ACR Appropriateness Criteria Acute Trauma to the Knee.

More than 500,000 visits to the emergency room occur annually in the United States, for acute knee trauma. Many of these are twisting injuries in young patients who can walk and bear weight, and emergent radiographs are not required. Several clinical decision rules have been devised that can considerably reduce the number of radiographs ordered without missing a clinically significant fracture. Although a fracture is seen on only 5% of emergency department knee radiographs, 86% of knee fractures result from blunt trauma. In patients with a fall or twisting injury who have focal tenderness, effusion, or inability to bear weight, radiographs should be the first imaging study obtained. If the radiograph shows no fracture, MRI is best for evaluating for a suspected meniscus or ligament tear, or the injuries from a reduced patellar dislocation. Patients with a knee dislocation should undergo radiographs and an MRI, as well as an angiographic study such as a fluoroscopic, CT, or MR angiogram.