Anterior Cruciate Ligament Tears: Causes, Prevention and Gender Differences

Anterior cruciate ligament, ACL, tears are two to four times higher in female athletes than in males.¹ That is a significant difference. One might find themselves asking why this is so much higher. To that person, my advice would be to read this riveting research paper and find out. This paper will discuss what an ACL is, how/why the injury occurs, female vs male ACL differences, and ways to help prevent this common injury. So, my dear reader, pull up a chair, grab a nice cold drink, and relax while you read this extravagant paper.

The ACL is a ligament that is located inside the knee joint and is made up of both the anteromedial and posterolateral bundles.² It sits in what is called the femur intercondylar notch and runs from the medial/anterior part of the tibial plateau superiorly, laterally, and posteriorly to the lateral femoral condyle where it inserts.² Together, the ACL and PCL, posterior cruciate ligament, work to direct and control sudden rotations at the knee.² Both ligaments along with other surrounding muscles help with knee stability.²

 Many believe that the way the ACL is torn is different in females compared to that of males, but they would be wrong. The ACL works to stabilize the knee from excessive rotation as well as hyperextension.² The way the ACL works is the same in both males and females.² Therefore, it only makes sense that the injury occurs in the same way. Studies have shown that ACL tears in females, and males, arise through either excessive twisting at the knee or landing on a hyperextended knee.^1,2 These two motions of injury can happen in both contact and non-contact situations.^2,3

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 Non-contact injuries make up about 70% of ACL injuries and therefore are the most common mechanism of injury.³ A noncontact injury usually occurs through cutting, deceleration, direction changes, and/or landing on one leg.^3,4 Aside from the common noncontact causes of injury, the ACL can also be torn through contact injuries. A contact injury usually results from a direct blow to the knee from either an object or another person.³ Knowing the general force of injury, whether contact or noncontact, makes it easier for people to understand why some sports have higher ACL injuries than others. For example, the sports with the highest amount of ACL injuries for female athletes are basketball, soccer, and team handball.^4,5 When one thinks about how often the athletes in both of these sports are cutting, landing on one leg, accelerating and decelerating, along with how much contact is usually involved, it is really no surprise that these two sports are at the top for ACL injuries.⁴

 So why, if males also play soccer, basketball, and handball, are females still more likely to tear their ACL? Well, females and males have both anatomical and neuromuscular differences that when looked at may be able to (explain this) help us understand this a little more. The main anatomical differences that are involved with ACL tears is the size of an individual’s ACL as well as the size of one’s intercondylar notch.⁵ However, some studies have concluded that females have smaller notches than that of males, while other studies have concluded that there is no significant difference between genders notch widths.^5,6  That being said, studies have also proven that a  person with a smaller intercondylar notch is more susceptible to an ACL tear despite what gender they may be.⁴ Further imaging scans, however, have confirmed that females generally have smaller ACL’s and that there is a correlation between the actual femoral notch size and ACL size.⁴ Therefore, if smaller ACL’s are generally housed in smaller notches and females generally have smaller ACL’s, then it would make sense that females generally have smaller notches as well.⁴ Due to the conflicting studies, more studies need to be performed before this suspicion can be confirmed or denied as an anatomical difference that put females at a higher risk for ACL injuries.

 Along with Anatomical differences, there are also Neuromuscular differences between genders. It has been proven that females not only take longer to generate maximum hamstring torque while doing an isokinetic test but also, that females tend to activate their quadriceps in response to a force pushing the tibia anteriorly on the femur rather than activating the hamstrings to stabilize the knee.⁴ Not only do females tend to use their quadriceps more than and in place of their hamstrings, but they also generally have different body mechanics when it comes to landing as well as squatting than males.^4,5,7 The difference that may be contributing to increased ACL injuries is that females exhibit a more valgus collapse and increased abduction at the knee during both landing.⁵ While squatting, females tend to have a more anteriorly rotated pelvis, contralateral pelvic drop, internal rotation and adduction at the hip, and pronation of the foot. These positions, despite how big or small they may be, are generally related to an ACL injury.⁵ There may not be a way to change anatomical difference to help decrease ACL injuries in females, but there are ways to help change neuromuscular differences.

 The first thing a physical therapist, PT, and/or a physical therapist assistant, PTA, can do to help prevent ACL tears in female athletes is to educate. Education is super important especially for injuries that are generally life-changing. Many people know that ACL tears are a common thing but almost no one knows what to do to lessen the chances of this happening to them. They just hope it never does. By educating individuals on the importance of using proper body mechanics, such as the proper way to land and squat, PT’s and PTA’s can decrease the likely hood of this injury. Along with educating people on what the ACL is, where it is at, and what it does, it is also necessary to emphasize the importance of exercising all areas of the body.

   A recent study that was done on preventive neuromuscular training, PNMT, with individual exercises found that strengthening and proximal control exercises each reduced the risk of ACL tears significantly while plyometric exercise also reduced the risk but not as significantly.⁶ The study also found that balance exercises alone did not show any decrease in the risk of ACL injury.^6,7  When adding multiple exercises together however, the study concluded that by combining plyometrics, strengthening, trunk and balance exercise to make a PNMT it had the greatest effect on ACL injury prevention.⁶ It is not enough to only work on strengthening or balance or even plyometrics. These exercises may help decrease the risk of injury individually but together they work a lot better. Just like the saying, there is strength in numbers, there is also increased strength with multiple exercises.

ACL injuries are one of the most common knee injuries in sports and they often result in the ending of sports careers.⁸ Not only this, but they are also often followed by/linked to other knee pathologies such as meniscal tears, avulsion fractures, and even Osteoarthritis.^7,8 PT’s and PTA’s may not be able to help every female athlete with ACL prevention, but they can still try to make a difference. When an athlete comes into the clinic with knee pain, or any other type of person, PT’s and PTA’s need to remember the importance of exercising everything. There is nothing that can be done about anatomical body differences, at least yet, between females and males but through education, improvement of both bad body mechanics and neuromuscular differences can be changed. The world may never fully understand everything about the ACL or be able to completely do away with ACL injuries but who better to educate and help try to prevent these injuries than a PT and/or PTA?

1. Study shows men and women tear ACL the same way in non-contact injury. ScienceDaily. https://www.sciencedaily.com/releases/2018/04/180418092031.htm. Published April 18, 2018. Accessed July 5, 2019.
2. Anterior Cruciate Ligament. Anterior Cruciate Ligament: Anatomy and Physiology. https://shp.missouri.edu/vhct/case3505/anat_physio.htm. Published November 29, 2012. Accessed July 9, 2019.
3. Salem, B.A. HS, Shi, M.D. WJ, Tucker, M.D. BS, et al. Contact Versus Noncontact Anterior Cruciate Ligament Injuries: Is Mechanism of Injury Predictive of Concomitant Knee Pathology? Arthroscopy Journal. https://www.arthroscopyjournal.org/article/S0749-8063(17)31048-4/pdf. Published January 2018. Accessed May 21, 2019.
4. The female ACL: Why is it more prone to injury? Journal of orthopaedics. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4805849/. Published March 24, 2016. Accessed May 21, 2019.
5. Carter, MD CW, Ireland, MD ML, Johnson, MD AE, et al. Sex-based Differences in Common Sports Injuries. Journal of the American Academy of Orthopaedic Surgeons. 2018;26(13):447-454. doi:10.5435/JAAOS-D-16-00607.
6. Sugimoto D, Myer GD, Barber Foss KD, Hewett TE. Specific exercise effects of preventive neuromuscular training intervention on anterior cruciate ligament injury risk reduction in young females: meta-analysis and subgroup analysis. Br J Sports Med. December 2014:282-289. doi:10.1136/bjsports-2014-093461.
7. Sugimoto D, Myer GD, Barber Foss KD, Pepin MJ, Micheli LJ, Hewett TE. Critical components of neuromuscular training to reduce ACL injury risk in female athletes: meta-regression analysis. Br J Sports Med Author manuscript.:1259-1266. doi: doi:10.1136/bjsports-2015-095596.
8. Michaelidis M, Koumantakis GA. Effects of knee injury primary prevention programs on anterior cruciate ligament injury rates in female athletes in different sports: A systematic review. Physical Therapy in Sport. 2014;15(3):200-210. http://search.ebscohost.com/login.aspx?direct=true&db=s3h&AN=96851601&site=ehost-live. Accessed May 22, 2019.