It’s an injury that can hit any athlete, but for reasons that remain uncertain, females are at a much higher risk to tear their anterior cruciate ligament.

The anterior cruciate ligament – commonly called the ACL – is the smallest ligament in the knee, connecting the shin bone to the thigh bone.

When the ACL is torn, the knee loses much of its stability.

“If you read the literature, the literature is clear,” said Michael Shaffer, physical therapist and athletic trainer at Iowa State’s Cyclone Sports Medicine. “If you compare – in the collegiate setting – men and women – especially soccer players or basketball players – there’s a much higher incidence in terms of women who would tear their ACL then men. In soccer, it’s anywhere from six to nine times. In basketball, it’s probably closer to three to six times as many as men.”

The Cincinnati Sportsmedicine Research and Education Foundation has estimated that about 1 in 10 female varsity collegiate athletes have some type of season-ending knee injury each year, including approximately 3,000 who tear an ACL.

Those are numbers ISU women’s basketball player Erica Junod knows all too well. The sophomore tore her ACL in practice on Nov. 5.

“Tearing my ACL never crossed my mind before,” Junod said. “It just wasn’t something I worried about.”

Junod might not have been worried, but others are.

ISU women’s soccer player Lauren Sims tore her ACL Oct. 14 in a game against Texas.

Sims has had over six months of recovery time since her surgery 10 days after the injury, but the injury is something she’ll always keep in the back of her mind.

“[Tearing your ACL] crosses everybody’s mind,” Sims said. “It doesn’t stop you from going out and playing hard, but it crosses your mind.”

Sims said as a soccer player it’s no longer a matter of if you’re going to tear your ACL.

“I knew that it could happen, and I knew that it probably would happen. It was just a matter of when,” she said.

Although the National Collegiate Athletic Association does not compile exact data on ACL injuries, it has estimated that a female athlete can be expected to tear the ligament once with every 300 participations in practice or games.

Orthopedic surgeon Peter Buck works at the McFarland Clinic in Ames and also serves as a consultant for the ISU men’s athletic teams. He said he sees “a ton of kids from both high school and college” come in with similar injuries to Sims’ and Junod’s. The strange thing, he said, is that there’s no way of telling why females are affected more than males.

“I don’t think we’re going to find one answer,” he said.

Theories range from women having wider hips putting more pressure on the knee ligament, women having smaller notches through which the ACL connects to the leg making it more susceptible to pinching and to hormonal fluctuations.

Shaffer said it’s really a combination of all those things, but he has read about another theory as well.

“If you look at some other research, you’ll see men and women use their muscles differently,” he said. “Women soccer players probably have the highest incidence of anybody because they have such strong quadriceps, and women – when they land or cut – seem more quadricep dependent rather than hamstring dependent.”

Shaffer said what that does is pull the shin bone forward out from underneath the thigh bone, creating a larger risk to tear.

ISU high jumper Gina Curtis has torn her ACL twice, leading to four surgeries – two reconstructive where the ligament was replaced and two less-invasive arthroscopic surgeries.

Curtis has heard the numbers relating to knee injuries, but they don’t worry her.

“I’m not really concerned. Reinjuring it never really crosses my mind,” she said. “There was probably a bigger fear of injury after I hurt it the first time then there is now.”

Curtis’ first reconstructive surgery was done in 1997 and involved replacing the torn ligament with one taken from a cadaver.

Buck said it’s those kind of surgeries that really don’t happen anymore.

“Taking a ligament from a cadaver is really our third choice,” he said. “Before there was always a chance of a transmission of hepatitis or AIDS. That’s not really a risk anymore, but there’s always a chance the body won’t really accept it.”

The first two choices are replacing the ligament with a graft from either the hamstring or the patellar tendon.

Buck calls the surgery involving the patellar tendon “the gold standard,” but “both surgeries are pretty equal,” he said.

While Sims had the patellar tendon surgery, Junod’s hamstring graft allowed her to return to the court competitively after just three months – one of the benefits to that type of surgery.

Shaffer said although using the hamstring graft has become popular over the last year or so, patellar tendon grafts also have benefits.

“It’s usually a little stronger than the hamstring graft, especially right away,” he said. “With the hamstring graft, the patient has to be careful not to do too much too soon.”

Last year, more than 95 Division I women’s basketball players tore a knee ligament requiring them to miss the rest of the season.

To put that into perspective, there are 318 Division I basketball teams. If 12 players play on each team, that’s a total of 3,816 women’s basketball players. Those who tear a knee ligament equals roughly 2.5 percent.

And it’s those 2.5 percent that researchers are trying to find a prevention program for. Programs have been started all over the country, but nobody knows if they are working.

“It’s really too early to tell,” Shaffer said. “There’s so much differing literature saying this and saying that. Nobody really knows.”

The uncertainty doesn’t bother Junod. Her team finished the season by losing in the second round of the NCAA tournament. She’s now preparing for next season.

Junod said she was a little uneasy to get back on the court, but now she’s not afraid.

“I held back a little, but then I realized I just have to go out and play, and be aggressive,” she said. “I try not to think about it. If I worry about it and don’t go all out, I think I’m more likely to reinjure my knee.”