Soccer is one of the world's most popular sports, and participation in women's soccer is increasing across all ages and skill levels. Soccer has a fast, aggressive playing style, with rapid lateral movements, cutting, and pivoting—all of which contribute to an inherent risk of injury that must be recognized and managed.

Female soccer players have a reported incidence of injury ranging from 12.6 to 23.3 per 1,000 match hours, compared to 11.7 to 35.5 per 1,000 match hours for males. The high incidence of injury in females underscores the importance of understanding sex-related differences in risk factors, injury prevention plans, and recovery. Based on current literature, concussions and anterior cruciate ligament (ACL) injuries show significant differences between the sexes.

Concussions
For all women's NCAA sports, soccer has the highest rate of concussions. Moreover, the rate of concussions in women's soccer is second only to football among all NCAA sports. Female soccer players have significantly higher concussion rates than males.

"Heading," in which a player purposefully directs the soccer ball using his or her unprotected head, can be dangerous due to high linear and rotational ball velocity. Most studies, however, indicate that purposeful heading is safe in the short and long term. Heading makes players vulnerable to concussion from head-to-player collisions, head-to-ground impact, or head-to-goalpost contact. Studies have reported that women primarily sustain concussions due to head-to-ground contact and player-to-ball contact, whereas men sustain a greater proportion of concussions due to player-to-player contact.

Concussions are multifactorial in nature, and the literature suggests that sex differences exist in the internal risk factors. Neck muscle strength and head size are both intrinsic risk factors. Smaller head-to-ball ratio, less neck girth, and less neck muscle strength translate to less stiffness in the neck. This creates significantly greater head acceleration in females, and thus increases concussion risk during head-to-ball impact or head-to-player impact. Because females have 20 percent less neck mass than males, their ability to use neck musculature as a shock absorber during head impact—to transfer kinetic energy to both the head and torso—is lessened. These intrinsic risk factors, combined with a history of previous concussions, would predispose a female player to concussions.

These sex differences in risk factors require physicians to have a sex-appropriate understanding to effectively employ concussion prevention strategies. For example, a preseason neck strength assessment can be used to identify players at higher risk due to a weaker neck. At-risk players might benefit from a training protocol that both strengthens and balances neck flexors and extensors, to increase neck strength and decrease head acceleration.

Protective headgear has been suggested as a protective measure to lessen acceleration during head-to-head impacts. Recent research, however, has shown that female soccer players actually demonstrate greater head acceleration while wearing headgear. Headgear may not provide adequate protection for female players.

Females and males also exhibit differences in concussion symptoms and in post-concussive neurocognitive testing. After a concussion, females report more symptoms and different symptom constellation than males do. Some studies show that females experience more headaches, fatigue, drowsiness, and noise sensitivity than males do; however, differences have not been consistent among studies. The lesson is that concussion symptoms may present differently between males and females and that concussion cannot be ruled out due to a lack of a certain symptom.

During post-concussive neurocognitive testing, female soccer players perform more poorly on decision making, planning tasks, and visual memory, and continue to face cognitive deficits 6 months after injury. Further research is necessary to determine why females might perform worse after concussions and have delayed symptom resolution compared to males.

ACL injuries
Compared to male soccer players, female soccer players are three times more likely to sustain an ACL injury, especially during match play. In a study of collegiate soccer players, the rate of ACL injury was 0.31 for women and 0.11 for men.

Females also tend to incur ACL injuries at a younger age then males do and are more susceptible to noncontact ACL injuries. Noncontact ACL injuries might occur when cutting, jumping and landing with knee near full extension, or when pivoting with a planted foot and knee near full extension. Noncontact injuries occur more often in the supporting leg in females; in males, they are more common in the kicking leg.

Several anatomic and biomechanical factors may contribute to the susceptibility of female soccer players to ACL injury (Table 1). Unfortunately, many of the anatomic considerations have little preventive potential.

Dynamic stabilization through neuromuscular control protects the knee joint. Many biomechanical and neuromuscular studies have suggested that preventive neuromuscular training may be effective in reducing ACL injuries in female athletes; the AAOS Clinical Practice Guideline on the Management of ACL Injuries supports neuromuscular training with a moderate strength recommendation; the issue is also addressed in the new Appropriate Use Criteria on Prevention of ACL Injuries. (See this issue's cover story, "New ACL AUCs, Checklists Now Available.")

Although one recent review reports that current data are not compelling enough to recommend its use, neuromuscular training programs are not expensive to implement. High-risk athletes might benefit from neuromuscular training programs focused on specific deficits identified through preseason screening tests. For example, a player with low hamstring-to-quad recruitment should employ neuromuscular training targeted at improving hamstring strength.

Recent research has also suggested that females are more susceptible to sustaining ACL tears during the pre-ovulatory phase of the menstrual cycle. The influx of hormones at this time can affect coordination and also induces the painful consequences of menstruation. Females taking oral contraceptives were not as affected by lessened coordination and more fatigue during this phase than nonusers. Oral contraceptive use might also decrease ligamentous laxity and increase dynamic stability of the knee in females, although these findings are still preliminary.

Lower extremity injuries are not as potentially life-threatening as concussions, but they can cause significant future impairment. Long-term sequelae associated with ACL injuries in women include early onset arthritis, subsequent susceptibility to ACL re-injury, and greater knee pain and instability. One study even suggests that osteoarthritis after an ACL injury can begin as early as age 31 years in females.

Because women are more likely to tear their ACL at a younger age than men, they face the potential sequelae earlier as well. These consequences are harmful to the future of a full, pain-free and active life for these female athletes, so designing preventative training programs is an essential future step.

Elizabeth G. Matzkin, MD, is a member of the AAOS Women's Health Issues Advisory Board, assistant professor in the Harvard Medical School department of orthopaedic surgery, and chief of women's sports medicine; Caroline Hu, BA, is a medical student at the University of Minnesota Medical School; and Shannon Conneely is a Yale University student who served a summer research internship in the department of orthopaedic surgery at Brigham and Women's Hospital.

Bottom Line

• The rate of concussions in women's soccer is the highest in all women's NCAA sports and is second only to football for all NCAA sports.
• Most data report that female soccer players have significantly higher concussion rates than males.
• Studies are mixed and further research is needed to understand sex differences in concussion.
• Female soccer players are three times more likely to sustain an ACL injury than males are, especially during match play.
• Further research is warranted to determine the risks of ACL injuries and the effectiveness of neuromuscular training programs for prevention of ACL injuries in female soccer players.

Putting sex in your orthopaedic practice
This quarterly column from the AAOS Women's Health Issues Advisory Board and the Ruth Jackson Orthopaedic Society provides important information for your practice about issues related to sex (determined by our chromosomes) and gender (how we present ourselves as male or female, which can be influenced by environment, families and peers, and social institutions). It is our mission to promote the philosophy that male and female patients experience and react to musculoskeletal conditions differently; when it comes to patient care, surgeons should not have a one-size-fits-all mentality.

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