Your surgeon may do arthroscopic knee surgery. This is done through small cuts made around your knee.

You might need “open” surgery, with bigger cuts. The type you need depends on the damage to the rest of your knee.

Knee Dislocation Recovery

After surgery, you may wear different knee braces as you heal. Some let you bend your knee -- to ease stiffness.

After you’re finished wearing splints or braces, your doctor should send you to a physical therapist to rehab your knee. You’ll do exercises to strengthen the leg muscles around your knee and work to bring a full range of motion back to your joint.

Your recovery will depend on how serious your injury is and whether you had damage to your blood vessels and nerves. If you got treatment quickly, you will likely heal well. Recovery from a knee dislocation can take a long time. You may need to rehab your knee for up to a year. You’ll recover faster if you stick to your doctor’s advice. Athletes who dislocate their knees may be able to return to their sports, but they might not be able to perform at the same level as before.

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Knee Dislocation Complications

Knee dislocation is a serious injury that can have major complications if it isn’t treated right away. If the dislocation causes a big loss of blood flow to your legs, your doctor may have to amputate. Knee dislocations also can lead to blood clots in deep veins of your legs (deep venous thrombosis).

Acute compartment syndrome is another common complication. This happens when the swelling in the muscles causes pressure to build up in the blood vessel, nerves, and muscles. If this happens, it’s painful. You’ll need to see a doctor right away.

WebMD Medical Reference Reviewed by Brunilda Nazario, MD on September 22, 2020

Sources

SOURCES:

OrthoInfo: “Common Knee Injuries,” “Compartment Syndrome.”

National Institute of Arthritis and Musculoskeletal and Skin Diseases: “Handout on health: Sports injuries.”

Journal of Athletic Training: “A review of knee dislocations.”

The Bone & Joint Journal: “Dislocation of the knee.”

Mayo Clinic: “Dislocation causes,” “Dislocation symptoms,” “Dislocation basics: Treatment and drugs,” “Ankle-brachial index,” “Electromyography (EMG).”

National Health Service (U.K.): “Dislocated Kneecap.”

Nationwide Children’s: “Patellar subluxation.”

Europe PMC: “The value of the ankle-brachial index for diagnosing arterial injury after knee dislocation: a prospective study.”

The Journal of Neurosurgery: “Combined common peroneal and tibial nerve injury after knee dislocation: one injury or two? An MRI-clinical correlation.”

Muscle & Nerve: “Fibular nerve damage in knee dislocation: Spectrum of ultrasound patterns.”

Neurosurgery Focus: “Combined common peroneal and tibial nerve injury after knee dislocation: one injury or two? An MRI-clinical correlation.”

Stanford Health Care: “Angiogram/Arteriogram.”

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