It is easy to understand why they are commonly torn. They are extremely important structures because they protect the ends of the femur and tibial bones from damage. Without these cartilages, the ends of the femur and tibial bones would be unprotected and would grind on each other with every step you took. This would lead to a wearing away and deterioration of the ends of these bones. When this happens, you have arthritis.
Arthritis is the painful and irreversible deterioration of the ends of the two bones.
When and arthroscope is inserted in a knee, both menisci can be seen along with surfaces of the femur, tibia, and patella. A typical view of a normal medial meniscus is shown below. Please also note the femur bone above the meniscus and the tibial bone below the menicus. Once the meniscal tear is found, it is trimmed so that the torn tissue is removed. This is usually done with a combination of instruments called biters and shavers .