Research On The Dimensions Of Knee Radiographs In Discoid Lateral Meniscus

Purpose: To establish the radiologic features of discoid lateral meniscus by special dimensions and analysis of the knee radiographs of discoid lateral meniscus, comparison with normal controls.Materials and Methods: The knee radiographs of 76 cases which proven by the arthroscopy, including 46 cases of complete type and 30 cases of incomplete type discoid lateral meniscus, are used as experiments. Knee radiographs of 80 cases with normal meniscus proven by arthroscopy are used as controls. We exclude patients who had significant degenerative knees and had significant trauma history. Values and characteristics are all observed before operation. All patients and controls undergo a standardized knee radiograph that is a non-weight bearing anterior-posterior and lateral view with a tube to film distance of 1.2 meters. The absolute values and relative normalized values of specific knee dimensions are compared between the discoid lateral meniscus and the controls. The values are lateral joint space, lateral intercondylar spine, fibular head's height; the characteristics are cupping of the lateral tibial plateau, squaring of the lateral femoral condyle and notching of the lateral femoral condyle. Results:Among these dimensions, widened lateral joint space and high fibular head show statistical signification differences between the discoid lateral meniscus group and the control group (p<0.01). The incidence of squaring of the lateral femoral condyle is higher in discoid lateral meniscus. The incidence of cupping of the lateral tibial plateau and notching of the lateral femoral condyle show no statistical differences. In the height of the fibular head, an absolute value below 12mm and the normalized ratio below 0.15 are considered to be the cutoff value, the sensitivity of diagnosis of lateral discoid lateral meniscus is 78%, the specificity is 65%. In the lateral joint space, an absolute value above 5mm and the normalized ratio above 0.06 are to be the cutoff value, the sensitivity of diagnosis of lateral meniscus is 73%, the specificity is 70%. If either the height of the fibular head and the lateral joint space is positive, the sensitivity is increased to 87%. Conclusions: Although the features mentioned above are not immediate, from our research we conclude that the plain radiography is useful in screening discoid lateral meniscus with the cutoff value of the height of fibular head and lateral joint space.