What is the most appropriate test to diagnose a meniscus tear?

Most Appropriate Test for Meniscus Tear Diagnosis

MRI is the most appropriate imaging test to diagnose a meniscus tear, with 96% sensitivity and 97% specificity at 3T, though both 1.5T and 3T MRI show similarly high diagnostic accuracy. 1

Clinical Context and Initial Approach

Before ordering imaging, radiographs should be obtained first if the patient meets Ottawa knee rules criteria (focal patellar tenderness, joint effusion, inability to bear weight) to exclude fractures. 1 In patients under 40 years old with acute knee injury, a knee effusion >10 mm on lateral radiograph should prompt consideration for MRI, as this can decrease delayed diagnosis and improve outcomes. 1

MRI as the Gold Standard

MRI is the definitive imaging modality for meniscal tears due to its superior soft tissue contrast resolution and multiplanar imaging capability. 1

Key Performance Characteristics:

• Sensitivity: 91.8% for medial meniscus, 80.8% for lateral meniscus 2
• Specificity: 79.9% for medial meniscus, 85.4% for lateral meniscus 2
• Overall accuracy: approximately 85% across all tear types and locations 3

Important Diagnostic Considerations:

• MRI accuracy is lower in ACL-injured patients compared to ACL-intact patients (medial meniscus: 81.7% vs 88.1%; lateral meniscus: 72.9% vs 88.0%) 2
• Longitudinal tears of the posterior horn of the medial meniscus in ACL-injured patients have particularly low diagnostic accuracy on MRI 2
• MRI can detect associated bone marrow contusions that predict concomitant soft-tissue injuries 1

Alternative Imaging When MRI is Contraindicated

Ultrasound as Primary Alternative:

Ultrasound is the recommended first-line alternative when MRI is contraindicated, with pooled sensitivity of 88% and specificity of 90%. 1, 4

• Highest accuracy for recent injuries (<1 month old), with specificity of 86% 1
• Joint effusion on ultrasound has 91% positive predictive value for internal derangement in acute knee trauma 1
• Major limitation: limited visualization of cruciate ligaments, portions of menisci, and articular surfaces 1, 4
• Performance is operator-dependent and varies with patient body habitus 4

CT as Secondary Alternative:

CT should be considered when ultrasound is unavailable or inconclusive. 4

• CT can predict meniscal injuries based on associated findings like tibial plateau depression patterns 1
• High specificity but lower sensitivity than MRI for soft tissue injuries 1
• Lateral tibial plateau depression >11 mm predicts higher risk of lateral meniscus tear 1

Clinical Testing to Augment Imaging

While imaging is essential, combining at least two positive clinical tests significantly enhances diagnostic accuracy (sensitivity 85%, specificity 73.3% for medial meniscus; sensitivity 92.3%, specificity 87.5% for lateral meniscus), approaching MRI performance. 5

Key clinical tests include:

• McMurray's test: 80% sensitivity, 73.3% specificity for medial meniscus 5
• Thessaly test: 70% sensitivity, 76.7% specificity for medial meniscus 5
• Joint line tenderness: 70% sensitivity, 53.3% specificity for medial meniscus 5

Common Pitfalls to Avoid

• Do not skip radiographs initially in acute trauma settings, as they guide subsequent imaging decisions 1
• Be cautious interpreting MRI in ACL-injured patients, as accuracy drops significantly for certain tear patterns 2
• Do not rely on ultrasound alone for complete meniscal evaluation due to limited visualization of certain anatomic regions 1, 4
• Post-surgical menisci are challenging: granulation tissue may mimic tears; diagnosis improves with comparison to preoperative images and operative notes 6
• MR arthrography and MRA are not routinely indicated for meniscal tear diagnosis 1