Football injuries in women: a literature review


V Brocklebank, G R McLatchie

Consultant Surgeon, University Hospital of Hartlepool, UK

Abstract
Football is a popular sport and it is estimated that women make up 22% of the 200 million players worldwide. The rate of injuries seen in women’s football is similar to that in men’s; ankle sprains making up most of the injuries in both sexes. However, there are some important sex specific injury patterns; in particular women are more likely to sustain an anterior cruciate ligament injury than men. Since this is an injury with major short term and long term implications the factors that might be responsible for the gender disparities have received attention. These include anatomical differences such as Q angle, neuromuscular characteristics (muscle imbalance), joint laxity and proprioception, and hormonal influences. Despite intense research fundamental questions remain unanswered so that, as yet, appropriately focussed measures to reduce the incidence of ACL injuries in women cannot be taken.

Key Words: Football, injuries, women, ACL, prevention.
Word Count: 1814

Introduction
Football is the most popular sport in the world.(6) In 2000 the International Football Federation estimated there were approximately 200 million players worldwide (6, 15) of which 22% were women (6). The first European Championships for women was held in 1982 and the first World Cup in China in 1991 (13). Football is associated with a high incidence of injuries in both sexes (9, 13, 14, 15), but the pattern of injuries differs between the sexes (6, 9). The frequency of major knee injuries, including anterior cruciate ligament injury (ACL) has been shown to be significantly higher in females compared with males and has received particular attention (1, 3, 6, 9-12, 15, 16). These injuries have significant implications, both in the short term with regard to participation and in the longer term with possible predisposition to osteoarthritis (6, 9). It is therefore important that research should focus on injury patterns to try to identify modifiable risk factors.

Rate and pattern of injury
Data from 1991 showed the rate of injury to be 7/1000 hours of practice and 24/1000 hours of match exposure in both male and female players (9, 15). It is difficult to compare studies when there is no standardised definition of injury, so recent analyses have recorded only those injuries that resulted in absence from one or more scheduled training sessions or matches, with the length of this absence being used to quantify severity(5, 9, 13). Several such studies have examined the injury rate in women’s football prospectively and have been consistent in showing it to be 1.3-4.4/1000 hours of practice and 9.1-14.3/1000 hours of match exposure. These are similar to studies of men’s football (9, 13, 14, 15). The general pattern of injury shows close to 80% occurring in the lower limb, (5, 9) commonest sites being the ankle, shin, and knee respectively (5, 13). Although football is a contact sport most injuries were sustained by a noncontact mechanism (9).

Ankle injuries
Ankle sprains, particularly inversion injuries, are the commonest in both sexes (6, 8), their high frequency meaning they receive focus for prevention and treatment. In a retrospective analysis of state representative female players in Australia, the incidence of ankle injuries was 24% and 100% of these were recurrent (5). In another study 43% of females continued to play football with ankle symptoms (5), which suggests that strategies to ensure adequate rehabilitation may have a major influence on the incidence of injury.
Stress fractures
Stress fractures are commoner in women’s football than in men’s (6), and tibial stress fractures were the most common major injury resulting in absence from sport for more than 30 days in a retrospective study of female players (6). The sex difference may be explained by the ‘female triad’: osteoporosis, disordered eating, and menstrual disturbance.(6) It is characterised by high training volumes and low energy intake and has been linked with increased frequency of stress fractures.(2) However the contact nature of football means that low weight is unlikely to improve performance (4), so without further study on its prevalence in female footballers its significance is unclear.

Knee injuries
Women sustain significantly more knee injuries than men in a variety of sports including football (6). In particular, women have been shown to sustain a disproportionate number of ACL injuries compared with men (1, 3, 6, 8, 9, 10, 11, 12, 15, 16).

Risk factors for injury
Commonly divided into intrinsic and extrinsic. Extrinsic factors include the playing surface and footwear, both of which have been associated with the risk of ACL injury.

Recently there has been a shift towards prospective studies of risk factors for injury. In one such study (9) preseason characteristics including general joint laxity, isokinetic muscle strength, BMI, and aerobic performance were recorded for 123 players and the results correlated to the injuries sustained during one season. It identified age over 25 years and general joint laxity to be the only significant risk factors. In another study (14) it was shown that the risk of traumatic injury to the lower limb was significantly increased by generalised joint laxity, knee hyperextension, lower concentric hamstrings/quadriceps ratio, higher exposure to football, and lower postural sway as recorded preseason. A low postural sway is equivalent to having better balance and a suggested mechanism of how this could increase injury risk is that those with better balance may try to avoid falling to a greater extent, but this then results in greater injury (14). Indeed, it has been recently shown that women possess significantly better single-legged balance than men (11), so if balance does prove to be a risk factor for injury then it might also contribute to sex specific injury patterns.

Anterior cruciate ligament injury
Most ACL injuries occur during games as opposed to practice in a noncontact incident commonly involving features such as sudden deceleration, pivoting, flexion, and rotation (6, 7).

Incidence of ACL injury
In a prospective study of 123 female footballers (9) 3 sustained an ACL injury during one season which equates to a rate of 0.31/1000 hours exposure to football. A similar rate was seen in a study of 146 players (14) of whom 5 sustained an ACL injury over the course of one season. It is now commonly acknowledged that women are significantly more at risk than men in the same sport (1, 3, 6 , 7, 8, 9, 10, 11, 12, 15, 16). National Collegiate Athletic Association data show that female footballers have a rate of 0.31/1000 hours exposure compared to a rate of 0.13 for male footballers (7).

Importance
The observed patterns have generated intense interest. In one study of 45 state representative female footballers (5) 3 players sustained an ACL rupture; all 3 withdrew from the team and they were the only players who had to do so as a result of injury. Successful treatment of the ACL injury often requires surgery and women in particular are thought to respond poorly to conservative treatment, perhaps because females depend on their ACL for knee stability more than males (7). The consequences of a major knee injury relate not only to short term function and ability to return to sport, but also long term function including a predisposition to the early development of osteoarthritis (9).

Explaining the gender disparity
A number of possible factors can be considered under the headings of anatomical, neuromuscular and hormonal.
Anatomical
Women have wider pelvises than men and a greater degree of genu valgum (7). A decreased intercondylar notch size has also been associated with an increased risk of ACL injury (6, 7, 8) but equally so in men and women so would not explain gender differences in incidence.

The effect of the Q, or quadriceps, angle may differ between males and females and has generated interest but as yet there has been no correlation between Q angle and incidence of ACL injury (6, 7).

General joint laxity has also been identified as a predictor of knee injury, including to the ACL, in women footballers (9, 14). However, it is difficult to examine joint laxity independently of muscle contraction and stiffness (8).

Neuromuscular
The hamstrings are a major agonist of the ACL and the quadriceps a major antagonist (7) and it has been suggested that there may be sex specific hamstrings/quadriceps muscle imbalance patterns (6, 7). However, there is currently no evidence that correlates this observation with knee injury incidence 11).

Hormonal
Hormonal association has been suggested as long ago as 1989 (6) when it was observed that female footballers were more susceptible to traumatic injuries during the menstrual and premenstrual phases compared with the rest of the menstrual cycle, and that women taking the oral contraceptive pill had a lower risk of injury than those who were not. In support of this a study of 17 handball players who sustained an ACL injury showed an increased incidence in the week before and the week after the onset of menstruation (8).

The mechanism by which hormones might influence injury susceptibility could occur at a number of levels (12). Oestrogen and progesterone receptors have been isolated on the human ACL (16) and may directly influence tissue remodelling through control of gene expression (12) but alternatively hormones might extend their influence on neuromuscular characteristics or even centrally, simply by affecting susceptibility to accidents (1, 16).

In summary, despite an increasing body of research into anatomical, neuromuscular, and hormonal factors that might contribute to the sex discrepancies in ACL injury, it remains a challenge.

Conclusion
The pattern of injuries in women’s football differs from those of male footballers in that women have a significantly greater risk of ACL injury. Since this gender discrepancy was first observed study design has become more refined and has addressed many of the acknowledged limitations and there are now good quality prospective studies examining possible causative factors. However, there have been no dramatic advances in determining which factors are most important. As the menstrual cycle is one of the most fundamental differences between males and females, the possibility that it has a major role in determining injury patterns is an attractive one and as such forms the basis of an expanding area of research, the goal of which is to identify factors which can be targeted by injury prevention strategies. In addition, the short and long term outcome of men and women who sustain ACL injury, and the impact of associated intra-articular damage, need to be studied further in order to achieve successful rehabilitation and prevention of early osteoarthritis.

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