Injuries of the anterior cruciate ligament (ACL) occur relatively frequently, in athletes and non-athletes alike. The mechanism of injury is often a non-contact twisting of the knee that results in immediate pain and swelling. It has been estimated that there are over 100,000 ACL reconstructions performed each year in the United States, and this number is reported to be increasing.
ACL reconstruction surgery has a success rate of 80-90%. However, that leaves an unacceptable number of patients that have unsatisfactory results. Eight percent of these poor results are thought to be due to knee instability or re-rupture of the ACL graft. Failure of an ACL reconstruction is often hard to describe. The patient can have complaints of knee instability, pain, stiffness, or the inability to return to desired activities. Treatment for failed ACL repair is complex and technically challenging, and the results of revision ACL surgery are not as good as an initial ACL reconstruction. It is, therefore, important to follow a specific approach to evaluate, diagnose, and treat potential ACL revision cases.
There is no specific injury that leads to failure. However, the time after surgery that failure occurred can help determine the cause of failure. Failures that occur within the first six months can be due to poor surgical technique, failure of graft healing, or too aggressive rehabilitation. Failures that occur after one year are usually due to another injury. Other factors that can lead to an unsatisfactory outcome are injury to other knee structures or leg alignment. Other structures injured in the knee may be the meniscus (lateral or medial) or the cartilage on the ends of the femur (thigh bone) or the tibia (shin bone).
These injuries need to be evaluated and may need to be addressed at the time of repeat surgery if necessary.
An evaluation for a failed ACL should include a thorough history and physical exam to determine the level of recovery and potential cause of failure. Repeat X-rays that include the entire leg, an MRI that may require a contrast injection for better detail, and possibly a CT scan or bone scan will often be required to determine causes of failure, other injuries, and plan for potential revision surgery. Issues to consider include injuries to other structures as previously described, but also location and size of the previous tunnels, types of graft material used, and fixation devices used to secure the graft. If it is determined that a revision ACL reconstruction is required, then a thorough discussion with the orthopedic surgeon should explain the plan, graft options, and other surgeries that may be required.
Treatment for a failed ACL may require a staged approach with other surgeries done first before the revision ACL surgery. Some other surgeries may include a knee scope to remove the old screws or other fixation devices and possibly bone grafting of the tunnels to allow new tunnels to be drilled later. Surgeries may require a “realignment” of the knee to allow a revision ACL a chance to be successful. If these other surgeries are required, the revision ACL surgery may not be able to be performed for up to six months after diagnosis.
Graft choices will be discussed, and the type of graft chosen will depend on many issues, including tunnel placement, previous grafts used, or requirement for other surgeries. Options for using the patient’s own ligaments (autografts) include the patellar tendon, hamstring tendons, or quadriceps tendon. Options for using donated ligaments (allografts) include Achilles tendons, patellar tendons, and tibialis tendons. All of the tissue-processing companies are required to abide by strict standards and techniques to minimize risks of disease transmission. If the guidelines from the American Association of Tissue Banks are followed, the risk of disease transmission is estimated to be one per 1,000,000 cases. Many studies have been performed that have shown safe and successful use of allograft ligaments for ACL reconstruction. However, the tendon chosen will often depend on specific issues unique to each patient.
The rehabilitation for a revision ACL reconstruction is similar to the initial reconstruction but may be more lengthy and less aggressive. It must be explained to patients that the results are less predictable than their initial surgery, and it is very important that they follow the staged rehabilitation. Each rehabilitation program will be individualized to match the type of revision surgery, graft fixation, and additional surgery that the patient requires. Weight bearing is often protected longer and return to sports is withheld compared to primary ACL reconstruction.
Revision ACL reconstruction is a complex undertaking and is recommended for patients that have instability both subjectively and objectively. The patient must understand that the results of revision ACL reconstructions are not as good as the initial ACL and the goal of the revision is to allow the patient to return to their daily activities, instead of return to competitive athletics. The patient should have realistic goals and understand all of the issues but can be reassured that with the proper evaluation, treatment, and rehabilitation, a successful outcome can be expected in most cases.