The meniscus is avascular structure within the knee. There are two of them in each knee on the medial (inside) and lateral (outside) of the knee. They are c-shaped and have no direct blood supply. They derive their nutrition from the fluid in the knee and from blood seeping in from the peripheries of the meniscus. They function as shock absorbers within the knees and essentially the "cushions" in the knee.
The problem when one injures the meniscus, is that it does not heal itself as it has no blood supply. For this reason, most meniscal surgeries involve removing the torn piece. The meniscus is however there for a reason and an attempt should be made, where possible, to save the meniscus and repair it.
At the time of arthroscopy, if the surgeon decides that the tear is repairable (most tears are irreparable), he will go ahead and suture the torn meniscus. We then try to stimulate blood to seep into the repair and aid healing. This is done by making "vascular channels" in the surrounding soft tissue within the knee. This then causes blood to ooze into the repair.
Another means of aiding the healing is to release stem cells into the knee. This is done by making small holes in the bone within the knee, in an area that is unimportant and not a weight bearing area. The area most commonly used is the notch of the femur. This allows stem cells to ooze out of the bone and into the knee, where the stem cells can reach the repaired area and aid healing.