The "sleeper's sign" is valid and suggestive of a medial sub-meniscal flap tear. - Lefevre, Nicolas; Klouche, Shahnaz; Sezer, Hasan Basri; Gerometta, Antoine; Bohu, Yoann; Lefevre, Edouard; Study investigators; Grimaud, Olivier; Herman, Serge; Meyer, Alain (Knee Surgery, Sports Traumatology, Arthroscopy, 2021)