Not Only Extrusion! A Thickened Medial Meniscus on Coronal MRI Also Points to Medial Meniscal Posterior Root Tears.

Medial meniscal posterior root tears (MMPRTs) can be challenging to diagnose even on magnetic resonance imaging (MRI). Despite several "signs" for MMPRTs, such as the "ghost sign" on sagittal images, truncation or cleft sign on coronal images, bony edema at the tibial root attachment, and meniscal extrusion on coronal images, the finding of increased maximal thickness of the medial meniscus (MTMM) on coronal images provides a simple, intuitive, and reproducible measurement for knee surgeons to identify MMPRTs. With a cutoff of 10 mm providing a sensitivity of 0.771 and specific of 0.942, the thickened meniscus sign is a valuable addition to the MMPRT literature. Even if exact measurements are not utilized due to racial anatomical or age related differences in baseline meniscal size, the identification of a thickened medial meniscus on coronal sequences still provides a clue to avoid missing MMPRTs, as well as differentiating them from other meniscal tear patterns, such as radial tears.