What kind of tear in a displace mensicus root please explain?

Tear at attachment. A meniscal root tear is a tear where the meniscus attaches posteriorly. If it displaced, the pt would need arthroscopic surgery to see if it could be repaired.
Serious. The meniscus is a crescent-shaped structure made of cartilage that acts as a shock-absorber in the knee. The end of the structure attaches to the tibia and is called the root. The majority of the outside of the structure has attachments to the capsule (laterally) and to the capsule and mcl (medially). A root tear means that this tether has been compromised.