ACL Reconstruction Failure

ACL reconstructions are one of the top surgeries that are performed in the United States.  At the last count according to the American Board of Orthopaedic Surgery, they were the sixth most common surgery.  However, in Vail, where we have a very active native and visiting population, it is probably one of the more common surgeries.  While ACL reconstructions in general are felt to be a very successful surgery, they still fail between 10-15% of the time.  In these particular patients, this can be a big problem because the results of revision ACL reconstructions are nowhere near as successful as the first time around.  When one is concerned that their ACL reconstruction has failed, patients often describe a traumatic event where they fall, twist, turn, or pivot and feel a pop.  In some patients, they may have more pain than they actually have a feeling of instability.  This particular subgroup of patients can be particularly worrisome because it may mean that they have quite a bit of underling arthritis in addition to their ACL graft not working.

Probably the most important thing to have when one is concerned that their ACL graft has failed is an evaluation by a sports medicine physician.  The physical exam can determine if the graft is loose or if the knee is shifting, which we call a pivot shift test.  It is important to have this exam because sometimes patients feel that their graft is not working when in fact we may have other things going on in their knee that is causing pain and a sense of instability rather than true instability.  In some of these patients, they may have “giving way” where their quadriceps mechanism pinches on some soft tissue and their knee “gives out”.  These patients may have some arthritis causing their symptoms or they may just have a very weak quadriceps mechanism which needs to be addressed rather than having a new ACL replacement.

Success of Revision ACL Reconstruction

The results of revision ACL reconstructions are about 70% successful in many series and only about 50% of athletes are successful in returning  back to full sports.  Therefore, a very thorough and detailed physical examination is necessary to minimize the risk of the new ACL graft failing.  It is not simple as simply putting in a new graft.  The reasons for this I will detail in the following paragraphs.

To put this in perspective, I performed 86 ACL reconstructions last year in Vail.  We are a big referral center for this.  For example, the whole country of Sweden only had 92 ACL revision reconstructions last year.  Thus, we have a lot of experience in revising ACL reconstructions.

Causes of Failed ACL Reconstruction

The most common cause of a failed ACL reconstruction in my series was an improperly placed graft in the first place.  While one would think that in 2017 that surgeons would know where to place ACL reconstruction grafts, this was not the case in our series of patients.  Most of the time the graft is placed in the wrong position on the thigh bone (the femur) because the surgeon used a transtibial ACL reconstruction technique.  This can often result in the graft being too much in the middle of the intercondylar notch or being too far forward.  In this position, the ACL graft does not resist twisting and turning very well.  The second most common cause of ACL graft failure was placing the tunnel too far back from its normal position (too posterior) from the ACL location on the tibia.  This also makes the graft too central and less likely to resist twisting, turning, and pivoting.

In our series, there were few patients who had the ACL graft placed correctly the first time that had a new reinjury which caused the ACL to fail.

The next most common cause of failure was the use of a cadaver graft in a young patient.  It is now well recognized that the use of cadaver grafts in young patients has a much higher failure rate, usually between 40-50%.  Therefore, using cadaver tissue should be reserved for a very small number of select patients under specific conditions in a young age group.  The other problem with using cadaver grafts in addition to them having a much higher rate of failure in a young age group, is that the body can reject them and cause the bone to resorb significantly around the grafts.  This can make it very difficult, if not impossible, to put a new ACL graft in place without having it fail as a first stage surgery.

How to Diagnose ACL Reconstruction Failure

It is recommended by surgeons who perform large numbers of ACL reconstructions that any failed ACL graft have a CT scan of their knee to assess both the positions of the tunnels and also to assess the size of the reconstruction tunnels.  Improperly positioned ACL reconstruction tunnels which could overlap with a properly positioned ACL reconstruction tunnel, or a tunnel that is too large, need to have a bone grafting of the tunnels or there is a much higher risk of having the ACL reconstruction graft fail.  Thus, it is important to obtain an CT scan of the knee if you have a failed reconstruction to ensure that this can be properly evaluated.  Unfortunately, MRI scans are not nearly as accurate as a CT scan to choose whether you need a 1-stage or 2-stage surgery for revision ACL reconstruction.

Other Causes of Failed ACL Reconstruction

The other common problem for an ACL graft failure is a new ligament or meniscal injury or a previous injury that was not recognized.  This can include either or both of the collateral ligaments, the medial collateral ligament (MCL) and the fibular (lateral) collateral ligament (LCL) or a new meniscus tear.  If one is concerned about a collateral ligament tear, stress x-rays must be obtained to objectively document the amount of joint line gapping. Meniscus tears along the rim of the meniscus or a meniscus avulsion off bone, called a root tear, are becoming increasingly recognized as a cause of failed ACL reconstruction grafts.  In particular, many peer-review publications have noted that a lateral meniscus root tear occurs about 10% of the time with ACL tears.  Therefore, the surgeon needs to make sure that they can both diagnose and properly treat and repair these lateral meniscus root tears at the same time as an ACL reconstruction or there is a much higher risk of the ACL reconstruction graft failing.

The other most common cause of an ACL graft failing is one’s native bony architecture.  One can be either too bow-legged, or too knock-kneed (varus and valgus alignment respectively) which can lead to an ACL graft receiving too much strain.  In addition, the backward slant of the tibia is also a very important portion of one’s bony architecture which needs to be reviewed for a revision ACL reconstruction.  Our veterinary colleagues have recognized this for a long time and found that ACL surgeries in dogs did not work well.  In effect, when one has a dog ACL reconstruction these days, the veterinarian is breaking the tibia and changing the slope of the tibia so it is flatter.  Thus, if one has a “canine type knee” where the slope is higher than normal, they are at higher risk of having an ACL revision reconstruction fail if it is not addressed.  Therefore, trying to perform surgery and decrease the slope of a tibia to flatten it out may be indicated in some patients.

While all these potential causes of an ACL graft failure seem ominous, a well-trained sports medicine physician should assess for all of them and ensure that your outcomes have the best chance of success.  In our published series following this protocol on approximately 90 patients,  we have cut our failure rate for revision ACL reconstructions to less than 10% at 3 years.

Finally, probably the most important thing to recognize is that a revision ACL reconstruction probably is behind the 8 ball in terms of having the same potential for healing as the first time ACL reconstruction.  Therefore, it is recommended that the earliest one ever returns to full activities after a revision ACL reconstruction is 9 months, and if one has a cadaver ACL reconstruction graft, this should probably be a year or longer before returning back to full activities.

In summary, revision ACL reconstructions can be complicated both in the workup and in their surgical procedure itself.  Ensuring that one has gone through a very thorough examination, both on clinical exam and stress x-rays ahead of time, should ensure one having the best chance of success in returning back to activities after a revision ACL surgery.

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