Are MR imaging signs of meniscocapsular separation valid?

PURPOSE: To define the positive predictive value (PPV) for the magnetic resonance (MR) imaging diagnosis of meniscocapsular separation in the knee. MATERIALS AND METHODS: The MR reports of 52 patients aged 16-75 years who had a prospective MR diagnosis of meniscocapsular injury were correlated with arthroscopic results. MR images obtained in 50 of these patients were retrospectively reviewed for specific signs of meniscocapsular separation, which included meniscal displacement peripheral meniscal corner tears, increased perimeniscal signal intensity, fluid deep to the medial collateral ligament, and abnormal lateral fascicles. MR findings were correlated with arthroscopic findings. RESULTS: For the prospective MR interpretations, the PPV for meniscocapsular separation was 9% medially and 13% laterally. Meniscal displacement (measured from the meniscal edge to the tibia) was as great as 10 mm medially or 13 mm laterally without meniscocapsular tears at arthroscopy. Meniscal displacement did not correlate with effusion. Meniscal corner tears had a PPV of 0% medially and 50% laterally. Fluid at the meniscocapsular border and fluid deep to the medial collateral ligament were poor predictors of meniscocapsular abnormalities. Abnormal-appearing meniscal fascicles had a PPV of 8% for lateral meniscocapsular-separation. CONCLUSION: The PPV for the MR diagnosis of meniscocapsular separation is low; the reported MR signs correlate poorly with arthroscopic findings.