Page ContentFailed ACL ReconstructionACL reconstruction is thought to be the fifth most common orthopedic procedure performed per year in the United States. With increasing activity levels, and thus more ACL reconstructions being performed, orthopedic surgeons will probably see graft failures more frequently.Failed ACL reconstruction can be defined as persistent instability and can be caused by a graft re-tear, graft laxity and failure to address other (secondary) restraints. Other issues that must be considered (even in the presence of an intact graft) are muscle function, pain and range of motion.The cause of recurrent instability is multifactorial. If the failed ACL reconstruction occurs within six months of the surgery, we define this as early phase failure. This can be attributed to poor graft quality, loss of graft fixation, inadequate graft incorporation, poor surgical technique, early return to sports and/or inappropriate physical therapy program.If the failed ACL reconstruction occurs after six months, we define this as late phase failure. Often traumatic re-injury is the cause of failure. However, other factors may be present including other ligament or meniscal injuries and/or poor tunnel placement. Younger patients have a higher incidence of recurrent tear.Other causes of failed ACL reconstruction include loss of motion (such as loss of terminal extension or more significant knee scarring called arthrofibrosis) and infection. When evaluating an ACL reconstructed knee, it is essential to address all these factors to determine whether a revision surgery is warranted and what the chances are for a successful outcome.