May 27, 2023

ACL injuries are a growing problem

ACL injuries are a growing problem
ACL injuries are a growing problemACL injuries are a growing problem

AS THE COVID-19 pandemic abates and athletes everywhere prepare to return to the arena, new light is being shed on a serious risk they face. The anterior cruciate ligament (ACL) is one of four that hold the knee together. Tearing it, as at least 2m people do every year, is among the most immobilising injuries someone can sustain. ACL tears are usually a consequence of an awkward movement in a fast-paced game such as football. The surgery and rehabilitation needed cost billions of dollars a year. It is becoming increasingly clear just how devastating—and possibly preventable—this injury really is.

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Doctors have always recognised ACL tears as serious, but used to think that returning to the fray was possible six months after surgery. Elizabeth Gardner, head orthopaedic surgeon at Yale University Athletics, reckons, however, that nine months to a year is more realistic. That is a significant chunk of an athlete’s career. Even then, surgery alone is no guarantee of recovery. Re-tear rates are as high as 20%, “a lot higher than you would expect for a surgery that we think we do really well and is so ridiculously well studied”, Dr Gardner says. On top of this, recent investigations suggest that as many as three-quarters of those who suffer an ACL tear go on to develop arthritis of the knee 15-20 years later.

ACL tears are increasingly frequent. In 2018 researchers at Boston Children’s Hospital found that, over the course of a decade, the number of them relative to other orthopaedic problems had tripled among Americans aged under 18. This may be a consequence of moves towards single-sport specialisation in American schools. The reduced variety of body-movements thus engendered tends to focus strain repeatedly on particular parts of the body.

Recent studies in countries around the world, including Australia, Finland and Norway, support the idea that more young people than ever before are sustaining ACL injuries. Australia’s sports authorities, in particular, are trying to discourage overspecialisation by schools. Another reason for the increase may be artificial turf, which has become much more widespread in schools in the past couple of decades. There is evidence that in some sports, notably American football, this surface is linked with a higher rate of ACL injuries.

One of the most curious features of ACL tears, though, is that they afflict women far more often than men—as much as eight times more, some investigations suggest. Why, is the subject of intensive research. But a clue may lie in an apparent connection with the menstrual cycle.

A study published in 2013, of a group of women skiers in the Alps, found, for example, that those in the pre-ovulatory stage of their cycles were more than twice as likely to suffer an ACL tear than were those in the post-ovulatory stage. A four-year survey of 113 female England footballers, published in March, also found a clear correlation. Muscle and tendon injuries were far more common in the late follicular phase of the cycle, just prior to ovulation, than in the other phases.


The reason for this menstrual-cycle link is unclear. The body’s oestrogen levels spike just before ovulation—the point when tear-frequency rises—and the ACL has oestrogen receptors, so this might help explain what is happening. But the ACL is not alone among ligaments in sporting such receptors, and uncertainty remains about the true connection.

Other contributory factors to women’s higher ACL-tear rates may be female body shapes and movement patterns. Compared with men, women have wider hips, more-inverted knees and “over-dominant” quad muscles (meaning that the quadriceps femoris muscle group in front of the thigh bone is relatively stronger than the hamstring group behind it). All these things put pressure on the elaborate workings of the knee joint. Women also tend to land in a more flat-footed manner than men do, and to pivot more awkwardly.

Anatomy is what it is, so not much can be done about sex differences in hip shape and knee orientation. All athletes, however, can be trained how to move more safely, and this is particularly relevant for women. Straightforward exercise classes in balance and agility have been found to reduce ACL tears by 50%. Strengthening the muscles around the knee—especially the hamstring—with focused exercises is another way to reduce the chances of a tear.

Dealing with the menstrual cycle has, in the past, been trickier, since it entails individual athletes keeping detailed track of their cycles. Modern gadgetry makes this easier. For example, the American women’s football team (proper football, not the gridiron sort), who are the current world champions, use FitrWoman, an app that monitors a user’s cycle and tells her on which days it may be risky to train intensely. This is something that the team’s quondam high-performance coach, Dawn Scott, reckons contributed to their retention of the World Cup in 2019. And back in football’s home country, England, FitrWoman is also making a mark. The women’s team at Chelsea football club, who won this year’s Super League, have adopted the app as well.

This is the sort of thing that could be encouraged more widely, by introducing it into school and college sports. That does, though, require an awareness of the problem—and this is still lacking. In 2019, for example, St Mary’s University, Twickenham, in England, conducted a survey of more than 14,000 female athletes. It revealed that 81% of those with coaches never discussed with them the impact of their menstrual cycles on training. Nearly three-quarters said they had received no education regarding the cycle’s effect on their exercise regimes and fitness, and vice versa.

The topic of menses can be taboo even at the highest level of sport. In 2015 Heather Watson, a British tennis player, withdrew from the Australian Open citing “girl things”. She was applauded for publicly linking her performance to her period, even in the vaguest of terms, which is still a rarity among professional athletes. From the top to the bottom of women’s sport, then, a bit more openness and physiological realism might work wonders for knee preservation and the avoidance of problems in later life. Considering the rigour of modern athletes’ training regimes, it is surprising this is not already happening.

A version of this article was published online on June 18th 2021

This article appeared in the Science & technology section of the print edition under the headline “Wounded knees”