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.
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.