The "sleeper's sign" is valid and suggestive of a medial sub-meniscal flap tear.

<bold>Purpose: </bold>To describe, evaluate and validate the diagnostic performance of a new clinical sign, the sleeper's sign, for the diagnosis of a medial submeniscal flap tear (MSMFT).<bold>Methods: </bold>This retrospective single-center series included patients aged 18-55 years old who underwent arthroscopic treatment in 2013-2015 for a medial meniscal tear. This study was performed according to STARD (standards for reporting of diagnostic accuracy) guidelines, and the reference test was a peroperative diagnosis of a MSMFT. The preoperative consultation reports were all analyzed to search for the sleeper's sign, defined as night time medial tibiofemoral pain when the patient is in the fetal position with both knees in contact and no pain during daytime activities.<bold>Results: </bold>Three-hundred and ten patients responded to the study criteria, mean age 41.7 ± 9.7 years old. The sleeper's sign was identified in 39 (12.6%) patients and a MSMFT was confirmed during arthroscopy in 47 (15.2%) cases, with significant agreement between this sign, arthroscopy (kappa = 0.78, p = 10-4) and MR-imaging (kappa = 0.72, p < 0.0001). The performance parameters of the sleeper's sign were: sensitivity 74.5 ± 12.5%, specificity 98.5 ± 1.6%, Youden index 0.73 and accuracy 96.9%. MR imaging was found to be more sensitive (91.5 ± 8%). Multivariate analysis identified the sleeper's sign as a risk factor of MSMFT during arthroscopy: OR 131.9 CI 95% [26.9-646.2], p < 0.0001 and a bone edema next to the flap tear on MR-imaging: OR 13, CI 95% [1.9-7.1], p = 0.008.<bold>Conclusion: </bold>The "sleeper's sign" is a new, valid, highly specific clinical sign for the diagnosis of a medial submeniscal flap tear. MRI was found to be more sensitive than the sleeper's sign.<bold>Level Of Evidence: </bold>II. [ABSTRACT FROM AUTHOR]