AUSTIN, Texas In the knee's general structure, the anterior cruciate ligament is hardly noticeable.
Until it tears.
Then, its importance is announced in painful cries and reinforced during months of rehabilitation.
Women athletes seem to be reminded of the anterior cruciate ligament's importance much more frequently than men.
Despite numerous studies to find an explanation, the reason remains debated. There is no conclusive evidence that shows why women are more susceptible to anterior cruciate ligament injuries than men.
Although it's the smallest of four main ligaments in the knee and virtually useless in everyday movement, the anterior cruciate ligament's mere initials inspire dread in athletes.
When a doctor says ACLas in torn ACLan injured athlete knows the season is ending prematurely and a grueling rehab schedule awaits.
And for every man who's endured that painful rehabilitation, two women have been grimacing right along.
Among the dozens of ACL casualties this year in basketball alone are collegians such as Tennessee's Tamika Catchings, Connecticut's Shea Ralph, Purdue's Erika Valek, Texas' Tai Dillard and the WNBA's leading scorer last season, Sheryl Swoopes of the Houston Comets.
Dr. T.O. Souryal, director of the sports injury clinic at Southern Methodist University, confirmed in a recent interview with ESPN.com that women are twice as likely to suffer ACL injuries.
"Over the last five to 10 years, we've stumbled onto the fact that the ACL injury rate in women is twice as high as it is in men," Souryal said.
However, according to an NCAA report, Souryal's figures appear much too conservative.
According to the NCAA, female athletes are six times more likely to suffer an ACL injury than men, with almost 2,200 female collegiate athletes sidelined with the injury each year.
Though small, the anterior cruciate ligament is most important for athletes. Not only does it keep the tibia (shin bone) from pushing forward on the knee, it also stabilizes the knee in rotation.
Activities that require a straight-ahead motion, like walking, jogging and swimming, don't place strain on the ACL. But in basketball, soccer and other sports that requires quick starts and stops, cutting and changing direction, the ACL is most vital.
In women, it's also more vulnerable.
Among the theories for that are ones based on structural and hormonal differences between the genders.
"In 1988, a study was done to look at predisposing factors for ACL injuries in general," Souryal said. "What we found was that there was a structural predisposition that is detectable on an X-ray. Some people are born with a narrow tunnel that entraps the ACL.
"Women have a narrower notch than men, which may sound obvious, but proportionately, it's even smaller than would be expected. Maybe this is one of the factors that predispose women to this injury."
One theory is that men produce more testosterone, a muscle-building hormone, so naturally their muscles are stronger and more resistant to injury. However, that could also be explained by the fact that boys tend to start playing sports earlier than girls, thus spending more time building muscle.
Postural faults could also be a factor.
Because of childbearing, one theory goes, the Q-angle, a slope from the hips to the knee, is more dramatic in women than men. Thus, there's more pressure on the knee and this leaves ligaments more susceptible to tears.
But Tina Bonci, assistant athletic director for sports medicine in women's athletics at the University of Texas, doubts that theory.
"Everybody seems to focus on that," she said. "But that has only shown femoral (thigh bone) and patella (kneecap) problems. Yes, you have to look at the Q-angle because it's not good structural alignment. That could cause a lot of irritation under the kneecap, but there's still a lot of work to be done to say this is one of the reasons (for torn ACLs)."
Bonci, who came to Texas in 1985, has written articles concerning the prevalence of ACL injuries in women. However, she's more interested in finding ways to prevent them.
"Those are things we can do something about right now," Bonci said.
She's made significant progress.
Torn ACLs had become almost as synonymous with Texas women's basketball as 20-win seasons. From 1985-92, 10 Texas basketball players tore the ligament.
Since '92, only Carla Littleton and Dillard have sustained that injury.
Bonci credits "screening protocol" for the decrease. The Texas trainers screened each athlete for postural faults, length of tendons, muscular strengths in quadriceps vs. hamstrings and made orthopedic evaluations in an attempt to determine deficiencies that could lead to ACL injuries.
"We know the hamstring muscle group works in synergy with the ACL in preventing anterior translation of the tibia on the femur," Bonci said. "Therefore, one of the goals is to strengthen the hamstring as much as possible because those two work together."
The main areas on which Bonci focuses for prevention are neuromuscular training and biomechanics on player technique.
Neuromuscular training aims at improving the complex interplay between the neurological system and the muscular system to result in more purposeful and coordinated movement.
To enhance that, Bonci introduced a series of maneuvers involving cutting, pivoting, jumping, landing and balancing.
The goal is to enhance body controlACL tears often occur when landing after jumping.
That leads to biomechanics of player technique, Bonci's second point of focus, which stresses drills to safely and efficiently execute skills of the game like jumping, pivoting and landing.
"Athletes do what is comfortable, but not necessarily biomechanically sound," Bonci said. "They're not getting the kind of instruction they need early on."
Bonci hopes to rectify that problem, too. She's developed a biomechanical workout that will be distributed to high schools.
It won't end women's ACL tears.
But it might help bring their numbers closer to men's.
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