ACL Injuries in Female Football Players

ACL injuries continue to represent the highest injury burden amongst professional women footballers [1]. Female athletes have up to an eight-fold increased risk of sustaining an ACL injury compared with their male counterparts [2]. The persistently high number of these injuries has
led to the introduction of an expert panel by UEFA to help gain a deeper understanding of ACL injuries in women’s game [3].

Risk Factors 

Several anatomical, biomechanical and hormonal risk factors have been proposed over the years. From an anato­mical perspective, a smaller notch width or notch-width index, a smaller ACL volume, an increased tibial slope and general increased ligament laxity compared to male athletes have been associated with increased risk of sustaining an ACL injury [4 – 8]. Endogenous hormonal fluctuations during the menstrual cycle, specifically variations in the levels of oestrogen and relaxin during the follicular and ovulatory phases may increase ACL injury risk due to overall elevated ligament laxity [8 – 10]. Although there is some research into the association between oral contraceptives and a reduced ACL injury risk, currently there is not enough high-quality research demonstrating this relationship [8, 11, 12]. 

One of the typical non-contact ACL injury mechanism in female football is a change of direction combined with deceleration prior to sidestepping and landing from a jump [13, 14]. Biomechanically, several kinematic, kinetic and muscle activation patterns have been found to be related to increased risk of sustaining an ACL injury. Increased knee valgus angles at both initial contact and peak contact in landing, increased ipsilateral trunk motion combined with higher hip adduction angles, reduced knee flexion angles and limited hip flexion angles as well as increased tibial external and internal rotation angles are kinematic patterns that have all been found to be associated with higher ACL injury risk [13, 15 – 18]. In terms of kinetic para­meters, landing with a more extended knee position and erect posture at initial contact is associated with higher vertical ground reaction forces and thus increased ACL strain [13, 19 – 21]. Anterior tibial translation due to shear forces and increased external knee abduction moments combined with elevated internal rotation moments signifi­cantly contribute to ACL peak strain [13, 22]. 

Neuromuscularly, sex-specific differen­ces in muscle activation have been shown. Excessive quadriceps activation compared with insufficient hamstring co-­contraction in females may contribute to limited knee flexion angles upon landing, which may increase ACL strain. In contrast, increased hamstring co-­contraction prevents valgus stress on the knee, while gluteus maximus and medius activity reduces peak knee abduction angles and increases knee fle­xion angles upon landing [13, 23]. In female athletes, decreased activation of the vastus medialis compared to the vastus lateralis as well as decreased ­activation of the medial hamstrings compared to the lateral hamstrings have also been demonstrated. This medial-­to-lateral imbalance may explain why many females lack the ability to resist excessive abduction loads in the knee joint [13, 24].

Is the key professionalisation?

Sex disparities in access to training facilities and optimization of a crowded match calendar and travel may also play an important role in the risk of ACL injuries between males and females. Similarly, football boots, pitches quality, and football size and weight have been based on male, but not tailored around females’ characteristics [8]. 

Perhaps the most important extrinsic risk factor that exists in women’s football is the discrepancy in resources available. For example, there is a tangible gap in the quality of pitches between the women’s and men’s games. Due to poor availability of high-quality grass pitches, women are forced to play on either poor-quality surfaces or more recently, artificial turf, as seen during the 2015 FIFA Women’s World Cup [26, 27]. This is almost unheard of in the men’s game. Whilst these surfaces help mitigate cancellation of female events due to adverse weather conditions, the risk that it may pose to the female ACL is often overlooked. Indeed, findings of a recent meta-analysis published in the Orthopaedic Journal of Sports Medicine indicate that an increased risk of ACL secondary to match participation on artificial turf is only seen in female football players and not their male counterparts [28, 29].  

Additionally, female football boot technology is someway behind that seen in men’s boots. Females exhibit several intrinsic anatomical differences in foot structure that may place them at a biomechanical risk of ACL rupture. Although there is a lack of research supporting the relationship between boot choice and ACL rupture risk, recent research by the European Clubs Association has found that 80 % of female players playing in major European leagues report discomfort with their football boots. Although major football brands are making progress with their goals of better supporting the needs of female players [31], the avai­lability of female-tailored boots is poor, or at best, poorly advertised [26]. 

The discrepancy in resource availability is further highlighted by reduced accessibility to gyms to aid injury prevention programmes. This not only due to a lack of sufficient equipment within these gyms, but also the barrier to female participation underpinned by long-stan­ding issues such as gender-based norms dictated by society. It has been suggested that females have a lower training age considering the amount of time and exposure an athlete has had to structured, coached, and progressive training [8, 30]. Another key principle could be promotion of effective communication and collaboration within the wider club-­ecosystem. As part of the UEFA Women’s Elite Club Injury Study, Ekstrand et al found that risk factors for injury with the highest average importance were “lack of communication between medical staff and coaching staff” and “load on players” [32]. Although this was in the context of hamstring injuries, the same principles could be applied to ACL injuries. The medical team could collaborate directly with the sports science department to implement effective load management strategies on the same level like it is done in men’s football, and these to be communicated with the coaching staff to facilitate forward planning and implementation of such measures, including management of player’s match minutes and training schedules [33]. 

Can an ACL injury be predicted?

Jauhiainen et al. used an extensive screening test battery of 880 female elite athletes to investigate the predictive potential of multiple predictive machine learning methods on the risk of sustai­ning an ACL injury. Despite analysing a large prospective data set, the predictive ability was too low for ACL injury risk assessment in clinical practice. The reasons for the low predictive model might have been due to the failure to record training and match load data, including short term changes in physical variables and training loads. Therefore, further studies are needed to investigate what exact type of data and machine learning approaches should be used for more accurate injury prediction [25]. 

Conclusion

Over 20 years of research has failed to combat the disparity in the burden of ACL injuries between male and female footballers. Future work should look to define specific ACL risk reduction mea­sures and demonstrate how these might be implemented in the elite football setting. To do this, we should not focus only upon the specific intrinsic risk fac­tors in women footballers, but also on the environmental and psychosocially driven risk factors that currently exist [8, 33].

References

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Autoren

Sebastian Kunz

is a consultant orthopaedic and trauma surgeon who is currently working as a club doctor at Chelsea Football Club. Prior to joining CFC, he was the medical director of Lanserhof at The Arts Club in London for over 4 years. Before moving to the UK, he worked for several years at ATOS MediaPark Klinik Cologne, MVZ Ortho Königsallee Düsseldorf, Lans Medicum Hamburg and he was a club doctor of Viktoria Köln.

Daire Rooney

is a doctor based in the UK with a keen interest in sports medicine and is the current Chelsea FC Academy doctor. As well as undertaking a BSc in Sport and Exercise Science at Loughborough University, he has also completed a MSc in Sport and Exercise Medicine at the University of Birmingham. He combines his
clinical work with various educational roles, such as being an editor for the Football Medicine Performance Association and a reviewer for the BJSM. He has a keen interest in research, with published work in the areas of injury surveillance and exercise medicine.