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Beginners' Guide to ACL Injuries: Surgical Interventions


Contrary to popular belief, ACL injury does not require surgical intervention. There are plenty of individuals who are living life and running several miles daily without an ACL because of their rehabilitation and physical therapy efforts. However, the ACL’s purpose is to prevent too much movement, and is important for the high intensities required by sport participation. It is much safer to have an ACL than to not have one when it comes to competitive athletics.

Every ACL reconstruction procedure will have a few things in common: the use of screws to secure the new ACL, the use of an arthroscope to see inside the knee, and portals or holes in the leg where the surgical instruments will enter the knee. This post will cover the different types of surgeries possible for ACL reconstruction. Mainly, we will discuss the various graft choices: bone patellar bone, hamstring tendon, cadaver tendon.

Before that happens, it is important to define two words that are associated with ligament surgeries: autograft and allograft. An autograft surgery means the replacement ligament will be harvested from you. Your own tissue will be used to create the new ligament. An allograft surgery means the replacement is harvested from a donor. In just about all cases, the donor is a cadaver.

Bone patellar bone (autograft)

This surgical procedure is probably the most scarring, but gives the most to the patient. When you see someone with a long vertical scar below their kneecap, chances are they had a bone patellar bone procedure for ACL reconstruction. But what does “bone patellar bone” mean? When you look at the knee, the quadriceps muscle attaches to the top of the knee cap, and the kneecap has a tendon, called the patellar tendon, which connects the bottom of the kneecap to the tibia (lower leg). “Bone patellar bone” refers to the patellar tendon.

knee anatomy with circle.jpg

The surgical procedure requires the doctor to disconnect the middle-most portion of the patellar tendon while including the bony connection at the patella and at the tibia. Before the new ACL is been harvested, the doctors have to prepare the area by clearing out the old ACL and addressing any other tissues that may cause a problem in the future (i.e. hanging cartilage, meniscus tear).

When the area looks clean, the tendon is harvested and the remaining patellar tendon is sewed together again. At this point, holes are drilled in the tibia and the femur that allow the new ACL to rest in the exact position as the old one. When the holes are set, the new ACL is guided through the tunnels and secured with a screw on each end. All instruments are removed once the doctor takes one last look around, and the incision and portals are closed shut.

In the last post, I mentioned the intercondylar notch and that there was a method doctors use to correct a narrow notch. Usually, this is done during the cleaning portion of the surgery. The doctors shave the notch wider so that the ACL has more space to do its job.

Bone Patellar Bone Autograft Video - video contains only animated procedure

Hamstring reconstruction (autograft)

The second type of surgery uses the hamstring tendon to reconstruct the ACL. The first step in this procedure is to harvest the new ACL. The surgeon disconnects the tendon of the gracilis (an adductor muscle) and the semitendinosus (a hamstring muscle) from their attachment to the tibia. Using a stripper tool, the doctor sheds the tendons from the muscles which gives him two long tendons to work with. To create the desired length, the tendons are folded in half, giving you tissue that is four times stronger than a single tendon.

Hamstring Graft cropped_LI.jpg

While the tendons are being cleaned and folded by the surgeon’s assistant, the knee is being cleared of the old ACL just as it would with a bone patellar bone surgery. Unlike the previous surgery, only one screw is used to secure the new ACL. One one end, there is a flat device that prevent the new ACL from moving backward once it is threaded. On the other end, a screw is used to wedge the tendons.

A “pro” for this surgical method is a ligament made of tendon, which is already able to withstand more force than a ligament. A second “pro” is an absence of a large vertical scar on the front of the knee. However, the “con” outweighs the “pros”, and that is a reduction of hamstring strength. Due to the requirement of the surgery to disconnect the gracilis and semitendinosus, your hamstring group is now two muscles instead of three. Prior to an ACL tear, the hamstring group acts as an ACL assistant. The hamstrings are the active method of keeping the tibia from moving too far forward on a fixed femur. With the removal of one of those muscles, your assistant is slightly weaker.

Hamstring Autograft Video - WARNING!!! Video contains both animated and real surgical procedures.

Cadaver reconstruction (allograft)

The final method of reconstructing the ACL is through the use of a cadaver or donor. As we said before, an allograft uses tissues that are not your own, similar to a transplant. Prior to the surgery, the donor tissue is removed and prepared for implantation. This could be either of the three commonly used tissues: the patellar tendon, the hamstring/gracilis tendons, or the actual ACL.

This type of surgery will follow the hamstring autograft procedure with the exception of the harvest portal. That means one less cut necessary. The drilling and threading will be exactly the same, and securing the new ACL with screws will most likely be the case. The biggest difference in using a donor is the chance of rejection.

With donor tissue, there will always be a chance that your body decides the new tissue isn’t good enough and will reject it. When the body rejects donor tissue in the case of an ACL reconstruction, the bone will not “accept” the donor tissue and grow around the screw to secure the new ACL into place, and the new ACL will become loose and dislodge from the tunnel. For cadaver reconstructions, somewhere within the first 6 months will be the time period where rejection is most likely. If the cadaver tissue remains in tact up to that point, you will have yourself one strong new ACL.