Purpose: The purpose of this study was to determine the utility of the radiographic 'condylar cut-off sign' to detect the presence of a complete discoid lateral meniscus in children and adolescents.
Methods: The radiographs of 166 subjects younger than 17 with complete discoid lateral meniscus as well as 153 age- and sex-matched subjects with normal meniscus were reviewed. The condylar cut-off sign, judged by the prominence ratio of the medial and lateral femoral condyles in tunnel view radiographs, was assessed. The prominence ratio was compared between the complete discoid and the normal group. Subgroup analysis was performed by dividing the subjects into two groups: those younger than 10 and those between 10 and 16. When a significant difference was identified between the discoid and the normal group, the sensitivity, specificity and positive and negative predictive values (PPV and NPV) according to the best cut-off value for the prominence ratio was determined.
Results: The prominence ratio was significantly different between the complete discoid and normal groups in children and adolescents as a whole (p < 0.001). The ratio was also different in the subgroup aged 10-16 (p < 0.001), but not in the subgroup younger than 10 (n.s.). In children and adolescents as a whole, the condylar cut-off sign showed 50.6 % sensitivity, 79.4 % specificity, 73 % PPV and 59.8 % NPV with a cut-off value of 0.8. In the subgroup aged 10-16, the values were higher, with 65.3 % sensitivity, 79.6 % specificity, 76.2 % PPV and 69.6 % NPV using the same cut-off value.
Conclusion: The condylar cut-off sign has a moderate degree of diagnostic utility for complete discoid lateral meniscus in adolescents aged 10-16. Early screening of complete discoid lateral meniscus in children or adolescents is important due to its vulnerability to meniscal tearing or arthrosis. The radiographic condylar cut-off sign can be used as a screening or supplementary diagnostic tool to detect the presence of a complete discoid lateral meniscus in this age group.
Level of evidence: II.
Keywords: Children; Condylar cut-off sign; Discoid lateral meniscus; Knee.