Knee Injury Evaluation After a Fall

Initial Imaging

The American College of Radiology recommends obtaining knee radiographs first in patients ≥5 years old presenting with acute knee pain after a fall, as MRI is not routinely used as the initial imaging study for acute knee trauma 1, 3
Radiographs should always be the initial study, and MRI without IV contrast is appropriate after normal radiographs to evaluate suspected occult fractures or internal derangement in skeletally immature children 1

The American College of Radiology recommends ordering MRI without IV contrast when radiographs show no fracture but the patient has persistent pain, focal tenderness, joint effusion, inability to bear weight, or suspected internal derangement 1, 2
MRI is particularly valuable in patients with a history of osteoporosis or previous knee injuries, as bone marrow contusions and occult fractures are common but radiographically invisible 2
In patients with suspected occult fracture, especially older patients with osteoporosis, MRI is the next appropriate imaging study after negative X-rays to detect occult fractures, meniscal tears, ligament injuries, and bone marrow contusions that are invisible on radiographs 1, 2

MRI detects meniscal tears, ligament injuries, and tendon pathology, including patellar tendinopathy and quadriceps tendon injury, which are invisible on radiographs 2
MRI also detects bone marrow contusions, occult fractures, including subchondral insufficiency fractures in older patients, and osteochondritis dissecans, particularly in adolescents 1, 2, 4
Articular cartilage abnormalities, popliteal cysts (Baker's cysts) and their rupture, and joint effusion extent and synovitis can also be detected by MRI 4, 5

The American College of Radiology explicitly recommends not skipping MRI if symptoms persist after negative radiographs, as meniscal tears, ligament injuries, and bone marrow contusions are invisible on radiographs but cause substantial morbidity 2
A thorough clinical examination including lumbar spine and hip assessment should be completed to consider referred pain from hip or lumbar spine before attributing all symptoms to knee pathology, especially if radiographs are unremarkable 5