The knee joint allows for flexion and extension. These functions allow the body to perform activities like walking, running, and sitting. Knee dislocations occur as a result of violent trauma and result in the femur and tibia not articulating with each other. In regards to normal knee anatomy, the bones of the knee are held together by strong ligaments. For a knee dislocation to occur, three out of four ligaments must rupture.
There are five types of knee joint dislocations and, they include: anterior, posterior, medial, lateral, and rotary. Rotary dislocations are usually posterolateral and are often irreducible. During this dislocation, the medial femoral condyle can button-hole through the medial soft tissues resulting in a “dimple sign”. As for posterior dislocations, the most common mechanism of injury include exaggerated hyperextension of the knee and dashboard injuries; posteriorly directed force with the knee flexed in 90 degrees.
The peroneal nerve is tethered at the fibular neck and can be injured during knee dislocations. Incidence of nerve injury ranges from about 14-35% (according to published data). The popliteal artery is tethered proximally by the adductor hiatus and distally by the soleus arch. Vascular damage is most common in anterior and posterior dislocation in approximately 40% of the cases. Arterial damage occurs in approximately 20-40% of all knee dislocations. Knee dislocations are associated with a high incidence of popliteal artery injury. With an established popliteal artery injury and resultant ischemia, blood flow must be restored within 6 hours. The posterior tibial and dorsialis pedis pulses should be carefully evaluated and compared to the other side in any patient with a knee dislocation. Look for any evidence of ischemia, diminished blood flow, or compartment syndrome.
An urgent reduction of the knee dislocation is mandatory. Beware of spontaneously reduced knee dislocations and its associated pathology. The physician will need to reevaluate the circulation after reduction. If the pulses are normal, the patient should follow-up in 48 hours with a clinical examination and non-invasive studies (ABI). If the patient’s ABI is 0.9 or more, then the patient will not have an arterial injury. If the patient’s pulses are abnormal or different, then the physician will need to perform an arteriography. If no pulses are palpable, then the physician will want to perform an immediate exploration in the Operating Room.
An arterial injury is treated with excision of the damaged segment and reanastomosis with a reverse saphenous vein graft and prophylactic fasciotomy. Early surgery will be performed if a ligament avulsion is present—an important ligament to reconstruct is the PCL—and/or if there is a posteriolateral corner disruption.
After a reduction of the knee, the patient is placed into a knee immobilizer or external fixator. A delayed elective reconstruction of the knee ligaments are usually done at a later date. The PCL is an important ligament to reconstruct.
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