ACL Repair vs. ACL Reconstruction

Techniques to Repair Rather Than Replace Knee Ligaments

knee exam
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The anterior cruciate ligament is one of four major ligaments in the knee joint. The anterior cruciate ligament (ACL) helps to function as one of the major stabilizers of the knee joint. Without an intact ACL, the knee joint may become unstable, and have a tendency to give out or buckle. This is especially problematic in certain sports that require a stable knee joint.

When an athlete tears the ACL, surgery is often recommended to restore stability to the joint.

Traditionally, ACL injuries have been treated with surgical reconstruction. This means, that the remnant of the torn ACL is removed, and a new ligament is created with tissue from elsewhere in the body, or donated from a cadaveric donor. ACL reconstruction surgery has been very successful, but there are concerns that it may not be the ideal solution for people who have injured their ACL.

In an effort to find a better solution for athletes who have injured their ACL, there has been an investigation into repairing the torn ligament. Performing ACL repair surgery has been done for several decades, but it has never worked very well. Results were always much worse when compared with ACL reconstruction. However, there has been new interest in techniques to repair the torn ACL, rather than reconstruct a new ligament.

ACL Repair

ACL repair surgery has never worked very well. Early studies investigating the results of people who underwent surgical repair of their ACL had a much higher rate of persistent instability. Studies have found that these people often needed additional surgical procedures.

One of the major reasons ACL repair has not worked well is that the environment surrounding the ligament caused the repair not to work.

In general, ligaments will heal without surgical intervention. For example, when someone tears the medial collateral ligament (MCL), they seldom require a surgical procedure. Similarly, ankle sprain injuries (torn ligaments in the ankle) seldom require surgical repair. Most often, these ligaments will heal without surgical intervention. So why is it the case that the anterior cruciate ligament in the knee does not heal?

The area surrounding the ACL is different. The other ligaments mentioned before are surrounded by soft tissues such as muscles and tendons. The anterior cruciate ligament sits right in the center of the knee joint. Surrounding the ligament is joint fluid, called synovial fluid. This synovial environment surrounding the anterior cruciate ligament is thought to be a major reason why the ligament does not naturally heal. Instead of this being an environment that supports healing, the synovial fluid actually inhibits a healing response. Furthermore, when surgery is performed to repair the torn ligament, the surrounding environment does not allow for normal reconstitution of the ligament. When these types of early ACL repairs were performed, the results were very poor.

Therefore, recent efforts to find a way to repair the ACL have focused on controlling that synovial fluid, and the environment that surrounds the healing ligament.

The hope is that by creating an environment conducive to healing, that the ligament can repair itself and not have to be replaced with a reconstructed ligament. After all, ligaments seem to want to heal, and if the ligament exists within the right environment to support that healing, it makes sense that this treatment could be possible.

ACL Reconstruction

In the case of ACL tears, the gold standard for treatment is ACL reconstruction. Reconstruction means that the old ACL is removed, and a new ligament is created using non-ACL tissue.

For most young athletes, this means using tissue from somewhere else in their body to create a new anterior cruciate ligament.

The most common locations to harvest tissue graft are from the patellar tendon in the front of the knee or the hamstring tendon in the back of the thigh.

Once the tissue has been obtained, it is inserted into the location of a normal ACL, and held in place with various types of fixation devices. Over time, the tissue graft heals in a good position and assumes the role of a normal anterior cruciate ligament.

ACL reconstructive surgery is often successful, but it does not come without downsides. One of the major problems of ACL reconstruction surgery is obtaining the tissue used to reconstruct the ligament. This tissue has to come from somewhere, and there are problems associated with removal from these other locations including pain, weakness, and altered joint mechanics.

Some people may choose to have donor tissue obtained from a cadaver, but these grafts have been shown to be weaker than a normal ACL and have a higher rate of failure, especially in younger athletic people. For the most part, donor grafts are used in people who no longer participate in competitive sports such as high school or collegiate athletes.  Donor grafts can be beneficial in the lower demand athletes such as weekend warriors.

Lastly, we know that people who undergo ACL reconstructive surgery have a much higher chance of developing arthritis in their knee joint, and often this occurs in the decades following ACL reconstruction. One of the reasons people may develop arthritis and there are joint is because of altered joint mechanics by having a nonnative graft used in place of the ACL.

Bridge-Enhanced ACL Repair

Bridge-enhanced ACL repair (also called BEAR surgery) is not the first technique that has been used to try to repair a torn ACL. However, this is the latest development and has shown some early results that have been promising.

The BEAR surgical technique was developed to address the problem of healing within the environment of the synovial fluid around the knee joint. By creating a micro-environment within the center of the knee, where the ACL is located, the researchers have tried to create a space where healing can occur.

The way the BEAR surgery works is to use a temporary suture device in the location of a normal ACL to hold the alignment of the knee joint in proper position while the ligament heals. Surgeons then implant a synthetic matrix around the ends of the torn ACL. Within this matrix, stem cells are injected in order to stimulate the healing process. 

Potential advantages of ACL repair surgery promoted by the surgeons developing these techniques  include:

  • Less pain because of no need to obtain the graft tissue
  • No large incisions, the procedure is done entirely arthroscopically
  • Retains native ACL tissue

The investigators readily admit that the long-term results of this surgical procedure are not well understood. It is not known if this procedure is better or worse than ACL reconstruction. 

There have been some promising early results for bridge-enhanced ACL repair surgery. Researchers have published their results of slightly less than 100 patients who have had this surgical procedure and showed results that are comparable to the early results after ACL reconstruction surgery.

MRI findings showed that these patients do heal their ACL, and the early results show that these patients have knees that are stable and allow them to return to sports activities. The results do not show that this procedure is better, or even as good, as ACL reconstruction in the long-term. In addition, while there are hopes that people who undergo ACL repair may not have high risk of developing knee arthritis, this has not been shown in the data.

Like many medical advancements, it often takes years or even decades to determine if a new treatment is as effective, better or worse than a standard treatment. That said, this is an encouraging step and creating a lot of interest in whether or not we can find a way for ACL injuries to heal.

A Word From Verywell

Injuries of the anterior cruciate ligament are potentially devastating injuries for young athletes. Even with successful reconstructive surgery, athletes face a long recovery, a potentially painful recovery, and the prospect of developing arthritis later in life. Research is ongoing to develop a better way to address ACL injuries.

One of the techniques proposed to better manage ACL injuries is repair of the ligament. Early research has shown some promising results, but there is no long-term data to support ACL repair over ACL reconstruction. The gold standard for treatment of ACL injuries is still reconstructive surgery. There is undoubtedly promise in new techniques to repair the ligament, but the jury is still out as to whether or not this surgical procedure is better, or may be worse, then ACL reconstruction. 

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Article Sources

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  • Perrone GS, Proffen BL, Kiapour AM, Sieker JT, Fleming BC, Murray MM. "Bench-to-bedside: Bridge-enhanced anterior cruciate ligament repair" J Orthop Res. 2017 Dec;35(12):2606-2612. doi: 10.1002/jor.23632