AFLW player Jacqui Yorston describes them as "the three letters no-one ever wants to utter".

An ACL (short for "anterior cruciate ligament") tear is the notorious knee injury footballers fear.

On average, they require 12 months of rehabilitation, and, as was the case when Erin Phillips fell to the turf during the 2019 grand final, they can send a stadium of raucous fans silent in one dreaded moment.

In Yorston's case, the injury occurred innocuously at a training session in January 2021.

The Gold Coast Sun hadn't done an ACL before, but she knew immediately what it was.

"I just had to wait for the scans to tell me how bad it was," she tells ABC Sport.

"Some people describe it like a pop, but I didn't feel a pop.

"I just felt instant pain."

Yorston remembers the team physio rushing to her side and asking her to roll over.

"But I couldn't lift my leg," she says.

As it turns out, Yorston's instincts weren't far off.

Scans would later show that in addition to tearing her ACL, she had also torn her MCL (medial collateral ligament), lateral and medial meniscus.

Family history, previous ACL injury two biggest risk factors

Kay Crossley is the director of LaTrobe University's Sport and Exercise Medicine Research Centre.

She has previously worked with the AFL on Prep to Play, an ACL injury prevention program, and is now leading work to prevent knee injuries in women's community football in Victoria.

The two biggest risk factors for doing an ACL, Professor Crossley says, are whether you have done an ACL before, and a family history of ACLs.

In this regard, Yorston's genes were working against her. One of six children, her mum had done three ACLs, and her brothers Josh and Ryan two each.

But the former Brisbane Lion never considered herself at particular risk.

"It was actually the fittest I'd ever felt coming into a season," she says.

"I've also got stockier, stronger legs than the average female, so I was like 'nah, I'll be right'."

As a result, Yorston says she spent weeks in a "daze" of shock and denial about the injury.

"I experienced a bit of devastation, as you can imagine," she says.

"The surgeon basically looked at me and went, 'that's a very ugly knee in there'".

While he assured her that the knee could be fixed, he warned the 21-year-old that her rehab journey would be a difficult one.

In this regard, Yorston says she was grateful to have her brother Josh to lean on — who was rehabbing from his second ACL at the time, also sustained playing football.

"People won't tell you how painful they are; he was the only one who told me [honestly]," she says.

"No joke, it was insane, it was the most painful thing I've ever been through."

Yorston adds that it took three weeks — and until the night she saw the surgeon — before she was finally able to put any weight on her leg.

"I said to him, 'how am I meant to do my rehab properly when I go back to work?'"

Part-timers take unpaid leave to juggle rehabilitation, work

Over four seasons of AFLW, Yorston has experienced the gamut of work arrangements to balance alongside football.

In season one, at 18 years old, she lived at home and was able to focus solely on football.

When she was traded to the Suns, however, she took up working four days a week, increasing to full-time just before she did her ACL.

In order to complete the necessary rehab for her knee, she would eventually take three and a half months of unpaid leave from work.

"My boss is really good," Yorston says.

"He was in the AFL system a while back with the [Sydney] Swans, so he understands the nature of it … I'm really grateful and lucky to be in the situation I am."

During this time, Yorston relied on income protection to get her by.

Under the current AFLW CBA, if a player loses income because of a football injury, they are entitled to 80 per cent of their net weekly income, or $2000, whichever is smaller.

While this helped keep Yorston afloat, she couldn't help but compare her situation to partner Tanah Boyd, who is a professional NRL player with the Gold Coast Titans.

"I'll tell you what's torture: torture is waking up at the same time as Tanah," Yorston says.

AFLW players more at risk than men

According to Professor Crossley, the differences in the conditions of men's and women's sport are part of what makes it difficult to understand why AFLW players are sustaining ACL injuries at higher rates than men.

While the exact ratio has fluctuated significantly, at one point in the early seasons, AFLW players were up to 9.2 times more likely than AFL men's players to injure their ACLs.

Since then, the ratio has broadly stabilised at anywhere between four and six times more likely.

Most promisingly, in 2021, ACL injuries in AFLW were at an all-time low.

In 2022, however, these types of injuries have, once again, trended upwards.

Professor Crossley warns that such figures need to be taken in context.

"They are small numbers and we just don't have enough years of data to know the true incidence," she says.

Professor Crossley qualifies this by saying that the discrepancy applies when "you do nothing", meaning, when no intervention is applied to address the gap.

"It's still way too high," she says. "We need to get the rates down."

Addressing the gendered gap in ACL injuries involves researchers teasing out the contribution of what Professor Crossley's team at LaTrobe call "modifiable" and "non-modifiable" factors.

"Modifiable" factors are those that can be changed; priority could be given to making women full-time athletes, for example, increasing their capacity to do the rehab and prehab work required to give them the best chance of staying injury free.

"Non-modifiable" factors, by contrast, include the big two (history of ACL injury and family history), but also so-called 'biological' or 'physiological' factors that might put women at higher risk.

One that has previously been floated, for example, is the idea that women's generally wider pelvises may put more strain through the knee.

This one, however, has been "debunked a fair bit", Professor Crossley says, adding that it fuels the myth that women's bodies are not up to the demands of sport.

"They also thought they couldn't run 10km on the track, or triple jump because of their 'weak pelvis'.

"There's a lot of sports that are relatively new to women because people thought they were too fragile for them, so I really think we need to get rid of this narrative."

The other risk factor that has garnered increasing media attention is the potential impact of hormones, such as estrogen and progesterone levels.

There is some debate, for example, over whether ligament laxity (or "looseness") changes over the course of woman's cycle, in turn increasing propensity for injury.

At the moment, however, Professor Crossley says evidence lags behind the hype.

"We need more research to understand the contribution of hormonal factors," she says.

"I think we'll find that it contributes a small amount to the injury risk."

Gender norms, socialisation play critical role in injury — and prevention 

Aaron Fox is a researcher at Deakin University's Centre for Sport Research and says the research his team has done demonstrates the complex interplay of both modifiable and non-modifiable factors.

For example, one difference his team has noted is that AFLW players are injuring their ACLs in different game-day scenarios than men.

While men often injure their ACLs in contested marking situations, one Deakin study showed that AFLW players frequently did ACL injuries in "non-contact" situations, such as when players have to react to an opponent changing direction.

"We concluded that there was this defensive nature to the way injuries are occurring in AFLW," Dr Fox says.

"So our hypothesis is that putting them in an unanticipated decision-making scenario is going to increase the load placed on the knee."

This, says Dr Fox, is a classic example of where teasing apart the reason for gendered differences gets so tricky.

Australian Rules Football is a "360 degree sport", he explains, involving many changes in direction.

With fewer women having grown up playing Australian rules football until recently, this means men are often better socialised to deal with the unique directional nature of the sport.

What this doesn't mean is that women's knees are inherently more susceptible to injury.

For example, Dr Fox points to research that shows that when it comes to dance — a sport many more girls participate in at a young age — men and women are equally likely to do their ACLs.

Such data, he says, supports the idea that the developmental opportunities provided to girls and women to participate in certain sports "have a significant impact [on likelihood of injury] down the track."

"Your upbringing, your training environments and your access to staff and facilities all have an impact on the way you move," Dr Fox says.

Especially relevant in an AFLW context, then, is the impact of players being part-time.

On ABC Sport's The W Podcast, Erin Phillips made headlines this season by arguing that making AFLW players full-time would reduce the rate of serious injuries sustained.

"I think that's a fair assumption," Dr Fox says.

"Injury prevention programs and strategies take time and effort to implement.

"Coaches, when they have a limited amount of time [with their players], might think 'why would I dedicate 15-20 minutes to this injury prevention program? I've got a limited amount of time to work with them, so let's focus on the important things.'"

Professor Crossley agrees.

Players face missing two seasons of football with likely August start

With the next AFLW season looking increasingly likely to begin in August 2022 — just four months after this season ends — ACLs will no doubt be on the agenda again.

One consequence of such a short turnaround is that players who injured their ACLs early this year will miss two full seasons of football.

This was a situation Yorston found herself facing this season, when the AFL originally flagged bringing the season forward to December.

"If the season was brought to December, which was first proposed, I would have been out of the game for two years. That would have been devastating."

As a result, and if the AFLW season is brought forward, Yorston's thoughts will be with those who are currently going through their ACL rehabilitation, including teammate Jade Pregelj.

"I have felt deeply for everyone who did [an ACL] this year.

"You don't realise the mental strain that it puts on you for the next 12 months."

Until AFLW players can be made full-time, Yorston wants to see more research and staffing resources put into prevention.

"I would love to see more research, and for all clubs to have someone who is going to conferences, regularly finding out the newest and most important information to pass on to players and coaches.

"I know it's expensive, but it'd save a lot of money in terms of paying knee reconstruction fees.

"It's such a high risk in our sport and it genuinely makes life so hard as a part-time athlete."