Diagnostic Testing for Meniscus Tear in Medial Knee Pain
MRI without IV contrast is the definitive imaging test for diagnosing meniscus tears in patients with medial knee pain, but only after initial plain radiographs have been obtained. 1
Initial Diagnostic Approach
Step 1: Plain Radiographs First
- Always begin with plain radiographs (anteroposterior, lateral, tunnel, and tangential patellar views) as the initial imaging study to rule out fractures, degenerative changes, loose bodies, and other osseous pathology before proceeding to advanced imaging. 1, 2
- Approximately 20% of patients inappropriately receive MRI without recent radiographs, which represents a common pitfall in clinical practice. 3
Step 2: Clinical Examination Tests
While imaging is essential, specific clinical tests can support the diagnosis:
- McMurray's test demonstrates 54-80% sensitivity and 73-89% specificity for medial meniscus tears, with significant diagnostic value (p=0.007). 4, 5, 6
- Joint line tenderness shows 50-70% sensitivity and 53-67% specificity for medial meniscus tears, with lower individual diagnostic accuracy. 4, 7, 6
- Thessaly test demonstrates 56-77% sensitivity and 76-88% specificity for medial meniscus tears. 4, 7
- Combining at least two positive clinical tests substantially improves diagnostic accuracy to 85% sensitivity and 73% specificity for medial meniscus tears, approaching MRI-level performance. 4
Step 3: MRI Without IV Contrast
If radiographs are normal or show only joint effusion but symptoms persist, proceed to MRI without IV contrast. 1
MRI Performance Characteristics:
- Pooled sensitivity of 88% and specificity of 90% for detecting meniscal tears across multiple studies. 1, 2
- 90% sensitivity and 83% specificity specifically for medial meniscus tears when correlated with arthroscopy. 4
- MRI accurately depicts meniscal abnormalities, articular cartilage damage, and associated bone marrow lesions with superior contrast resolution and multiplanar imaging capability. 1, 2
Alternative Imaging Modalities (Limited Role)
Ultrasound
- Ultrasound has 85-88% sensitivity and 86-90% specificity for meniscal tears, with highest specificity in recent injuries (<1 month). 1
- However, ultrasound enables only limited visualization of portions of the menisci and is not routinely used as the primary diagnostic modality for suspected meniscal tears. 1
- Ultrasound is excellent for detecting joint effusions (91% positive predictive value for internal derangement) and quadriceps tendon tears (approaching 100% sensitivity/specificity). 1
CT Arthrography
- CT arthrography may evaluate menisci with 86-100% sensitivity and specificity but is not routinely used as first-line imaging. 1
MR Arthrography
- MR arthrography is not routinely indicated for suspected meniscal tears. 1
Critical Clinical Considerations
Age-Related Context
- The majority of people over 70 years have asymptomatic meniscal tears, and the likelihood of a meniscal tear in either a painful or asymptomatic knee is not significantly different in patients 45-55 years of age. 2
- The key distinguishing feature of a symptomatic tear is the presence of mechanical symptoms (such as locking) combined with focal tenderness, not just the presence of a tear on imaging. 2
Common Pitfalls to Avoid
- Never order MRI without obtaining recent radiographs first unless there is a contraindication to radiography. 3
- Do not rely solely on individual clinical tests (McMurray, joint line tenderness) to make surgical decisions, as they have low diagnostic value when applied individually. 6
- Consider referred pain from hip or lumbar spine pathology if knee radiographs are unremarkable. 3
- Document laterality using specific codes (right/left) rather than unspecified codes for improved clinical clarity. 3