Ligaments are strong bands of tissue that fasten the bone ends together and stabilize the joint.
There are two ligaments inside the knee that can be reconstructed with the assistance of the arthroscope: The cruciate ligaments restrict both the forward and backward motion of the knee and its rotation. They may be torn by sudden twisting motions of the knee beyond its normal range.
Not all cruciate ligament injuries need to be reconstructed; it depends on your age, level of activity, type of activity, and what you expect from your knee. A frank discussion with your doctor will help both of you determine whether surgery would be beneficial.
If you enjoy active sports, it would be appropriate to have surgery.
If you have a sedentary-type job and are not active in your leisure time, you may not require surgery.
Unfortunately, a simple repair by suturing the torn ligament together again is not effective. A successful repair involves completely replacing the torn ligament. There are a number of ways to accomplish this, depending on the preference of the surgeon.

Ligament reconstruction is most commonly performed utilizing using the hamstring tendons from the back of the knee. The surgeon folds over these tendons four times into a strong, thick band and passes it through the knee. The advantage of this technique is that the patella tendon is left intact. There does not appear to be any damage caused to the hamstring muscles. Results using this technique are extremely good. Both of these methods require an extra skin incision (about 1 inch in length) to harvest the tendons to be used.
Some surgeons use the patella tendon graft. The orthopedic surgeon takes the central strip of the patella tendon and roots this through the knee through tunnels drilled in the tibia and femur. This creates a new ligament to replace the torn one.