MRI findings with arthroscopic correlation for tear of discoid lateral meniscus: comparison between children and adults

Background: Discoid lateral meniscus is more susceptible to tear than normal meniscus. A comparison study for tear types of discoid lateral meniscus between children and adults has not been reported. Purpose: To compare tear type of surgically proven discoid lateral meniscus between adults and children, and to analyze diagnostic performance for tear type of discoid lateral meniscus using magnetic resonance imaging (MRI). Material and Methods: Knee MR examinations of 53 children and 84 adults who had discoid lateral menisci identified at arthroscopic surgery were retrospectively evaluated with consensus by two radiologists for tear type including displacement of torn meniscus. MRI findings were compared with surgery as the reference standard. The difference of tear type and displacement of torn meniscus between children and adults in arthroscopic finding was analyzed using the Fisher's exact test or the Chi-squared test with Bonferroni's correction. Results: At arthroscopy, complex tear (children, n = 22; adults, n = 56) and peripheral tear (children, n = 17; adults, n = 8) differed significantly between children and adults (P = 0.006 for complex tear, P = 0.002 for peripheral tear). Displacement of torn meniscus was seen in 28 cases of children and 41 cases of adults, not a statistically significant difference. In children, the positive predictive value (PPV) for horizontal tears was 90%, for peripheral tears 60%, and for complex tears 57%. PPV in adults for horizontal tears was 78%, peripheral tears 25%, and for complex tears 89%. Conclusion: Complex tears were more commonly found in adults than children and peripheral tears were more commonly found in children than adults. MRI has a high PPV for diagnosing the type of tear in discoid lateral meniscus for horizontal tears in children and adults and for complex tears in adults.