ACL Injuries: Female Athletes At Increased Risk

More women and girls are playing sports than ever before. The spectacular performance of women in the Olympics, along with the increase in the popularity of women's professional sports, have had a profound influence on little girls. "Be like Mike" has given way to "Be like Mia!"

The speed, power, and intensity displayed by female athletes have dramatically increased over the past decade. Such more aggressive style of play has led, predictably, to an increase in musculoskeletal injuries. One of the more common is a sprain or rupture of the anterior cruciate ligament (ACL).

ACL: vital role in many sports

Straight-ahead sports like jogging, swimming, and biking place little stress on the ACL. Sports such as soccer, basketball and volleyball that involve cutting, planting and changing direction, in which the ACL plays a vital role, put athletes, particularly females, at greatest risk of ACL injury.

Less than a third of all reported ACL injuries involve contact from an outside force such as an opposing player, goalpost or another object on the field/court. Over two-thirds are non-contact ACL injuries resulting from

• One-step/stop deceleration

• Cutting movements

• Sudden change in direction

• Landing from a jump with inadequate knee and hip flexion (at or near full extension)

• Lapse of concentration (resulting from unanticipated change in the direction of the play)

Women suffer more ACL injuries

• Recent studies reveal that young female athletes are up to eight times more likely than boys to tear their ACLs and are more prone to non-contact ACL injuries

• According to the Centers for Disease Control and Prevention more than 46,000 female athletes age 19 and younger experienced a sprain or strain of the ACL in 2006.

• Nearly 30,000 of the injuries required reconstructive surgery.

No easy explanation 

Women may be more prone to non-contact ACL injuries because they run and cut sharply in a more erect posture than men, and bend their knees less when landing from a jump.

Why women and girls are more prone to ACL injuries than men and boys defies easy explanation is also likely due to a number of anatomical and hormonal differences between men and women:

1. Narrower intercondylar notch and smaller ACL: Not only does the intercondylar notch (the groove in the femur through which the ACL travels) tend to be smaller in women, but so is the ACL itself, leading it more prone to injury.

2. Wider pelvis: Women typically have a wider pelvis, which makes the thigh bones angle downward more sharply than in men. The greater the so-called "Q" angle, the more pressure is applied to the inside (medial aspect) of the knee, which can cause the ACL to tear.

3. More lax ligaments: Women's ligaments tend to have more "give" (laxity) than men's. Research has also shown that women's muscle tissue is more elastic than males. Excessive joint motion combined with increased flexibility may be a significant contributing factor in the higher rate of torn ACLs among women.

4. Slower reflex time: Research shows that the muscles stabilizing the knee may take a millisecond longer to respond in women than in men. Scientists suspect that this small difference in contraction time also leads to a higher rate of injury.

5. Greater Quadriceps/Hamstring Strength Ratio: Poor hamstring strength may contribute to ACL injuries in both sexes. If the hamstring cannot balance the power of the quadriceps (front thigh muscle), the imbalance can cause significant stress to the ACL, leading to injury.

6. Changes in estrogen levels. One recent study suggests that changes in estrogen levels during a woman's menstrual cycle may affect ACL strength, predisposing women to the higher injury rate.  A 2007 article in The British Journal of Sports Medicine, however, found  "no conclusive evidence directly linking an increase in ACL injury to a predictable time in the menstrual cycle." 

Strength training, conditioning, coaching reduces risk

Several recent studies demonstrate that the rate of ACL injury among women can be significantly reduced by proper training and conditioning.

According to Dr. Thomas Haverbush, a Michigan orthopedic surgeon, a training program developed at the University of Vermont Medical School designed to prevent ACL injuries in skiers led to a 69% decrease in the number of knee injuries among ski patrol personnel and instructors who received the training compared with those who did not.

In the same article, Dr. Haverbush reported that a six week training program in Cincinnati in which athletes were trained to rely more on hamstring muscles than quadriceps in order to protect the knee could reduce the ratio of knee ligament injuries in female athletes as compared to men from five times higher to only one or two times higher.

Most recently, a study reported in the American Journal of Sports Medicine suggests that the ACL injury rate for  female athletes, particularly non-contact ACL injuries, can be significantly reduced if the athlete follows a specific exercise program called the Prevent Injury and Enhance Performance (PEP) program before practices and games.

Designed in 1999 by a team of experts at the non-profit Santa Monica Orthopedic and Sports Medicine Research Foundation, the PEP program consists of a series of 19 warm-up, stretching, strengthening, plyometric, and sport-specific agility exercises that can be completed in less than 30 minutes without any specialized equipment.

In general, experts say there are four ways to reduce the risk of ACL injury: 

1. Proper leg muscle strength training and core training.

2. Proper neuromuscular (balance and speed) training.

3. Proper coaching on jumping and landing and avoiding any straight knee landing.

4. Proper footwear and orthotics if necessary (the amount of traction or "grippiness" of athletic shoes needs to fall within an optimal range that minimizes rotational friction to avoid injury yet optimizes transitional friction to allow peak performance in activities such as cutting and stopping).