Are Hormone Fluctuations Leading to More Women’s Knee Injuries?

Women’s sports have been on the rise. The participation rate for girls is at its highest since at least 2012 and investment in women’s professional teams is surging, too — just look at the record-breaking ratings for the WNBA the last couple of years or the new world-class stadium built for the Kansas City Current pro women’s soccer team. 

Another trend has become more apparent, as well: women and girls experience a higher number of knee injuries compared to men. In fact, young girls and women are between two and eight times more likely than men to tear their anterior cruciate ligament, aka ACL.

Why is that? And is there anything you can do about it if you’re a woman athlete?

What happens when you twist your knee

The ACL is one of four ligaments that connect your thigh bone to your shin. They hold your knee together and control the rotation and movement of your shin bone. Your knee also contains cartilage that cushions its bones and serves as shock absorbers. A sudden twisting motion or hyperextension of your knee can cause you to stretch or tear a ligament, cartilage or other tissues like the meniscus.

Sports like skiing, soccer, basketball and football have a higher risk for these kinds of connective tissue injuries. Treatment might include rest, pain medication, muscle-strengthening exercises or a knee brace. A complete tear to the ACL, for example — one of the most common knee injuries — requires reconstructive surgery, and recovery takes at least a year. In the worst cases, it can be career-ending for athletes.    

Why do women get more knee injuries  

Why do women injure their connective tissues more than men?  

That’s precisely what Jenny Robinson, PhD, a University of Washington Assistant Professor of Orthopaedic Surgery and Sports Medicine and Mechanical Engineering, is trying to find out.  

Women’s sport and exercise science is still relatively new, so there is still much to learn, but scientists suspect that some of it has to do with the fact that, in general, women and men have different anatomies. Women’s wider hips increase the angle between the thigh bone and shin, and women may move differently than men when playing sports. Differences in neuromuscular activation patterns — the way the brain sends signals to the muscles to move and contract — might help account for different injury rates, too.  

Another factor is the focus of Robinson’s Tissue and Regenerative Engineering Lab at UW’s Institute for Stem Cell and Regenerative Medicine. Robinson and her team are homing in on how the cells in connective tissues like ligaments and cartilages respond to changes in hormone levels and to how you move and stress the knee.

“With many of these injuries, there’s a quick turn and a high amount of strain,” Robinson says. “We’re trying to understand what the cells are doing at that moment of injury. Are female cells responding differently based on fluctuations in sex hormone levels that occur during the menstrual cycle or in life transitions such as pregnancy and menopause? It appears as though they are.”  

The research is still in its fledgling phase — Robinson says scientists weren’t widely looking at sex differences in orthopedic cells including ACL cells until at least 2016 — but early results show that female cells may not produce as much collagen, or as strong collagen, at certain stages of hormone changes a woman’s lifespan, such as in the menstrual cycle.

Collagen is key to regeneration, the process of restoring damaged tissues to full function following an injury. If female cells produce less collagen and the collagen that is there is weaker at certain times, it might make women athletes more susceptible to injury.  

Other things contributing to knee injuries in women

It’s not just physiological differences — social factors play a role too, like the fields women play on and the resources they have access to for training and nutrition.  

Facilities  

Despite Title IX and related developments in women’s athletics, young girls and women lack access to the kinds of training facilities and fields that men play on. Imagine the difference between running on a perfectly manicured turf field, versus one with divots and holes. This is often the difference between men’s and women’s playing facilities, and playing on a poorly maintained field can lead to injury. The same is true for gear —  companies are just beginning to design cleats for women soccer players, for instance.  

Training  

Most coaches and trainers recognize that strategic strength training helps women athletes get strong and avoid injury. For example, professional soccer players worldwide use the FIFA 11+ protocol to warm up, which has been found to significantly reduce leg injuries in women athletes. However, women have been historically discouraged from strength training, and stigma around women “bulking up” persists. 

Nutrition  

Women athletes are often told to eat less than they need to stay strong and fit. This may be for aesthetic reasons — for example in gymnastics, figure skating and cheerleading — or because they have mistaken ideas about how their weight might affect their performance. This can result in a condition called the female athlete triad, which includes unhealthy weight loss, menstrual irregularities and weaker bones. 

How to prevent and recover from women’s knee injuries  

There’s plenty that women athletes can do right now to prevent and recover from knee injuries, even as researchers like Robinson seek to better understand what’s causing them.  

Whether you want to avoid an injury or are recovering from one, it’s important to work with specialists who understand your sport and respect your athletic goals — from trainers to surgeons. If you’re trying to prevent an injury, Robinson suggests prioritizing the basics like regular strength training, good nutrition and plenty of time for rest and recovery.

“These things seem very straightforward, but I do think they are key,” she says.

She offers similar advice for those healing an injury: Work closely with your doctor or physical therapist to slowly regain strength and mobility, all while fueling properly and allowing your body to rest.

Above all, she says, remember that recovery takes time and “give yourself grace.”

The future of women’s knee injury prevention and recovery  

Understanding where you are in your menstrual cycle could soon offer women athletes a window into their performance capabilities. New apps allow women to track biomarkers so they can make more informed decisions about how to train for their sport — when to push and when to back off.  

But you don’t need an app to benefit from Robinson’s research. If you track your menstrual cycle, you might consider going easy on days when you know you’re ovulating, since early research shows that tissues may be more vulnerable during ovulation and the luteal phase, the second half of the menstrual cycle following ovulation, due to high or fluctuating hormone levels.  

Remember, though, that we’re just beginning to understand the messages that hormones send to our cells and how that relates to injury and regeneration.  

Also, Robinson says, “Every woman’s body is different.”

If you’re feeling truly depleted, it’s best not to push through, regardless of where you are in your cycle.  

In the future, Robinson hopes her research might lead to the development of a strategy or device to help women athletes recover from knee surgery more effectively.  

“Our hope is that we can find something that we can tell the surgeon to do during the actual reconstructive surgery or right after — during recovery and physical therapy,” says Robinson. “That would be really cool.”