ACL Reconstruction: The Technical Stuff
The Anterior Cruciate Ligament (ACL) is formed from two distinct bundles. The Posterolateral bundle (PL) is responsible for providing stability with the knee straight, while the Anteromedial bundle (AM) provides stability with the knee bent. By far the most important bundle for daily function and sporting activities is the PL bundle. Recent studies have shown better results and suggest better long-term function when the PL bundle is reconstructed.
Graft Choices
There are many different grafts that can be chosen for ACL reconstruction. Determing he “right” graft for you involves factors such as your tissue extensibility, availability of graft and number of ligaments needing reconstruction. Each has advantages and disadvantages, but ultimately all will give good results when placed in the proper position.
Autograft
Auto means self, and autografts are taken from your own body. The choices include hamstring tendons, quadriceps tendon and patellar tendon. Using autograft results in less cost, no chance for disease transmission, but has some donor related morbidity. I prefer to use a double looped hamstring graft since it more closely recreates the normal double bundle anatomy of the native ACL and causes very little donor morbidity.
Allograft
Allo means other, and allograft comes from donated human tissue. The choices are many and include hamstring tendons, quadriceps tendon, patellar tendon, Achilles tendon, and tibialis tendon. These donated tissues are obtained from nationally accredited tissue banks that maintain strict criteria for their grafts. There is some inherent risk of disease transmission from donated human tissue and current statistics report the risk of HIV to be 1 in 2 million and Hepatitis C 1 in 750 thousand. Using allograft can decrease the operative morbidity and are excellent choices for multi ligament reconstructions and use for people who are “loose jointed” with hyper laxity.
Fixation and Healing
The grafts are placed through tunnels within the bone, which will heal around the new graft similar to placing a fence post deep into the ground with concrete. The biologic healing usually occurs by 3 months. In the interim the graft needs to be held rigidly, which is accomplished by a number of different types of fixation devices. Some of these devices are metal and others are made of a plastic material. These devices can stay in the body and do not need to be removed routinely. Most grafts will be fully replaced by blood vessels and your own tissue after approximately 9 months. It may take allograft a little longer to incorporate.
ACL Graft Failure and Revisions
The most common cause for failure of an ACL reconstruction is improper placement of the bony tunnels that serve as anchor points for the new ligament. Meticulous attention to detail can result in near anatomic placement for the ACL graft resulting in a durable graft that will function similar to the native ACL.