Management of Acute Knee Dislocation Before Surgical Intervention

Introduction

Knee dislocations are uncommon but serious injuries. These injuries not only pose a potential threat to the limb involved, but often result in long-term pain and functional disability. What was thought to be an injury pattern caused by high-energy collision in motor vehicles or in collision sports, has also emerged as a common diagnosis in the ever-increasing obese population. Although diagnosis and initial management principles have progressed over the past several decades, ultimate treatment strategies remain controversial. Having a high index of suspicion and taking the right steps in initial evaluation and management are paramount to maximize potential outcomes and avoid disastrous consequences associated with these complex injuries.

Evaluation

Knee dislocations are typically the result of high-energy, violent trauma. Therefore the initial evaluation should always begin in the same fashion as that for a polytrauma patient. Where appropriate, a primary survey consisting of assessment of the patient's airway, breathing, and circulation (ABCs) is performed first. The secondary survey seeks life-threatening injuries and conditions. Polytrauma patients require a thorough neurologic and vascular examination, followed by an assessment of the chest, abdomen, and pelvis in addition to a detailed musculoskeletal examination of the extremities and spine. Whenever possible, the medical history should be reviewed while the patient is assessed for common polytrauma conditions, such as hypovolemia and concussion. Once the basics of trauma care have been attended to, the injured extremity should be carefully examined.

The vascular and neurologic examinations are of utmost importance and are detailed in the following sections. Starting with visual inspection, all open injury sites should be identified and cleansed. Palpation of bony prominences, areas of soft tissue swelling, and key insertion sites provides important information. If possible, the extensor mechanism should be tested to ensure the status of the quadriceps and patellar tendon. If the patient is unconscious or cannot cooperate, these structures should undergo magnetic resonance imaging (MRI) followed by a physical examination, when possible. Lastly, a complete ligament examination is conducted to assess the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), fibular collateral ligament (FCL), medial collateral ligament (MCL), and posterolateral and posteromedial structures using translation and rotation testing. Stress view imaging may be helpful, but may not be appropriate in the acute setting.

Classification

A patient with two or more torn major ligaments may have sustained a knee dislocation. This definition accounts not only for those knees that are dislocated at the time of evaluation but also for those that have spontaneously reduced. Clinically, the degree of ligament disruption can be misleading. Because ligaments may not appear completely disrupted, especially on MRI, the severity of these injuries can be easily underestimated.

The following variables are the basis for classification and complete description of a dislocated knee: (1) direction of dislocation, (2) open or closed, (3) high- or low-energy trauma, and (4) time from dislocation. Schenck has also recommended that the extent of ligamentous injury be included in the classification of knee dislocations (see Chapter 21 ).

The direction of dislocation may be unidimensional (anterior, posterior, medial, or lateral) or a rotatory combination. If the knee has spontaneously reduced, classification is based on direction of instability. Anterior dislocations caused by hyperextension of the knee are the most common, occurring in 40% according to Green and Allen's review of 245 knee dislocations. Posterior dislocations, often caused by a high-energy dashboard mechanism, accounted for 33% of the cases. Medial and lateral dislocations were present in 18% and 4% of the cases, respectively.

In 1963, Kennedy's biomechanic study in cadavers elucidated the mechanisms for both anterior and posterior dislocations. This investigation demonstrated that by progressively hyperextending the knee, the posterior capsule ruptured followed by the posterior cruciate ligament (PCL) and the anterior cruciate ligament (ACL). Without adequate ligamentous restraint, the knee dislocated in an anterior direction. A high posteriorly directed force on the proximal tibia in knee flexion caused a posterior dislocation.

Posterolateral dislocations are the most common type of rotatory dislocations. The flexed and weight-bearing knee undergoes a sudden rotatory moment that abducts and internally rotates the lower leg on the femur. This causes the medial femoral condyle to “buttonhole” through the anteromedial capsule, which may be irreducible. Inspection of the knee will reveal a transverse groove in the skin along the medial joint line secondary to invagination of the medial capsule. This “dimple sign” becomes more prominent with attempted reduction and is pathognomonic of the irreducible posterolateral dislocation.

Open dislocations of the knee are emergencies that require antibiotics and urgent irrigation and debridement in the operating room. Open injuries, present in 19% to 35% of knee dislocations, are most commonly seen with anterior and posterior mechanisms.