CHAPTER 42 ■ INJURY: KNEE CYNTHIA A GRAVEL INTRODUCTION Acute pain or injury to the knee is a common complaint in the emergency department (ED) Many injuries are minor and require only limited therapy; others, however, require consultation with an orthopedist, either in the ED or as an outpatient after pain and inflammation subside The emergency physician can provide appropriate therapy or determine the need for consultation, based on a comprehensive history, physical examination, and an appropriate radiographic evaluation DIFFERENTIAL DIAGNOSIS The differential diagnosis of acute and subacute knee injuries is summarized in Table 42.1 The pertinent anatomy is illustrated in Figures 42.1 and 42.2 Acute Injuries Fractures Preadolescents with open growth plates (physes) are especially susceptible to fractures Since pediatric bone strength may be less than pediatric ligament strength in some cases, an injury that would cause a ligamentous injury in adults may cause a Salter–Harris type physeal fracture in children For bones around the knee, the epiphyses close by 17±1 years in females and by 18±1 years in males Fractures of the distal femoral epiphysis are classified by the Salter–Harris pattern (see Chapter 111 Musculoskeletal Trauma ) and by the displacement of the epiphysis (usually lateral or medial) The injury usually follows significant trauma (e.g., being struck by a car with the knee hyperextended or during contact sports when sustaining a lateral hit with the foot fixed by cleats) Distal neurovascular status should be assessed because compromise of the popliteal artery occurs in 1% of cases and peroneal nerve injury occurs in 3% of cases Fractures of the proximal tibial epiphysis are rarer than those of the distal femoral epiphysis but are more likely to involve vascular compromise because of the proximity of the popliteal artery to the posterior aspect of the tibial epiphysis With both fracture types, the patient will have severe pain, refusal to bear weight, extensive soft tissue swelling, limited range of motion (ROM), and commonly, hemarthrosis For both injuries, radiographs are usually diagnostic but may be