ACL Surgery Options

ACL RECONSTRUCTION OPTIONS

Although ACL injuries span the length of time (even veterinarians reconstruct ACL tears in animals) ACL reconstruction has only occurred over the last several decades. All American surgeons who regularly perform ACL reconstructions do so with arthroscopy, thus limiting the length of skin incisions and deeper dissection. The ACL rarely “partially” tears- usually it is completely disrupted. In special cases of partial tears, actual “repair” of the native ligament is possible. However, in complete tears, “repair” of one’s own ACL fibers has very poor results. This is why surgeons use the word “reconstruction”; we fix the knee by replacing the old ACL fibers with a new graft that eventually turns into a new ACL. In a repair, the remaining fibers are sewn together, but we know from many studies that this simply doesn’t work. Much more predictable results occur when the ACL is reconstructed with a tendon from somewhere else, that through the process of “ligamentization” becomes a new ACL.

The main surgical option worth discussing is the choice of graft. Ligaments and tendons share a very similar structural framework, both having connective tissue components like collagen. The main difference is in their roles. Tendons connect muscles to bones, essentially forming the link that allows limb movement. The tendon is the “tether” of the motor (muscle) to the base (bone). Ligaments, on the other hand, are the stabilizing structures that connect bones to each other at the joints. Without ligaments our joints would collapse underneath us. When the ACL is torn, a tendon from somewhere else is placed in the ACL’s exact location, and in time the tendon becomes your new ACL.

As seen in the diagram, the first decision is whether to use your own tendon or a donor tendon from another person, also known as “cadaver tendon”. Using cadaver tendon has become more common, and is an excellent option for the very young (pre-teen) or in patients over 40. Very careful testing of cadaver tendons has lowered the risks of disease transmission to very low levels, now estimated to one in millions.

The typical patient uses his/her own tendon for ACL reconstruction. The two main options are the hamstring tendons or the patellar tendon. There are four main hamstring tendons at the back of the thigh: the semimembranosis, semintendinosis, the gracilis, and the biceps femoris. If the hamstrings are utilized, the semintendinosis and the gracilis are used. Happily, the tendons have an amazing ability to regenerate (called the “salamander effect”!), thus leaving patients with very little functional deficit after the leg has healed. Surprisingly, as the hamstring muscles transition into tendon and course down the back of the thigh, they swing around the back of the knee to the front of the tibia (the shin bone). So, while the hamstring tendons power knee flexion, they do so not through an attachment at the back of the knee, but at the front. Many patients mistakenly assume that borrowing their hamstrings for ACL reconstruction means they’ll have an incision in the back of their thigh, but because of the anatomic considerations just mentioned, the incision is actually in the front of the knee. More to the point, the incision for hamstring harvest is right where we need to make an incision for ACL reconstruction no matter which tendon we elect to use as the donor. That small incision gives the ideal window to release the hamstrings at their distal (“far”) insertion, and with a “tendon stripper” obtain the tendon we use to simulate the new ACL.

The second main tendon harvested for ACL reconstruction is the patellar tendon. The patellar tendon (or sometimes referred to as the patellar ligament) connects the patella (kneecap) to the top of the tibia. Harvesting the entire tendon would of course devastate the knee, and only the central one-third of the tendon is harvested. When harvest occurs, the bony ends of the tendon are also secured, so that the final graft harvested actually has the bony ends left intact. This is why the patellar graft is sometimes referred to as the “bone-tendon-bone” graft.

Besides using one’s own tissue, the other main option to consider is an “allograft” or cadaver graft. This is tissue from another human being which has undergone a rigorous cleansing and sterilization process. Allograft options include the above-mentioned hamstring and patellar tendons, and also includes several other tendon options from the lower leg which very favorably replicate one’s own ACL.

When considering ACL reconstruction options, it is important to consider how strong the new graft will be. Surprisingly the newly reconstructed graft is stronger than a regular ACL once healing has occurred. Examine these numbers from a classic study:

Note how the doubled hamstring tendons (folded gracilis and semitendinosis tendons) yield an ultimate load of over 4,000 Newtons, with a cross section over 50% greater than a patellar tendon graft! More on these biomechanical data later.

Besides using one’s own tissue, the other main option to consider is an “allograft” or cadaver graft. This is tissue from another human being which has undergone a rigorous cleansing and sterilization process. Allograft options include the above-mentioned hamstring and patellar tendons, and also includes several other tendon options from the lower leg which very favorably replicate one’s own ACL.