The characteristic arthroscopic 'eyelid- turnup' sign indicated for partial-thickness longitudinal medial meniscus tear.

BACKGROUND: Medial posterior horn meniscal tear is difficult to be visualized in full view during arthroscopy and is occasionally undetected when the superior surface seems intact. OBJECTIVE: The purpose of this study is to describe a characteristic arthroscopic sign indicating the occult partial-thickness longitudinal medial meniscus tear extending only to the inferior articular surface. METHODS: This study was a retrospective analysis of available arthroscopic knee surgery between January 2016 and December 2017. The videos were studied and data was recorded for the number of cases showing the presence of 'eyelid-turnup' sign and coexisting partial-thickness medial meniscus tear. Sensitivity and positive predictive value of the sign were calculated. RESULTS: Of all the 491 videos of medial meniscal tear available for review, partial-thickness longitudinal medial meniscus was torn in 26 cases. Six out of 26 patients could be diagnosed with partial-thickness longitudinal tear under direct vision. Of the other 20 patients which could not be diagnosed under direct vision during arthroscopy until the tear was pressed by a probe, 17 patients were diagnosed by the positive 'eyelid-turnup' sign. The other 3 patients showed negative 'eyelid-turnup' sign and were then diagnosed by the hints of preoperative MRI and intra-operative exploration. The sensitivity of the sign was 85%; the positive predictive value was 89.5%. CONCLUSIONS: The 'eyelid-turnup' sign of meniscus pressed by a probe at arthroscopy is a characteristic indicator for occult inferior partial-thickness longitudinal tears of midbody and posterior horn. Early identification of this special sign may help reduce the likelihood that the occult partial-thickness longitudinal tear will be missed during arthroscopy.