Posted by Turner Nolan
STEAM project
11/21/2024
“What do you knee’d?”
A contrast of different auto and allograft options for ACL reconstruction:
Whether we’re getting a paper cut, or slipping on ice, we all somehow end up getting hurt sometime in our lives, and for those in sports unfortunately one of the most common ways to get hurt, is your Anterior Cruciate Ligament (ACL) to get ruptured or torn, (Boden et al, 2021). In recent years there has been a noticeable uptick in sports related incidents including the ACL at all levels of competition, resulting in higher cases of ACL reconstructions (ACLR) (Boden et al, 2021). Without the use of an ACL, the risk of chronic knee pain and other complications is far greater than if you were to get a replacement, (Beard et al, 2022). An ACLR is the process of harvesting tissue from either yourself (autograft) or from another person or cadaver (allograft) and using it as a new ACL after removing the remnants of the previous ACL, (Macaulay et al, 2012). An ACLR is a common surgical procedure, with about 100,00 to 300,00 ACL reconstructions happening a year in the states, and with all of that there still isn’t a commonly agreed graft option (Macauly et al, 2012). Factors like, a patient’s age, activity level, preferred sports, level of competition, risk to injury, and whether or not they have had a previous ACLR, are all important in the choice of what tissue to use for the graft, (Boden et al, 2021). Seeing as how most patient’s decision on which tissue to use is based on their Surgeon’s recommendation, it’ s important for both parties to be to compare and contrast all of the available tissue graft options, (Boden et al, 2021).
The ideal graft for use in an ACLR should have similar properties to those of the native ligament, (Boden et al, 2021). So before we can get to talking about the best graft options we need to understand the ACL itself. The ACL is there to provide anteroposterior and rotary stability to the knee, (Boden et al, 2021). The ACL is comprised of two fibrous bundles based on their tibial insertions sites, working together to stabilize the knee to counter rotary and anterior tibial loads (Boden et al 2021). The ACL is made up of an organized collagen matrix with thick bundles of collagen fibers surrounded by loose connective tissue, making it a dense regular connective tissue, with good tensile strength and resistance to stretching in the direction of the collagen fiber orientation, (Boden et al, 2021). So when looking for our best grafting options we want to find tissue that has good tensile strength, is able to the tibia from dislocating, has high rotary strength, and can keep the knee stable overall, (Macauly et al, 2012).
There are two common sources for graft tissue in ACLRs, ourselves (autografts) and other people or cadavers (allografts), that each have their own benefits and disadvantages, (Macauly et al, 2012). Allografts have a theoretical advantage of elimination of donor site pain, because the tissue would be from a cadaver and not the patient themselves, decreased pain, and rehabilitation times, but they do have more associated risks of failure, (Macauly et al, 2012). Allografts should be a second resort when autografts aren’t an option, like for patients who have multi-ligament injuries, are over the age of forty and may not have very strong tissue to give, have already had an ACLR and have had autografts in the past, or in situations where the patient does not plan on being very active and is low risk of further ruptures, (Boden et al, 2021). Autografts are the main graft choice of the more active patient population, and include three main options surgeons typically use, bone- patellar tendon- bone (BPTB) grafts, hamstring (HS) tissue, and quadriceps tendon (QT) tissue, (Macauly et al, 2012).
BPTB autografts consist of a central portion of the patellar tendon with corresponding bone plugs from the patella and tibia, and has been considered the, “benchmark” graft for ACLR, (Boden et al, 2021). BPTB gained it’s reputation because they have been found to have lower failure rates, and higher return to sport rates than either HS or QT autografts, and are also the most widely used graft between the three, (Boden et al, 2021). BPTB work as a good ACLR autograft because tendon and ligaments are both dense regular connective tissues, with the same basic structure of a collagen matrix with bundles of organized collagen fibers, what also helps is the bone plugs from the BPTB graft when relocated to the tibia and femur heal similar to that of a fracture rather than soft tissue healing, bone plug to native bone taking around six weeks, soft tissue healing eight to twelve weeks to fully incorporate, (Boden et al, 2021). While BPTB autografts are consistently good, there are some potential risks associated, like anterior knee pain related to the harvesting of the BPTB, or a small potential of ruptures or fractures in the patella tendon and patella itself respectively, (Boden et al, 2021). BPTB autografts generally work best for younger athletic patients, still active in sports, but are skeletally mature so the relocation of the bone plugs doesn’t affect bone growth, (Boden et al, 2021).
Hamstrings in terms of tissue types are the most different of all the options, being skeletal muscle, it is characterized by bundles of elongated cells, and surrounded by connective tissue appearing striated and organized, and can be folded on itself after harvesting to increase graft diameter and strengthen the tissue as an ACLR, (Boden et al, 2021). HS autografts are generally less used than BPTB autografts due to their higher failure rate, damage done to the hamstring, knee flexion weakness, integration time, and overall damage done to the patient’s ability to run or sprint in the long run, (Boden et al, 2021). The HS autograft does have some benefits found in its strength, little pain caused in the donor site, smaller incision size, overall less postoperative knee pain, and very importantly available to those who are skeletally immature and have not finished growing, (Macaulay et al, 2012).
Quadriceps tendon, like patellar tendon and the ACL is a regular dense connective tissue, with the same tensile strength and stretch resistance based on fiber orientation as the other two fibers and can even be harvested to account for both skeletally mature and immature patients, (Macaulay et al, 2012). QT autografts can be harvested at a thicker or thinner width depending on whether the patients is having a ACLR or ACLR revision respectively, and can be harvested with or without bone blocks dependent on whether the patient is skeletally mature or immature respectively, (Boden et al, 2021). Problems can occur during and after ACLR including lasting pain and weakness in the quadriceps, patellar fractures as a result of bone block harvesting, bleeding from the quadriceps post operation, and excess swelling/fluid build up in the leg post operation, (Boden et al, 2021).
ACL ruptures are a very common injury, that is only becoming more common, and finding the ideal graft option for your ACLR is a tricky decision, that most patients leave to their surgeons, (Macaulay et al, 2012). Its not only important for the surgeon to know what the best graft option is for each individual patient, based on their lives, but it is also important for the patients to know what is best for them based on the lives they live and want to live (Boden et al, 2021). I hope my STEAM submission can introduce people to the differences in grafting options, and help them find what they “knee’d”.
Buerba, R. A., Boden, S. A., & Lesniak, B. (2021). Graft Selection in Contemporary Anterior Cruciate Ligament Reconstruction. JAAOS Global Research & Reviews, 5(10), e21.00230. https://doi.org/10.5435/JAAOSGlobal-D-21-00230
Macaulay, A. A., Perfetti, D. C., & Levine, W. N. (2012). Anterior cruciate ligament graft choices. Sports health, 4(1), 63–68. https://doi.org/10.1177/1941738111409890
Beard, D. J., Davies, L., Cook, J. A., Stokes, J., Leal, J., Fletcher, H., Abram, S., Chegwin, K., Greshon, A., Jackson, W., Bottomley, N., Dodd, M., Bourke, H., Shirkey, B. A., Paez, A., Lamb, S. E., Barker, K., Phillips, M., Brown, M., Lythe, V., … ACL SNNAP Study Group (2022). Rehabilitation versus surgical reconstruction for non-acute anterior cruciate ligament injury (ACL SNNAP): a pragmatic randomised controlled trial. Lancet (London, England), 400(10352), 605–615. https://doi.org/10.1016/S0140-6736(22)01424-6