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Abstract
Background To identify mechanisms and patterns of anterior cruciate ligament (ACL) injury in adult women’s professional football by means of video match analysis.
Methods ACL match injuries sustained in Germany’s first women’s league during the 2016–2017 to 2022–2023 seasons were prospectively analysed by three expert raters using a standardised observation form. Epidemiological and injury data, as well as the medical history of ACL tears, were obtained from media reports and the statutory accident insurance for professional athletes.
Results Thirty-seven ACL injuries sustained in official football matches were included in the video analysis, of which 24 (65%) had associated knee injuries, mainly meniscus and collateral ligament injuries. According to the categorised contact mechanisms, 17 (46%) were non-contact injuries, 14 indirect contact injuries (38%) and six direct contact injuries (16%). Of the 17 non-contact injuries, seven (41%) occurred during the first 15 min of the match. Contact mechanisms did not differ between primary and secondary ACL injuries to the same or the contralateral side. Most injuries (80%) of field players occurred during horizontal movements such as sprinting (n=9, 26%), change-of-direction manoeuvres (n=7, 19%), stopping (n=5, 14%) and lunging (n=5, 14%). Four distinct repetitive patterns of ACL match injuries were identified: (1) non-contact ‘pressing ACL injury’ (n=9), (2) indirect contact ‘parallel sprinting and tackling ACL injury’ (n=7), (3) direct contact ‘knee-to-knee ACL injury’ (n=6) and (4) non-contact ‘landing ACL injury’ (n=4).
Conclusion Most of the identified patterns of ACL injuries in women’s professional football have great potential for prevention.
- Injury prevention
Data availability statement
Data may be obtained from a third party and are not publicly available. Data may have been obtained from a third party and are not publicly available. Epidemiological background data were available from the VBG. These data are not publicly available. The authors have no permission to make the data available. No administrative permissions were required to access the raw data. The VBG prepared and shared the specific files to the University Medical Center Wurzburg. Data protection and confidentiality agreements were signed prior to study research.
This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.
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WHAT IS ALREADY KNOWN ON THIS TOPIC
The risk of anterior cruciate ligament (ACL) injury in professional women’s football is high.
Little is known about frequent injury patterns in this high-risk population.
WHAT THIS STUDY ADDS
The four typical injury patterns for ACL injury in women’s professional football were (1) non-contact ‘pressing ACL injury’, (2) indirect contact ‘parallel sprinting and tackling ACL injury’, (3) direct contact ‘knee-to-knee ACL injury’ and (4) non-contact ‘landing ACL injury’.
A high proportion (80%) of ACL injuries were sustained during horizontal (rather than vertical) movements, and 41% of non-contact injuries occurred in the first 15 min of play.
HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY
The results provide insight into how ACL injuries occur in women’s professional football and identify typical situational patterns that should be considered in risk-reduction strategies.
Timing appears to be a contributing factor in non-contact injuries, suggesting a high potential for prevention through adequate match preparation, neuromuscular activation and load management.
Preventive exercises should consider improving lateral and rotational trunk stability during one-legged stance during sprinting and upper-body contact with rotation. In addition, alternative tackling and landing techniques could be taught for these at-risk situations.
Background
Professional female football players are at high risk of an anterior cruciate ligament (ACL) injury.1 In the last two decades, the incidence of ACL injuries in girls has seen a major increase,2–4 with incidences increasing from 0.06 per 1000 hours5 to 0.1–0.2 per 1000 hours.6–8 Female athletes participating in intermittent team sports (including football) are reported to have a 2–6 times higher risk of injury than male athletes.9 10 The annual prevalence of ACL injuries in female players ranges from 0.5% to 6.0%. For both male and female players, studies have consistently shown a 7–65 times higher incidence of ACL injury during match play.10 ACL reconstruction surgery is often required, followed by a long rehabilitation period. A 2016 systematic review showed a rate of 26% of a second ACL injury to either knee after return-to-play in athletes under the age of 25.11 ACL injuries can not only lead to long-term physical impairment, reduced athletic performance and premature career ends but are also associated with an increased risk of osteoarthritis.12 13
Video analysis plays a vital role in sports injury prevention research by allowing the detailed examination of biomechanics, movement patterns and player behaviour.14 This detailed analysis provides valuable insights for the development of targeted interventions and strategies to reduce the incidence of sports injuries.15 16
Previous video analysis studies investigating ACL injury mechanisms in football players primarily focused on men17 18 or mixed cohorts. In the mixed cohort study of non-professional athletes, Brophy et al identified a defensive pressing pattern as a common cause of ACL injuries in women.19 This finding was supported by Lucarno et al 20 in a female-only study that found the defensive pressing pattern to be the leading cause of ACL injuries among three main injury patterns.20
Despite these two studies, essential information is still lacking in women’s football on ACL injury mechanisms. Indeed, a more detailed knowledge of injury situations in women’s professional football may help establish more targeted injury prevention measures.14 Thus, the purpose of this study was to identify mechanisms and patterns of ACL injuries in women’s professional football in a first-league setting by using video match analysis, with particular emphasis on differences between first and secondary ACL injuries, differences in associated knee injuries and the role of foul play, timing of injury and substitution.
Methods
This prospective study was conducted from the 2016–2017 season to the 2022–2023 season. The study included all ACL injuries sustained during official matches of a football team of the first women’s national league in Germany (1. Frauen Bundesliga). Only female players who sustained an ACL injury during an official match in the first national league, German Cup or Champions League were included. Injuries sustained during matches with the national team were systematically excluded. Injuries and contact mechanisms were defined by video match analysis as previously described by our study group21–23 and according to current guidelines.24 Briefly, a contact injury was defined as any injury due to external forces directly at or adjacent to the injured body site, either by contact with another player or with an object such as the goal or the ball, immediately before or at the same time as the suspected injury. Indirect contact injuries were defined as any injury due to external forces that did not directly cause the injury but affected the natural movement process and indirectly led to the injury. Non-contact injuries were defined as any injury that did not involve contact with another player or object.
Inclusion and exclusion criteria, the procedure of video production, the provision of video footage, data collection and video analysis were identical to those described in previous literature reports.21–23 25 In short, this prospective cohort study is based on the nationwide ACL registry in German football, to which all professional football clubs in the German first division were invited to report all new ACL injuries of their players.26 In addition, national media reports on professional football players were systematically screened on a weekly basis in various German online and print media. After the registration of a new ACL injury, either through direct notification by the players and clubs or through media reports, a standardised questionnaire was sent to the injured player directly or via a team member. These medical data were entered into the database of the national insurance company, Verwaltungs-Berufsgenossenschaft (VBG). The VBG receives all time-loss injury reports from the team physicians. The data from the media reports were systematically compared with the physician’s reports and, if necessary, completed. Associated knee injuries were systematically assessed from the team physician’s reports.
Standardised video analysis
Three expert raters with experience in professional football (LA, TD and CK) reviewed and classified each injury-causing event according to the applied observation form, which had been used in previous similar studies.21 27 28 A detailed description of the video analysis process is given elsewhere.21–23 In short, we used video footage provided by DieLigen GmbH, publicly available video footage from the German broadcasters ARD and ZDF and video matches uploaded from the social media channels of the respective football clubs. The footage was captured by at least one camera in the stands of each football stadium. Information on the approximate time of the injury was taken from the website of the German football magazine ‘kicker’ (https://www.kicker.de) and, if necessary, from an additional Google search (name of player AND injur* AND name of opposing team). Each clearly identified injury situation was cut to a sequence of approximately 10–15 s before and approximately 5–10 s after the injury event to assess the specific match situation, the injury circumstances and the referee’s decision. In addition, all available replays from the television broadcast (in slow motion and from different perspectives) were added to the sequence. In the next step, LA, TD and CK independently assessed the video footage using the described observation form. First, LA and TD analysed the videos and held an initial consensus meeting. A third rater (CK) was added subsequently. In a subsequent consensus meeting, the assessments were compared, and deviating assessments were discussed and harmonised by consensus. Frequent repetitive injury patterns were grouped and described by consensus.
Equity, diversity and inclusion statement
Our study focused on professional female football players in Germany. The research team consisted of one woman and seven men. The authors’ disciplines included sports medicine, orthopaedics, traumatology and strength, conditioning and exercise science. All the authors were from Germany. We acknowledge that our study excludes semiprofessional and amateur football.
Statistical analysis
Absolute numbers and proportions were reported. The injury mechanism and the role of substitution were analysed with χ2 tests and Fisher’s exact tests. The χ2 tests were used to compare injury proportions between the two halves of the match and the third part of each half. Cohen’s measures and κ measures were used to analyse inter-rater reliability for the observation form. 95% CI are reported. The significance level was set at p<0.05. All analyses were conducted using IBM SPSS Statistics, V.28.0.
Results
All 37 ACL injuries (100%) sustained during official matches were included in the video analysis (figure 1). Thirty-four injuries were captured by one camera view and three injuries by two camera views. Most injuries (n=31) occurred in national league matches, compared with only three injuries each in the German Cup and the Champions League. Two ACL injuries were sustained by goalkeepers and 35 by field players: 13 defenders, 16 midfielders and 6 forwards. The mean age was 23.4±3.6 years (range: 18–32 years); the mean weight was 61.6±5.8 kg (range: 48–70 kg), and the mean height was 168.6±4.9 cm (range: 158–184 cm).
Flow chart. A total of 132 league matches: 33–37 cup matches and 6–10 Champions League matches were played per season.
The concordance analysis of reliability for the final observation form showed substantial concordance (κ=0.61) with very good concordance (κ>0.8) for 14% of the variables, substantial concordance (κ=0.61 to 0.80) for 43% of the variables and moderate concordance (κ=0.41–0.60) for 43% of the variables. Concordance was particularly low for the rater’s own decision of foul play (0.206).
ACL-associated knee injury
Of the 37 ACL injuries, 21 (57%) were first-time index injuries and 16 (43%) were secondary injuries. Of the 16 secondary injuries, nine (56%) were secondary ipsilateral (to the same side) graft ruptures, and seven (44%) secondary injuries were contralateral ruptures. Two athletes in this cohort sustained their overall third ACL injury. Associated injuries were recorded in 24 athletes (61%). Lateral meniscus injury was noted in 18 athletes (49%), medial meniscus injury in 11 (30%), medial collateral ligament in four (11%) and lateral collateral ligament in one athlete (3%). We found no association between lesion pattern and injury pattern or mechanism.
Contact injury mechanism
The stratified contact mechanisms showed 17 non-contact injuries (46%), 14 indirect contact injuries (38%) and six direct contact injuries (16%).
The contact mechanism did not differ significantly between primary and secondary ACL injuries (injury to the same or contralateral side) (figure 2), but there was a non-significant trend towards a higher non-contact rate in second ACL injuries.
Proportion of contact mechanisms for ACL injury during match play in women’s professional football. Contact mechanisms were divided into contact (dark green), indirect contact (light green) and non-contact (very light green). Of the 37 ACL injuries, 21 were first-time injuries, nine were secondary ipsilateral (to the same side), and seven were secondary contralateral injuries. ACL, anterior cruciate ligament.
General and football-specific movements
The most common injury situations for field players were horizontal movements (80%). The injury situations for field players are described in detail in table 1:
General and football-specific movements of field players
Four recurrent patterns of ACL match injuries in women’s professional football were identified. The patterns differed significantly in their mechanisms and match characteristics: (1) non-contact ‘pressing ACL injury’ (n=9), (2) indirect contact ‘parallel sprinting and tackling ACL injury’ (n=7), (3) direct contact ‘knee-to-knee ACL injury’ (n=6) and (4) non-contact ‘landing ACL injury’ (n=4). (table 2, figures 3–6).
Most common recurrent patterns of injuries to the anterior cruciate ligament in women’s professional football (field players)
Illustration of the ACL injury pattern in women’s professional football: ‘pressing ACL injury’. The blue-white player’s left knee was injured in this situation. (1) The defending player is running towards the opponent in possession of the ball. (2) She changes direction with a non-contact sidestep cut. (3) Assumed injury frame. (4) Loss of balance. ACL, anterior cruciate ligament.
Illustration of the ACL injury pattern in women’s professional football: ‘parallel sprinting and tackling knee injury’. The blue-white player’s left knee was injured in this situation. (1) Parallel sprinting duel towards the ball. (2) Upper-body tackle and indirect mechanical perturbation while the left leg is on the ground. (3) Assumed injury frame. (4) Loss of balance. ACL, anterior cruciate ligament.
Illustration of the ACL injury pattern in women’s professional football: ‘knee-to-knee injury’. The blue-white player’s left knee was injured in this situation. (1) Player versus player duel with the defender shielding the ball. (2) She is tackled from behind with a direct lateral impact to the knee joint. (3) Assumed injury frame. (4) Loss of balance. ACL, anterior cruciate ligament.
Illustration of the ACL injury pattern in women’s professional football: ‘landing ACL injury’. The black player’s left knee was injured in this situation. (1) Jump over a defender. (2) Non-contact landing with the left leg and visual/neurocognitive perturbation with the head following the ball. (3) Assumed injury frame. (4) Loss of balance. ACL, anterior cruciate ligament.
Two goalkeeper injury situations were identified: (1) the goalkeeper running out of the penalty area to jump shot and clear a ball in front of an attacker. While landing, she had indirect contact with the attacker, who collided with her trunk, which resulted in twisting her knee and (2) after a corner kick, the goalkeeper watched the ball fly across the goal area and out of bounds. While sidestepping, she twisted her knee without any contact.
Field area and foul play
The comparison of the two pitch halves for field players showed no significant differences between the defender’s half (54%; 95% CI 36 to 71) and the forward’s half (46%; 95% CI 29 to 63, p=0.494). When each pitch half was subdivided into seven areas, the defensive area between the penalty area and the centre line had the highest percentage of ACL injuries in women’s professional football (n=9, 24%). Foul play was rarely called by the referee (n=6, 16%) and only in cases of direct contact (n=4, 11%) or indirect contact (n=2, 5%) injuries.
Timing of injury and role of substitution
The two match halves did not differ significantly with regard to injury distribution. The first half (35%; 95% CI 20 to 53) showed a lower proportion of injuries than the second half (65%; 95% CI 47 to 80, p=0.0109). When the match time was divided into six 15-min periods and substitution was taken into account, the first period (0–15 min) showed the highest number of ACL injuries with significant differences to the second period (16–30 min) (p=0.0116) (figure 7A,B). Of the 17 non-contact ACL injuries, seven (41%) occurred during the first 15 min of the player’s individual match time.
(A) Distribution of match injuries in women’s professional football divided by (A) time in effective match minutes and (B) time in minutes.
Of the 37 players who sustained an ACL injury, six (16%) had been substituted. Of these six injuries, four (67%) occurred during the first 15 min of the match, and the other two (33%) occurred during the first 30 min after the substitution.
Pitch condition
There was no rain (0%) in any of the observed injury match situations.
Discussion
The most important finding of this study was the identification of four common patterns of ACL injuries in official matches of the first women’s league in Germany: (1) ‘pressing’ (2) ‘parallel sprinting and tackling’, (3) ‘knee-to-knee‘ and (4) ‘landing’. We found that a high proportion of 80% of ACL injuries occurred during horizontal movements such as sprinting, stopping, change-of-direction manoeuvres and lunging; only a small proportion of injuries resulted from vertical actions (landing and jumping). This finding is consistent with that of previous research,20 indicating that knee control may be more important during high-risk horizontal movements than during vertical movements.
Contact mechanisms
We found that 84% of ACL injuries in women’s professional football occurred without direct contact with the injured knee, which is almost identical to previous findings in women’s19 20 and men’s football.17 18 21 In addition, there was a non-significant trend towards a higher non-contact rate of second ACL injuries on either the same or the contralateral side, which has been described for the first time in women’s football. The study also extends findings from ACL-associated knee injuries in women’s professional football for the first time.29 30
Injury pattern: direct knee-to-knee ACL injury
Football is a sport in which the main aim is to control a ball with the lower extremities and in which physical contact is allowed. Therefore, it is not surprising that direct knee-to-knee contact injury mechanisms were associated with ACL injuries in 16% of situations, which is comparable to previous reports in women’s (11%) and men’s (12%) professional football.18 20 In most situations, the injured player was in possession of the ball and the defender was coming mainly from the side or from behind; therefore, the knee contact was probably not visible to the player and thus unexpected. Less often, the injured player was tackling as a defender. Both situations may result in high-impact knee abduction with the leg on the ground.
Foul play was only called in cases of direct knee-to-knee contact injuries. Further research is needed to evaluate how often such tackles lead to severe knee injuries especially when the tackle is not visible to the player or the player is unable to anticipate the knee contact. Injury prevention may focus on increasing awareness and anticipation among the players of these high-risk situations, which may involve better screening of opponents behind the player. However, its effectiveness is unknown.
Injury pattern: parallel sprinting and tackling ACL injury
At 32%, our study reports similar proportions compared with some studies (34%)20 but lower than other studies (51% tackling injuries).19 In this indirect contact mechanism, we identified a new common (19%) injury pattern specific to women’s football that has not been described before: the parallel sprinting and tackling ACL injury.
‘Parallel sprinting and tackling’ injuries occur when two opponents sprint in parallel at a seemingly high speed to play the ball rolling away from them. These situations often occur on the sidelines, with the attacker trying to reach the ball at the last moment before it rolls out of bounds. The injured players were at a disadvantage because they were slightly behind the defender but still trying to touch the ball with the foot that was closer to the opponent and with the other (injured) foot firmly on the ground. At that moment, the attacker received an upper-body tackle from the defender shielding the ball. This tackle caused the attacker’s torso to move laterally in relation to the stance limb and the knee to move into knee abduction, resulting in an ACL injury.
Lateral perturbation of the trunk is important component of the mechanism during this dynamic high loading of the stance limb before or during ground contact of the injured leg.31–33 Trunk position and external knee abduction loading may be mechanically related because lateral trunk position may create abduction loads at the knee.31 32 These frontal plane biomechanics are then further altered by rotation of the upper body while the foot is stationary on the ground, which adds rotational forces to the knee.
This mechanism has a high potential for prevention because trunk and lower extremity control in such high-risk situations may be improved through neuromuscular training.34 35 Core strength training should specifically target lateral and rotational trunk stability during one-legged stance after sprinting and upper body contact with rotation.36 In addition, alternative tackling and landing techniques should be taught for these high-risk situations, such as falling backwards on the turf and sliding on the back, and/or rolling backwards over the shoulders after upper-body contact.37
Injury pattern: pressing ACL injury
We identified 24% of ACL injuries due to non-contact defensive pressing, which is significantly lower than the percentages reported in the literature on women’s (58%–73%)19 20 and men’s (33%–66%)17 18 professional football. One of the main reasons for this difference is that the other literature reports combined non-contact and indirect contact injuries that occurred during defensive pressing, while we divided these situations into different pattern descriptions.
Injuries occurred during a change-of-direction manoeuvre by the attacker in possession of the ball directly in front of the injured defender and a subsequent—and according to the authors, reactive rather than anticipatory—run towards the ball by the injured defender. Injured players seem to have a high horizontal speed before the injury, followed by a rapid deceleration or change-of-direction manoeuvre in close proximity to the attacker.
Although these specific situations occur regularly in training and competition, it is yet unclear why they lead to immediate knee collapse and subsequent ACL injury. Further research should investigate why such mechanically simple horizontal deceleration manoeuvres lead to match injuries in women’s football, whereas male athletes are typically injured during more strenuous jumping manoeuvres.21 38 39 Due to the close proximity and short reaction time of the defender, a high visual and/or cognitive demand can be proposed as a potential neuromuscular mechanism.40
Injury pattern: non-contact landing ACL injury
The fourth most common injury mechanism (11%) is jumping over an opponent and landing on one leg with immediate knee collapse. Most research on predicting ACL injury risk over the past decades has focused on vertical landing differences.41–44 Our study shows, however, that these injury situations are less common than previously proposed and that research should focus more on understanding horizontal injury mechanisms. For vertical injury prevention, valgus torque seems to be a crucial factor,41 and proprioceptive deficits in women have been shown to result in quadriceps-dominant activation during landing with delays in hamstring activation that are not seen in men.44 Women are often affected by the same knee valgus collapse that leads to ACL injury as men but often have significantly higher knee and hip flexion during injury than men.45
Time of injury and its relevance for injury prevention
Nearly half of all non-contact injuries occurred during the first 15 min of effective match play. This confirms previous reports in a men’s and sex-mixed cohort in professional football of a high proportion of ACL injuries in this early time period5 18 and extends the findings to the non-contact injury mechanism. Our study (35%) contradicts previous findings in women’s professional football (55%)20 and men’s (55%)18 professional football, which found a higher proportion of ACL injuries in the first half. Timing seems to be an essential factor in non-contact injuries, indicating a high potential for prevention through adequate match preparation and activation. Players and staff members responsible for warm-up may therefore focus more on appropriate warm-up regimens and neuromuscular activation specific to ACL protection46 as well as on monitoring accumulated fatigue throughout the preseason and season.
Clinical implications
In women’s football, there is low-level evidence that multicomponent training programmes reduce ACL injuries by half.47 48 The identified common injury mechanisms suggest considerable potential for prevention. Multifaceted preventive approaches are needed that focus on the respective basic and sports-specific movement patterns and the most important specific (contact) mechanisms of injury-causing situations.
Strengths and limitations
The strength of this study is its prospective systematic data collection in the highest national women’s professional football league in Germany over seven consecutive seasons. To ensure high-validity data, this study used insurance data registered directly by team physicians. This study had a high identification rate of 100%. The study design was identical to that of previous studies, which increases comparability with men’s football and other team sports. The main limitation is that most injury situations could only be analysed with a single camera view with limited image quality, especially for injury situations far away from the midline camera position. Systematic bias due to the video analysis by three raters cannot be excluded. The third rater, who was added subsequently, may be biased due to previous results and interpretations. Data from training sessions were not available. Therefore, the injury patterns in training sessions may differ from those in matches. In addition, it is unknown whether the injury mechanisms and playing situations differ from those of amateur or youth football players. This observational study did not include precise analytical methods, such as biomechanical analysis, which adds uncertainty to the reported injury mechanisms.
Conclusion
We identified four typical injury patterns leading to ACL injury in women’s professional football, which differ significantly in terms of injury mechanisms and match situations. However, most of the common ACL injury patterns identified in women’s professional football have great potential for injury prevention.
Data availability statement
Data may be obtained from a third party and are not publicly available. Data may have been obtained from a third party and are not publicly available. Epidemiological background data were available from the VBG. These data are not publicly available. The authors have no permission to make the data available. No administrative permissions were required to access the raw data. The VBG prepared and shared the specific files to the University Medical Center Wurzburg. Data protection and confidentiality agreements were signed prior to study research.
Ethics statements
Patient consent for publication
Ethics approval
Institutional Review Board (IRB) approval was obtained from the Ethics Committee of the University of Regensburg (ID 17-895-101).
Acknowledgments
This study was conducted in cooperation with the German Statutory Accident Insurance for the Administrative Sector VBG and the Deutsches Kreuzbandregister (German ACL registry), who provided the data set on professional female football players.
References
Footnotes
X @Hendrik_Bloch, @Chrs_Kln
Contributors LA, DS, WK, CK and HB collected the data and the video footage. TD, CK and LA analysed the video footage. LA, TD, HB and CK analysed the data. All authors, but mainly LA, were responsible for the conception and design of the study. LA, TD, HB and CK interpreted the data. LA wrote the first draft of the paper, which was critically revised by all co-authors. LA is responsible for the overall content as guarantors. All authors have read and approved the final manuscript.
Funding Costs for accessing the video match footage from DieLigen were met by the University of Cooperative Education for Sports and Health, Baunatal, Germany.
Competing interests CK and HB are employed by the VBG.
Patient and public involvement Patients and/or the public were involved in the design, or conduct, or reporting, or dissemination plans of this research. Refer to the Methods section for further details.
Provenance and peer review Not commissioned; externally peer reviewed.