Injury Prevention and Rehab

Multiple ACL Tears

Dr. Don Kirkendall is a world renowned exercise physiologist / injury specialist with experience at the highest levels of the game. He is a member of the U.S. Soccer Sports Medicine Committee, a fellow of the American College of Sports Medicine and is a member of the editorial board of Soccer Journal. He currently works with the FIFA Medical Assessment Research Center (F-MARC). Dr Kirkendall works with all the US National teams on many aspects of nutrition and sports injuries. He is a much sought after presenter and writer on subjects ranging from high performance nutrition to sports injury prevention.
This posting has been modified from the original that appeared in Southern Soccer Scene.

 Multiple ACL Tears in Girls

acltearRead the soccer news? Pay attention to word of mouth? Not only do girls tear their ACL at a faster rate than boys, but they either re-injure or injure the other knee at a greater rate than boys. UNC has 4 players out with an ACL injury…one suffered her fourth ACL tear. I can’t remember the exact numbers, but on the US U19 team that won the world championship in Canada a couple years ago, there were 11 players with something like 14 ACL tears. This year, at Texas A&M, twin freshmen women tore their left ACL on successive days. Unfortunately, there are no solutions, only questions.

There are many questions and more assumptions based on clinical observations about why women tear their ACL and why women have more multiple injuries. Here are some risk factors often discussed.

Gender: the main risk of an ACL injury is being female. The injury rates are reported to be 3-6x higher in females than males(not raw numbers. There are more males with an ACL tear because of higher participation numbers)

Age: ACL injuries are mostly non-existent in athletes (male or female) under the age of about 14 years. The number of ACL injuries in girls rises rapidly and peaks at about age 18, drops a bit during college age before declining substantially. It’s an injury of 14-24 year olds.

Q-angle: This is the angle between the (lower) leg and thigh. The general female population has a larger Q angle due to the wider female pelvis, but most female athletes have a narrower pelvis and a Q angle closer to that of men. Much is said about the Q-angle, but no study has ever shown Q-angle to be predictive of ACL injury.

Menstrual cycle: Normal menstrual cycling has some effects on ligament laxity. One paper said that most ACL injuries occurred in the last half of the menstrual cycle, but subsequent studies have not shown this to be a factor in ACL injury.

Notch width index: As you have seen in an x-ray, the femur has a substantial notch at the knee. The thought is that a narrow notch is indicative of a small ACL and is used as a de facto statement on the size of the ACL. Some studies have suggested that small ACL’s tear, no matter if they are in a male or a female. Due to body size differences between men and women, it just happens that more women tear their ACL because their ACL is small. The practical question: you are an athlete and are told you have a narrow notch. Are you going to stop playing?

Motor Control: Most of the research agrees that women cut and jump/land differently than men. They change direction or prepare for a jump in a more erect stance than men. Now players cut, jump, and land day in and day out yet don’t tear their ACL all that often. All it takes is some minor change, like from a bump by an opponent, to throw off the normal motor pattern. The ACL tears when the foot hits the ground with a near erect knee and hip and the quadriceps contract pulling the tibia forward just enough to tear the ACL. It’s a complex series of events that normally works pretty well, but given a minor bump can lead to a tear. Prevention programs stress lowering the center of gravity with flexed knees and hips.

Knee Valgus: When landing, some girls hit the ground knock-kneed (X-legged). This is usually a rotation of the femur at the hip, not at the knee. Nonetheless, the ACL tears with a little valgus upon landing and this valgus likely wouldn’t happen to the same degree if the landing was done with more of a flexed knee and hip.

Relative strength: A new research observation suggests that the weaker woman trying to cut, land or jump does it more erect because of her weaker quads. In the lab, when men cut, land, and jump wearing a weight vest (making them weaker on a force/kg body weight basis), they do so in a more erect stance. Close observation of the activities of prevention programs shows a number of activities designed to improve quad strength.Much more research is needed to confirm this most recent finding.

But this doesn’t answer the question on multiple ACL injuries in some women. A recent Japanese project showed that women with multiple injuries had their first injury very young (16y) vs women with only 1 injury (20y). This could be very important. An early injury leaves the door open for another injury. Those with a multiple injury had the most narrow notch width, and few women returned to their desired level of activity after the 2nd injury.

Some other observations. Injuries to the same knee are not related to the surgical technique. No matter what graft is use and how it is implanted, the re-injury rates are similar. After the first injury, the other knee is at a greater risk of injury – it seems that the injured leg is weaker and the body sort of protects it, but still allows the good leg to carry on like before the injury. Doctors continually look back at past diagnoses for clues and it’s shown that in athletes with an ACL injury, the risk of an ACL to the other knee is 3x as high as is the risk of a re-injury. Injuries tend to run in families. If an older sister had the injury, the younger sister is at an elevated risk. One coach wondered if young girls are playing ‘up’ in age and having to play more intensely. Who knows? Could be, it’s worth a look. Finally, if the concept of motor control of the knee during cutting and landing is at the root of ACL injuries, the smart player, coach and parent will insist on performing prevention exercises that teach proper cutting and landing techniques in all players, not just those coming back from an injury. Bad technique led to the first injury and if the technique isn’t changed, there is a likelihood of another injury. See the F-MARC 11 on the website for one example of a prevention program. Another example can be found at

Copyright © 2006 Donald T. Kirkendall

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