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Corresponding author at: Physical Therapy Section, Department of Physical Therapy, Faculty of Health Sciences, University of Malaga, Arquitecto Francisco Peñalosa 3, 29071 Malaga, Spain.
Anterior cruciate ligament (ACL) injury is a prevalent sport-related injury that can threaten an individual’s sporting career.
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Contributing to characterize ACL injuries may help in improving the way professionals prevent and/or approach these undesired events.
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Injury surveillance through media-based platforms is becoming a valid, efficient, and versatile research resource that contribute substantially to epidemiological reports quality in elite soccer.
Abstract
Background
Anterior cruciate ligament (ACL) injury is a severe and complex sport-related injury that can threaten an individual’s sporting career. The purpose of this study is to investigate the epidemiological patterns of ACL ruptures in Spanish male first-division soccer players.
Methods
The Transfermarkt and Besoccer online electronic databases were screened for ACL injuries between 2010–2011 and 2019–2020 seasons. Injury incidence, injury mechanism, side of the injury, recurrence of the injury, days of recovery and severity, player’s position, dominance, season, and moment in which the injury occurs were collected.
Results
A total of 110 ACL ruptures were registered, with 15.45% of them being re-ruptures either ipsilateral (6.36%) or contralateral ruptures (9.09 %). The ACL incidence rate was 0.0364 per 1000 h of total play with a 68-fold risk in matches compared with training. Predominant injury mechanism was non-contact (56.36%) and the mean lay-off time was 218.8 days, with higher incidence in September-October and March-April. Goalkeeper was found to be the less affected position.
Conclusions
This investigation identified an average of 11 ACL tears per season in the Spanish first-division soccer league, most of them occurring in matches with approximately one ACL injury per team every two seasons. Our results from media-based platforms are in accordance with reports based on data from healthcare databases. Further research is needed to corroborate these findings in equivalent contexts.
Descriptive studies are classified as Level III evidence according to Daly et al., 2007.
]. The Spanish male first-division soccer league is comprised by 20 teams, each team playing two times against each other with a total of 38 matches per season. Other international and domestic competitions such as UEFA Champions League, UEFA Europa League and Copa del Rey usually take place during the same season. Frequently players competing in the first divisions are recruited by their national teams, with further match and training exposure and higher physical loads.
It has been stated that a greater risk of injury exists during a match than in training [
]. A study by the UEFA Champions League reported by Walden et al. demonstrated that both English and Dutch teams sustained a higher injury rate and a higher injury severity during a match compared to seven Mediterranean teams. Despite this difference during the matches, no differences were found between the teams during the training sessions. When comparing national competitions to international tournaments, there is a higher incidence of injuries in international competitions, which mainly take place by the end of the season. During this period accumulated fatigue, higher density of matches, and environmental conditions may play a role [
]. It is a complex injury, whose return-to-sport success rate depends on various factors such as pain, range of motion, instability, and torque of the quadriceps. it has been observed that less than 65% of the players return to their previous level of competition 3 years after the ACL injury [
]. In addition, a player who has previously injured the ACL has a greater chance of suffering a reinjury, either ipsilateral or contralateral. The gradual introduction of research-based prevention programs is decreasing the incidence and recurrence of ACL injury in recent years [
Epidemiology Of Recurrent Anterior Cruciate Ligament Injuries In National Collegiate Athletic Association Sports: The Injury Surveillance Program, 2004–2014.
]. A higher incidence of ACL injury has been identified in collision sports, when compared to non-contact. Soccer is not only a contact sport but a modality where high-impact and rotational movements occur [
]. In spite of the contact of this sport, 70–80% of injuries occur without contact, usually landing after a jump or when performing a sudden deceleration [
Current scientific literature is incorporating a great burden of studies focusing on the epidemiology of ACL injury in several populations. However, previous research involving the impact of this lesion on a renowned sport league is scarce. Despite the transcendence of ACL injury and the importance of the Spanish soccer league, there has not been an ACL epidemiological study in professional soccer players in Spain available yet. The aim of this study is to determine injury incidence rate and the distribution of ACL ruptures along the season, and to estimate injury related lay-off in the Spanish male first-division soccer league for 10 consecutive seasons (2010/2011 to 2019/2020).
2. Methods
2.1 Screening process
To investigate the epidemiology of ACL rupture injury, a retrospective cohort study was implemented. Data were retrieved from electronically accessible soccer databases. ACL ruptures were screened in all professional players participating in the Spanish male first-division soccer league (La Liga) across 10 consecutive seasons, from 2010-2011 to 2019/2020, including pre-seasons. The Spanish La Liga has been comprised by 20 teams during this period with no exception and with an average of 585.2 players per season. A total of 380 games per season are played (38 each team) in La Liga. The first 4 positions qualified for the UEFA Champions League whereas from 5th to 7th they compete in the UEFA Europa League. These tournaments are very important competitions at a European level and take place in the following season, with the Champions League being the most prestigious [
]. All these competitions are held simultaneously to La Liga throughout the entire season, along with Copa del Rey, another domestic tournament in which more than 100 participating teams from four different divisions take part with a knock-out format (one game) until semifinals [
Data for all teams were collected from two open-source sports databases: Transfermarkt and Besoccer, and written consent was obtained by both sources. Both databases were selected to access the injuries of La Liga players longitudinally. Approval was obtained by the institutional ethics review board.
From the main page, searches were made for each team for 10 consecutive seasons from the 2010–2011 to 2019–2020 season. When a tear of ACL was encountered, a new search was deepened in La Liga teams’ official websites to confirm the injury and to find out whether the player was eligible to be included in the study.
2.2 Data extraction
Data were analyzed and when an ACL injury was encountered, further targeted search was performed. Those players suffering a complete ACL tear or operated partial tear and participating in the Spanish male first-division were included. Those subjects with a non-operated partial tear, ligament strain, or those with injuries occurring in lower categories or other leagues were excluded.
For every professional player included in the study the following characteristics were analyzed: season and moment in which the injury occurs, age, height, position, dominant side, injury mechanism (contact or non-contact), side of the injury, recurrence of the injury, days of recovery. Moment of the competition in which the injury occurs was divided into preseason (from June to August including those occurring both in training and friendly competitions) and season (from September to May). In addition, those injuries occurring during the season were classified based on the occurrence during a training session or during a match, and based on to the competition (La Liga, Copa del Rey, UEFA Champions League and UEFA Europa League).
Recovery days were counted until unrestricted practice, even if they start training with the rest of the team previously. Reinjury was counted from the year in which the search was started, including as non-reinjury those players who had injured the ACL in seasons prior to 2010/2011. Those players who got injured prior to July 2010 and reinjured during 2010–2011 were considered as new injuries in this study as it is intended to study the number of re-ruptures occurred in the abovementioned 10-year period. When the ACL tear occurred in trauma or a high-impact collision with another player, and those cases in which the injury occurred after a collision, even those cases when contact occurred in the air and the player fell unbalanced were categorized as contact injury mechanism. Those injuries involving racing, jumping, pivoting, or decelerating actions, without any type of contact with other players were classified as non-contact injury mechanism. Due to the heterogeneity of the players’ participation with the national team and inherent difficulties to accurately calculate their exposure, those injuries were not included in the study.
2.3 Statistical analysis
Statistical analysis was performed using the statistical SPSS software (v. 25.0). Continuous variables were reported as mean ± SD, while categorical variables were reported as raw number and percentage of the total. Continuous variables were compared using the independent-sample t tests, and categorical variables were compared using the chi-square test. P-values < 0.05 were considered statistically significant.
Incidence of ACL rupture was calculated by dividing new injury cases by the total number of at-risk players during a given time period. Incidence rate was calculated by dividing the number of injured players by the hours of exposure, and results were expressed “per thousand”. Hours of exposure of the matches were calculated by multiplying the number of matches by 1.5 hours. Hours of training exposure were approximated by estimating the duration of the training as 1.5 hours, and 5.5 days of training per week and they would be multiplied by the competition weeks.[
A total of 110 ACL ruptures were registered in 93 different players, and 17 reinjuries were identified in this 10-season period (Table 1). The mean players’ age was 25.8 years (range, 17–36) (Figure 1), with a mean height of 1.79 m. Up to half of the subjects (68.18%, 75/110) were right-footed, while 27.27% (30/110) were left-footed, and only 1.81% (2/110) were ambidextrous. Dominance could not be clarified in a few cases (2.72%, 3/110).
Table 1Demographics and incidence rate and proportion of anterior cruciate ligament (ACL) injuries across the 10 seasons.
Season
Total players
Mean age
ACL injuries (preseason and season)
Incidence proportion (of total players)
ACL injuries in La Liga
Incidence rate of ACL injuries (per 1000 hours of match)
The mean injury-related lay-off time was 218.8 days to play again. ACL rupture has occurred more frequently without contact (56.36%) compared to those ruptures produced by contact (27.27%). The mechanism of injury was not identified in 16.36% of the cases. ACL re-ruptures accounted for 15.45%, of which the contralateral injury occurred in 9.09% of cases and ipsilateral in 6.36%.
An overall incidence rate of ACL ruptures of 0.018 per 1000 hours during La Liga competition was calculated. This incidence was 0.00026 per 1000 hours of training. Based on these data, the competition injury rate was 68 times higher than the training injury rate. An overall incidence rate of ACL ruptures of 0.0016 per 1000 hours during the season, including first division competition (La Liga), National Cup (Copa del Rey), European tournament (UEFA Champions League and Europa League) and training. This incidence was 0.00147 per 1000 hours of competition and 0.0013 per 1000 hours of training. Based on this data, the competition injury rate was 1.41 times higher than the training injury rate. Oppositely, the incidence rates of ACL injury in matches and training during preseason were similar. The incidence proportion was 1.87% of all La Liga players (n = 5852). According to this, it can be estimated that 10.3 ACL tears occurred every year and 0.51 injuries were declared at each team per season, which corresponds to one rupture every two seasons (Table 1).
3.2 ACL injury and position on the pitch
Table 2 gathers injury and reinjury rates of ACL and their relationship to player position. There were no significative differences between defenses (32.72%), midfielders (29.1%) and forwards (28.18%), but both rates were significative lower in goalkeepers (10%) (Figure 2). Recurrences have been more common in footballers who play as midfielders (6.36%) and forwards (5.45%).
Table 2Incidence rate of anterior cruciate ligament (ACL) injuries across the 10 consecutive seasons based on position. injury mechanism and different moments of the season.
Season
ACL ruptures
Field positions (n = 110)
Injury mechanism (n = 92)
Moment *
Pre-season
Season*
Goalkeeper
Defender
Mildfielder
Forward
Contact
Non contact
Friendly matches
Training
La Liga
Copa del Rey
UEFA
Training
2019/2020
7
0
3
0
4
1
6
2
0
4 (0.0126)
0
0
1 (0.0057)
2018/2019
15
0
6
4
5
5
9
2
0
11 (0.0344)
0
0
2 (0.0113)
2017/2018
6
1
2
0
3
2
4
1
2
2 (0.0061)
0
1 (0.0166)
0
2016/2017
15
3
6
2
4
3
9
1
1
12 (0.0360)
0
0
1 (0.0054)
2015/2016
7
2
2
3
0
2
3
2
0
4 (0.0117)
0
1 (0.01602)
0
2014/2015
11
2
3
3
3
5
4
0
0
5 (0.0156)
1 (0.0105)
2 (0.0341)
3 (0.0170)
2013/2014
14
1
3
8
2
2
8
0
2
7 (0.0216)
0
2 (0.0337)
2 (0.0112)
2012/2013
11
0
4
4
2
3
5
1
0
5 (0.0140)
3 (0.0282)
0
2 (0.0101)
2011/2012
14
0
4
6
4
4
8
0
2
6 (0.0168)
1 (0.0094)
0
5 (0.0256)
2010/2011
10
2
2
2
4
3
6
0
1
6 (0.0172)
0
0
3 (0.0314)
Total
110
11 (10%)
36 (32.72%)
32 (29.1%)
31 (28.18%)
30 (27.27%)
62 (56.36%)
9
9
62 (0.0186)
5 (0.0005)
6 (0.00097)
19 (0.0013)
*Incidence rate has been calculated in La Liga and training (only season training).
ACL injury was not homogeneous during the season, and two peaks of incidence were identified in September-October and March-April (Table 3). Most injuries occurred in autumn (30.90%), followed by spring (27.27%), and winter (23.36%); being summer the season with the lowest encountered number of injuries (17.47%) (Figure 3).
Table 3Comparative table between different studies.
ACL Injuries In Men’s Professional Football: A 15-Year Prospective Study On Time Trends And Return-To-Play Rates Reveals Only 65% Of Players Still Play At The Top Level 3 Years After ACL Rupture.
The distribution of the ACL injury was not homogeneous across different competitions. Not all seasons have the same incidence of ACL injury, and significant differences were identified throughout the analyzed period (p > .05). Both 2015–2016 and 2017–2018 seasons were found to be the most critical periods, with significant differences compared to other seasons(p < .05) (Table 2).
4. Discussion
ACL rupture is one of the most studied knee injuries in sport population, being among the most prevalent in soccer. This study, the first of its kind to describe the epidemiology of ACL ruptures through electronically accessible databases in high level soccer players in the Spanish male first-division, revealed an average of 11 ACL ruptures presented in every team of the Spanish La Liga during the 10-season analyzed period, which represents more than half of the participating teams experiencing an ACL episode per season. This 10-month long competition is believed to be among the four most important soccer leagues in the world, with a recognized socioeconomical burden. Data regarding ACL ruptures and RTP periods in these populations have been previously published for similar leagues [
The average height of ACL injured professional players in our series was 1.79 m, with an average age of 25.89, being most of them were right-footed (68.18%). Similar studies conducted in the Italian [
] leagues revealed that ACL injury occurred at younger ages, in comparison to the Spanish tournament. However, the mean age reported by these leagues (24–25.3 years old) is within our reported range (Table 3).
Recovery periods and functional outcomes have shown similarities among equivalent studies [
]. The mean ACL lay-off period in the Spanish league has been found to be 218.8 days whereas Middle East league and German Bundesliga documented 225.4 and 244 days off until unrestrictive practice, respectively [
]. Recovery periods length depends on medical criteria and the evolution of each player, among many other factors, which may be an explanation for the wide range identified in our study, with RTP times ranging from 122 to 407 days.
One of the complications of this injury is suffering a re-rupture. Walden et al. reported in his study that the reinjury occurs in 7% of the cases [
ACL Injuries In Men’s Professional Football: A 15-Year Prospective Study On Time Trends And Return-To-Play Rates Reveals Only 65% Of Players Still Play At The Top Level 3 Years After ACL Rupture.
]. Our study found a 15.45% of recidivism rate, with 9.09% of chances of suffering an injury to the contralateral knee and 6.36% to the ipsilateral knee.
The injury mechanism of ACL injury in our series is commonly related to non-contact contexts (56.36%), while contact injuries accounted for 27.27%. German and Italian leagues have also identified non-contact as the most prevalent mechanism, with slightly higher percentages [
] (Table 3). According to Walden et al. injury situations in which a non-contact ACL rupture occurs are usually related to players reproducing a pressing gesture, where a lateral movement or a sudden step to reach other player or the ball is implied; Those situations involving balance regaining when landing right after kicking or heading the ball are also involved [
ACL Injuries In Men’s Professional Football: A 15-Year Prospective Study On Time Trends And Return-To-Play Rates Reveals Only 65% Of Players Still Play At The Top Level 3 Years After ACL Rupture.
]. These data are in line with our reported findings.
The most injured positions in our study were defenders, whose function is to perform lateral movements and pressing. The position with lower ACL injury incidence was the goalkeeper, surely due to their game is not as dynamic as the rest of the players’, and even though it includes sudden, abrupt lateral displacements as part of their specific actions (Table 2).
Not all field positions showed similar rates of recurrent ACL ruptures (Table 2). Goalkeepers were those with the lowest percentage of re-ruptures (1.81%). According to Blazkiewicz et al., the majority of injuries in goalies occurs acutely on the elbows, wrists, and hands (especially the fingers), followed by overuse injuries in hip muscles and knee joint surfaces [
]. Midfielders (6.36%) and forwards (5.45%) were the field players presenting higher ACL re-ruptures rates, being non-contact the predominant injury mechanism in both cases (Table 4, Table 5). Actually, no re-rupture due to contact was found in these positions. The highest incidence of ACL re-injury due to contact was found in forwards. As their function is to score a goal, they are supposed to the defense and assume their pushes. This may explain why defenders was the second position with higher ACL re-rupture rates due to contact. On the other hand, midfielders were the most frequently injured players due to non-contact mechanism. These players usually accomplish defending, attacking and organizing tasks which are known to be related to non-contact mechanisms for ACL injury [
ACL Injuries In Men’s Professional Football: A 15-Year Prospective Study On Time Trends And Return-To-Play Rates Reveals Only 65% Of Players Still Play At The Top Level 3 Years After ACL Rupture.
The present study demonstrates an average of 0.55 injuries per team which implies 11 ACL injuries per year. The incidence per 1000 hours of activity is 0.0016 however it differs from matches to training. We have calculated an incidence of 0,00147 per 1000 hours of match whereas the incidence per 1000 hours of training was 0.0013. Incidence rate during matches is thus 1.5-fold higher compared to training (Table 2). These results are not in line with those obtained by Grassi et al. in the Italian league and by Schiffner et al. in the German league, with an incidence of 0.0618 and 0.04 per 1000 hours of play, respectively. According to the study by Rekik et al. there is an incidence of 0.076 per 1000 hours of play, being the incidence lower in European leagues than they are in the Middle East leagues. Reasons for this may be the fact that second division teams were included in the sample [
]. The incidence rate reported from the other European studies seem to consider only incidence rate in first division league, which would be more in line to the incidence rate in La Liga competition (0.0186 per 1000 hours) than with the total incidence rate. Studies performed on European teams agree that a greater chance of injury during matches than during training exists, although variations have been found between the studies. In this sense, Walden et al. reported a 20-fold higher injury risk during a game than during training. (Table 3).
Injury temporary distribution has not been homogeneous throughout a given year in our series (Table 3). The lowest incidence period was found to be summer, at the beginning of the season, probably due to the type of exigence along with the lack of competition events. We have identified two peaks of incidence during the year, October and March/April. This could indicate that initial training loads should be modulated and that fatigue from preparatory sessions of the competition may affect the performance of the players. The second peak of incidence is in March and April, which is the final stage of the season; May is when the competitions end (La Liga, Copa del Rey, UEFA League and Champions League), but there are not as many matches as in March and April, but injuries continue to occur due to the competitive level demanded by the finals.
However, the distribution of ACL injury has shown a relatively homogeneous pattern throughout the 10 seasons, with three exceptions in which lower incidences (of injury 6–7 ACL ruptures) have been detected (Table 2). A division of the 10 season-period was made and the resulting two blocks of 5 seasons were independently analyze. In the 2015–2020 season-period, a reduction of 10 injuries was identified than in the 2010–2015 seasons; that is, a reduction of 1.2%. In addition, we find that in recent years the injuries produced in training have decreased by 2.85% (7 ACL injuries in 2015–2020 and 20 injuries in 2010–2015), although a slight increase in its incidence has been found during games (1,075 %). No great variations were found in the injury mechanism between the seasons or in the different field positions, except in the midfielders, where a reduction of 2.55% of injury rate was found. Not all seasons have the same incidence of the ACL, the 2017–2018 2015–2016 seasons stand out with significant differences compared to other seasons. Incidence rate has been 1.87% of all La Liga players, although there has been variability according to the seasons.
The reduction of ACL tears in the last 5 years may be due to the implementation of prevention programs, since it has been shown to reduce the risk of ACL injury [
], it may be interesting to give more emphasis in the months in which we find the incidence peaks done at the end of the training to work in a fatigue condition, since it may be a risk factor for injury to occur [
An ACL tear is a serious injury which represents a potentially career-threatening issue. Often ACL injured players are forced to leave the competition until next season. Moreover, according to this study, the player who has previously injured the ACL has a 15.45% risk of reinjury. This has become an issue of particular concern in female populations, whom ACL injury and re-injury rates have been reported to be higher [
]. However, our study specifically focused in male soccer players. A similarly designed study comparing overall rates of ACL injury in equivalent samples could be of interest.
This is the first study to investigate the epidemiology of ACL in Spanish professional male soccer league, including relevant data regarding incidence and mechanism of ACL injury, and its distribution along the season. The strength of this study includes the sample size, the study period, and the professional status of the population. Few studies have analyzed as many professional soccer players, over as many exposure time, at such level of competition. This epidemiological study gathers information from 10 consecutive seasons, providing long-term knowledge which can be useful to develop a specific preventive and intervention programs for this injury in these populations. Due to size characteristics and the employed methodology conclusions can be made with sufficient empirical evidence and validity.
A number of limitations related to our analysis must be considered. Despite the sample being nationally representative of professional soccer players, amateur level was not included in our analysis. While some generalization of our findings may be relevant to that population, the wide variety, unique conditions and demands of this population necessitates additional analyses. There would be benefit to replicating this research in different cohorts according to their competition level, economic strength, and geographical or environmental issues. In addition, due to heterogeneity regarding participating players with national teams, exposure times from training sessions and matches in these cases were not considered for the purpose of this study.
All epidemiological analysis of injury data are dependent upon the quality of the employed data collection system. We do recognize some missing or inaccurate data in our study for several reasons, such as unreported injury episodes, diagnostic overlap, among others, which may have biased the reported findings. Another possible source of bias in our study could be the fact that data were obtained from electronic accessible databases, to the detriment of medical reports as a source of health information. Additionally, injury mechanism was not always specified in medical reports or official pages, so the related percentage to each injury mechanism may vary. Parallel systematic video analysis studies focusing on injury mechanisms would help to both accurately calculate and correlate these data. Furthermore, no comparison between databases was made, although the available information on injuries did not significantly differ between them.
5. Conclusions
This study shows that each La Liga team suffers on average 11 ACL tears per season with an incidence of 0.0016 per 1000 hours of play, being non-contact the most frequently reported mechanism. A higher risk of ACL injury has been identified in matches compared to training exposure. Our results are in accordance with reports based on data from healthcare databases. Thus, we can conclude injury surveillance through media-based platforms may constitute valid research resources and may serve as an alternative for epidemiological reports in elite soccer. Additional longitudinal research is needed to corroborate these findings in equivalent contexts and minimize these data.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors would like to thank BeSoccer and Transfermarkt for their support and for granting access to their electronic resources.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Epidemiology Of Recurrent Anterior Cruciate Ligament Injuries In National Collegiate Athletic Association Sports: The Injury Surveillance Program, 2004–2014.
ACL Injuries In Men’s Professional Football: A 15-Year Prospective Study On Time Trends And Return-To-Play Rates Reveals Only 65% Of Players Still Play At The Top Level 3 Years After ACL Rupture.
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