October 21, 2021

I, Science

The science magazine of Imperial College

Naomi Dinmore investigates why female athletes are more predisposed to suffer from an injury in the Anterior Cruciate Ligament - and why it might not just be down to biology.

2nd May 2021. Women’s Super League. Second half: Manchester City 2, Birmingham City 0. Having scored the first two goals of the match, Man City Striker Chloe Kelly is in the box, ready for the next shot.

Crack. Kelly goes down after a clash of knees with Birmingham player Rebecca Holloway. She stays down, visibly in pain. Five paramedics surround her, before she is stretchered off. Later, it is confirmed that she sustained serious damage to her knee.

A painfully abrupt end to her otherwise shining season. At 23 years old, she is one of the six shortlisted for WSL player of the season, and was one of the potential strikers for the Team GB Squad for the Tokyo 2020 Olympic Games.

She’s not alone – this particular type of knee injury in the Anterior Cruciate Ligament (ACL) is a common, yet debilitating injury for many players of sports like football, hockey and tennis, which involve running with frequent changes in direction and twisting of the knees.

The ACL is a strong band of tissue that connects your thigh bone to your shin bone, aiding in mobility and keeping your knee stable. Injuring this ligament can cause your knee to give way, making bearing the weight of your body unbearable.

It is estimated that women experience these types of knee injuries at 3-6 times the rate of men. This disparity is heightened in recreational players. What might have just started as a casual kickabout could end you up with reconstruction surgery and months, sometimes years, of recovery.

That’s what happened to hockey player Katy Matthews. Matthews currently plays recreationally in a Derbyshire league, but at age 15 tore her ACL playing for Belper Hockey Club, resulting in a long recovery including reconstruction surgery. “There was obviously no structure in my knee ligament-wise and so it just gave way,” she said. “I couldn’t go back to playing hockey for 18 months.”

So, what makes women at higher risk for ACL injuries than men?

This has been a widely studied area of research since the 1990s, when the disparity was first noticed. It is often attributed to biology – because women tend to have wider hips, the knees are often aligned at an inward angle, resulting in extra stress to the ligaments. Underdeveloped muscles around these ligaments could particularly affect recreational players. Other theories suggest that genetics or hormones are the reasons for these differences in the sexes – but there has been no conclusive evidence to show that either is the case.

Despite over two decades of research and interventions, the sex disparity for ACL injuries has still not been solved.

Therefore, it might not just be down to biology.

This is what a team of researchers from The University of Manitoba and the University of Nottingham have suggested. “The research in the field of ACL injury has focused predominantly on exploring this disparity in terms of sex-based biological factors: hormones, anatomy, biomechanics and things like that”, said Stephanie Cohen, a researcher of how environment impacts health, “we wanted to bring a gender perspective.”

Gender is about social contexts, rather than biological factors. Cohen suggested that in many areas throughout a girls’ life, the environment we are in can impact our biology. From a young age, “throwing like a girl” is seen as bad, and from a young age, boys tend to socialise more through sport. “Maybe when we get to adult women athletes, we are so habituated into using our bodies in certain ways,” she said.

Another factor could be to do with the environments sports players themselves are in. In March, a post went viral on social media showing the shocking difference in gym equipment – weights, machines, and space – given to the men’s and women’s National Collegiate Athletic Association basketball teams. Not having the resources to train properly could result in underdeveloped muscles, increasing likelihood of injury.

The researchers also suggested other social factors: differences for women and men in rehabilitation, relationships to coaches, and how men and women express pain differently. “It’s not that biology doesn’t matter at all, but that the biology might actually be quite entangled with these other social factors” Cohen said.

Matthews has continued playing hockey recreationally, but is still worried about the long-term consequences. “You kind of trust your knee a bit less”, she said, “it’s so much likely to happen again if it’s happened before.”


Naomi Dinmore is a student doing an MSc in Science Communication, with an undergraduate degree in Physics and Music. She is also the Web Editor for I, Scienceand is a lover of all things nerdy!