Diagnosis and Treatment of Lateral Meniscus Body Tear
MRI is the definitive imaging modality for diagnosing a tear in the body of the lateral meniscus, with 96% sensitivity and 97% specificity, and should be obtained after initial radiographs to exclude fractures. 1
Diagnostic Algorithm
Initial Imaging Approach
- Obtain radiographs first in all acute knee trauma cases to rule out fractures before proceeding to advanced imaging 1, 2
- Apply Ottawa knee rules criteria to determine if radiographs are indicated 1
- In patients under 40 years with acute knee injury, a knee effusion >10 mm on lateral radiograph should prompt MRI consideration 1
MRI Protocol
- Both 1.5T and 3T MRI systems provide equivalent diagnostic accuracy for meniscal tears, with no significant improvement at higher field strength 2
- MRI demonstrates superior performance compared to CT (which has high specificity but lower sensitivity) and ultrasound (88% sensitivity, 90% specificity) for soft tissue injuries 3, 1
- MRI can detect associated bone marrow contusions that predict concomitant soft-tissue injuries 1
Clinical Examination Considerations
- While clinical tests (McMurray's, Thessaly, joint line tenderness, Apley's) are useful, combining at least two positive clinical tests achieves 92.3% sensitivity and 87.5% specificity for lateral meniscus tears 4
- Clinical examination alone is insufficient—MRI remains necessary for precise diagnosis and surgical planning 4, 5
- MRI can change management from surgical to conservative in up to 48% of patients presenting with a locked knee 3, 2
Important Diagnostic Pitfalls
Avoid These Common Errors
- Do not skip radiographs initially, as they guide subsequent imaging decisions and may reveal fractures that alter management 1
- Beware of MRI pseudo-tears: The anterior meniscofemoral ligament can mimic a lateral meniscus tear on MRI and requires arthroscopic confirmation 6
- In elderly patients (>70 years), asymptomatic meniscal tears are extremely common, making MRI findings potentially misleading—correlate with clinical symptoms 1
- MR arthrography and MRA are not routinely indicated for meniscal tear diagnosis 3, 1
Special Considerations for Lateral Meniscus
- Lateral tibial plateau depression >11 mm on CT predicts higher risk of lateral meniscus tear 3, 1
- In ACL-injured patients, lateral meniscus oblique radial tears (LMORT) of the posterior horn are common and require specific classification for treatment planning 7
- Displaced lateral meniscus tears into the popliteal hiatus produce a characteristic "double popliteal tendon sign" on sagittal MRI cuts 8
Treatment Decision Framework
Surgical Indications
- Tears in the white zone (avascular) typically require partial meniscectomy 8
- Higher grade LMORT lesions (grades 3-4) should be surgically repaired at time of ACL reconstruction, as repair demonstrates biomechanical results comparable to intact meniscus and superior to partial meniscectomy 7
- Displaced tears causing mechanical symptoms (locking) warrant surgical intervention 8