The roots extend into the bone of the tibia and anchor the horns of the meniscus.
A root tear separates the root from the rest of the meniscus, and makes the meniscus incompetent.
Function of the meniscal root
A key function of the meniscus is the conversion of vertical load into circumferential load, so that forces are displaced to the outer edges of the meniscus rather than right through the cartilage of the two bones where they make contact. The integrity of the root is essential and a tear here is a potential disaster because if left unrepaired the situation is equivalent to a meniscectomy. However, surgeons have only understood this fairly recently and repair of a meniscus root tear is not a skill yet acquired by most knee surgeons.