The ACL, short for anterior cruciate ligament, is a piece of strong connective tissue in the knee. The ACL connects the thigh bone (femur) to the shin bone (tibia). Its primary function anatomically is to passively resist anterior translation of the tibia on the femur. In other words, it’s designed to assist in stopping the shin bone from sliding forward on the shin bone, especially when your leg is planted firmly on the ground. Resisting such motion is especially important in athletics – which commonly include variations of cutting, jumping, and landing maneuvers that may require passive and dynamic stability of your leg.
In most cases of an ACL injury, especially for younger athletes or those who live an active lifestyle, the standard management of a full ACL tear is reconstructive surgery. This procedure involves harvesting tissue from another area of your body or from a cadaver, otherwise known as the graft, and surgically implanting it in to the affected knee. Essentially, medical doctors are able to recreate a brand new ACL and restore the stability of the knee joint. There is still some debate regarding graft choice for each individual. There is no current consensus on a “perfect” graft choice and it is dependent on the presentation of each case. A few of the most important factors to consider are age, activity level, and level of competition.
It’s also important to note that ACL reconstruction surgery is not required for function. In fact, some individuals (referred to as “copers”), can return to their prior level of function with only conservative management like physical therapy. More on this topic in the future!
Graft choices are broken down into two overall categories: autografts and allografts. An autograft is essentially tissue taken from another part of the same individual’s body. Common autograft choices are the patellar tendon (sometimes called bone-tendon-bone or BTB), hamstring tendon, or quadriceps tendon.
An allograft is tissue taken from a donor. Allografts are most commonly taken from the patellar tendon, hamstring tendons, or Achilles tendon.
A benefit of the autograft group overall is that they do not require sterilization prior to surgical implantation. This is because they are taken from the same individual getting the new ACL. In addition, research suggests that the rate of a second ACL injury is 4x lower in young patients with autograft reconstruction. There is also some evidence that the rate of successful return to sport is higher in young, active patients with an autograft reconstruction.
The primary concern with the autograft group is donor site morbidity. In other words, with any of the autograft choices, there is trauma to the area where the graft is being taken from. Therefore, each autograft choice has some unique considerations during the rehab process.
Here are the pros and cons of each type of autograft.
The patellar tendon graft has historically been the gold standard for ACL reconstruction mainly due to the fact that it was the first widely adopted method. There exists some evidence that this graft is favorable to hamstring grafts because the graft consists of bone on either end of the harvested tendon, which may yield a faster rate of healing.
Cons of the BTB graft are mainly related to an increased rate of anterior knee pain. Pain the front of the knee is a common consideration during the rehab process, but is something that be effectively managed.
Possible pros of a hamstring graft include decreased donor site morbidity compared to the patellar graft and less of a chance of anterior knee pain.
Possible cons include delayed initiation of hamstring strengthening. But, a stronger body of research is needed to make a definitive claim on this topic.
This is the “newcomer” of the autograft group. The quad tendon possesses characteristics that are predictable, similar to both the hamstrings and BTB grafts. From an evidence perspective, additional high quality studies are required determine its efficacy in ACL reconstruction.
Overall, there is not strong evidence to suggest that there is a significant difference in the overall outcome of ACL reconstructions utilizing either patellar tendon or hamstring graft. Individual considerations such as the patient’s specific sport or preferred activity, as well as surgeon preference, become important factors in the decision making process.
Despite the decreased risk of a second ACL injury with autograft reconstruction in the younger population, evidence suggests that the rate of a second ACL injury after surgery normalizes at about 40 years of age. This is likely the target demographic for ACL reconstruction via allograft. Pros include decreased donor site morbidity, and cons include the need for sterilization of the graft.
The most important takeaway from the current body of literature pertaining to graft choice in ACL reconstruction is the need for strong consideration of patient’s age and activity level. In general, it seems that autografts have the best outcomes in the young active population while allografts should be considered for an older, less active individual. When it comes to deciding between autograft types, the individual’s sport or preferred activity and the surgeon’s preference and/or skillset are important factors to consider.
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