EASILY MISSED INJURIES AROUND THE KNEE

Most fractures around the knee are easily detected on high-quality radiographs. However, some fractures and musculotendinous and ligamentous injuries have subtle findings and may be difficult to detect even with optimal images; these injuries include tibial plateau fractures, Segond fractures, stress fractures, fibular head fractures and dislocations, injuries to the patella and extensor mechanism, and Salter type fractures. Clinically suspected tibial plateau fractures unseen on standard views may be seen on tangential or tunnel projections. Segond fractures usually have a characteristic appearance on anteroposterior radiographs but occasionally are seen only on tunnel views. Stress fractures of the proximal tibia may be accompanied by a vague band of increased sclerosis or endosteal callus on either side of the epiphyseal scar. Correct diagnosis of fibular head dislocations requires clinical suspicion, since these injuries often are not recognized on initial radiographs. Careful evaluation of the congruity of the tibiofibular joint on the lateral projection is the key to diagnosis. Vertical patellar fractures are often nondisplaced and are best evaluated with sunrise or Merchant views; avulsion fractures from the proximal or distal poles, with lateral views; and osteochondral fractures, with sunrise or internal oblique views. Salter I injuries can be visualized on oblique and anteroposterior views obtained with stress applied to the knee. Some occult Salter I fractures are diagnosed on follow-up radiographs, which show periosteal reaction. Imaging modalities other than radiography are rarely needed to diagnose fractures but are useful for evaluating the extent of displacement or confirming soft-tissue injuries.