MR imaging of displaced meniscal tears of the knee - Importance of a "disproportional posterior horn sign"

Purpose: Meniscal tears associated with displaced fragments are clinically significant. We propose the "disproportional posterior horn sign" as a supp ortive criterion to identify a posterocentrally displaced meniscal fragment on MR imaging studies. If the meniscal posterior horn in the central porti on appears larger than that in the peripheral section, it is considered pos itive for "disproportional posterior horn sign". Material and Methods: MR images obtained in 42 patients with 43 lesions, co nfirmed to have displaced meniscal tears, were included in this study. The MR images were retrospectively evaluated for the presence of the "dispropor tional posterior horn sign", as well as the other known signs. Results: The "disproportional posterior horn sign" was seen in 9 (20.9%) of 43 lesions, including 1 lateral discoid meniscal tear, 5 lateral meniscal tears and 3 medial meniscal tears. Five of them also had other signs of a d isplaced meniscal fragment. However, the remaining 4 cases only exhibited t he "disproportional posterior horn sign". For the other MR signs, the "abse nt bow tie sign" was detected in 40 (93%) of 43 lesions, the "flipped menis cus sign" in 27 (62.8%) of 43 lesions, the "double posterior cruciate ligam ent sign" in 17 (39.5%) of 43 lesions and the "notch fragment sign" in 22 ( 51.2%) of 43 lesions. Conclusion: The "disproportional posterior horn sign" is helpful in demonst rating a posterocentrally displaced meniscal fragment, especially when othe r characteristic signs are unremarkable or absent.