How likely is an athlete who undergoes ACL reconstruction to tear the ACL graft in the surgical knee or tear the intact ACL in her opposite knee? And are there risk factors that increase an athlete’s chance for suffering a noncontact ACL injury? In this Ask Dr. Geier column, I attempt to answer those questions for an adult athlete who has suffered a second ACL tear.

Marie writes:

Hey Dr. Geier,

Bad news. I’ve torn the ACL on my other knee while playing derby. I have a ton of questions and was wondering if you would be willing to answer them, since they seem to be something you would talk about on your podcast.

I’ve been looking at some articles on bilateral ACL tears and am finding different numbers on what percentage of athletes tear both. I’ve seen a paper suggesting that 24% of athletes who undergo ACL reconstruction and return to sports will have a second ACL surgery. What do you think this is an accurate number?

I was also reading about intercondylar notch width and bilateral ACL tears. My MRI shows that my intercondylar notch is narrow. Do you think that anatomy plays a large role in ACL tears or is this not a well validated hypothesis?

Last question. I haven’t been able to find any numbers on what the risk is of having to undergo a third ACL surgery (like a revision surgery), if you return to sports after having two ACL reconstructions. I know that I can return to sports after this surgery, but have no clue what the risk is.

Those are good questions, Marie! As for the risk of a second ACL injury, people are often surprised that there is a chance that the athlete injures the opposite, healthy knee. In fact, it might be just as likely as tearing the graft in the previously injured knee.

Can an ACL brace prevent tear the ACL graft?

Risk of tearing the graft or the ACL in the opposite knee

Many studies have published data showing the risk for tearing the reconstructed ACL or the contralateral knee’s ACL. I tend to quote the database collected by the MOON Study Group. That group of orthopaedic surgeons has been collecting data on ACL surgeries done at many centers in the United States since the early 2000s. In their population, the surgeons found that 3.0% of the patients had torn the ACL graft in the surgical knee by two-year follow-up. 3.0% of the patients had torn the contralateral, healthy knee’s ACL in that time.

Risk factors for a tear of the ACL graft

As for risk of ACL tears generally, many factors are thought to play a role. Anatomy and size of the ACL, limb alignment, intercondylar notch width, neuromuscular control, landing mechanics, hormones and more have all been suggested to influence an athlete’s risk of ACL tear.

The intercondylar notch is the space in the femur where the ACL resides. The thought is that someone with a narrow notch could develop impingement on the ACL, increasing the risk of injury. Some studies have suggested that a narrow intercondylar notch is associated with increased rates of ACL tears. And orthopaedic surgeons often do widen the notch during ACL reconstruction. We use a burr to remove a small amount of bone from the lateral wall of the femur, called a notchplasty.

Even if we tested for notch width in healthy athletes, we don’t know the real significance of that information. To my knowledge, surgeons are not performing surgery to widen the intercondylar notch in healthy patients to prevent a theoretical ACL tear.

Also read:
Ask Dr. Geier: Nonoperative treatment of ACL tears
Ask Dr. Geier: Return to sports after ACL surgery

Female soccer player suffers ACL injury

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Whitney DC, Sturnick DR, Vacek PM, DeSarno MJ, Gardner-Morse M, Tourville TW, Smith HC, Slauterbeck JR, Johnson RJ, Shultz SJ, Hashemi J, Beynnon BD. Relationship Between the Risk of Suffering a First-Time Noncontact ACL Injury and Geometry of the Femoral Notch and ACL: A Prospective Cohort Study With a Nested Case-Control Analysis. Am J Sports Med. August 2014 42 1796-1805

Wright RW, Dunn WR, Amendola A, Andrish JT, Bergfeld J, Kaeding CC, Marx RG, McCarty EC, Parker RD, Wolcott M, Wolf BR, Spindler KP. Risk of Tearing the Intact Anterior Cruciate Ligament in the Contralateral Knee and Rupturing the Anterior Cruciate Ligament Graft During the First 2 Years After Anterior Cruciate Ligament Reconstruction: A Prospective MOON Cohort Study. Am J Sports Med. July 2007 35 1131-1134.