Injuries to the menisci can occur from twisting your knee too far, or simply because of wear and tear from aging.
There are many types of meniscal tears. They can tear in all directions, up and down, across and even in a combination of directions.
Most meniscal tears occur in the back portion of the meniscus. When the knee bends, like when you are squatting, the thighbone pushes against this torn area causing pain. Furthermore, a meniscal tear can cause symptoms of your knee giving out, clicking or catching and sometimes locking. This occurs because the torn piece of the meniscus can actually move around inside the joint because the space in the joint is very small. When the torn piece of the meniscus moves, it often becomes caught between the bones of the joint, the thighbone and shinbone.
When tissue is damaged, blood provides the necessary nutrients for it to heal properly. Unfortunately, most of the meniscus has no blood supply and cannot usually heal itself when it is damaged.