Although some knee dislocations present with obvious deformity, most multiligament knee injuries spontaneously reduce. One must have a high index of suspicion, particularly in the polytrauma setting where these injuries may go overlooked. Important elements from the history include injury mechanism, direction of force, and position of the leg.
After obtaining a history, a thorough physical examination must be performed. Careful visual inspection should note any deformity, wound, or skin discoloration. Patients with a knee dislocation will often have a large effusion and even swelling of the entire extremity. The presence of a dimple sign or tight compartments must be assessed. A detailed neurovascular examination of both lower extremities must be performed. Evaluation of the sensory and motor functions of peroneal and tibial nerves should be well documented and followed serially. Careful assessment of the circulatory status of the limb should include observation of capillary refill, palpation of the popliteal, posterior tibial and dorsalis pedis pulses, as well as Doppler ankle brachial indices. Keep in mind that a patient with brisk capillary refill and palpable pulses may still have a vascular injury.
In the acute setting, swelling and pain often prevent a detailed ligament examination. However, the best possible assessment should be obtained. The four main ligamentous structures include the ACL, PCL, MCL with posteromedial capsule, and the lateral collateral ligament with posterolateral corner. Each of these structures must be systematically evaluated for stability. The most sensitive test for ACL rupture is the Lachman test performed with the knee held in 20 to 30 degrees of flexion.18 The most sensitive test for detecting PCL injury is the posterior drawer test performed with the knee in 90 degrees of flexion.19 The collateral ligaments are assessed by applying varus and valgus stress at both 30 degrees of flexion and full extension. Laxity in full extension denotes disruption of a cruciate ligament and the posteromedial or posterolateral capsule in addition to collateral injury. These patients will exhibit rotatory instability that must be identified initially and addressed at the time of surgery. Techniques for a comprehensive knee examination have been described in a previous chapter.
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