Ultrasound Evaluation of the Knee

Standard Scanning Protocol

The suprapatellar recess examined with the knee in 30° flexion using longitudinal and transverse scans provides the most sensitive anatomic window for detecting joint effusions and synovial proliferation, which are the most clinically significant findings on knee ultrasound, as recommended by the American College of Rheumatology 1
Perform both longitudinal and transverse scans in this position, applying parapatellar pressure to displace fluid into the suprapatellar pouch, according to the European League Against Rheumatism 1, 2
Visualize the femur, articular cartilage, and any joint cavity fluid, as suggested by the American College of Rheumatology 1, 2
Scan for loose joint bodies, which may be present in the infrapatellar pouch, as recommended by the European League Against Rheumatism 1, 2

Joint effusion/synovial proliferation is the most common finding, and cartilage thinning or lesions can also be detected, as reported by the American College of Rheumatology 1, 2, 4
Loose joint bodies in suprapatellar, infrapatellar, and popliteal regions can be identified, according to the European League Against Rheumatism 1, 2
Bony abnormalities, such as erosions, osteophytes, and irregular bone surfaces, can be visualized, as suggested by the American College of Rheumatology 1, 2, 4

Use high-frequency transducers of 10 MHz or higher to detect even minor synovitic lesions and small effusions, as recommended by the American Institute of Ultrasound in Medicine 1, 4, 5
Active flexion/extension of the knee during scanning can help detect vascular pathology, according to the European League Against Rheumatism 4

Never assume absence of loose bodies based on negative ultrasound, as ultrasound cannot rule out their presence if not visualized, as warned by the American College of Rheumatology 1, 2, 3
Overlooking the comma-shaped extension between gastrocnemius and semimembranosus when evaluating for Baker's cyst can lead to misdiagnosis, as cautioned by the European League Against Rheumatism 1, 2, 3
Missing small calcifications visible on ultrasound but not on plain radiographs can occur if not carefully evaluated, as noted by the American Institute of Ultrasound in Medicine 5