Re-Tearing an ACL After Surgery

Anterior cruciate ligament injuries (ACL tears) are a common and feared injury for athletes. When an athlete tears their ACL the knee typically feels unstable and may give out when they try to cut or pivot on the leg. While this may not prevent participation in every sport, it does cause significant problems when trying to play many sports like soccer and basketball.

Female athlete on the ground with a knee injury
Tom Stewart / Getty Images

ACL reconstruction surgery does not repair the damaged ligament, but rather creates a new ligament using other tissue from the leg (often the patellar tendon or hamstring tendon). Furthermore, an unstable knee can increase the risk of developing early arthritis. For these reasons, many athletes, especially young high school and college-age athletes, will choose to have ACL reconstruction surgery to make a new ligament that stabilizes the knee joint. The surgery is most often successful and assuming the athlete performs the appropriate rehabilitation after surgery, most athletes are able to return to their sport. However, there are possible complications of ACL surgery, including re-tear of the new ligament.

There are a number of different reasons that an ACL can be re-torn after surgery. Some of these issues are related to the surgery, some related to the recovery, and some related to the patient. Let's look at each of these, and what someone who tore their ACL can do to prevent a repeat injury to the same knee.

Surgical Factors

One of the most important aspects of ACL surgery success is how well the graft is positioned inside the knee joint. Not every surgical procedure is performed with the same degree of precision, and there are variables that can lead to problems if the new ACL is not properly positioned. The graft must restore the function of the normal ligament, therefore it must be positioned in a similar fashion to the normal ligament.

Inaccurate positioning of the graft can lead to abnormal mechanics of the joint and an increased chance of re-injury. Finding a surgeon who regularly performs ACL surgery can help. In addition, new techniques have emerged to try to restore normal ACL anatomy, although these haven't necessarily been shown to make much of a difference for patients.

Another factor of the surgery that seems to matter is the actual size of the graft used to create the new ACL. Smaller grafts have been shown to have less durability than larger grafts in some studies. Lastly, it has been shown that donor grafts have a higher re-tear risk than a patient's own tissue, particularly in patients under the age of 25. For this reason, most surgeons have opted to use autograft (a patient's own tissue) rather than allograft (donor tissue) in young athletes.

Recovery From Surgery

Proper rehabilitation after ACL surgery is critically important to the success of the reconstructive surgery. Not only must the new graft become a part of your knee, a process called graft incorporation, but you need to restore normal muscle strength to ensure the knee is well protected.

Graft incorporation times may vary, but most surgeons recommend protecting the knee for a minimum of six months after surgery using autograft (your own tissue) or nine months after allograft (donor tissue) surgery.

When the new ACL is positioned in the knee joint it is typically held in place with an implant. These implants come in many shapes and sizes (buttons, screws, posts), and some are made of metal while others dissolve. However, all of these implants are just holding the graft while your body incorporates the tissue so that it becomes your new ACL. That process takes time, and doing too much activity, too soon in your rehab, can lead to damage or re-tear of the graft.

The other important factor following surgery is regaining normal muscle function of the entire extremity. We know that many ACL tears are the result of poor neuromuscular control of the extremity; these are the words used to describe the stability of movement of the body. Some athletes have excellent neuromuscular control—their body is always in a strong, stable position, no matter what movement they are making. Other athletes have poor neuromuscular control, and their body gets into positions that increase the chance of injury, such as tearing the ACL. Part of recovery from surgery is to correct any issues of neuromuscular weakness that may have led to the initial ACL injury and may prevent the chance of future injury.

Return to play assessments, to confirm the athlete has regained enough strength and stability to return safely to playing sports, can be an important part of the recovery process to minimize risk of a second injury.

Patient Factors

There are some aspects of ACL surgery and the risk of re-tear that you can't do much about. For example, younger people and those returning to high risk sports (involving cutting and pivoting) have a higher chance of re-tear of their ACL after reconstructive surgery. Athletes under the age of 25 who return to playing sports have been shown to have a particularly higher chance of re-tear of their ACL than others.

As mentioned, there is not much you can do about factors such as your age or sport,, but your surgeon and therapist should be extra aware of these situations where a young athlete may be at a particularly high risk for re-injury to their ACL and adjust their rehab accordingly. The idea is to take the information about risk factors and adjust the variables that you can control to minimize the possibility of re-injury to the ACL.

Know Your Risk, Optimize Your Rehab

The bottom line is to know if there are aspects of your recovery that put you in a position of the increased chance for re-injury to your new ACL. If you are at higher risk for re-injury of your ACL, make sure your rehab is optimized to ensure that everything you do is focused on preventing another ACL tear.

There are other factors that may also influence the risk of re-injury to the ACL that need more investigation including the sport and position played, the aggressiveness of the athlete, and the amount of contact that occurs. These are hard to measure and therefore hard to study, but they may also be important in understanding the risk of injury.

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