Dislocations of the knee are rare. They are true orthopedic emergencies and have a significant association with soft tissue injuries and neurovascular compromise. A dislocated knee occurs most commonly after a major force is applied to the knee joint such as from a motor vehicle collision, other high-speed trauma, or a sports injury. The etiology has recently been changing to also occur during activities of daily living and other low-level trauma, especially in obese patients.1-4 A dislocated knee can occur after a total joint replacement.5 The forces necessary to cause a dislocation of the knee joint can often fracture the bones of the leg.
Complete dislocation of the knee joint results in a gross deformity that is confirmed by plain radiographs. Reduction by the Emergency Physician may be reasonable if the Orthopedic Surgeon is not immediately available or if the injured extremity shows signs of distal neurologic or vascular compromise.
A careful examination of the distal extremity must be performed and documented.6 It must include an assessment of the capillary refill, the dorsalis pedis pulse, the posterior tibial pulse, peroneal nerve function, and tibial nerve function.
ANATOMY AND PATHOPHYSIOLOGY
A knee dislocation is the displacement of the tibiofemoral articulation (Figure 110-1). It can involve the rupture of the anterior cruciate ligament, the posterior cruciate ligament, the joint capsule, or the collateral ligaments of the knee.7 Anterior knee dislocations are the most common type of knee dislocation. This injury is defined as anterior displacement of the tibia relative to the femur (Figures 110-1A and 110-2). It results from an acute hyperextension injury to the knee joint that ruptures the anterior cruciate ligament as well as part of the posterior cruciate ligament and the posterior joint capsule. The collateral ligaments usually remain intact. Tibial spine fractures, osteochondral fractures of the tibia or femur, and meniscal injuries can be associated with the rupture of the anterior cruciate ligament. In children, hyperextension injuries are more likely to cause a distal femoral epiphyseal separation rather than a complete dislocation.
The classification of knee dislocations. A. Anterior. B. Posterior. C. Lateral. D. Medial. E. Rotary.
Radiograph of an anterior knee dislocation. (Used with permission from reference 16.)
An anterior knee dislocation may be associated with a popliteal artery injury in 30% to 40% of patients.8 The popliteal artery is at particular risk for injury because it is anchored proximally at the adductor hiatus and distally at the soleus arch. The collateral circulation around the knee joint is relatively poor. Therefore, disruption of the popliteal artery may result in significant distal ischemia and limb loss if the reduction is delayed. It ...