The ACL Family Tree

Is ACL Injury In Your Genes?

It’s a conversation that happens on sidelines and in physio clinics all the time..

"My brother/sister did their ACL, and now I've done mine."

For years, we've wrestled with this question: Is it just bad luck, or is there a genuine family link?

Well thanks to an interesting 2022 paper by Hasani and colleagues, we’re starting to see that there is something about this speculation.

This 2022 systematic review and meta-analysis has laid the foundation for our current understanding. Since then, further research has zoomed in on specific high-stakes groups, from elite professionals to our youngest athletes, adding crucial layers of detail.

In this deep dive, we'll unpack that landmark review, see how its findings have been tested in the real world, and explore a remarkable case study that brings the complexity of risk to life.

Let’s get into it.

What this Landmark 2022 Review Found

A systematic review and meta-analysis is the gold standard in research; it gathers all high-quality studies on a topic - in this case, 12 of them- and combines their data to find the overall truth. The findings from this paper are the bedrock of our knowledge on this topic.

• First-Time Injury Risk: The main headline from the review was clear - an athlete with a first-degree relative (a biological parent or sibling) who has torn their ACL has 2.5 times greater odds of suffering their own first-time ACL injury compared to an athlete with no family history. This wasn't a small finding; it was a powerful, combined statistic that confirmed the link.

• Subsequent Injury Risk: The risk doesn't disappear after your first injury. The review found that having a family history increases the odds of a second ACL injury (to either the graft or the other knee) by 2.4 times. The researchers broke this down further:

  • The odds of a graft rupture increased by 1.8 times.

  • The odds of a contralateral (other knee) injury increased by 2.3 times. When directly compared, the risk of tearing your graft versus your other knee was similar for those with a family history.

• The Gender Question: Crucially, when looking at first-time injuries, the review found that if a family history is present, the sex of the athlete does not change the risk. The increased odds were the same for both males and females.

• Why Does This Happen? The review explored the complex reasons behind this link. It's likely a combination of inherited traits and shared environments.

  • Nature (Genetics): Inherited anatomical factors like a steeper tibial slope or a narrower femoral notch are thought to play a role.

  • Nurture (Environment): Families often participate in the same sports, meaning they share the same exposure to high-risk movements. The review cited a study showing that 65% of people with a family history sustained their injury playing the same sport as their injured relative.

Putting This Evidence To The Test

The 2022 review gave us the big picture.

But what happens when we zoom in on specific, high-stakes groups like professional athletes or kids? Subsequent research has done just that.