Avulsion of the meniscal root.
Root avulsion is a precursor to meniscal extrusion
In a meniscal root avulsion the meniscus is initially not damaged and neither is its connections to the capsule around the outer rim - it is just the root that is torn out. If not promptly repaired surgically, however, the meniscus is likely to become incompetent and the joint unstable, and the meniscus may extrude over the edge of the tibial plateau.
Avulsion of both posterior meniscal roots associated with acute rupture of the anterior cruciate ligament Mariani PP, Iannella G, Cerullo G and Giacobbe M. J Orthop Traumatol. 2015 Sep; 16(3): 259–262.
Biomechanical Consequences of Lateral Meniscal Posterior Root Avulsions. Geeslin AG, Civitarese DM, Turnbull TL, Dornan G, Fuso F and LaPrade RF. Orthop J Sports Med. 2015 Jul; 3(7 suppl2): 2325967115S00111.
Incidence, Presentation, and Treatment of Pediatric and Adolescent Meniscal Root Injuries. Wilson PL, Wyatt CW, Romero J, Sabatino, MJ and Ellis HB. Orthop J Sports Med. 2018 Nov; 6(11): 2325967118803888.