Among major knee injuries, one of the most common is a tear to the anterior cruciate ligament (ACL), one of four ligaments that work together to form a hinged joint and stabilize the knee during movement. The ACL runs diagonally in the middle of the knee, preventing the shin bone (tibia) from sliding out in front of the femur, as well as providing rotational stability to the knee. It can be injured by sudden stops or changes in direction or from landing incorrectly from a jump. In addition to imaging and special tests for identifying meniscus tears and injury to other ligaments of the knee, physicians will often perform the Lachman test to see if the ACL is intact. Not all ACL tears require surgery.
ACL reconstruction surgery involves taking a piece of tendonous tissue to replace the ACL (tendons and ligaments share similar tissue composed primarily of collagen protein). The two most common sources of replacement tissue are the knee cap (patellar) tendon and the hamstring tendon, the muscle behind the knee. Tissue taken from a person's own body is called an autograft. Tissue taken from a deceased donor is called an allograft.
The underlying concept in reconstructive surgery is that a tendon is surgically placed into the knee exactly into the position where the torn ACL was located. The tendon is fixed to the bone with biodegradable screws. About 95 percent of the time the body will then reestablish the blood supply to the tendon, and over the weeks following this blood supply will bring new fibroblast cells that will repopulate the tendon, bringing it back to life. The "new living ACL" is seemingly just as good as the original and should last a lifetime. The operation is usually performed by an orthopedic surgeon using an arthroscope.