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Nearly every person knows a female athlete and, therefore, knows someone who faces a high risk of undergoing an anterior cruciate ligament, ACL, injury. Female athletes have a four to six times greater chance of sustaining an ACL injury than their male counterparts and this is largely because of the female anatomy and the menstrual cycle (Balanchandar et al. 2017). Unfortunately, the link between the female body and ACL tears has not been deeply investigated which is particularly concerning as the number of female athletes worldwide continues to grow year by year. For most of history, research that has been conducted, especially in sports, has been based on male bodies and simply applied to female bodies. As a result, many unknowns about the female body and knee-ligament injuries still exist today.

In recent years, a growing number of researchers have been working with female athletes and tracking their menstrual cycles to determine the exact reason as to why their ACLs are rupturing at such disproportionate rates compared to males. Vivek Balachandar, Jan-Luigi Marciniak, Owen Wall, and Chandrika Balachandar have compiled the information they gathered from seventeen different studies into the article “Effects of the Menstrual Cycle on the Lower-Limb Biomechanics, Neuromuscular Control, and Anterior Cruciate Ligament Injury Risk: A Systematic Review” (Balachandar et al. 2017). The majority of the studies the researchers reviewed involved females who had no known history of knee-related injuries and who were not taking oral contraceptives at the time of the study unless the subjects were used specifically to evaluate the effects of oral contraceptives on knee stability. Oral contraceptives could be a confounding factor as they tend to keep knee ligaments as well as hormone levels more stable and controlled (Balachandar et al. 2017). As the authors of the article analyzed earlier studies, they considered the strength of the evidence that had been presented based on the study design, sample size, control groups, and general protocols of the study before establishing their own theories about menstrual cycles and ACL injuries.

The authors concluded that a female faces the highest chance of enduring an ACL injury in the preovulatory phase of her cycle (Balachandar et al. 2017). During the preovulatory period, females experience an increase in ligament laxity in the body which suggests a woman’s muscles, ligaments and limbs are looser than they are in other phases of the cycle. The change in laxity during the month occurs in response to hormones, such as estradiol, progesterone, LH, and FSH, that fluctuate. For instance, Vivek Balachandar, Jan-Luigi Marciniak, Owen Wall, and Chandrika Balachandar write that several studies have “identified the presence of estrogen receptors within human ACLs, which, when activated, produce a decrease in fibro blast proliferation and subsequent decrease in type 1 collagen synthesis.” They go on to clarify that the decrease in fibro blast proliferation and type 1 collagen synthesis, which are two connective tissues in the knee, cause the ACL to weaken and become unstable, thus leading to a higher risk of injury (Balachandar et al. 2017). Estrogen is most abundant during the follicular and preovulatory phases of the menstrual cycle which is roughly the first half of the cycle. It is during this stage that the estrogen receptors within the knee are the most activated. Subsequently, women face a higher risk of sustaining trauma to the ACL during this time. Estrogen decreasing fibroblast proliferation is only one of several ways in which hormonal imbalances affect ACLs.

A separate study conducted by Tomás Fernández-Jaén, Juan Manuel López-Alcorocho, Elena Rodriguez-Iñigo, Fabián Castellán, Juan Carlos Hernández, and Pedro Guillén-García, investigated possible correlations between the female anatomy and ACL injuries. The three medical professionals speculated that the size of the intercondylar notch in the femur plays a role in ACL tears. The intercondylar notch is a groove located at the bottom of the femur that aids in stabilizing the knee. In this study, the width of the intercondylar notch was compared between subjects who had torn and normal ACLs as well as subjects who were female and male. There were two significant revelations that surfaced. The researchers found that, overall, women had a narrower intercondylar notch; the mean intercondylar notch width for women was 17.4 millimeters with a standard deviation of 3.1 millimeters; meanwhile, for men, the mean width was 19.3 millimeters with a standard deviation of 3.3 millimeters. The results also indicated that the risk of sustaining an ACL tear was greater for a subject with a smaller intercondylar notch (Fernández-Jaén 2015). Thus, this study depicts that since females tend to have narrower intercondylar notches, they face a greater chance of injuring their ACL. These findings confirm that the size of the intercondylar notch contributes to the increased ACL injuries in females. This also suggests it is extremely possible that there are other aspects of the female anatomy that influence the rate of ACL tears.

The authors who analyzed the seventeen studies in the “Effects of the Menstrual Cycle on the Lower-Limb Biomechanics, Neuromuscular Control, and Anterior Cruciate Ligament Injury Risk: A Systematic Review” illustrated several limitations that surfaced throughout the studies they reviewed. The authors stated that various studies lacked a substantial sample size primarily because this topic of research is relatively new. The authors also wrote that these studies could have represented the population more accurately if there was not a single person in any study who had a faulty history with knee injuries or had a suspected pregnancy in the previous year (Balachandar et al. 2017). Although most researchers did their best to control these variables, there is inevitable uncertainty in the evidence. Another limitation briefly addressed was the fact that many subjects in these studies likely experienced irregular menstrual cycles (Balachandar et al. 2017). This is a major factor that needs to be discussed in greater detail in this study and in future research. Almost no female has a menstrual cycle that reflects the “perfect” twenty-eight day cycle that science tends to suggest most women experience. If scientists could conduct research on a pool of women with consistent cycles in which it could be identified what day of the cycle a woman was in, the exact time in which women are at a higher risk of facing an ACL injury could be determined. The relationship between menses and ACL injuries could become more accurate if, as suggested by the authors, researchers required a serum analysis throughout the study in order to more accurately determine the length and pattern of each individual’s cycle. Overall, the authors did a fairly well job of acknowledging a variety of limitations that surfaced throughout the studies.

This information is incredibly important because women are currently facing a widespread issue that is not getting the attention or research it deserves. Ignoring the rampant rise of ACL injuries in females will not cause it to disappear. In fact, it will only cause the injury rates to ascend; more girls are joining sports every single year which suggests that the rates of injury will only increase. Studies similar to this one will inspire more scientists to conduct research on female subjects which is vital because the biological differences between men and women are stark, particularly when it comes to how their differences impact injuries and injury prevention. ACL injuries are excruciatingly painful both physically and mentally, as well as financially, and discovering new ways in which these injuries can be mitigated is vital for women across the world. Not only do scientists need to initiate studies regarding this topic, men and women everywhere need to recognize the issue and start a conversation about it.



Balachandar V, Marciniak JL, Wall O, Balachandar C. 2017. Effects of the menstrual cycle on lower-limb biomechanics, neuromuscular control, and anterior cruciate ligament injury risk: a systematic review. Muscles Ligaments Tendons J. 7(1):136-146. Doi:10.11138/mltj/2017.1.136.

Envision Radiology. 2015. #ACL Injuries: Females #Athletes At Increased Risk: Twitter.

Fernández-Jaén, T, López-Alcorocho JM, Rodriguez-Iñigo E, Castellán F, Hernández JC, Guillén-García P. 2015. The importance of the intercondylar notch in anterior cruciate ligament tears. Orthop J Sports Med. 3(8). Doi:10.1177/2325967115597882.

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