Radiographic evaluation of complete and incomplete discoid lateral meniscus

• Radiographic features of fibular height, lateral joint space, cut off sign can be used for screening of a complete DLM
• Radiographs are not a reliable screening tool for an incomplete DLM.
• Thin variant of complete DLM seem to have plain radiographic features similar to incomplete DLM.

ObjectivesThe aim of this retrospective study was (1) to evaluate the radiographic features to differentiate arthroscopically confirmed complete and incomplete discoid lateral meniscus (DLM) (2) to determine the cutoff values for any parameter that was found to differentiate complete from incomplete DLM.Materials and MethodsWe retrospectively analyzed plain knee radiographs of 130 arthroscopically proven DLM. Seventy-nine patients had complete DLM and 51 patients incomplete DLM. Knee radiographs from 52 patients with arthroscopically proven normal lateral meniscus acted as control group. Radiographic parameters measured included fibular height, lateral joint space, condylar cutoff sign, height of lateral tibial spine, obliquity of lateral tibial spine, squaring of the lateral femoral condyle, and cupping of the lateral tibial plateau.ResultsAmong radiographic parameters, high fibular head, widening of the lateral joint space and femoral condylar cutoff sign showed statistically significant (p < 0.0001) differences between complete and incomplete DLM. At specific threshold points of fibular height < 11mm, lateral joint space > 6mm and condylar cutoff sign < 0.80, the diagnosis of complete DLM revealed 87.3% sensitivity, 81.6% specificity and 78.4% positive predictive value (PPV) for the fibular height, 81.0% sensitivity, 86.6% specificity and 83.1% PPV for the lateral joint space, and 86.1% sensitivity, 83.5% specificity and 80% PPV for the condylar cutoff sign.ConclusionsRadiographic features of fibular height, lateral joint space and condylar cut off sign can be used for screening of a complete type of DLM. However, radiographs are not a reliable screening tool for an incomplete DLM.Level of evidenceIV, Case Series