Does flexion MRI improve the diagnosis of meniscal ramp lesions in children?

BACKGROUND: Ramp lesions of the knee, characterized by tears at the meniscocapsular junction of the posterior horn of the medial meniscus, are frequently associated with anterior cruciate ligament (ACL) ruptures, occurring in approximately 28% of pediatric cases. These lesions are often underdiagnosed because their subtle features are difficult to detect on conventional MRI scans performed with the knee in full extension. Emerging evidence suggests that MRI performed with the knee in flexion may improve the visualization of ramp lesions by allowing joint fluid to enter the posterior recess, thereby enhancing diagnostic accuracy. HYPOTHESIS: The diagnostic performance of a knee MRI is better in flexion than in extension. MATERIALS AND METHODS: A prospective comparative study was conducted on 62 patients, with a mean age of 14 years (range 10-18). All patients had a knee MRI in both extension and flexion before ACL reconstruction. The MRI outcome measures were: fluid interposition between the capsule and the posterior horn of the medial meniscus, and fluid infiltration behind the meniscus. The diagnosis of meniscal ramp lesion was confirmed during arthroscopic exploration, our gold standard. RESULTS: Eleven patients (17.7%) had a ramp injury at arthroscopy. Extension MRI identified 3 of these cases, whereas flexion MRI identified 9. Flexion MRI had a sensitivity of 82% and a specificity of 65%, while extension MRI had a sensitivity of 27% and a specificity of 92%. The degree of agreement (concordance) between flexion MRI and the gold standard was low (p = 0.05) but better than that between extension MRI and the gold standard, which was very low (p = 0.16). 18 patients were diagnosed with a ramp lesion on flexion MRI, but not confirmed on arthroscopy. DISCUSSION: Clinically, incorporating flexion MRI into preoperative protocols could reduce missed diagnoses of ramp lesions, which are important to identify as they influence surgical planning and patient prognosis. Among the 18 false positives on flexion MRI, there were 2 bucket-handle tears, 1 radial tear and 1 vertical tear of the medial meniscus. LEVEL OF EVIDENCE: II; Prospective Comparative Study.