So having a displaced meniscus root mean that the meniscus is already torn? how did it get torn? can it be fixed? please explain

Meniscal tear: Meniscal tears tend to happen with twisting motions of the knee with weightbearing. Sometimes they can be repaired, often the torn part needs to be excised (partial meniscectomy).

Yes.: Usually a patient will remember a distinct injury that will be painful on the inner/back side of your knee. Arthroscopic surgery can take care of the problem.