Knee Dislocation

What is a knee dislocation?

knee dislocation
A knee dislocation. Image © Jonathan Cluett, M.D.

A knee dislocation is an unusual and extremely serious injury. A knee dislocation occurs when the thigh bone and shin bone lose contact between each other. A knee dislocation is different from a patellar dislocation. A patellar dislocation, also called a "kneecap dislocation," occurs when the kneecap comes out of its groove on the end of the thigh bone.

Causes of Dislocations

Knee dislocations are often high-energy traumatic injuries. These injuries can occur with automobile crashes, severe falls, and sports injuries. A knee dislocation is often confused with a subluxation, but these are not the same injuries. A subluxation is a word used to describe a partial dislocation. This is the type of sensation that occurs when the knee "gives out" due to a damaged ligament. A knee dislocation is a more severe injury that occurs when the end of the thigh bone completely loses contact with the top of the shin bone. After the knee dislocates, it usually must be reset in to proper position, compared to a subluxation that will "slip" back in to position.

While many knee dislocations are these high-energy, more severe traumatic injuries, a knee dislocation can also occur from an unusual twist or misstep. In fact, probably about 40% of knee dislocations can occur with these less severe injury mechanisms. That said, the same concerns for damage to surrounding soft-tissues exists, and the injuries are evaluated and managed in a similar way.

When the knee dislocates, significant damage is done to the soft-tissues that surround the joint. The ligaments of the knee are always damaged when a knee dislocation occurs. Determining which ligaments are damaged is one of first steps of evaluating a knee dislocation. Almost always, both the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) are torn. In addition, the collateral ligaments, cartilage and meniscus can also be damaged. A knee dislocation is particularly concerning because of the damage that often occurs to the important nerve and vascular structures around the knee. In fact, vascular injuries can be so severe that the leg health can be threatened to the point of requiring emergency vascular surgery.

Signs of Dislocation

Typical symptoms of a knee dislocation include severe pain, swelling, and deformity of the joint.  The lower extremity often looks shortened, and any movements of the extremity will cause significant pain. About half of knee dislocations are repositioned prior to imaging of the extremity. This may be the result of the knee having been manipulated prior to a patient reaching the hospital.

Whenever a knee dislocation is suspected, x-rays are performed to evaluate if the joint is dislocated. If a dislocation has occurred, the joint will be repositioned, called "reducing the joint." Once the dislocated joint is reduced, your doctor will carefully evaluate and monitor the nerves and blood vessels that surround the joint.

In order to properly evaluate the blood vessels, your doctor may obtain special tests of the blood vessels (such as an angiogram) and possibly admit you to the hospital for careful monitoring of your blood vessels.

Treatment Options

In the early stages after a knee dislocation, the priority is ensuring proper treatment of any vascular or nerve injuries. Once it is certain these structures are healthy, attention can be turned to addressing the ligament, cartilage and meniscus damage that occurred at the time of the dislocation. It is usually necessary to surgically reconstruct the damaged ligaments. Most often, multiple ligaments must be reconstructed. The most commonly reconstructed ligaments after a knee dislocation are the ACL and PCL. Areas of cartilage damage are repaired, and meniscus tears are either cleaned up or repaired.

Complications after a knee dislocation include issues related to nerve and vascular injury. The most common problems after knee dislocation are either knee stiffness or chronic instability of the knee. Adhering to your prescribed physical therapy of the knee joint will help you minimize the chance of developing one of these complications.

It is especially important that anyone who has sustained a knee dislocation, or is suspected to have sustained this injury, have the blood supply to the extremity carefully assessed. If the blood flow to the lower extremity is disrupted following a dislocation, this can lead to amputation of the extremity. When these vascular injuries are detected, they can typically be repaired, but this has to be done in a timely fashion and treatment cannot be delayed. Most people who sustain a knee dislocation will either have their blood flow assessed by close monitoring, or special studies to evaluate the vascular flow through the extremity.

A Word From Verywell

A knee dislocation is a rare, serious injury. Most knee dislocations can be repositioned without much difficulty, but there is concern for significant injury to ligaments, blood vessels, and nerves. For that reason, even if a knee dislocation is properly repositioned, further evaluation of these associated structures is necessary.