A Deeper Look at Injuries to the Anterior Cruciate LigamentSo many young people (especially athletes) injure their anterior cruciate ligament (ACL), it has become a major concern among sports health professionals. Girls and women seem to be at greater risk than their male counterparts. Much research has gone into trying to understand the risk factors in order to prevent this potentially disabling injury.
In this literature review, researchers at the McClure Musculoskeletal Research Center at the University of Vermont teamed up with others from the Department of Ocean and Mechanical Engineering in Florida and the Department of Kinesiology at the University of North Carolina to take a closer look at what might be going on.
They carried out a computer search for articles published over a 60 year span of time from 1951 to 2011. They found 21 articles on the hormonal, genetic, and cognitive factors that might contribute to anterior cruciate ligament injuries. These are considered intrinsic factors. Intrinsic refers to something within us.
Two other risk factors of interest included previous injury and extrinsic (outside ourselves) factors. Extrinsic risk factors examined include things like the weather, shoe wear, playing surface, time of year, indoor versus outdoor play, and even the amount of rainfall for outdoor events.
Some of these extrinsic risk factors may create greater risk for ACL knee injuries when combined together. For example, certain types of grass trap the cleats of the athletes shoes increasing the risk of an ACL (or other knee) injury. Wet and rainy weather is better than dry weather before soccer games played outdoors. Hot weather is a risk factor for ACL injuries in open stadiums when compared with cooler temperatures.
With females it's easy to think the major difference is hormonal and look for a connection with the menstrual cycle. But there isn't a standard way to accurately determine where a girl or woman is in the menstrual cycle at the time of the ACL injury.
Some studies have attempted to see if females are more likely to injure their knees at a particular time in the menstrual cycle. It's also possible the risk is no different over the course of time for females. But due to a variety of study designs and differing ways of analyzing the data, no consensus or agreement has been made.
Scientists have discovered receptor sites on the anterior cruciate ligament (ACL) for hormones such as estrogen and progesterone. Just the presence of these places for hormones to attach to cells suggests hormones may influence ligaments. But what the connection is or exactly how these hormones affect the ACL is a big unknown right now.
Hormonal influences aren't the only possible reasons why females are susceptible to ACL injuries. We know that women playing basketball and soccer are much more likely to injure their ACLs than men playing these same sports at the same level. There may be some anatomic reasons for this. For example, women have a different shape to the bone structure forming the knee. The female ACL is more elastic and less stiff than the male ACL. Female athletes move differently than male athletes and with that difference comes a difference in muscle activation patterns.
The conclusion of this literature review is that it's highly likely there are multiple factors involved in ACL injuries among females. Whether this is a combination of intrinsic factors, extrinsic factors, or both remains to be proven.
Two areas still being researched are genetic links and brain function. Genetic factors associated with ACL tears have been identified in two studies. And slower mental processing with slower reaction time has been reported in another study. More studies are needed to really examine each of these factors individually and also when combined together in different ways. With more information about risk factors, it might be possible to screen athletes for risk and use prevention strategies to avoid such injuries.
Helen C. Smith, MS, ATC, et al. Risk Factors for Anterior Cruciate Ligament Injury: A Review of the Literature -- Part 2: Hormonal, Genetic, Cognitive Function, Previous Injury, and Extrinsic Risk Factors. In Sports Health. March/April 2012. Vol. 4. No. 2. Pp. 155-161.
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