What is the recommended approach to diagnose a meniscal tear?

How to Diagnose Meniscal Tear

MRI without IV contrast is the definitive imaging test to diagnose meniscal tears, with 96% sensitivity and 97% specificity at 3T, though both 1.5T and 3T MRI show similarly high diagnostic accuracy. 1, 2

Initial Diagnostic Approach

Step 1: Obtain Radiographs First

• Always start with plain radiographs (AP, lateral, tunnel/Rosenberg, and tangential patellar views) in patients with acute knee trauma or persistent knee pain to exclude fractures before proceeding to advanced imaging 1, 2
• In patients under 40 years old with acute knee injury, a knee effusion >10 mm on lateral radiograph should immediately prompt MRI consideration, as this can decrease delayed diagnosis and improve outcomes 1, 2
• Radiographs detect only 83% of fractures and miss virtually all soft-tissue injuries, so negative radiographs do not exclude meniscal pathology 3

Step 2: Clinical Examination (While Awaiting Imaging)

• For traumatic tears: Look for history of trauma during a pivot maneuver, medial knee pain location, and positive medial joint line tenderness (this combination has LR+ = 8.9 and LR- = 0.10) 4
• For degenerative tears: Look for progressive onset of pain, medial knee pain location, pain while pivoting, absence of valgus/varus misalignment, and full passive knee flexion (this combination has LR+ = 6.4 and LR- = 0.10) 4
• McMurray test, Apley test, and "bounce home" maneuvers aid diagnosis, along with joint line tenderness and presence of knee effusion 5
• Critical caveat: Clinical examination alone has low diagnostic benefit in acute knee trauma, with higher-than-suspected incidence of injuries found on MRI 3

Step 3: MRI - The Gold Standard

When to Order MRI

• Order MRI when radiographs are negative or show only joint effusion but pain, mechanical symptoms (locking, catching, popping, giving way), or clinical suspicion persists 1, 2
• MRI should be performed within 6 weeks of acute trauma for optimal visualization of certain injuries 2
• The majority (93.5%) of patients presenting with acute knee injuries have soft-tissue injuries rather than osseous injuries, making MRI essential 1, 3

MRI Advantages

• MRI accurately depicts meniscal tears, associated bone marrow contusions, ligamentous injuries, articular cartilage abnormalities, and joint effusions 1
• MRI shortened diagnostic workup, reduced additional procedures, and improved quality of life in the first 6 weeks, potentially reducing productivity loss 1
• MRI can change management from surgical to conservative in up to 48% of patients presenting with a locked knee 2

Critical Age-Related Consideration

• In patients over 70 years old, the majority have asymptomatic meniscal tears, making MRI findings potentially misleading 1, 2
• In patients 45-55 years old, the likelihood of a meniscal tear being present in either a painful or asymptomatic knee is not significantly different 1, 2
• In elderly patients with osteoarthritis, focus MRI interpretation on bone marrow lesions and synovitis/effusion, which better correlate with knee pain than meniscal tears 1, 2

Alternative Imaging When MRI is Contraindicated or Unavailable

Ultrasound (First-Line Alternative)

• Ultrasound has pooled sensitivity of 88% and specificity of 90% for meniscal tears, with best performance in recent injuries (<1 month old, specificity 86%) 1, 2
• Joint effusion on ultrasound has 91% positive predictive value for internal derangement in acute knee trauma 2
• Major limitation: Performance varies significantly with operator skill and patient factors (body habitus, joint effusion), and cannot comprehensively evaluate intra-articular structures 1, 3

CT (Second-Line Alternative)

• CT has high specificity but low sensitivity for meniscal tears compared to MRI 1
• CT is useful when ultrasound is unavailable or inconclusive 2
• Lateral tibial plateau depression >11 mm on CT predicts higher risk of lateral meniscus tear and should prompt MRI if available 1, 2
• CT shows 80% sensitivity and 98% specificity for detecting bony avulsion fractures but remains inferior to MRI for soft-tissue evaluation 1

What NOT to Order

• MR arthrography and MRA are not routinely indicated for meniscal tear diagnosis 1, 2
• SPECT/CT bone scan shows lower sensitivity, specificity, and accuracy than MRI for meniscal injuries 1

Common Pitfalls to Avoid

• Do not skip initial radiographs in acute trauma settings, as they guide subsequent imaging decisions and exclude fractures 1, 2
• Do not dismiss the diagnosis because radiographs are negative, as they miss virtually all soft-tissue injuries 3
• Do not delay MRI in young patients (<40 years) with significant effusion (>10 mm), as this can lead to delayed diagnosis and worse outcomes 1, 2
• Do not over-interpret meniscal tears in elderly patients, as asymptomatic tears are extremely common and may not be the pain source 1, 2
• Do not rely solely on clinical examination in acute trauma, even by experienced clinicians, as MRI frequently reveals unexpected injuries 1, 3