You didn't mention the cause of your meniscal tear. Were you in an accident or playing sports of some kind? Most meniscal tears occur in athletes, overweight adults, and aging adults.
In the case of young adults and meniscal injury, a force with a twist is usually what causes a meniscal tear. In obese or older adults, break down of the cartilage occurs over time. The cartilage may thin out and disintegrate over time. A sudden force can dislodge it.
The meniscus is a C-shaped piece of tough cartilage in the knee. There's one on each side of the knee joint: medial (inner edge) and lateral (outer edge). Medial meniscus tears are by far the most common. Next come lateral tears followed by tears of both at the same time.
In a recent study of 150 adults between 17 and 113 years old, 90 had a medial tear and 28 had a lateral tear. Only 9 had tears of both menisci.