The Serious Long-Term Effects of ACL Reconstruction Surgery

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We tend to take for granted that our bodies are finely tuned machines and complex neural circuitry allows them to do the amazing things we’re designed to do. A 2011 study shows that these essential circuits are first messed up by an ACL injury, and then by the long-term effects of ACL reconstruction surgery (1).

Long-Term Effects of ACL Reconstruction Surgery

Before I get into the ACL surgery side effects, let’s review what the ACL is. The anterior cruciate ligament (ACL) is one of four main ligaments that provide stability and precise motion to the knee.

The ACL runs through the middle of the knee and attaches the bottom of the femur (the long upper-leg bone) to the top of the tibia (the larger lower-leg bone). The ACL is responsible for controlling front-back motion and rotation in the tibia, which stabilizes the knee.

The ACL can become torn or damaged, and these injuries are quite common in athletes, such as soccer and football players, and other active people who place intense forces on their knees. When the ACL is injured, this causes excess rotation and motion in the tibia and makes the knee unstable as shown in this brief video.

The conventional go-to treatment for a torn ACL is surgery to reconstruct the ligament. If you’ve followed this blog for any length of time, you know that ACL surgery side effects are numerous. We know, for example, the reconstructed knee never functions like it did originally because the mechanics of the knee are permanently altered following ACL surgery (2).

Why? The ACL graft, the new ligament, is attached at a steeper angle, which can not only cause rotational instability in the knee but can also disrupt the normal sense of proper position.

Additional long-term effects of ACL reconstruction surgery include the fact that despite popular belief, knee arthritis is not prevented by ACL surgery, and in fact, the operation may cause arthritis to set in sooner (3). Also either knee, the knee operated on or the opposite knee, has a six times greater chance of tearing following ACL surgery in active patients who return to sports after the surgery (4).

And just when we think we’ve encountered it all, another study showing still more long-term effects of ACL reconstruction surgery side pops onto our radar screen, like the one below.

Learn more about the treatment of ACL without surgery.

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Nerve Interaction With Ligaments Like the ACL

The severe failings of modern orthopedic surgery are twofold: focusing on one body part and only considering its mechanics. I’ve blogged extensively on the fact that there is no such thing as a “knee.” There is a machine called the “spine-leg” that has a part that’s specialized that we could call “the knee.”

So by making everyone think that the knee acts in isolation of its other parts, we’re doing a huge disservice to reality as the knee works in concert with the spine, hip, and ankle parts of that machine. The second major issue is that modern orthopedic surgery completely forgets about the wiring of the body. What do I mean?

We see all about us these days ever-sophisticated electromechanical devices. One that you may have seen is the complex of gears, joints, and levers that make up the machinery for stabilizing a camera. You can find these devices to stabilize your phone or a GoPro or on every mid-priced drone being sold with a camera. This serves to make the picture ultra-steady despite movement.

These devices have been around for a long time, but they cost tens of thousands of dollars and are used only by professional movie photographers and your local news station filming from its chopper cam. Now they’re miniaturized and mass produced.

Let’s say this apparatus gets broken in some way so that it no longer works correctly to stabilize the camera. We know that there are two major categories that we need to consider to see why it’s not working: mechanical and electrical. The mechanical part is easy enough, as all we need to do is to inspect the gears, joints, and levers.

However, if there’s nothing wrong there, we also know that there could be problems in the wiring or complicated circuitry that tells the device which position the camera is in relative to the ground and how to move to counteract that movement. However, for modern orthopedic surgery, it’s all about inspecting the gears, joints, and levers of the body, and there is no focus on the wiring and circuitry.

The paper I’m reviewing this morning concerns the wires and circuitry of the ACL. While the ligament has mechanical functions, like stabilizing two bones that make up the knee, it also has a large number of position sensors that provide information to the muscles of the leg on how to fire through a bit of wiring call the “gamma loop.”

Think of this as like the sensors in the joints of the camera stabilization system that then tell the motors to adjust the position of the camera. Said another way, the sensors in the ACL tell the quadriceps muscle (the big one in the thigh) how much to fire and when. So a busted gamma loop means that the ACL isn’t coordinating muscle firing that in turn protects the knee by adjusting the overall joint position.

Research on the ACL and the Gamma Loop

This 2011 study used a number of different modalities to measure the activity of the gamma loop in patients without an ACL tear, with an ACL tear, and with an ACL reconstruction (1). The researchers found that, not surprisingly, just tearing your ACL impacts this significant bit of neural wiring. This makes sense as the ACL has tiny position sensors that could be injured in the same trauma that tore the ligament.

Also, loose ACL fibers won’t pull on the intact sensors the same way. Also, not surprisingly, they found even worse function of the gamma loop when the ACL was surgically reconstructed. Why? There is no way to hook up the thousands of microscopic position sensors in the tendon graft that serves as the new ACL so that the body can react to pulling on the artificial ligament.

No matter how you cut it, ACL surgery is not a replacement of the original equipment but a 1980s attempt at replacing what was lost. What you get doesn’t function like what was there, which is one of the big reasons we push suitable ACL tear candidates toward ligament healing using our proprietary same-day stem cell injection. The goal is to keep the mechanical function and wiring as intact as possible.



(1) Konishi YU. ACL repair might induce further abnormality of gamma loop in the intact side of the quadriceps femoris. Int J Sports Med. 2011;32(4):292-296. doi:10.1055/s-0030-1270488

(2) Kovacic JJ in Complications of Anterior Cruciate Ligament Surgery, AAOS Monograph Series 2005. Accessed August 25, 2020.

(3) Barenius B, Ponzer S, Shalabi A, Bujak R, Norlén L, Eriksson K. Increased risk of osteoarthritis after anterior cruciate ligament reconstruction: a 14-year follow-up study of a randomized controlled trial. Am J Sports Med. 2014;42(5):1049-1057. doi:10.1177/0363546514526139

(4) American Orthopaedic Society for Sports Medicine. “Second ACL Injuries 6 Times More Likely After Reconstruction.”

Learn about Regenexx procedures for knee conditions.
Chris Centeno, MD is a specialist in regenerative medicine and the new field of Interventional Orthopedics. Centeno pioneered orthopedic stem cell procedures in 2005 and is responsible for a large amount of the published research on stem cell use for orthopedic applications. View Profile

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NOTE: This blog post provides general information to help the reader better understand regenerative medicine, musculoskeletal health, and related subjects. All content provided in this blog, website, or any linked materials, including text, graphics, images, patient profiles, outcomes, and information, are not intended and should not be considered or used as a substitute for medical advice, diagnosis, or treatment. Please always consult with a professional and certified healthcare provider to discuss if a treatment is right for you.

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