For Dr. William Garrett, watching female athletes compete in the Olympics this summer was, at times, excruciating.

“When I’d see the women making sudden stops on hard floors, or the gymnasts make a landing on the floor exercises – I cringe every time,” says Garrett, an orthopedic surgeon and team physician for Duke University.

One thing in particular made Garrett sweat: the fickle anterior cruciate ligament, one of four major ligaments in the knee and the one that has, since the 1970s, proven to be something of a ticking time bomb for post-pubescent female athletes.

In certain sports – especially soccer, basketball, lacrosse and volleyball – that require quick turns and hard, abrupt landings girls are up to eight times as likely to rupture their ACL as are boys. It’s a vexing problem that, despite considerable study, still isn’t entirely understood.

Reasons for the increase

Why girls? The suspected culprits can be broken down into two categories:

• Biomechanical differences. In part because the higher risk among girls doesn’t occur until puberty, some believe that estrogen plays a key role. While males see an increase in testosterone around this time, aiding the building of muscle, girls see an increase in estrogen, which may make tendons such as the ACL more relaxed, and thus more susceptible to injury.

• Anatomical differences. One intense area of study has been the anatomical differences between boys and girls post-puberty. Females at this age are more prone to be knock-kneed, have weaker hip muscles and have dominant quadriceps (muscles on the front of the thigh) versus hamstrings, according to Dr. James Fleischli with the OrthoCarolina Research Institute in Charlotte.

As a result, they tend to stand more upright with knees extended when they land or make sudden turns, which may stress the ACL.

Treatment typically requires surgery to replace the torn ligament, then months of rehabilitation to restore strength and range of motion.

Rise in female athletes

The prevalence of ACL injuries among female athletes is a relatively new phenomenon, dating to 1972 and enactment of the federal Title IX legislation mandating equal opportunities for males and females in sports associated with educational programs that receive federal funding.

The number of female knees twisting and landing on hard courts and playing fields has since skyrocketed: In 1971-72, the last school year before Title IX went into effect, there were 294,051 female high school athletes.

In 2009-2010 that number had grown to nearly 3.2 million. (The number of male athletes during that period also grew, from 3.7 million to 4.5 million.)

A growing emphasis on playing just one sport has also contributed to the problem, adds Dr. Alex Creighton, associate professor of orthopaedics at UNC Chapel Hill,

“Sometimes injuries are just bad luck,” says Creighton. “Sometimes being exposed to the same thing over and over is more likely to result in an injury.”

Not knowing exactly why girls are more susceptible to ACL problems has made warding off the injury especially challenging.

Based on what is suspected, some efforts have been made to identify “at-risk” female athletes – those who are knock-kneed or land in a more upright position or with their hips straighter. But those efforts – most notably one that appeared to benefit the Norwegian women’s team handball team – have required the extensive use of video analysis and an on-site physical therapist, expenses most programs can’t afford.

Efforts have also been made to create training programs tailored specifically to heading off ACL injuries.

The Sports Medicine Research Laboratory at UNC Chapel Hill has developed the Performance Enhancement and Kinetic Control, or PEAK, program, which incorporates ACL-specific exercises into an overall warmup program. The Capital Area Soccer League in Raleigh began using it last year for 600 female players.

Of course, in sports another way to find out what works is to ask the best team around. Talent is key, but rare is the team riddled with injuries that wins a championship.

Conditioning programs

Staying healthy last year helped Charlotte’s William A. Hough High School’s girl’s soccer team win the state championship and the Powerade/ESPN Fab 50 National Championship.

Head Coach David S. Smith attributes the team’s success to several factors, notably the team’s focus (“The girls are so businesslike ... They’re a joy to coach”) and a high-tech turf field that helps prevent the knee-grabbing that can result in an ACL injury.

He’s also quick to note the emphasis on conditioning.

“A lot of the kids, especially the girls, are in physical conditioning classes at school, like weightlifting,” says Smith, a social studies teacher who has coached at the high school level for 16 years. Those classes, he says, are taught by other coaches who can tailor a conditioning program to an athlete’s specific sport and needs.

He also credits the school’s athletic trainer, Meghan Hughes, for playing an active role in practice.

“She spends a lot of time with the kids, asking them what issues they’re dealing with, suggesting specific exercises,” says Smith. “She spends a lot of time on conditioning.” But, he adds, at this point there’s nothing specific they do that addresses ACL injuries.

Until more is known about why girls are more susceptible to ACL injuries and what can be done to try to prevent them, those following the issue say there’s not a lot more that can be done.

“Obviously, it’s a concern,” says UNC’s Creighton. “I don’t think we’ve found the holy grail yet.”