Arthroscopic and magnetic resonance images of an inferiorly displaced meniscal flap tear.

Dear Editor, The menisci are important tissues in the healthy knee due to their shock absorption and load distribution properties. Meniscal tears are important clinically due to pain and swelling and the mechanical symptoms they cause such as locking. The arthroscopic anatomical classifi cation of meniscal tears was described by Dandy in 1990.1 In the paper, he noted that the majority (69%) of meniscal tears were vertical types which gave rise to bucket handle tears. The other types of tear morphology included horizontal which gave rise to fl aps, radial, cystic degeneration, and tears with inverted fragments. In particular, the paper reported that 6% of medial meniscal tears were inverted fragments which arose from horizontal fl ap tears or ruptured bucket handle fragments. Such inverted fragments could be found tucked beneath the intact meniscal rim. Dandy made a note that inverted tears were often diffi cult to recognise but could be identifi ed by thickening and rounding of the meniscal margin. Various papers published in radiological journals have described the magnetic resonance imaging (MRI) and ultrasonographic appearance of medial meniscus tears with an inferiorly displaced fl ap.2-5 On MRI, the displaced fl ap could be seen adjacent to the medial tibial plateau and deep to the medial collateral ligament.2 It was noted, however, that inferior fl ap tears can be inconspicuous and easily overlooked by both radiologists and orthopaedic surgeons. Anecdoctally, such fl ap tears with displacement of the fragment inferiorly into the medial gutter are not a rare fi nding during arthroscopic debridement. Despite this, the orthopaedic literature contains few reports on the arthroscopic appearance of the inferiorly displaced fl ap tear. We present a case report of a patient with an infolded medial meniscal fl ap tear identifi ed at arthroscopy. This fi nding was not noted in the initial report of the MRI scan. Postoperatively, the MRI fi lms were reviewed and the inferiorly displaced fl ap was identifi ed retrospectively. The images of both the arthroscopy and the MRI scan are presented.