Epidemiology of Female Versus Male Athletic Injuries

Introduction

The world of sports has historically been dominated by males and much of our knowledge surrounding athletic injuries originates from our understanding of the male athlete. Data on injuries sustained by the female athlete is often underrepresented in sports medicine research, and as the number of female athletes participating in sports continues to grow, there is a significant need for an improved overall understanding of the female athlete and the associated injuries. Specifically, since 1972, the year Title IX was established, there has been a nearly 1000% increase in females playing high-school sports and a 600% increase in female participation in collegiate varsity sports. Female athletes may be predisposed to specific risk factors that increase their chance of injury, such as differences in anatomy and biomechanics compared to males, and these risk factors can be easily overlooked when they are not fully understood. In order to counter these risks, acknowledgment of gender-based differences in injury presentation is necessary for proper injury assessment and treatment to allow for successful return to play and reduced risk of reinjury. A better understanding of injury patterns and an increase in prevention programs tailored specifically to the female athlete are important to ultimately provide the most effective care for this growing population.

With increasing representation of both males and females in a variety of sports, comparative studies focusing on gender differences in injury rates and mechanisms are also increasing. However, female athletes continue to be underrepresented in the development of solutions and interventions based on such studies. For example, FIFA 11+ is a well-established prevention program developed for soccer players to decrease the risk of anterior cruciate ligament (ACL) injuries. In a systematic review, a 30% reduction rate was reported for male soccer players and a 22% reduction was seen in females, but only three of the nine studies reviewed included female athletes. Therefore there is a lack of data for females using this current prevention program, while females are two to eight times more likely to experience an ACL injury than males. Additionally, a separate systematic review reported that current prevention programs for ACL injuries have reduced risk by 85% in males compared with only 52% in females. Continuing to study the differences and applying them to the development of prevention programs and treatment methods specific to the female athlete is imperative in avoiding the physical, psychologic, and financial burdens that come with injuries. A greater understanding of the vast anatomic, physiologic, hormonal, and biomechanical gender differences is key to maintain successful female participation in athletics. This chapter will focus on the epidemiology of female athletic injuries, with the goal of providing clinicians evidence-based data to better understand just how common (or uncommon) certain injuries are, in order to be able to better guide patients, parents, and coaches.

Epidemiology Basics

Numerous studies have reported the epidemiology of injuries in female athletes compared to male athletes. In more recent years, differences in the types of injury, mechanisms of injury, and potential biological and anatomic explanations for differences in rates have also been explored. In 2018, Lin et al. performed a literature review of existing published data that discussed gender differences in epidemiology, risk factors, management, and outcomes among common sports injuries. Interestingly, there was a higher incidence in females in three main injury types: bone stress injuries, ACL injuries, and concussions. In 2019, Brant et al. studied the rates of lower extremity injuries across gender-comparable sports at the high-school level over a period of 10 years. In all the eight sports studied, females had a higher rate of injury than males (9.14 vs. 7.30 injuries per 10,000 athlete exposures (AEs), respectively). Out of all the injuries reported, 56% of them were sustained by females. Additionally, females had a higher injury rate within each individual sport, the highest seen in soccer (15.87), and females sustained a greater number of injuries within each specific injury type in every sport studied, except track and field. Among the incidences, females also experienced a higher percentage of severe injuries, characterized by over 3 weeks of time away from participation or medical disqualification, in each sport except volleyball. This study also noted that among the incidences of injuries, magnetic resonance imaging evaluation was higher in females, relating to an increased medical cost for females who sustained injuries.

In a separate study, Rechel et al. reported the epidemiology of injuries at the high-school level that required surgery over a 5-year period and found an overall rate of 1.45 per 10,000 AEs and 6.3% of all high-school sport-related injuries nationally. Among gender-comparable sports, including soccer, basketball, and baseball/softball, females experienced a higher overall injury rate of 1.20 compared with males at 0.94 per 10,000 AEs ( P = .004) and a significantly greater injury rate within soccer and basketball. Baseball and softball were the only gender-comparable sports where males had a higher rate of injury incidences, but it was not found to be significant. Of note, over half of soccer and basketball injuries were related to the knee and females made up a significantly greater proportion of those knee injuries in both sports (74.4% in soccer and 68.8% in basketball). Overall, 68.7% of injuries sustained by females were of the knee and 1.6% were of the shoulder when compared to males in whom 41.5% of injuries were o the knee and 11.1% were of the shoulder ( P < .001). In addition, females experienced complete ligament sprains at a significantly higher rate than males (54.1% vs. 23.2%; P < .001), whereas males faced more fractures (30.0% vs. 17.5%; P < .001) and dislocations (9.1% vs. 1.1%; P < .001). Notably, 90.8% of complete ligament sprains occurred at the knee. Interestingly, of the 48% of injuries that required medical disqualification for the season, 45.3% were complete ligament sprains while 18.6% of injuries resulting in time loss of less than 1 week from participation were fractures. Furthermore, injuries resulting in medical disqualifications from sports activities for the season occurred in 55.6% of females compared to 45.0% of males. In a separate study, Chan et al. reported the epidemiology of Achilles tendon injuries at the collegiate level. Although the injury rate was comparable between females and males, it is worth noting that females had greater time loss, higher rates of season-ending injuries, and higher operative rates, as well as poorer postoperative performance. Additionally, the recurrence rate among female athletes was almost twice as high compared to male athletes.

In 2018, Baugh et al. described the epidemiology of injuries specific to volleyball teams in the National Collegiate Athletic Association (NCAA) using data from 2013 to 2014 and 2014–15 seasons. Consistent with the previous epidemiologic studies mentioned, female athletes experienced injury at a significantly higher rate overall (7.07 per 10,000 AEs) compared with males (4.69) as well as a higher rate of time-loss injuries, indicated by greater than 24 h of participation restriction, compared with males (2.62 vs. 1.75). The lower extremities were found to be the most frequently injured location in both time-loss injuries and non-time-loss injuries, and females had a higher proportion of lower extremity injuries within both groups. Specific to time-loss injuries, ankle and knee injuries were the most frequent type sustained by female athletes, whereas concussions due to ball contact and hand and wrist sprains occurred most frequently in male athletes. It was noted that the higher injury rate seen in females could be attributed to the higher rates of injury during practices and in preseason compared with males.

With respect to the mechanism of injury, each of the abovementioned studies that analyzed gender differences in this area reported that males were more likely to experience an injury after player-to-player contact, whereas females experienced primarily noncontact injuries. ^, In a similar sense, a higher rate of overuse-related injuries was found in females compared to greater ball contact-related injuries found in males. Additionally, significantly higher rates of injury were sustained during competition compared to during practice among all athletes. ^, After providing possible explanations as to why this trend may exist (e.g., increased aggressiveness, exposure to high-risk activities and physical contact, and illegal activity), Rechel et al. recommended developing new rules, strict officiating, and implementing drills in practice that teach high-risk skills to improve these rates. It is worth mentioning that this study also discussed areas to focus on when implementing prevention efforts for male-dominated sports, such as football and wrestling. However, prevention techniques for female athletes and even for gender-comparable sports were not described. For example, the authors provided explanations for understanding the mechanism of shoulder injuries and recommendations for potential solutions for prevention of these injuries, which occurred at a higher rate in male athletes, but at a lower overall rate compared with other injuries. No such suggestions for the prevention of knee injuries were mentioned, which made up the greatest proportion of total injuries requiring surgery and also had significantly higher rates in females. The authors merely suggested that efforts should be made and only cited other studies that have provided explanations as to why the gender differences may exist in complete ligament sprains of the knee. On the contrary, Brant et al. mentioned the importance of improving preventative care particularly for females, given their high risk of lower extremity sports injuries, in order to reduce rates of injury and the impact injuries can have on athletes. Similarly, Baugh et al. discussed possible explanations and specific prevention methods that alluded to the gender differences found in the mechanisms of injury, type of injury, and the time during the season that the injury occurred. The authors also suggested that future research should address these differences.

Concussion Epidemiology: Gender-Based Differences

Studies on concussions have become increasingly popular, particularly in contact sports such as football and hockey, and mainly focus on male athletes involved in these sports. However, female athletes have been shown to have arguably higher rates of concussion incidences, especially in gender-comparable sports. Specifically, one literature review exploring gender differences in concussion incidence found that 9 out of the 10 studies reviewed had reports of higher concussion rates in females. As an entire chapter is dedicated to understand concussions in the female athlete, this section will focus primarily on epidemiologic differences in concussions between males and females.

A study published in 2019 by Kerr et al. described the epidemiology of sport-related concussions across 20 sports at the high-school level during the 2013–14 to 2017–18 school years. Overall, 9542 concussions were reported for an overall injury rate of 4.17 per 10,000 AEs, with football having the highest rate of 10.40. However, among gender-comparable sports (i.e., soccer, basketball, swimming, baseball/softball, cross-country, and track and field), females experienced higher concussion rates than males (3.35 vs. 1.51), as well as a larger proportion of recurrent concussions (9.3% vs. 6.4%). Interestingly, the rate of recurrent concussions decreased over the course of the 5-year study period. This trend is most likely due to legislations implementing mandatory concussion protocols in youth and high-school athletics, which have been passed in all 50 American states and the District of Columbia beginning in 2009. ^,

Since the passing of these traumatic brain injury laws, studies have demonstrated an increase in concussion rates, possibly due to increased awareness and reporting, and a decrease in recurrent concussion rates, likely accredited to the improved management of removal from play and return-to-play requirements. It is worth mentioning that studies consistently show higher rates of concussion incidences in females than males over time among gender-comparable sports, both before and an even greater increase after the passing of concussion policies ( P < .001). Similar results were found in a previous study looking at 20 sports among high-school players between 2008 and 2010. Over the course of the study, 1936 concussions were reported for an overall rate of 2.5 per 10,000 AEs and accounted for 13.2% of the total injuries. Comparing all sports, football had the highest percentage of concussions (47.1%) and the highest rate (6.4). Within gender-comparable sports, females had a significantly higher concussion incidence rate than males (1.7 vs. 1.0), and in 18 out of the 20 sports studied, females experienced more recurrent concussions than males.

O'Connor et al. studied high-school concussion trends between 2011 and 2014 and reported a 56% higher incidence rate in females (1.56) than males (1.00) in gender-comparable sports. The researchers also found that although there was no gender difference in the number of symptoms, 44.4% of males reported symptom resolution within less than 7 days versus only 32.2% of females. The authors noted that a possible explanation for this trend could be based off of social norms and their influence on likeliness to report symptoms. For example, male athletes may believe that they are expected to have a “tough attitude” about injury, whereas females may be less likely to be influenced by their peers' opinions on concussions. ^, At the collegiate level, Davis-Hayes et al. studied sport-related concussions among the Columbia University varsity athletes in a 15-year retrospective cohort consisting of 68.5% males and 31.5% females. Despite the difference in representation, the prevalence of having at least one concussion was greater in female athletes than in male athletes (23.3% and 17.0%, respectively; P = .01). Notably, in contrast to the previously mentioned studies, no gender differences were found in the return-to-play duration, the number and types of symptoms, or the neurophysiologic test performance. A study by Zuckerman et al. reported that the relative risk of sustaining a concussion among female athletes at the collegiate level was 53% higher in basketball, 83% higher in soccer, and 265% higher in baseball/softball when compared with male athletes. Notably, this same study reported that the risk in women's lacrosse, a noncontact sport, was 64% higher than that in men's lacrosse, a contact sport, despite the rule changes implemented in women's lacrosse to reduce contact. Generally speaking, reports consistently showed player-to-player contact as the most frequent mechanism of concussion injuries in male athletes, with incidence rates between 55% and 77% compared to 40%–53% in females. Player-to-playing surface contact or player-to-ball contact tend to be the most common cause of concussions in female athletes, with incidence rates reported between 34% and 45% compared to 18%–24% in males. ^{, , ,}

Interestingly, a retrospective, self-report-based study in collegiate athletes observed association patterns between concussions and musculoskeletal injuries. Overall, those who reported a history of concussion were more likely to also report a history of ankle sprains and knee injuries compared to those with no concussion history ( P = .004). Females were found to have increased reports of concussions, ankle sprains, and knee injuries at rates of 29.5%, 48.9%, and 41.0%, respectively, compared with males with rates of 18.0%, 43.0%, and 23.0%, respectively. Specific to females, those who reported multiple concussions had significantly greater odds of also reporting ankle sprains and knee injuries compared to those without a concussion history (73.5% vs. 39.0%). However, this trend was not seen in females who reported a history of only one concussion and it was not found to be statistically significant in male athletes with a history of either one or multiple concussions. An important limitation of this study is that the type of relationship between concussions and musculoskeletal injuries was unclear with regard to which injury came first, as the study was conducted based on self-reported injury histories without a timeline, but the researchers did determine that a relationship existed in this population.

Many researchers have attempted to provide reasonable explanations for gender-based differences observed in concussion rates, mechanisms, severity, and the associated number of symptoms. A range of potential factors that have been described include neck musculature and strength, cerebral blood flow and cerebrovascular organization, and differences in hormonal environments. ^, However, a physiologic basis for explaining the gender differences in the risk of sustaining a concussion is controversial because of the very limited evidence of supporting data and minimal understanding of the role these factors may play. Additional studies directly assessing a variety of factors and their relation to observed gender differences in concussion rates are necessary in order to ensure a proper approach toward prevention and treatment methods on an individual basis.