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Epidemiology of time loss groin injuries in a men’s professional football league: a 2-year prospective study of 17 clubs and 606 players
  1. Andrea B Mosler1,2,
  2. Adam Weir1,3,
  3. Cristiano Eirale1,
  4. Abdulaziz Farooq1,
  5. Kristian Thorborg4,
  6. Rod J Whiteley1,
  7. Per Hӧlmich1,4,
  8. Kay M Crossley2
  1. 1 Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar
  2. 2 La Trobe Sport and Exercise Medicine Research Centre, La Trobe University, Victoria, Australia
  3. 3 Academic Medical Center, Amsterdam Center of Evidence Based Sports Medicine (ACES), Amsterdam, The Netherlands
  4. 4 Department of Orthopedic Surgery, Sports Orthopedic Research Center-Copenhagen (SORC-C), Copenhagen University Hospital, Amager-Hvidovre, Victoria, Copenhagen, Denmark
  1. Correspondence to Dr Andrea B Mosler, Department of Rehabilitation, Aspetar Orthopaedic and Sports Medicine Hospital, PO Box 29222, Doha, Qatar; andrea.mosler{at}aspetar.com

Abstract

Background/Aim Groin injury epidemiology has not previously been examined in an entire professional football league. We recorded and characterised time loss groin injuries sustained in the Qatar Stars League.

Methods Male players were observed prospectively from July 2013 to June 2015. Time loss injuries, individual training and match play exposure were recorded by club doctors using standardised surveillance methods. Groin injury incidence per 1000 playing hours was calculated, and descriptive statistics used to determine the prevalence and characteristics of groin injuries. The Doha agreement classification system was used to categorise all groin injuries.

Results 606 footballers from 17 clubs were included, with 206/1145 (18%) time loss groin injuries sustained by 150 players, at an incidence of 1.0/1000 hours (95% CI 0.9 to 1.1). At a club level, 21% (IQR 10%–28%) of players experienced groin injuries each season and 6.6 (IQR 2.9–9.1) injuries were sustained per club per season. Of the 206 injuries, 16% were minimal (1–3 days), 25% mild (4–7 days), 41% moderate (8–28 days) and 18% severe (>28 days), with a median absence of 10 days/injury (IQR 5–22 days). The median days lost due to groin injury per club was 85 days per season (IQR 35–215 days). Adductor-related groin pain was the most common entity (68%) followed by iliopsoas (12%) and pubic-related (9%) groin pain.

Conclusion Groin pain caused time loss for one in five players each season. Adductor-related groin pain comprised 2/3 of all groin injuries. Improving treatment outcomes and preventing adductor-related groin pain has the potential to improve player availability in professional football.

  • hip
  • sports
  • soccer
  • pubis
  • adductor
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Introduction

Groin pain is common in football1–3 and can affect both player and team performance.4 5 However, injury prevention programmes have often failed to demonstrate significant effects.6–8 Determining the extent of a sport injury problem through accurate injury surveillance is a key component of successful injury prevention models.9 10 Better characterising the burden of groin injury in football may assist in designing injury prevention strategies.

Groin injury epidemiology has been described for a selection of teams,1 2 11 12 in subelite11 13 or junior football players.14 However, epidemiology for this injury has not been described in detail for an entire professional league. Previous studies of groin injury epidemiology have predominantly investigated European football, but little is known about other geographical regions.

Heterogeneous classification systems have been used to report groin injury in football. This has made it difficult to synthesise the findings of clinical research in this area. A systematic review of groin injury epidemiological studies highlighted the need for prospective studies to be of higher quality, and report detailed data on specific diagnostic categories.3 A recent consensus meeting standardised the taxonomy and terminology used to describe hip and groin pain, and provided a guideline to be used by clinicians and researchers.15 However, to date, no epidemiological studies of groin injury in football have been reported using the recommended classifications.

The primary aim of our study was to examine the incidence, prevalence and characteristics of time loss groin injury over two consecutive seasons of the entire Qatar Stars League (QSL).

Methods

Injury surveillance data were conducted prospectively for the QSL during the 2013–2014 and 2014–2015 football seasons through the Aspetar Injury and Illness Surveillance Programme.16 The QSL is the highest level of professional club football in Qatar and currently comprises 14 clubs in the first division and 18 clubs in the second division. Each season, the bottom two first division clubs are relegated to the second division, and top two clubs from the second division are promoted to the first division.

All first division teams were invited to participate in the study and the consistently high-performing second division clubs, with full-time doctors employed by the Qatar National Sports Medicine Programme, were also included. The reliability of the injury surveillance and exposure data was monitored closely by the research team, with injury absence time checked for accuracy against the exposure data. Teams were excluded for that season if they failed to supply injury and exposure data for more than 1 month of that season.

Time loss injuries and individual player participation (training and match play exposure) were recorded by each club doctor using standardised methods described previously.1 16–18 These methods are in accordance with the ‘Consensus statement on injury definitions and data collection procedures in studies of football (soccer) injuries’.19 Prior to the season, club medical staff were provided with a study manual containing information on the injury definitions and process of data collection. For each injury, the club doctor completed a standardised injury card containing information on the injury type, recurrence, mechanism, location, diagnosis and severity plus activity undertaking when injured (training or match). Injury surveillance data were requested monthly by the research team, and the accuracy was regularly checked and clarified with the club doctor as required. The reporting of this study follows the ‘Strengthening the Reporting of Observational studies in Epidemiology’ (STROBE) statement.20

Study population

All participants were male professional football players who competed during the 2013–2014 and/or 2014–2015 football seasons. Demographic information, such as age, height, weight, leg dominance, current and history of hip/groin injury, were obtained through the mandatory preparticipation screening process, as previously described.21 22 Ethical approval for this study was obtained from the Shafallah Medical Genetics Centre, Approval number: 2012–017 and the Institutional Review Board, Anti-doping Lab Qatar, Approval number: F2013000003.

Operational terms

Definitions used for the data collection of this study were based on previous reports of epidemiology in football (table 1).1 13 18 23

Table 1

Operational definitions adapted from Werner et al 1 and Ekstrand et al 23

The injury cards used by the club doctors to register a groin injury included; injury location classification based on that described previously,24 as well as a more detailed description of the doctor’s clinical diagnosis(es). One of the authors (ABM) used all these clinical information to categorise the groin injuries according to the classification system decided upon at the 2014 Doha agreement meeting.15 The categorisation for each groin injury was independently checked by a second author (AW) and clinical notes consulted if there was any doubt regarding categorisation. Groin injuries were, therefore, classified into the following categories: the four clinical entities, hip-related groin pain or other, according to the definitions determined in the Doha agreement meeting (table 2).15

Table 2

Classification system of groin pain in athletes, adapted from Weir et al 15

Statistical analyses

The proportion of all time loss injuries recorded in the cohort that were diagnosed as groin injury was determined. The overall, training and match play incidence rates of groin injury per 1000 playing hours were calculated using the following formula: number of injuries/exposure hours×1000. Poisson 95% CIs for the incidence rates were then calculated, and incidence rates were compared using the χ2 test.17 25 Injury burden was also calculated using the following formula: number of total days lost/player exposure hours×1000.23 Descriptive statistics were used to determine the prevalence of players sustaining a groin injury per club per season and the number of groin injuries sustained per club per season. Descriptive statistics were also used to determine the severity and characteristics of the groin injuries sustained during these two football seasons. All analyses were performed using IBM SPSS V.21.

Results

Study participants

A total of 17 different clubs provided complete injury and exposure data in either season and were included in the cohort. One first division club was excluded as it failed to supply complete data in either season, leaving 13 first division and 4 second division clubs. The included second division clubs had either participated in the first division in one of the seasons or been high performing in the second division. A total of 606 male football players were included in the cohort with demographic information as follows (mean±SD): age=26±4.9 years, height=177±6.9 cm, weight=73±9.2 kg and body mass index=23±2 kg/m2. The percentage of football players who were right dominant was 80%, while 20% were left dominant. The cohort included 11% goalkeepers, 33% defenders, 37% midfielders and 20% forwards. Players were exposed to a total of 205 466 playing hours, of which 183 557 hours were spent training and 21 909 hours in match play. The mean exposure per player per season was 234±114 hours, of which 209±105 hours was training and 26±18 hours exposure in match play.

Incidence, prevalence and burden of groin injury

A total of 1145 time loss injuries were recorded in the study cohort over these two football seasons. Of these injuries, there were 206 (18%) groin injuries sustained by 150 individual players. Overall incidence of groin injury was 1.0/1000 hours (95% CI 0.9 to 1.1). The incidence of groin injuries was higher during match play 3.5/1000 hours (95% CI 2.7 to 4.3) than in training 0.7/1000 hours (95% CI 0.6 to 0.8) (p<0.0001). The median prevalence of players injured per club per season was 21% (IQR 10–28%). There were 6.6 (IQR 2.9–9.1) time loss groin injuries sustained per season per average club roster of 30 players. The overall injury burden was 24.3 days/1000 hours, with a higher burden for match play (91.6 days/1000 hours) than training (16.3 days/1000 hours).

Characteristics of groin injury

Of the 206 groin injuries recorded, the severity of time loss was as follows (table 3): 16% were minimal, 25% mild, 41% moderate and 18% severe, with a median absence of 10 days/injury (IQR 5–22; figure 1). The median numbers of days lost due to groin injury for each team was 85 days (IQR 35–215) per season.

Figure 1

Severity of time loss groin injury (n=206).

Table 3

Characteristics of groin injuries sustained

Groin injury incidence appeared to be higher in the early season phase (September to November) of the football year (1.2/1000 hour and 37% of all injuries sustained; table 3). However, there were no statistically significant differences found between the overall or training incidence rates of the four defined phases of the football season (p>0.08). Match incidence rate during early season was higher than that in midseason (p=0.01). More injuries occurred on the dominant side (58%), and 6% of injuries were bilateral (table 3). The majority of injuries occurred during training (63%) and were of gradual onset (68%). During the study period, there were 171 (83%) first-time injuries and 23 (11%) early and 12 (6%) late recurrence injuries. The overall recurrence rate for groin injuries was 20%, with a recurrence rate of 27% for the sudden-onset injuries and 18% for the gradual-onset injuries.

Injury categories

Adductor-related groin pain was the most commonly diagnosed entity (68%) followed by iliopsoas (12%) and pubic-related (9%)  groin pain (table 4). The majority of cases were diagnosed as a single entity (87%), but there were also 18 (9%) cases where 2 entities were diagnosed and 8 (4%) cases where 3 entities were diagnosed. There were only three cases of multiple entities that did not include adductor-related groin pain (table 4). Of the single entity cases, 17% were of minimal severity, 29% mild, 41% moderate and 13% severe. For the multiple entity cases, there were no cases that were of minimal severity, 12% mild, 35% moderate and 54% severe.

Table 4

Categories of groin injury diagnosis (n=206)

Discussion

In our study, the overall incidence of time loss groin injury was 1.0/1000 hours (95% CI 0.9 to 1.1) in a professional football league over two consecutive seasons. There was a five times higher injury incidence rate in match play than training (p<0.0001). At the club level, 21% (IQR 10%–28%) of players in each club had a time loss groin injury each season. There were 6.6 (IQR 2.9–9.1) groin injuries sustained, resulting in a median of 85 days (IQR 35–215) lost per club per season. More than half (59%) of the injuries resulted in more than 1 week of time loss, and more unilateral injuries were found on the dominant side. Adductor-related groin pain was the most common diagnosis (68%) and only two cases of hip-related groin pain (1%) were recorded.

Comparison with other epidemiological studies

Our findings of a high incidence, prevalence and burden of groin injury in a professional football league extend previous reports among professional football team cohorts.1 2 26 The groin injury incidence in the UEFA Champions League over 10 seasons was 1.1/1000 hours (95% CI 1.0 to 1.2),1 remarkably similar to our findings of 1.0/1000 hours (95% CI 0.9 to 1.1). The higher incidence during match play 3.5/1000 hours (95% CI 2.7 to 4.3) than training 0.7/1000 hours (95% CI 0.6 to 0.8) (p<0.001) also replicates the UEFA results (3.5/1000 match hours vs 0.6/1000 training hours, p<0.001). It is interesting that our findings demonstrate such similarity to that of UEFA club data, as the QSL is considered to have a lower standard of play according to international rankings of the National team and Qatari clubs. The incidence rate reported in our study is higher than those previously reported for subelite football cohorts.11 13 27

How does injury rate relate to exposure and phase of the football season?

Our study is the first to report groin injury burden as a function of exposure, with an overall rate of 24.3 days/1000 hours of player exposure. This groin injury burden is higher than the 19.7 days/1000 hours previously reported for hamstring injuries.23 A QSL club can expect 6.6 (IQR 2.9–9.1) time loss groin injuries per season, similar to the UEFA findings of 7.2 injuries per season.1 Player prevalence of 21% means that 6–7 players per average club roster of 30 players are likely to sustain a groin injury per season. More than half (59%) of the time loss injuries sustained were moderate or severe. The number of days lost due to groin injury per club per season was high (median=85 days, IQR 35–215). Since low injury rates correlate with team success in football,5 effective prevention and treatment of groin injury is recommended.

There was a trend towards overall groin injury incidence being highest in early season, and match incidence rate was significantly higher in early compared with the midseason phase of the football year (p=0.01). The highest rate (33%) of adductor muscle injuries also occurred in early season in a study of UEFA club data.2 It is likely that these higher rates of groin injury in early season reflect the increase in match workload that occurs during this phase.28 29 Therefore, improved match play preparation during the preseason may be beneficial to reduce the number of groin injuries occurring during this part of the season.28 In our cohort, a predominance of unilateral injuries occurred in the dominant leg (58%) compared with the non-dominant leg (36%), consistent with the findings of previous studies.13 This suggests that kicking load and/or mechanics may be a factor in the development of groin injury in unilateral presentations. Kicking has also previously been found to be the most frequent injury mechanism in acute adductor strains in football players.30 More detailed analyses of groin injury mechanism was beyond the scope of our study, but such investigations may assist in developing more directed injury management and prevention strategies.

Classification of groin injuries according to the Doha agreement

Adductor-related groin pain was the most common groin pain entity,24 both as a single entity (139/180) and in conjunction with other entities (23/26). This extends the findings of prospective studies that have also found adductor injury to be the most common groin injury diagnosis in European teams.1 13 The use of the Doha agreement classification system to categorise the groin injuries in our cohort meets the current gold standard agreed upon by the expert group.15 The standardised terminology and diagnostic criteria described in this classification system may allow for better reproducibility of these findings, and specificity of groin injury prevention programmes.

Relationship between groin pain, hip-related diagnoses and cam morphology

Hip-related groin pain was very uncommon in our study, accounting for only 1% of groin injuries recorded. It is possible that ambiguity in the Doha agreement classification system for this category resulted in an underestimation of hip-related groin pain in our cohort. However, the low percentage of cases diagnosed as hip-related groin pain (1%) may also be specific to this cohort of predominantly Arab football players. Hip joint-related diagnoses constituted 5% of all groin injuries diagnosed in European professional football.1 There has been considerable interest in the relationship between cam morphology of the hip, femoroacetabular impingement syndrome and groin pain in football.31–34 Interestingly, previous investigations of bony hip morphology in QSL football players have determined a high prevalence of cam morphology (72% of players).34 The relationship between the presence of cam morphology and development of groin pain requires further investigation with prospective study design. However, it seems that hip joint pathology may be of lower incidence in the QSL in comparison to other professional football leagues,1 despite the apparent high prevalence of cam morphology.

Limitations

This study was initiated prior to the publication of the Doha agreement meeting,15 and minimal reporting standards on groin pain in athletes.35 Therefore, these data represent post hoc rather than a priori categorisation. However, the categorisation of groin injury according to the entity approach24 has been in use for several years in Qatar. The QSL club doctors have previously received education and specific training to enable standardisation of clinical examination and groin injury diagnosis prior to the data collection for this study. Despite this training, there may be limitations in the accuracy of the categorisation of the injury data. In cases where there was doubt about the classification, the medical records were assessed by two members of the study team (AM and AW) to optimise accuracy. The data collection for this study followed methodological recommendations for epidemiological data collection in football,18 and this has been standard process in Qatar for 5 years prior to the study commencement.17 However, missing data and unknown inaccuracies within the data set could potentially have affected the results of our study.

Finally, using a time loss injury definition is likely to underestimate the true burden of groin pain in football.26 Our injury definition excluded groin pain without time loss, which is relevant considering the gradual onset of most (68%) of the groin injuries. Regular use of questionnaires about the presence and impact of groin pain on the football player would provide better insight into the overall burden of this injury.26 36 37 The translation, cross-cultural adaptation and validation of such questionnaires for the commonly spoken languages and nationalities of the QSL football players would assist such future research.

Summary

Time loss groin injury is common in professional football players in Qatar, accounting for 18% of all time loss injuries. One in five players (IQR 9%–28%) will have a time loss groin injury each season. A club can expect 6.6 (IQR 2.9–9.1) groin injuries, resulting in a total of 85 days (IQR 35–215) lost per season. Over half of these groin injuries will result in more than 1 week of time loss, and match play incidence is higher than training. Adductor-related groin pain is the most common diagnosis (68%). Optimising treatment and prevention strategies is recommended for club medical staff, particularly focussing on adductor-related groin pain.

What are the new findings?

  • Groin injury incidence, prevalence and burden are high in a men’s professional football league.

  • Match play injury incidence rate is higher than training and significantly higher in early than in mid football season.

  • Unilateral groin injuries were more prevalent on the dominant than non-dominant side.

  • Adductor-related groin pain was the most common groin pain entity (68%); hip-related groin pain was 1%.

How might it impact on clinical practice in the near future?

  • The high incidence and burden of time loss groin injury found in this study emphasises the need to better understand and prevent these injuries.

  • A specific focus on optimising treatment outcomes and preventing adductor-related groin pain is recommended for football teams.

Acknowledgments

The authors would like to sincerely thank Rima Tabanji and all the staff of the National Sports Medicine Program of Aspetar Orthopaedic and Sports Medicine Hospital who were integral to the data collection.

References

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Footnotes

  • Contributors ABM designed the study, contributed to data collection, analysed and interpreted the data and drafted the article. CE, AW and AF designed the study, contributed to data collection, analysed and interpreted the data and revised the article. KT, PH, RJW and KMC designed the study, interpreted the data and revised the article. All authors approved the final revision of the article.

  • Competing interests None declared.

  • Ethics approval Shafallah Medical Genetics Center and Institutional Review Board, Anti-doping Lab Qatar.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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