There are three methods of creating a replacement ACL. The first, shown above, uses the patellar tendon, which connects the patella to the tibia. The middle third of the tendon and a small portion of bone on either end is harvested and used as the new ACL. This is called a patellar tendon autograft, because your own tissue is used.
Another autograft method uses the semitendinosus-gracilis (hamstring) tendons, which connect muscles in the back of the thigh to the lower leg. Two small portions of these tendons are harvested and removed through a small incision in your leg, then they are looped to form a strong new ACL.
The third method of creating a replacement ACL uses an allograft, meaning the tendon comes from a source other than your own body, such as a donated achilles tendon.