Overview

A knee dislocation means the thighbone (femur) and shinbone (tibia) have lost contact with each other at the knee joint. This is completely different from a kneecap (patellar) dislocation, where only the small bone at the front slides out of place.

This is an emergency. A knee dislocation threatens the blood supply to the lower leg and can damage nerves, and it always injures the ligaments that hold the knee together. It needs to be treated in a hospital immediately.

Why It Is an Emergency

The artery that runs behind the knee (the popliteal artery) is commonly injured in a knee dislocation, and the damage is not always obvious. Sometimes the artery is only bruised on the inside, so the foot can still have a pulse at first and then lose blood flow later. If an arterial injury is not treated in time — commonly within about 8 hours — the risk of losing the leg rises sharply.

Nerve injuries are also common, especially to the peroneal nerve, which can cause numbness, tingling or weakness in the foot.

What to Do If You Suspect It

Call for emergency help or go to a hospital emergency department immediately
Do not try to "pop the knee back in" yourself
Keep the leg as still as possible
Note and report any numbness, tingling, pale or cold foot, or loss of pulses — and mention if the foot changes colour or temperature

Some knee dislocations shift back into place on their own before medical evaluation. If that happens, the knee is usually very swollen and grossly unstable — treat it as a dislocation and seek emergency care anyway.

How It Happens

Knee dislocations most often follow high-energy trauma such as a motor vehicle collision or a significant fall. But they can also happen from seemingly minor twists — stepping in a hole, an awkward landing or a sports tackle — especially in people with higher body weight.

How It Is Diagnosed and Treated

In the emergency department, clinicians check the position of the knee, pulses and nerve function, and take X-rays. They measure the ankle-brachial index (a pulse comparison) and typically use CT angiography to check the artery behind the knee, even if the foot looks pink and pulses feel normal.

Treatment starts with putting the knee back in place (reduction). If the artery is injured, a vascular surgeon repairs it immediately. The ligaments are usually reconstructed later, after the swelling settles.

References

Merck Manual Professional Edition. "Knee (Tibiofemoral) Dislocations." https://www.merckmanuals.com/professional/injuries-poisoning/dislocations/knee-tibiofemoral-dislocations
StatPearls. "Knee Dislocation." https://pubmed.ncbi.nlm.nih.gov/29262122/
Randall ZD, et al. "The known and unknown reality of knee dislocations: A systematic review." Injury. 2024;55(11):111904. https://doi.org/10.1016/j.injury.2024.111904

This information is for education only and is not a medical diagnosis. InjuryAtlas does not replace an assessment by a qualified health professional. If you have severe pain, visible deformity, numbness, loss of function, or symptoms that are getting worse, seek medical care promptly.

Knee Dislocation