Differential Diagnosis for Posterolateral Knee Pain

Anatomic Structures and Associated Pathologies

The American College of Radiology suggests that lateral compartment osteoarthritis produces lateral-sided pain with characteristic radiographic findings 1
Baker's (popliteal) cysts commonly cause posterior knee pain and often communicate with the knee joint 1

Hip pathology must be evaluated when knee imaging is normal, as hip disease commonly refers pain to the knee 1, 2
Lumbar spine pathology should be considered when knee radiographs are unremarkable and clinical evidence suggests spinal origin 1, 2
Initial evaluation requires plain radiographs (minimum anteroposterior and lateral views) before advanced imaging 2
Approximately 20% of patients with chronic knee pain inappropriately receive MRI without recent radiographs, which should be avoided 1, 2
Subchondral insufficiency fractures may show normal initial radiographs, later demonstrating articular surface fragmentation and subchondral collapse 1

Obtain anteroposterior and lateral knee radiographs first to exclude fractures, osteoarthritis, osteophytes, and loose bodies 1, 2
If radiographs are normal or show only effusion but pain persists, MRI without IV contrast is indicated 2
MRI excels at identifying meniscal tears, ligamentous injuries, bone marrow edema, popliteus tendon pathology, and Baker's cysts 3, 4
Consider hip radiographs if knee examination and imaging are unrevealing 1, 2