Meniscus tears are common. They account for one in 70 cases and have approximately 60 to 70 cases per 100,000 persons. Medial meniscus posterior root tears, or MMPRTs, represent bony avulsions or complete radial tears within one centimeter of the root origin. Functionally, they're equivalent to total meniscectomy with loss of hoop stress and increased peak contact forces. The menisciotibial ligament, or MT ligament, originates at the posterior medial aspect of the tibia, and it anchors the posterior body and horn of the meniscus. Recently, we've been learning more about its biomechanical role, namely that it serves in meniscus stabilization, centralization, and most importantly, as a restraint to extrusion. Extrusion has been associated with posterior medial meniscus root tears and the subsequent and rapid osteoarthritis that oftentimes follows them. Along with this recent recognition of extrusion in the absence of meniscus tear, we've also noticed that root repair does not always correct the extrusion. Therefore, extrusion is likely due to additional factors other than just the root attachment itself. Therefore, the purpose of our study was to understand the association between MT ligament, the medial meniscus extrusion, and subsequent root tears. In doing so, we hope to determine the progression and ideology of meniscus extrusion over time. We reviewed serial MRIs from 2010 to 2020 at a single academic institution. Extrusion criteria consisted of two or more MRIs with at least one demonstrating extrusion and one demonstrating a root tear. Of note, this was independent of the relative timing of the above two factors. In terms of exclusion criteria, we excluded patients with prior knee surgery or patients that had an intervention between their MRIs. All of our MRIs were performed on 1.5 to 3 Tesla institutional scanners as per a standardized institutional protocol. They're analyzed independently by two board-certified MSK radiologists, and in terms of outcomes, we looked at extrusion, MT ligament status, and the presence of a root tear. Overall, we looked at 27 root tears in 26 patients. Their average age was 56. Average follow-up was two years, and they had a median of two MRIs, but some patients had three or four MRIs. In terms of conversion to a root tear, this occurred at a mean of 1.7 years after the patient's initial MRI. What I'd really like to highlight of our results is that MT ligament disruption as well as extrusion was present on MRI prior to the MRI that then demonstrated root tear for every single patient. This is an example case right here. At time zero, there's MT ligament edema, but the root is intact. Four months later, the patient had continued pain, had a repeat MRI. Here there's MT ligament attenuation. Now there's meniscus extrusion, and there is partial root tearing, but some fibers remain in continuity. Eight months later, there's a repeat MRI. At this point, the MT ligament is completely disrupted. The root is completely torn. The meniscus has displaced. At final follow-up, extrusion progressed in 96% of knees, namely all knees had extrusion pre-tear at an average of 3.3 millimeters. Post-tear, this increased to 5.5 millimeters. And for those patients with three or four MRIs, this increased to 5.8 millimeters at the time of final follow-up. We also noted a modified outer ridge grade progression, namely medial femoral condyle ICRS, sorry, outer bridge grade went from 2.4 to 3.5, whereas medial tibial plateau outer bridge grade went from 1.6 to 3.0, both of these being statistically significant. Additionally and noteworthily, nine patients or a third of the cohort converted to arthroplasty at a mean of three years after their initial MRI or one and a half to two years after their root tear. Given our findings, we propose the following root tear chronology. Initially, patients have MT ligament stress and attenuation. As the MT ligament attenuates and stretches, there's early extrusion. Subsequently, there's a medial meniscus posterior root tear and increasing extrusion as now both the MT ligament and the root are gone in terms of resisting extrusion. And finally, there's the rapid onset of osteoarthritis. In terms of our discussion, there's currently a positive literature on the chronologic etiology of root tears. We believe our study is novel and its inclusion of two or more serial MRIs, and it suggests that extrusion and MT ligament disruption predisposes to root tears. This also aligns with previous studies which have demonstrated extrusion without root tear. Again, I'd like to highlight that all patients had MT ligament disruption prior to their root tear. This is important as isolated root repair does not fully correct meniscus extrusion, and this serves a potential role of MT ligament repair or meniscus centralization at the time of root repair. In conclusion, all patients demonstrated MT ligament disruption and meniscus extrusion prior to medial meniscus posterior root tear. Our findings suggest MT ligament disruption and extrusion represent early predisposing events to meniscus root tear. And furthermore, this provides a possible explanation as to why extrusion is not corrected with isolated medial meniscus root repair. Thank you for your time and attention.

meniscus tears

MT ligament

extrusion

root tear

arthroplasty