As participation and intensity in sports has increased, the prevalence of knee ligament injury has also increased. The granddaddy of them all is injury to the Anterior Cruciate Ligament, or better known as the ACL. Not all ACL injuries require surgery, but surgery is recommended if the ligament is torn, especially for those who are young and active. We do have clients who ask us, “Which ACL surgery is the best for me?” There are a few different options to choose from. One of the variables is the graft type. The graft is the tissue a surgeon replaces the torn ligament with. You and your surgeon will meet and decide prior to surgery. Knowing which one to use can be a difficult a decision, but we would like to make you aware of some of the options.
As stated, there are several different types of grafts that can be used to replace a torn ACL. Surgeons can use what is called an autograft, which is taken from you; or an allograft, which is taken from someone else, usually a cadaver. The two words are very similar, so to help you remember let’s think about the prefixes, “auto” and “allo”. The prefix auto means self, ie a graft from you. The prefix “allo” means other, so to remember that one think of the “other” graft or “another” person.
The three main types of autografts to ponder are the 1) patella tendon, 2) the hamstring tendon, or 3) the quadriceps tendon. Conversely, the main type of allograft is a harvested tendon from a cadaver. Cadaver grafts can also be the patella tendon, as well as other options such as the Achilles tendon, posterior tibialis tendon or the tensor fascia latae tendon.
Pro & Cons of Autograft
Each of the autograft choices has pros and cons to consider. First, the patellar tendon, aka the Bone Patella Tendon Bone graft or BPTB, requires the surgeon to remove one-third of the patella tendon, which is between the kneecap and the shinbone, and reattach it in place of the ACL. This type of graft is the strongest according to maximal load testing and was considered the gold standard for many years. However, it sometimes results in a difficulty straightening the knee fully after surgery especially for those who don’t work very hard on extension in physical therapy. The BPTB graft is usually not recommended for those who have to kneel at work or for young children because of the proximity of the harvested area to the growth plate.
Secondly, the hamstring graft requires the surgeon to remove the tendon of the semitendinosus muscle, which is one of the three hamstring muscles, and the gracilis tendon, another muscle in the thigh. An acronym for the hamstring graft is ST/G. The ST/G graft usually is less painful post operatively compared to the BPTB technique. However, the overall long-term recovery for the ST/G graft is longer than the BPTB due to the removal of one of hamstring tendons, which delays strengthening of the hamstring muscle during rehab. This graft may not be ideal for athletes, sprinters and active adults in sports because of the reports of hamstring pain while sprinting.
Schematic of insertion of Hamstring and Patellar Graft
Thirdly, the Quadriceps Tendon graft, or QT graft, removes one-third of the quad tendon, which is between the kneecap and the front of the thigh. The results of this graft are similar to the BPTB graft, which is a faster rehab but some may have difficulty achieving full knee extension after surgery (Sloane, 2014). Interestingly, people who had a QT graft versus a BPTB graft tend to gain back their full knee extension faster.
Pro & Cons Allograft
Again, the main type of allograft is a harvested tendon from a cadaver. Cadaver grafts can be the patella tendon as well as other options such as the Achilles tendon, posterior tibialis or the tensor fascia latae. Overall, compared to autographs, the tangible range of motion and gross strength normalization is many times faster with cadaver grafts; but the research is clear that the actual physiological healing tends to be sower than autographs. Moreover, because the cadaver tissue is dead it takes longer for the tissue to re-vascularize and become incorporated as a structural unit in the body. For that reason it does take longer to fully recover and return to sport after an autograph. Interestingly they do actually cost more than the autografts too.
For people over the age of 25, the re-tear rates are equal between cadaver grafts and the autografts. However, the re-tear rate for those under 25 is much higher with a cadaver graft especially in the late stages of the rehab. For that reason, they are not recommended for those under the age of 25 (Engelman, 2017). The increased failure rate or re-tear may be in part due impatience on the part of the young, active population returning to activities to quickly. More likely however, the increased re-tear rate is due to the poor re-vascularization of the graft or because the graft never fully re-vascularized into the body.
Additionally, some people do not like the idea of having something “foreign” in their body. This is understandable because there is an increased risk of a disease being passed on from the cadaver graft versus the autograft. However, the allograft undergoes a thorough sterilization process before being used in an ACL surgery and infection rates are very low.
The decision of which ACL graft that is best can be tricky, but hopefully this information can help you make the best choice for your situation. Once you and your doctor have determined which type of graft is best for you, then physical therapy is the next step after surgery to help you regain your strength, ROM and help you control your pain. There are many factors that your physical therapist will take into consideration when planning a recovery program for you, including the type of graft. Your doctor may or may not provide a protocol to follow, which will include weight-bearing status, the use of open or closed chain exercises, and the number of degrees of flexion he expects you to achieve in a certain timeframe. Rehab after an ACL surgery can be a tough process, but it is important to follow the advice of your physical therapist as he plans an rehabilitation program for you based on your doctor’s protocols to achieve the fastest possible pace and maximize your potential.
Engelman, G.H., et al., Comparison of allograft versus autograft anterior cruciate ligament reconstruction graft survival in an active adolescent cohort. Am J Sports Med, 2014. 42(10): p. 2311-18.
Slone, H.S., et al., Quadriceps Tendon Autograft for Anterior Cruciate Ligament Reconstruction: A Comprehensive Review of Current Literature and Systematic Review of Clinical Results. Arthroscopy, 2014.