Waiting on ACL Surgery Protects Knee Cartilage

Repairing the ACL within a few weeks or months of injury has become the standard of care. However, is this really best for the patient? A new study demonstrates that we may be harming more patients with this approach than we’re helping. Let’s review.

ACL Reconstruction

I have seen many surgeons conclude that ACL reconstruction is one of the most successful orthopedic surgeries ever devised. Having said that, the actual high-level research on the procedure is not all that impressive. For example, this randomized controlled trial demonstrated that the patients who didn’t get ACL surgery did pretty well. In addition, patients often decide to get ACL surgery despite feeling fine a month or two after their ACL tear to stave off arthritis. However, research has shown that the procedure doesn’t reduce the rate of arthritis, meaning that those who get the procedure have just as much arthritis as those who don’t. In addition, the return to high-level sports for patients who get an ACL reconstruction is not that great at eight months post procedure. 

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The KANON Trial

You would think that given the popularity of the procedure, we would have lots of high-level research showing that ACL surgery works. We really don’t. One of the few randomized controlled trials out there, which was performed at Lund University in Sweden, is called the KANON trial, which stands for Knee Anterior cruciate ligament NONoperative versus operative treatment. The authors of that study relay that prior to their research, there were only two high-level studies performed on ACL surgery (Sandberg et al in 1987 and Anderson et al in 1989).

The New Research on ACL Surgery and Cartilage Loss

The new study was just published in February and was a reanalysis of the five-year data from the previously published KANON trial, which itself didn’t find that ACL surgery was the bomb. The striking finding of the new research was that the patients who were randomized to get early ACL surgery had more cartilage loss in their knee at five years postsurgery than those who were randomized to get physical therapy and later decide if they still needed surgery. How much more? About twice as much cartilage loss!

Why Is This Happening?

First, this is the first high-level study to look at ACL surgery and cartilage loss in a randomized fashion where half of the patients were assigned to an early surgery+rehab group and half to a delay surgery+rehab group. Second, you also need to realize that in the original KANON trial, 98% of the patients in the early surgery+rehab group had surgery compared to only 39% in the delay surgery+rehab group. Meaning, what this cartilage comparison is measuring is the negative effects of the ACL surgery.

Hence, if this finding holds up across multiple studies, why would this be the case? First, realize that an ACL reconstruction surgery doesn’t replace the original equipment, so what you end up with is, at best, an imperfect substitute for what you had. See my video below for a better explanation:

Meaning, the tendon graft that replaces the ACL has the following biomechanical problems when compared to having a torn ACL:

  1. It goes in at a much steeper angle than the original ACL, reducing the ability of the reconstructed ligament to stabilize the knee in various positions. Is that better than leaving the torn ACL alone (more on that below)?
  2. The reconstructed ligament is unlikely to have the same tension as the original, meaning that if it’s too tight, it may cause cartilage surfaces to wear faster.
  3. There is likely intrinsic damage done to the whole knee caused by drilling the graft tunnels, using anesthetics and steroids in the knee post-op (which have been shown to be toxic to cartilage), and inserting anchors.

Another thing to consider in the KANON trial is that some of the patients in the delayed-surgery group who opted not to get surgery may have had some natural healing of the ligament. In addition, they may have also been more diligent in correcting the biomechanical problems that in some patients caused the ACL to tear in the first place. Hence, it’s not a surprise to me that patients with early ACL-reconstructed knees are worse off on average than those who decided to wait to see if they really absolutely needed an ACL surgery or were fine with just physical therapy alone.

The New Concepts Pioneered by the KANON Trial

I see all around me, every day, younger and younger kids getting their ACL tears surgically reconstructed within weeks of their injury. While we can help about 60–70% of these avoid surgery with a precise injection of their own bone marrow concentrate, that still leaves 30–40% who have ACL tears we can’t help. This trial tells us that right now, the best evidence supports surgeons telling patients to wait to get their ACL reconstructed and to then do so only if absolutely necessary and that doing it this way will likely protect their knee better than pulling the trigger on early surgery.

The upshot? ACL surgery is not all it’s cracked up to be. I’ll be reviewing a few recent studies in upcoming blogs that all point in the same direction: delaying the decision to have ACL surgery or looking at other nonsurgical options is likely a good idea.

Learn more about ACL repair without surgery.

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.