ACL repairs failed in the past as the normal synovial fluid in the joint would prevent the healing of this ACL. This process is called resorption, where your body slowly breaks down and absorbs the repair over time.
So surgeons began searching for a way to encourage your body to accept the repair and enable it to heal on its own. The first major breakthrough in this area was the development of the autograft, which uses a tendon from another part of your body to replace your ACL.
While this method was an improvement, it still had its limitations as the new tendon was not always as strong as the original. Additionally, there was still the risk of resorption, albeit to a lesser extent.
The use of an allograft uses a tendon from a deceased donor. This method eliminates the need to harvest a tendon from another part of your body, but there is still the risk of resorption as your body may reject the allograft. In addition, allografts are not as strong as autografts and have a higher failure rate, especially in younger patients.