Why Did My ACL Fail?

A tear of the anterior cruciate ligament (ACL) is the most common ligament injury of the knee. There are 100,000 to 200,000 ACL tears each year in the United States. There are approximately 200,000 ACL reconstructions performed each year. Unfortunately, we as human surgeons cannot completely recreate a “normal” ACL, and just as you can tear the ACL you were born with, you can also tear the reconstructed ligament.

What is your risk of re-tearing your ACL?

A study from 2014 examined the incidence of anterior cruciate ligament re-injury and the risk factors involved. The Multicenter Orthopaedic Outcomes Network (MOON) consortium collected data from almost 2700 patients in the MOON database who underwent ACL reconstructions between 2002 and 2008. They obtained follow up information for over 80% of the patients more than two years after the surgery. They analyzed this data to identify the incidence of re-injury to the ACL graft or a tear of patient’s opposite knee ACL. At two-year follow up, 4.3% of the patients had torn the surgical graft in the injured knee while 3.6% of them had torn the opposite knee ACL. Among graft options for the initial ACL reconstruction, the odds of a re-tear of the graft did not differ between patellar tendon autograft and hamstring autograft. The authors also compared their results by age of the patient and whether or not the graft used was an auto graft from the patient’s own knee or an allograft from a donor, They stated that their data “clearly display that for both graft choices, the younger the age, the greater the failure; but allograft, especially in patients younger than 30 years old, has a clinically relevant difference in failure.” For example, if an autograft is used in an ACL reconstruction in an 18-year-old patient, the risk of failure is 6 percent; if an allograft is used, the risk of failure jumps to 20 percent. Patients who received an allograft or graft from a donor were 4.69 times as likely to suffer a second injury compared to the autograft patients. Another study presented at the 2013 annual meeting of the American Orthopaedic Society for Sports Medicine, shows that the overall rate of another injury within 2 years to the ACL—on the same or the opposite knee—is six times greater among athletes who undergo ACL reconstruction surgery and return to sport than among those who have never had an ACL tear.The authors analyzed the data obtained at 6-year follow up. The graft failure rate was 5.6 percent, with an ACL tear rate for the other knee of 6.5 percent, for a combined recurrent ligament disruption rate of 12.1 percent. Furthermore, athletes in the ACLR group who suffered another ACL injury did so soon after they returned to play. Approximately 30% were injured in less than 20 athlete-exposures (AE), and 52.2 % were injured in less than 72 AEs.

What are the main reasons the ACL fails?

During ACL surgery five things must be accomplished.

  1. There must be an adequate graft. If an adequate graft is not obtained, then this could predispose to failure. The ACL is not repaired or sewn together, it is actually reconstructed with tissue obtained from the patient (autograft) or from a cadaver or donor. The three common autograft choices are the patellar tendon or hamstring tendons from the same knee, or a donor graft of similar type. Autografts are incorporated more quickly and are preferred in younger active patients because they have have significantly lower failure rate. Numerous studies have evaluated the failure rate of hamstring grafts and patellar tendon grafts. These continually show little difference. Each graft has its own downside “robbing Peter to pay Paul”, but if the surgery is done correctly you can be confident you will have a strong graft that will be able to restore your knee function. Donor grafts may be a good option for older less active individuals who wish to avoid the additional pain that occurs with obtaining the autograft. (graft site morbidity). However, they should be avoided in the younger athlete due to the significantly higher failure rate.
  2. The graft must be put in the right position. Positioning the graft in the knee through drill holes in the tibia and femur is essential to restoring knee function and graft success. A graft misplaced may constrain the range of motion of the knee or will be at risk for higher tensions and higher failure rates.
  3. The graft must be tensioned appropriately. Regardless of the graft choice, it must be placed in the knee at the right tension to restore stability while allowing anatomical range of motion and rotation of the knee. A loose graft will not restore the stability required, and a graft that is over tensioned will be at risk once again of either limiting knee motion of it will be predisposed to failure.
  4. The graft must be anchored in the tunnels firmly. The graft must be fixated in the sockets that are created in the femur and tibia with rigid fixation that will allow early range of motion of the knee and aggressive rehab without loosening of the graft or the fixation devices. Various fixation techniques have been developed by bioengineers involved in sports medicine research and development so that if used correctly this should not be an issue.
  5. The graft should not be exposed to external stress. It is important that the tunnels are directed in the correct manner and sharp bone edges are avoided during the reconstruction to prevent damage to the graft during incorporation or return to sports.

Other Potential Causes of ACL Failure

  1. Failure of revascularization or return of the blood supply. This is the cause of failure that we know the least about and at this point cannot control. This is a failure of the biology of the knee. Fortunately this is rare, but even if everything is done right, in some cases the graft does not incorporate or regenerate like it should. Remember the grafted tissue is serving as a template or scaffold for the knee to build another ACL. Once we put the graft in the knee and leave the operating room, it is up to the body to do its job. Future research is looking into stem cells and other regenerative technologies that may one day help us stimulate this process. Unfortunately at this time these techniques are not proven or available.
  2. Anatomic Predisposition. It is well known that patients that tear their ACL are at greater risk for tearing their opposite knee ACL than the general population, and they are also at greater risk for a second tear of the same ACL. This may be related to anatomical variances that predispose the patient to this increased risk. For example a narrow space in the femur where the ACL is located, decreased internal rotation of the hips, and neuromuscular imbalance have all been associated with a greater potential for tearing the ACL. ACL prevention programs exist to help decrease this risk.
  3. Just bad luck. While we have spent decades in orthopaedic sports medicine perfecting ACL surgery and analyzing what is best for our patients, it is impossible to recreate the exact replica of your native ACL. The risk of re-tear exists, and it is greatest in young athletes that are returning to high risk sports that caused the tear in the first place. It is essential that you and your physician and therapist prepare you for returning to your sport and perform functional tests prior to returning to your individual sporting activity.

What Questions Should I Ask My Doctor?

Obviously make sure you find an orthopedic sports medicine specialist that is experienced in ACL surgery. A surgeon that does 100 ACL reconstructions per year and has been doing them for a long time with good outcomes is a good start. What is their graft choice and why? Most surgeons have a bias and find out their reasons for their bias. While this is a good question, most sports medicine surgeons are experienced with all grafts options and surgical techniques and if the surgery and rehab is done well you can expect probably an 90 % chance of a successful result. Finally, while there definitely are patients that have had their ACL reconstructed with successful results, beware of allograft tissue if you are an active young athlete based on the literature and results published.

Reference:

  1. Kaeding CC, Pedroza AD, Reinke EK, Huston LJ. ACL Injury after ACL Reconstruction: Analysis of 2695 Primary ACL Reconstructions for Risk Factors. Presented at the 2014 American Orthopaedic Society for Sports Medicine’s (AOSSM) Annual Meeting.
  2. Mark V. Paterno, PhD, PT, SCS, ATCinclude Mitchell Rauh, PhD, PT, MPH, FACSM; Laura C. Schmitt, PhD, PT; Kevin R. Ford, MS; and Timothy E. Hewett, PhD, FACSM.“Incidence of Second Anterior Cruciate Ligament (ACL) Injury 2 Years after Primary ACL Reconstruction and Return to Sport”