High Signal on Medial Aspect of Knee on MRI
High signal intensity on the medial aspect of the knee on MRI most commonly indicates bone marrow edema, meniscal pathology (tear or degeneration), or medial collateral ligament injury, depending on the specific anatomic location and signal characteristics.
Interpretation Based on Anatomic Location
Medial Meniscus Signal Changes
High signal that clearly extends to the meniscal surface on multiple images indicates a meniscal tear with >90% likelihood, representing an actual disruption that can be identified and treated arthroscopically 1.
High signal confined to the meniscal substance (not reaching the surface) most likely represents intrasubstance degeneration, not a true tear amenable to arthroscopic treatment 2, 3.
Signal seen on only one MRI image has much lower predictive value—only 55% of medial menisci with such signal are actually torn at arthroscopy 1.
When signal in the posterior horn of the medial meniscus does not unequivocally extend to the superior or inferior joint surface, a tear is unlikely (only 10% arthroscopic correlation), and conservative management is recommended 3.
Bone Marrow Edema Pattern
High T2/FLAIR signal in the medial femoral condyle or medial tibial plateau represents bone marrow edema, which appears as decreased signal on T1-weighted and increased signal on T2-weighted sequences 4.
Bone marrow lesions (BMLs) in the medial compartment correlate strongly with knee pain, especially in males or patients with family history of osteoarthritis, and new or increasing BMLs are associated with increased pain 5.
Subchondral insufficiency fractures most commonly involve the medial femoral condyle in middle-aged to elderly females and present as bone marrow edema on MRI, often with normal initial radiographs 5.
Medial Collateral Ligament and Soft Tissue
High signal along the medial collateral ligament indicates ligamentous injury, with MRI demonstrating high accuracy (sensitivity 91-93%, specificity 88-96%) for ligamentous pathology 6.
Paratendinous soft tissue edema with intermediate to high T2 signal indicates medial epicondylalgia involving the common flexor tendon 5.
Age-Related Interpretation Pitfalls
In patients over 70 years, most meniscal tears are asymptomatic, so MRI findings may be misleading and should not automatically be attributed as the pain source 7, 8.
For patients aged 45-55 years, meniscal tear prevalence does not differ between painful and asymptomatic knees, making it impossible to attribute symptoms to the tear based on imaging alone 5, 8.
In elderly patients with osteoarthritis, prioritize bone marrow lesions and synovitis/effusion over meniscal tears when correlating imaging with pain, as these findings better predict symptomatic disease 5, 8.
Clinical Decision Algorithm
Identify the exact anatomic structure showing high signal (meniscus, bone, ligament, or soft tissue) 9.
For meniscal signal: Determine if signal definitively extends to the articular surface on multiple images—if yes, likely tear; if equivocal or confined to substance, likely degeneration 1, 2, 3.
For bone marrow signal: Assess for subchondral insufficiency fracture pattern (especially medial femoral condyle in older females) versus traumatic bone marrow contusion 5.
Consider patient age: In elderly patients, do not over-interpret meniscal tears; focus on bone marrow lesions and synovitis as pain generators 7, 8.
Correlate with clinical presentation: MRI should supplement, not replace, history and physical examination findings 3.
Common Pitfalls to Avoid
Do not diagnose a meniscal tear when high signal does not unequivocally reach the meniscal surface—this represents degeneration in 90% of cases 2, 3.
Do not attribute knee pain to meniscal tears in elderly patients without considering bone marrow lesions and synovitis, which are better pain predictors 5, 8.
Do not rely on signal seen on only one MRI slice—tears are much less likely (45-70% false positive rate) compared to signal on multiple images 1.
Do not skip initial radiographs—they are essential to exclude fractures and assess for osteoarthritis before attributing symptoms to soft tissue findings 7, 6.