Why Does ACL Reconstruction Fail?
Dr. Cunningham sees ACL reconstructions fail for a number of reasons. Failure of an ACL reconstruction is most commonly due to shortcomings in the surgical technique. The most common example of inadequate surgical technique is improperly placed femoral and/or tibial tunnels. In ACL reconstruction surgery, an ACL tendon graft is seated into a bone socket in the femur and into another bone socket in the tibia. Ideally, these bone sockets are placed exactly where the original ACL attached to one’s femur and tibia. Unfortunately, some surgeons use surgical techniques that do not perfectly replicate these ACL attachments sites in the knee and they place their bone sockets outside of these native ACL attachment sites. When an ACL graft is then secured in mal positioned bone sockets, the graft will see unusual biomechanical forces and over time the ACL graft will stretch out and/or tear with minimal trauma.
A second surgical factor that can lead to premature ACL graft failure is using donor tendon (allograft) instead of using one’s own tendon (autograft) to reconstruct a torn ACL. Numerous orthopedic studies have conclusively demonstrated that if one’s ACL is reconstructed with an allograft, that the failure rates are higher, particularly in young people (less than 30 years of age) or in those who do a lot of cutting and pivoting sports (ie. skiing). Using a tendon graft taken from the patient (autograft) and placing the graft perfectly in the knee gives the highest chance of never again tearing one’s ACL. The reason for this is that your body recognizes your tissue as its own and grows it securely into the bone. Autograft tissue also has new blood vessels grow into it and nourish it and strengthen it, whereas allograft tendons are not incorporated into one’s knee as well.
A third cause of an ACL reconstruction failing is not recognizing and addressing laxity in other ligaments that work in conjunction with the ACL to help stabilize the knee. For instance, when one tears their ACL, they commonly also tear their MCL. Although MCL tears can heal without surgery, Dr. Cunningham finds that severe (Grade 3) MCL tears often only partially heal and remain somewhat lax. If the ACL is then reconstructed in surgery and the loose MCL is not also reconstructed, then this persistent laxity in the MCL puts the ACL at higher risk of re-tearing as the ACL is seeing increased forces during cutting and pivoting sports. Similarly, patients can also tear ligaments on the outside of their knee (their LCL and/or posterolateral corner) which do not heal well without surgery, so if these are not addressed then the ACL will likewise see increased forces and can fail prematurely.
Finally, a reconstructed ACL can fail simply by having another bad, twisting fall while playing sports, much like the injury that tore your native ACL. Even a perfectly reconstructed ACL can tear if subjected to severe enough injury forces. However, a well reconstructed ACL using autograft tissue is not more likely to tear than the normal ACL in your other knee unless one returns to cutting and pivoting sports before you have all your strength in the muscles that support the knee and the ACL.