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Knee (Tibiofemoral) Dislocations

By Danielle Campagne, MD

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Patient Education

Knee dislocations are commonly accompanied by arterial or nerve injuries. These dislocations may spontaneously reduce before medical evaluation. Diagnosis is by x-ray. Vascular and neurologic evaluation is required. Immediate treatment is closed reduction and treatment of vascular injuries.

Most anterior dislocations result from hyperextension; most posterior dislocations result from a posteriorly directed force to the proximal tibia while the knee is slightly flexed. Most knee dislocations result from severe trauma (eg, in high-speed motor vehicle crashes), but seemingly slight trauma, such as stepping in a hole and twisting the knee) can sometimes dislocate the knee, particularly in morbidly obese patients.

Dislocation always damages

  • Structures that support the knee joint, causing joint instability

Joint instability due to extensive ligament injury is a common long-term complication of knee injury.

Other structures that are commonly injured include the

  • Popliteal artery (particularly in anterior dislocations)

  • Peroneal and tibial nerves

Popliteal artery injury may initially affect only the intima and thus does not cause distal limb ischemia until the artery later becomes occluded. Undiagnosed arterial injury has a high risk of ischemic complications, which may lead to amputation.

Symptoms and Signs

Dislocation causes deformity that is clinically obvious. However, some dislocations spontaneously reduce before medical evaluation; in such cases, the knee remains very swollen and grossly unstable.

Fullness in the popliteal fossa suggests hematoma or popliteal artery injury.

Diagnosis

  • X-rays

  • Vascular evaluation

Dislocation should be suspected if an injured knee is grossly unstable. Anteroposterior and lateral x-rays are diagnostic for dislocations that have not spontaneously reduced.

Vascular and neurologic evaluations are particularly important.

Popliteal artery injury should be suspected regardless of whether ischemia is evident. Some experts believe that serial clinical evaluations of the distal pulse can rule out a popliteal artery injury if the pulse is normal over a period of time. The ankle-brachial BP index (ABI) should always be measured (see Diagnosis); values ≤ 0.9 are very sensitive for vascular injury. Some experts also recommend duplex ultrasonography even if the ABI is > 0.9 and no findings suggest ischemia. If the ABI is ≤ 0.9 or if any findings suggest ischemia, immediate vascular surgical consultation and/or diagnostic testing is required. Tests may include CT angiography (which should be done liberally), conventional angiography, and ultrasonography.

Treatment

  • Immediate reduction

  • For vascular injury, immediate vascular repair and fasciotomy

  • Later elective ligament reconstruction

Treatment is immediate reduction to 15° of flexion.

Vascular injuries are repaired immediately, and if tissue ischemia is present, fasciotomy may be necessary.

For gross instability, an external fixator is sometimes applied. Anteroposterior and lateral x-rays are usually taken to confirm reduction.

Knee ligaments can be reconstructed later, after the swelling resolves.

Key Points

  • Many knee dislocations are accompanied by popliteal artery or nerve injuries.

  • Knee dislocations always damage structures that support the knee joint, causing joint instability.

  • Most knee dislocations are clinically obvious, but they may spontaneously reduce before they are evaluated; so suspect dislocation if an injured knee is grossly unstable.

  • Always measure the ankle-brachial index because the popliteal artery is commonly injured by knee dislocation.

  • Immediately reduce the dislocated knee and repair vascular injuries.

* This is the Professional Version. *