Risk factors for groin injury in sport: an updated ...

Downloaded from http://bjsm.bmj.com/ on April 9, 2015 - Published by group.bmj.com

BJSM Online First, published on April 1, 2015 as 10.1136/bjsports-2014-094287

Review

Risk factors for groin injury in sport: an updated systematic review Jackie L Whittaker,1 Claire Small,2 Lorrie Maffey,3,4 Carolyn A Emery5,6 ▸ Additional material is published online only. To view please visit the journal online (http://dx.doi.org/10.1136/ bjsports-2014-094287). 1

Faculty of Kinesiology, Sport Injury Prevention Research Centre, University of Calgary, Calgary, Alberta, Canada 2 Pure Sports Medicine, London, UK 3 Faculty of Medicine, Division of Sport Medicine, University of British Columbia, Vancouver, British Columbia, Canada 4 School of Rehabilitation Science, McMaster University, Canada 5 Faculty of Kinesiology, Sport Injury Prevention Research Centre, University of Calgary, Calgary, Canada 6 Department of Pediatrics and Department of Community Health Sciences, Alberta Children’s Hospital Research Institute for Child and Maternal Health, Cummings School of Medicine, University of Calgary, Calgary, Canada Correspondence to Dr Jackie L Whittaker, Sport Injury Prevention Research Centre, Faculty of Kinesiology, University of Calgary, 2500 University Dr NW, Calgary, Alberta, Canada T2N 1N4; [email protected] Received 1 October 2014 Revised 9 March 2015 Accepted 11 March 2015

ABSTRACT Background The identification of risk factors for groin injury in sport is important to develop and implement injury prevention strategies. Objective To identify and evaluate the evidence examining risk factors for groin injury in sport. Material and methods Nine electronic databases were systematically searched to June 2014. Studies selected met the following criteria: original data; analytic design; investigated a risk factor(s); included outcomes for groin injury sustained during sport participation. The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines were followed and two independent authors assessed the quality and level of evidence with the Downs and Black (DB) criteria and Oxford Centre of Evidence-Based Medicine model, respectively. Results Of 2521 potentially relevant studies, 29 were included and scored. Heterogeneity in methodology and injury definition precluded meta-analyses. The most common risk factors investigated included age, hip range of motion, hip adductor strength and height. The median DB score across studies was 11/33 (range 6–20). The majority of studies represented level 2 evidence (cohort studies) however few considered the inter-relationships between risk factors. There is level 1 and 2 evidence that previous groin injury, higher-level of play, reduced hip adductor (absolute and relative to the hip abductors) strength and lower levels of sport-specific training are associated with increased risk of groin injury in sport. Conclusions We recommended that investigators focus on developing and evaluating preparticipation screening and groin injury prevention programmes through highquality randomised controlled trials targeting athletes at greater risk of injury.

BACKGROUND

To cite: Whittaker JL, Small C, Maffey L, et al. Br J Sports Med Published Online First: [ please include Day Month Year] doi:10.1136/ bjsports-2014-094287

Groin injuries are common in many sports that involve rapid acceleration and deceleration, sudden changes in direction and kicking such as soccer,1–12 rugby,13 Australian rules football,14 ice hockey,15 Gaelic football and cricket.15 16 In addition to frequent occurrence, prospective collection of injury data over consecutive soccer seasons has demonstrated that those with a previous groin injury are at a 2.4 (hazard ratio; 95% CI 1.2 to 4.6) times greater risk of groin injury than payers with no previous history.10 This vicious cycle of injury and re-injury may result not only in reduced performance and missed training/competition but chronicity, the end of an athletic career and future mobility disability. According to van Mechelen,17 the prevention of sport injuries occurs through a four-step process

beginning with establishing the extent of the specific injury through a validated injury surveillance system. This is followed by identifying injury risk factors and causal mechanisms through prospective analysis of specific injury patterns, development and introduction of preventative strategies and evaluation of these strategies by determining their impact on injury incidence. Throughout this process it is important to acknowledge that a sport injury is unlikely to result from a single risk factor but rather as a consequence of complex interactions of multiple risk factors and inciting events.18 Thus, studies aimed at identifying risk factors for groin injuries in sport should utilise a prospective design and ensure an adequate sample size to facilitate biostatistical methods that consider the interrelationships between various risk factors.19 Consensus regarding the risk factors for groin injury is lacking and this may be due, in part, to methodological limitations and heterogeneity of previous studies. Our 2007 systematic review of risk factors for groin strain injury in sport reported a deficiency in prospective studies.20 Based on the studies available at that time (n=11; 2 crosssectional and 9 prospective), there was support for an association of previous injury and greater hip adductor to abductor strength ratio, sport specificity of training and amount of preseason sportspecific training as individual risk factors in groin strain injury. Although this review did not include a formal assessment of the quality or level of evidence of the included studies, it reported significant concerns regarding the internal validity of the included studies. Further, it recommended that any future studies examining risk factors for groin strain injury in sport employ consistent injury definitions, use validated and reliable injury reporting systems to quantify outcome measures and consider the inter-relationships between risk factors by controlling for potential confounding variables (eg, player exposure and previous injury). As identification of risk factors and their causal mechanisms is a precursor to the development of effective prevention strategies, the lack of consensus related to risk factors for groin injury in sport has likely hindered the process of developing and evaluating groin injury prevention strategies in sport. The objective of this review was to update this previous systematic review and summarise the evidence related to risk factors for groin injury in sport, including critical appraisal of the literature.

METHODS This review was conducted according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines.21

Whittaker JL, et al. Br J Sports Med 2015;0:1–8. doi:10.1136/bjsports-2014-094287

Copyright Article author (or their employer) 2015. Produced by BMJ Publishing Group Ltd under licence.

1


Review Data sources and search Relevant studies were identified by searching nine online databases, selected based on their relevance to the research topics, from inception to June 2014. These databases included: MEDLINE (1966-present), CINAHL (Cumulative Index to Nursing and Allied Health Literature; 1982–present), Cochrane database for Systematic and Complete Reviews (1975–present), Cochrane Controlled Trials Registry (1975–present), Cochrane Injuries Group Trials Register, Sport Discus (1980–present), EMBASE (Excerpta medical databases; 1974–present), PubMed (public Medline) and SCOPUS. A combination of medical subject headings (MeSH) and text words were used to execute each search. Table 1 outlines the search terms used by injury, anatomical region or tissue type and risk concept along with the combinations of search terms that formed each search strategy. The only limits set were that studies be published in a peer-reviewed journal. The Cochrane database for Systematic and Complete Reviews was included to identify any systematic reviews and/or meta-analyses such that their reference lists could be manually searched alongside those of all selected studies to identify relevant articles not identified by the search strategies. Manuscripts were organised using the reference management software package, EndNotes V.7.1 (Thomson Reuters, 2013). The number of references obtained from each search strategy for each database was recorded and a running total constructed. After accounting for duplication, the titles and corresponding abstracts of all returned records were reviewed by ( JLW) to identify potentially relevant studies. Finally, the full text of all potentially relevant studies was reviewed to determine final study selection by ( JLW, CAE).

Study selection Studies were included if they investigated the association between any potential injury risk factor (defined as any factor

Table 1

that may increase the potential for injury) or injury prevention strategy with groin injury (defined as any or all of the following; groin or hip adductor injury or muscle strain, tenderness on palpation of the hip adductor or flexor muscles, adductor bonetendon junction or pubic symphysis and/or pain on resisted hip adduction). Additional inclusion criteria included: primary research of original data, analytic design (eg, experimental, cohort, case–control or cross-sectional), an outcome measure of groin injury sustained during sport participation, an objective exposure measure of one or more potential risk factor or injury prevention strategy for groin injury in sport and study participants who were involved in any sport that involved rapid acceleration and deceleration, sudden changes in direction and kicking. The definition of groin injury was modified slightly (omitted lower abdominal muscles) from the original systematic review to be consistent with clinical entity of adductor-related pain proposed by Holmich et al22 and, as a greater number of studies focusing on the hip adductors and adductor bonetendon junction were available than at the time of the original review. Studies were excluded if the injury outcome was only described in general terms such as thigh or hip injury, were not written in English or involved animal models or cadavers. Further, conference proceedings/abstracts, review articles (systematic and narrative), case series or case studies, editorials, commentaries and opinion-based papers were excluded.

Data extraction and study rating process Data extracted from each study included; study design, study location and population (sport, level, age, sample size), injury outcome (definition), injury estimates (incidence proportion, incidence rate, prevalence), measures of risk (difference in means, correlations, OR, incidence rate ratios; IRR and risk ratio; RR), risk factors and

Search strategy and results of the systematic literature search, with total number of unique articles per database

MeSH or text words*

MEDLINE

PubMed

CINAHL

EMBASE

Sport Discus

Scopus

CCTR

CDSR

1 and 6 1 and 7 1 and 8 1 and 9 1 and 10 2 and (3 OR 4) and 6 2 and (3 OR 4) and 7 2 and (3 OR 4) and 8 2 and (3 OR 4) and 9 2 and (3 OR 4) and 10 5 and 6 5 and 7 5 and 8 5 and 9 5 and 10 1 and (6 OR 7 OR 8 OR 9 OR 10) and 11 2 and (3 OR 4) and (6 OR 7 OR 8 OR 9 OR 10) and 11 5 and (6 OR 7 OR 8 OR 9 OR 10) and 11 Individual Database Totals No. of articles included in systematic review

269/269/17 4/1/0 1/1/ 0 1053/860/4 133/0/0 47/0/0 2/1/0 0/0/0 195/167/3 4/0/0 39/9/0 0/0/0 0/0/0 58/14/0 2/0/0 75/0/0 28/0/0

170/2/0 37/4/0 1/0/0 545/93/1 487/62/0 3/0/0 0/0/0 0/0/0 25/1/0 19/4/0 38/0/0 15/3/0 1/1/0 76/8/0 57/3/0 29/0/0 1/0/0

177/87/0 0/0/0 1/0/0 2/0/0 3/0/0 4/0/0 5/0/0 6/0/0 7/0/0 8/0/0 9/0/0 10/0/0 11/0/0 12/0/0 13/0/0 14/0/0 15/0/0

24/3/0 10/0/0 278/57/0 1542/647/0 34/0/0 2/0/0 0/0/0 12/2/0 147/64/0 0/0/0 7/0/0 1/1/0 49/4/0 112/20/0 0/0/0 63/0/0 3/0/0

1/1/0 0/0/0 1/0/0 18/1/0 0/0/0 1/0/0 2/0/0 3/0/0 4/0/0 5/0/0 6/0/0 7/0/0 8/0/0 9/0/0 10/0/0 11/0/0 12/0/0

193/3/0 28/0/0 224/3/0 636/28/0 120/0/0 18/1/0 6/1/0 22/3/0 90/19/0 0/0/0 41/0/0 6/1/0 56/3/0 85/5/0 2/2/0 48/0/0 9/3/0

6/0/0 0/0/0 0/0/0 23/0/0 1/0/0 0/0/0 0/0/0 0/0/0 6/1/0 0/0/0 0/0/0 0/0/0 0/0/0 0/0/0 0/0/0 2/0/0 0/0/0

1/0/0 0/0/0 1/0/0 40/39/0 3/0/0 2/0/0 0/0/0 2/0/0 8/6/0 1/1/0 1/0/0 0/0/0 1/0/0 1/0/0 0/0/0 11/0/0 2/0/0

4/0/0 1914/1322/24 24

3/0/0 1507/181/1 1

16/0/0 183/87/0 0

4/0/0 2288/798/0 0

13/0/0 26/2/0 0

5/4/0 1589/76/0 0

0/0/0 38/1/0 0

1/0/0 75/46/0 0

References

8/8/4 4

Cell values represent potentially relevant/unique (eg, not a duplicate)/included in systematic review. *1=Groin (MeSH), 2=hip (MeSH), 3=adductor (tw), 4=flexor (tw), 5=osteitis pubis (tw), 6=athletic injuries (MeSH), 7=sprain, 8=strain (MeSH), 9=sport injur×(tw), 10=injur×(tw), 11=wounds and injuries (MeSH), 12=risk factors (MeSH); CCTR, Cochrane central register of controlled trials; CDSR, Cochrane database for systematic and complete reviews; CINAHL, Cumulative index to nursing and allied health literature; EMBASE, Excerpta medical databases; MeSH, medical subject heading; tw, text word.

2



Review results (significant and non-significant). If available, injury estimates (injury rates) were used to calculate point estimates of IRR (IR exposed/injury rate in unexposed). Two authors (lead author and one of three coauthors) independently assessed the quality and level of evidence of each study. Quality of evidence was evaluated based on criteria for internal validity (study design, quality of reporting, presence of selection and misclassification bias, potential confounding) and external validity (generalisability) using the Downs and Black (DB) quality assessment tool which assigns an individual score calculated out of 33 total points for each study (10 points for reporting, 3 points for external validity, 7 points for bias, 3 points for confounding and 1 for power: see online supplementary appendix 1).23 The level of evidence represented by each study was categorised based on the Oxford Centre of Evidence Based Medicine (OCEBM) model (see online supplementary appendix 2).24 As per study exclusion criteria, levels 1a, 2a, 3a (systematic reviews), 4 (case series) and 5 (opinion-based papers) were not included. Discrepancies in DB scoring or OCEBM categorisation were resolved first by consensus between the two reviewers who rated the study and if required, by the senior author (CAE).

Data synthesis Extracted data, quality and level of evidence were summarised for each study. The quantity, quality and level of evidence for the most commonly investigated modifiable and non-modifiable risk factors for groin injury in sport were collated.

RESULTS Identification of studies An overview of the study identification process is provided in figure 1. The initial search yielded 7760 articles (including eight identified through reference list search), 5239 duplicates were removed leaving 2512 potentially relevant articles. Following the

removal of studies not meeting inclusion criteria based on abstract review (eg, injury and injury risk were not investigated, population or dance form did not match criteria) this was narrowed to 70. Subsequent to further manuscript evaluation by the two independent reviewers ( JLW and CAE), 41 were excluded leaving 29 studies deemed appropriate for inclusion to the systematic review. Electronic or hard copies of two potentially relevant articles were not available for review and as they had not met similar inclusion criteria for the previous review, published in 2007, they were excluded.25 26 One study27 included in the previous systematic review was excluded as it did not provide an independent estimate of groin injury (eg, combined low back, groin and hamstring injuries), while another study included in the previous review,15 that included abdominal muscle strain in the injury definition, was included as 83% of the reported injuries were related to the adductor muscles. Owing to inconsistent methodology and injury definition as well as the heterogeneity of the risk factors examined meta-analysis was precluded (see online supplementary table S1).

Study characteristics Characteristics of the 29 included studies are summarised in online supplementary table S1. These consisted of 2 intervention studies (1 randomised controlled trial, 1 quasi-experimental), 21 cohort (19 prospective, 1 historical, 1 pilot), 5 case–control and 1 cross-sectional study representing approximately 14 different countries. The median number of participants per study was 219 (range 18–2299) and the combined total number of athletes investigated across studies was 12 131 (9925 males and 2206 females). Twenty-eight of the studies are believed to have included male athletes (11 of these did not specify the sex of their participants however based on the sport investigated it is likely the participants were male) spanning the ages of 12–38 years, while five studies included female athletes (age

Figure 1 Study identification Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) flow sheet. Whittaker JL, et al. Br J Sports Med 2015;0:1–8. doi:10.1136/bjsports-2014-094287

3


Review range 15–41 years). Among the 23 follow-up studies 13 had a follow-up time greater than one season (range 9 weeks—9 seasons), 7 had at least 50 injury cases (range 4–672) and 9 utilised a multivariate statistical approach to identify risk factors for groin injury in sport. Of the 19 studies published since 2007, 1 was a randomised controlled trial, 14 were cohort (12 prospective, 1 historical and 1 pilot) and 4 were case–control. Six of these 19 studies utilised multivariate statistical approaches and 5 had at least 50 injury cases.

Injury estimates Descriptions of injury estimates (incidence proportion, incidence rate, prevalence), effect estimates (IRR, RR, OR) and significant and non-significant groin injury risk factors are presented in online supplementary table S1.

DISCUSSION To our knowledge, this is the first systematic review examining risk factors for groin injury in sport that considers both a formal evaluation of study quality and level of evidence. Overall the quality and level of evidence investigating risk factors for groin injury in sport has improved in the past 7 years since our systematic review in 2007.20 Specifically, there are a greater number of prospective studies with larger sample sizes employing multivariate statistical techniques.

Key findings—risk factors

The quantity, quality and level of evidence for the most commonly investigated modifiable and non-modifiable risk factors for groin injury in sport are summarised in table 2. The most common risk factors investigated included age, hip range of motion, hip adductor strength, height and weight. There is level 1 and 2 evidence that previous groin injury, higher level of play, reduced hip adductor strength (isolated and relative to hip abductor strength) and lower levels of sport-specific training are associated with increased risk of groin injury in sport. Further, there is consistent evidence to suggest that older age, higher weight or body mass index (BMI), height, reduced hip range of motion (ROM) and performance on fitness tests such as jump height, leg power (squat), 40 m sprint, sidestepping, kicking and VO2max estimated from a shuttle run are not associated with groin injury in sport.

Consistency across the literature support previous groin injury, higher level of play, reduced hip adductor strength (absolute and relative to the hip abductors) and lower levels of sport-specific training as risk factors for groin injury in sport. To date, many authors have speculated on the mechanisms underlying these risk factors. The general consensus regarding the mechanism by which previous injury is a risk factor is inadequate rehabilitation following the initial injury and/or inherent physiological risk in certain individuals that puts them at greater risk of both the initial and subsequent injuries.2 10 15 31 The risk associated with higher level of play may result from a higher intensity in training and game play as well as a greater number of training hours.32 Decreased levels of hip adductor strength (both absolute and in comparison to the hip abductors) may result in decreased muscle capacity, imbalances between the synergistic functions of hip adductor and abductor muscles, and increased risk of muscle injury during movements involving side-to-side cutting, striding, quick acceleration/deceleration and sudden direction changes.9 15 Sport-specific training (specifically, pre-season) may address muscle weakness and imbalance as well as promote function specific recruitment resulting in more effective utilisation and less muscle fatigue.20 Consequently reduced sport-specific training may place an athlete at higher injury risk when faced with an increase in training load as the playing season begins. Although there have been valuable contributions made to the evidence base related to identifying risk factors for groin injury in sport in the past 7 years the conclusions of this systematic review and that of the previous20 are surprisingly similar. Specifically: ▸ previous groin injury, ▸ reduced relative hip adductor strength and ▸ reduced sport-specific training were all identified as risk factors for groin injury in sport previously. Previous groin injury, and reduced hip adductor strength have also been identified as risk factors for groin/hip injury in field-based sports in a recent systematic review of seven studies.44 In addition, Ryan et al44 reported that older age, higher BMI and reduced hip abductor ROM are risk factors for groin/hip injury in field-based sport. The discrepancies between these findings and those of the current review are likely due to the limited scope of sports considered and the inclusion of studies investigating both hip and groin injuries in the field-based sport review. Of the 29 studies included in the current review, 12 investigated older age as a risk factor for groin injury in sport (see online supplementary table S1). Of these, all but two studies (including one randomised controlled trial (RCT), eight cohort) found no association between older age (both as a dichotomous and continuous variable) and groin injury in sport (see table 2). Similarly, five of six included studies investigating BMI and six of nine investigating hip ROM found no association between the exposure variables and groin injury.

4


Quality and level of evidence The highest level of evidence demonstrated by all reviewed studies was level 1b (Individual randomised controlled trial). The majority (21/28) of studies were classified as level 2b which corresponds to cohort studies. The median methodological quality for all 29 studies, based on the DB criteria, was 11/33 (range 6–20) with an initial moderate between rater agreement of 65.5% (κ=0.62).43 The aim of the DB criteria is to assess scientific study methodological quality (inclusive of randomised and non-randomised intervention as well as observational studies). Owing to the majority of included studies being observational in nature, seven items (4, 8, 14, 19, 23, 24 and 27; totalling 10 points) on the DB checklist were not applicable. Therefore, 27 of the 29 articles did not have the opportunity to achieve a full score due to their study design. Areas in which the included studies were consistently limited included: incomplete description of how the sample was representative of the population of interest (eg, insufficient description of participant characteristics such as sex, history of previous groin injury, training exposure), limited description of the characteristics of those lost to follow-up, use of invalid or unreliable measures, insufficient reporting of how participants lost to follow-up and differing length of follow-up were accounted for in statistical analyses, inadequate sample size and lack of adjustment for potential modification and confounding by factors such as exposure and previous injury. Further, several of the case–control studies that report a matched design did not account for matching in their analyses (eg, independent t tests vs paired t tests).

Synthesis of results


Weight BMI Body fat Hip ROM Hip Add strength Hip Abd strength GMd activation TrA thickness/activation Knee muscle strength Knee ROM Calf flexibility Clinical tests† Fitness tests‡ GrOS/function Exposure§ Stretching and cross-training Sport specific training Age Sex Height Previous injury Game play Level of play Player position Years of sport experience Occupational demands Skeletal maturation Leg morphology

Modifiable

a

1 (20)

1 (20)

SIG

1 (20)

1 (20)

1 (20)

NOT

b: High-quality RCT c

a

2

1 (12)

SIG

1 (12)

NOT

b: True or quasi experimental

1 (10) 1 (11)

1 (11) 1 (15)

4 (15–18) 1 (13)

1 (15) 2 (10–13) 1 (18)

1 (18)

1 (10) 3 (9–18) 1 (11)

1 (11)

SIG

1 (18) 2 (11–18) 2 (11–18) 2 (11–16)

6 (13–18) 1 (16) 6 (11–18)

1 (11) 1 (9) 1 (9) 1 (18) 4 (11–18) 2 (16–18) 3 (16–18)

4 (13–19) 5 (13–18) 3 (11–18) 5 (9–18) 2 (11–15) 1 (9)

NOT

b: Prospective cohort

1 (9)

SIG

1 (9) 1 (9)

1 (9) 1 (9) 1 (9)

1 (9)

NOT

b: Retrospective cohort c

a

3

1 (11)

1 (7) 2 (9–11)

1 (7) 2 (7–11)

SIG

1 (11)

1 (11)

1 (11) 1 (9) 1 (11)

NOT

b: Case–control

1 (10)

1 (12)

1 (12)

SIG

2 (10–12) 1 (10) 1 (12)

1 (10)

NOT

Pilot cohort cross-sectional

4

5

7 6 3 9 9 4 1 2 1 1 1 3 5 3 4 1 1 12 4 8 5 2 3 5 4 1 1 1

Total studies

Cell values represent number of studies (range of Downs and Black quality assessment tool scores/23 for cohort studies and/32 for RCT’s). As per exclusion criteria, systematic reviews (1a, 2a and 3a), case series (4) and opinion-based papers (5) were not included (shown in dark grey). *Level of evidence is based on the modified Oxford Centre for Evidence-Based Medicine Model. †Including tenderness on palpation, pain, joint stability (knee and ankle) and positive active straight leg raise test. ‡Includes jump height, leg power (squat), 40 m sprint, sidestepping, kicking and VO2max estimated from a shuttle run. §Includes measures of training and match exposure as well as weekly sports participation. Abd, abduction; Add, adduction; ASLR, active straight leg raise test; BMI, body mass index; GMd, glutaeus medius; GrOS, groin outcome score; IO, internal oblique; LE, lower extremity (knee and ankle); NOT, not significant finding; RA, rectus abdominins; RCT, randomised control trial; ROM, range of motion; SIG, significant finding; TrA, transversus abdominis.

Non-modifiable

Risk factor

Risk factor

Level of evidence*

1

Table 2 Summary of significant and non-significant groin injury risk factors by quantity, quality and level of evidence


Review

5


Review What can we learn from other injuries? Looking beyond the groin injury literature, the current findings are relatively consistent with a recent systematic review and meta-analysis (including 34 studies) of risk factors for hamstring injury in sport45 which identified previous hamstring injury, quadriceps peak torque and older age as the exposure variables most consistently associated with hamstring muscle strain-type injury. The discrepancy in findings regarding increasing age as a risk factor for groin and hamstring injury may be related to the relatively narrow age range (mean age ≤25.8 years with SDs ranging between 0.8 and 4.6 years) represented in the 12 studies that have investigated age as a risk factor for groin injury. Further, the conclusion that increasing age is a risk factor for hamstring injury45 is potentially influenced by the findings of one study by Arnason et al2 Accordingly additional consideration of the prospective relationship across between age and injury risk across a wider age span for both muscle groups is recommended.

Limitations Meta-analyses were not possible due to inconsistent methodology and heterogeneity of the definition of groin injury in the included studies. Further, despite a comprehensive search strategy and rigorous approach to study selection it is important to acknowledge the possibility of omitting a relevant study and inclusion of only English language manuscripts. As the conclusions and recommendations contained within this review are based on a synthesis and evaluation of existing literature they are limited by its inadequacies. In several instances (eg, game play, fitness tests) there was a lack of consistent high-quality evidence to support nominating a particular exposure variable as a risk factor due to inadequate reporting of concepts essential to establishing internal and external validity. The biggest threats to internal validity were related to the possibility of selection bias and potential confounding. Specifically, due to the lack of reporting of participant characteristics it was often difficult to determine if the athletes selected for a study differed systematically from those in the source population (selection bias). Equally important was the consistent omission of the characteristics of those lost to follow-up, which made it impossible to determine if those lost to follow-up were systematically different from those retained in the study. The inability to assess for selection bias not only questions the internal validity of several studies, it impacts the degree to which the findings of these studies can be generalised to the larger athletic population from which the sample was drawn (external validity). As stated earlier, it is highly unlikely that a groin injury is a result of a single risk factor, but rather the consequence of complex interactions between multiple risk factors and inciting events.18 Multivariate biostatistical techniques can be used to explore these complex interactions given an adequate sample size. Bahr and Holme19 estimated that 50 injury cases are needed to detect a moderate to strong association between a risk factor and sport injury. Of the 29 studies included in this review only nine employed these techniques, of which only three had 50 or more injury cases and were able to assess these interactions.9 15 31 As a result, the association between the potential risk factor and groin injury reported in the studies that did not employ these techniques may be biased as they failed to consider any potential confounder (eg,. extraneous variables that may have distorted the relationship between the exposure variable and groin injury). The last point of consideration is that studies to date may not have considered all possible risk factors for groin injury in 6

sport. For example, a recent systematic review and position statement released by the American Medical Society for Sports Medicine highlights that although there is a lack of clinical data a high ratio of workload-to-recovery time may lead to overuse injuries and burnout in youth sport.46 To the best of our knowledge the relationship between measures of over training or physiological fatigue and groin injury and sport have yet to be investigated.

Recommendations Both prospective cohort and intervention study designs are important for identifying potential risk factors for injury in sport.19 While prospective cohort studies are critical for establishing temporality between a risk factor and subsequent injury, RCTs provide the strongest evidence for the causal nature of a risk factor (eg, hip abductor and adductor strength, decreased levels of sport-specific training) and the effectiveness of modifying that factor on injury outcomes. Based on the additional prospective studies undertaken in the past 7 years (involving larger samples and employing multivariate statistical techniques), consistency of the finding of the current review with those of the previous review20 and the challenges and high cost of undertaking high quality prospective cohort studies, it is recommended that investigators shift their focus from prospective cohort to high quality RCTs. Specifically, future research should include RCTs that target athletes at greater risk of groin injury during sport (eg, high levels of play, previous injury) with prevention programmes that include interventions targeting the hip abductor and adductor muscles in conjunction with off and preseason sport specific training. To date two separate intervention studies aimed at addressing modifiable risk factors (eg, dynamic balance, muscle strength and agility), for sport-related lower extremity and groin injuries have been undertaken.32 47 Engebretsen et al47 investigated the effectiveness of an injury prevention programme on high-risk (eg, previous injury and/or reduced function) soccer players, while Holmich et al32 selected a cluster (soccer team) design to facilitate implementation. Unfortunately both studies lacked sufficient statistical power to demonstrate a significant effect of the proposed intervention on the occurrence of sport-related groin injuries and Engebretsen et al47 report that player compliance to the training programmes was poor with only 19.4% of the groin injury high-risk group carrying out the minimum recommended training volume. Other reasons for null findings in these studies may be that the intervention did not sufficiently address the risk factors present. For example, there is a body of evidence suggesting that persistence of neuromuscular changes post-injury may have detrimental long-term consequences that contribute to re-injury through increased joint load, decreased movement, and decreased loading variability.48–53 Consequently, prevention programmes focused on purely building strength without restoring coordinated motor control (eg, eliminating protective cocontraction) may not prove as effective. Regardless of the lack of effect detected in these two landmark intervention studies, valuable lessons can be learned from both, the least of which is the importance of developing an implementation strategy and then tracking and accounting for adherence to the prevention programmes in the analysis.

SUMMARY The quality of studies investigating risk factors for groin injury has improved in the past 7 years. Whittaker JL, et al. Br J Sports Med 2015;0:1–8. doi:10.1136/bjsports-2014-094287


Review There is relatively consistent level 1 and 2 evidence to suggest that previous groin injury, higher level of play, reduced hip abductor and adductor strength and lower levels of sport-specific training are associated with increased risk of groin injury in sport. Further, there is consistent level 2 evidence suggesting that higher weight, BMI or height, reduced hip ROM and performance on fitness test such as jump height, leg power (squat), 40 metre sprint, sidestepping, kicking and VO2max estimated from a shuttle run are not associated with groin injury in sport. Based on the work performed in the field in the past 7 years and the challenges and high cost of undertaking high-quality prospective cohort studies aimed at identifying risk factors for groin injury in sport it is recommended that investigators turn their focus to high-quality randomised controlled trials targeting athletes at greater risk of injury (those at a high level of play with a previous injury) with prevention programmes targeting the hip abductor and adductor muscles in conjunction with off and preseason sport-specific training.

2 3

4 5

6 7

8

9

10

11 12

What are the new findings 13

▸ There has been an improvement in the quality (eg, larger sample size, employing multivariate statistical techniques) and level of evidence of studies investigating risk factors for groin injury in sport in the past 7 years. ▸ There is level 1 and 2 evidence that previous groin injury, higher level of play, reduced hip adductor strength and lower levels of sport-specific training are associated with an increased risk of groin injury in sport. ▸ Based on the work performed in the field, it is recommended that investigators turn their focus to high-quality randomised controlled trials targeting athletes at greater risk of groin injury in sport with prevention programmes targeting the hip abductor and adductor muscles in conjunction with off and preseason sport-specific training.

Twitter Follow Jackie Whittaker at @jwhittak_physio Acknowledgements The authors would like to acknowledge the assistance of the University of Calgary, Faculty of Kinesiology librarian Alex Hayden as well as research assistants Lisa Loos, Leticia Janzen and Rhys Johnson. Contributors JLW and CAE were responsible for the conception and design of the study. JLW and CAE independently reviewed the literature. JLW extracted data from the included studies, while all four authors were involved in rating the literature. JLW was the primary author in preparing the manuscript however all authors contributed to the interpretation of the findings, critical revision of the manuscript and reviewed the document prior to submission. Funding The Sport Injury Prevention Research Centres is supported by an International Olympic Committee Research Centre Award. JLW is funded through an Alberta Innovates Health Solutions Postdoctoral Clinician Fellowship. CAE holds a Professorship in Pediatric Rehabilitation Alberta Children’s Hospital Foundation.

14 15 16

17 18

19 20 21

22

23

24

25 26 27 28

Competing interests None. Provenance and peer review This paper was commissioned by the 1st World Conference on Groin Pain in Athletes, Doha, Qatar, November 2014; externally peer reviewed.

29 30 31

REFERENCES 1

Werner J, Hagglund M, Walden M, et al. UEFA injury study: a prospective study of hip and groin injuries in professional football over seven consecutive seasons. Br J Sports Med 2009;43:1036–40.


32

Arnason A, Sigurdsson SB, Gudmundsson A, et al. Risk factors for injuries in football. Am J Sports Med 2004;32(1 Suppl):5S–16S. Crow JF, Pearce AJ, Veale JP, et al. Hip adductor muscle strength is reduced preceding and during the onset of groin pain in elite junior Australian football players. J Sci Med Sport 2010;13:202–4. Ekstrand J, Hagglund M, Walden M. Epidemiology of muscle injuries in professional football (soccer). Am J Sports Med 2011;39:1226–32. Anderson DD, Chubinskaya S, Guilak F, et al. Post-traumatic osteoarthritis: improved understanding and opportunities for early intervention. J Orthop Res 2011;29:802–9. Ibrahim A, Murrell GA, Knapman P. Adductor strain and hip range of movement in male professional soccer players. J Orthop Surg 2007;15:46–9. Witvrouw E, Danneels L, Asselman P, et al. Muscle flexibility as a risk factor for developing muscle injuries in male professional soccer players. A prospective study. Am J Sports Med 2003;31:41–6. Eirale C, Tol JL, Whiteley R, et al. Different injury pattern in goalkeepers compared to field players: a three-year epidemiological study of professional football. J Sci Med Sport 2014;17:34–8. Engebretsen AH, Myklebust G, Holme I, et al. Intrinsic risk factors for groin injuries among male soccer players: a prospective cohort study. Am J Sports Med 2010;38:2051–7. Hagglund M, Walden M, Ekstrand J. Previous injury as a risk factor for injury in elite football: a prospective study over two consecutive seasons. Br J Sports Med 2006;40:767–72. Hagglund M, Walden M, Ekstrand J. Injuries among male and female elite football players. Scand J Med Sci Sports 2009;19:819–27. Paajanen H, Ristolainen L, Turunen H, et al. Prevalence and etiological factors of sport-related groin injuries in top-level soccer compared to non-contact sports. Arch Orthop Trauma Surg 2011;131:261–6. O’Connor D. Groin injuries in professional rugby league players: a prospective study. J Sports Sci 2004;22:629–36. Orchard J, Wood T, Seward H, et al. Comparison of injuries in elite senior and junior Australian football. J Sci Med Sport 1998;1:83–8. Emery CA, Meeuwisse WH. Risk factors for groin injuries in hockey. Med Sci Sports Exerc 2001;33:1423–33. Tyler TF, Nicholas SJ, Campbell RJ, et al. The association of hip strength and flexibility with the incidence of adductor muscle strains in professional ice hockey players. Am J Sports Med 2001;29:124–8. van Mechelen W, Hlobil H, Kemper HC. Incidence, severity, aetiology and prevention of sports injuries. A review of concepts. Sports Med 1992;14:82–99. Meeuwisse WH, Tyreman H, Hagel B, et al. A dynamic model of etiology in sport injury: the recursive nature of risk and causation. Clin J Sport Med 2007;17:215–19. Bahr R, Holme I. Risk factors for sports injuries—a methodological approach. Br J Sports Med 2003;37:384–92. Maffey L, Emery C. What are the risk factors for groin strain injury in sport? A systematic review of the literature. Sports Med 2007;37:881–94. Liberati A, Altman DG, Tetzlaff J, et al. The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate health care interventions: explanation and elaboration. PLoS Med 2009;6:1–28. Holmich P. Long-standing groin pain in sportspeople falls into three primary patterns, a “clinical entity” approach: a prospective study of 207 patients. Br J Sports Med 2007;41:247–52. Downs S, Black N. The feasibility of creating a checklist for the assessment of the methodolical quality both of randomised and non-randomised studies of health care interventions. J Epidemiol Community Health 1998;52:377–84. Howick J, Phillips B, Ball C, et al. Oxford centre for evidence-based medicine: levels of evidence secondary Oxford centre for evidence-based medicine: levels of evidence 2009. http://www.cebm.net/ oxford-centre-evidence-based-medicine-levels-evidence-march-2009/ Ekstrand J, Gillquist J. The avoidability of soccer injuries. Int J Sports Med 1983;4:124–8. Williams JGP. Limitation of hip joint movement as a factor in traumatic osteitis pubis. Br J Sports Med 1978;12:129–33. Cusi MF, Juska-Butel CJ, Garlick D, et al. Lumbopelvic stability and injury profile in rugby Union players. NZ J Sports Med 2001;29:14–18. Chalmers S, Magarey ME, Esterman A, et al. The relationship between pre-season fitness testing and injury in elite junior Australian football players. J Sci Med Sport 2013;16:307–11. Cowan SM, Schache AG, Brukner P, et al. Delayed onset of transversus abdominus in long-standing groin pain. Med Sci Sports Exerc 2004;36:2040–5. Grote K, Lincoln TL, Gamble JG. Hip adductor injury in competitive swimmers. Am J Sports Med 2004;32:104–8. Hagglund M, Walden M, Ekstrand J. Risk factors for lower extremity muscle injury in professional soccer: the UEFA Injury Study. Am J Sports Med 2013;41:327–35. Holmich P, Larsen K, Krogsgaard K, et al. Exercise program for prevention of groin pain in football players: a cluster-randomized trial. Scand J Med Sci Sports 2010;20:814–21.

7


Review 33

34 35 36

37 38

39 40

41

42 43

8

Jansen J, Weir A, Denis R, et al. Resting thickness of transversus abdominis is decreased in athletes with longstanding adduction-related groin pain. Man Ther 2010;15:200–5. Le Gall F, Carling C, Reilly T. Biological maturity and injury in elite youth football. Scand J Med Sci Sports 2007;17:564–72. Malliaras P, Hogan A, Nawrocki A, et al. Hip flexibility and strength measures: reliability and association with athletic groin pain. Br J Sports Med 2009;43:739–44. Morrissey D, Graham J, Screen H, et al. Coronal plane hip muscle activation in football code athletes with chronic adductor groin strain injury during standing hip flexion. Man Ther 2012;17:145–9. Nevin F, Delahunt E. Adductor squeeze test values and hip joint range of motion in Gaelic football athletes with longstanding groin pain. J Sci Med Sport 2014;17:155–9. Orchard J, Farhart P, Kountouris A, et al. Pace bowlers in cricket with history of lumbar stress fracture have increased risk of lower limb muscle strains, particularly calf strains. J Sports Med 2010;1:177–82. Schick DM, Meeuwisse WH. Injury rates and profiles in female ice hockey players. Am J Sports Med 2003;31:47–52. Steffen K, Myklebust G, Andersen TE, et al. Self-reported injury history and lower limb function as risk factors for injuries in female youth soccer. Am J Sports Med 2008;36:700–8. Tyler TF, Nicholas SJ, Campbell RJ, et al. The effectiveness of a preseason exercise program to prevent adductor muscle strains in professional ice hockey players. Am J Sports Med 2002;30:680–3. Verrall GM, Slavotinek JP, Barnes PG, et al. Hip joint range of motion restriction precedes athletic chronic groin injury. J Sci Med Sport 2007;10:463–6. Viera AJ, Garrett JM. Understanding interobserver agreement: the kappa statistic. Fam Med 2005;37:360–3.

44 45 46

47

48 49

50

51

52

53

Ryan J, DeBurca N, Mc Creesh K. Risk factors for groin/hip injuries in field-based sports: a systematic review. Br J Sports Med 2014;48:1089–96. Freckleton G, Pizzari T. Risk factors for hamstring muscle strain injury in sport: a systematic review and meta-analysis. Br J Sports Med 2013;47:351–8. DiFiori JP, Benjamin HJ, Brenner JS, et al. Overuse injuries and burnout in youth sports: a position statement from the American Medical Society for Sports Medicine. Br J Sports Med 2014;48:287–8. Engebretsen AH, Myklebust G, Holme I, et al. Prevention of injuries among male soccer players: a prospective, randomized intervention study targeting players with previous injuries or reduced function. Am J Sports Med 2008;36:1052–60. Glatthorn JF, Berendts AM, Bizzini M, et al. Neuromuscular function after arthroscopic partial meniscectomy. Clin Orthop Relat Res 2010;468:1336–43. Delahunt E, Prendiville A, Sweeney L, et al. Hip and knee joint kinematics during a diagonal jump landing in anterior cruciate ligament reconstructed females. J Electromyogr Kinesiol 2012;22:598–606. Pietrosimone BG, McLeod MM, Lepley AS. A theoretical framework for understanding neuromuscular response to lower extremity joint injury. Sports Health 2012;4:31–5. Hall L, Tsao H, MacDonald D, et al. Immediate effects of co-contraction training on otor control of the trunk muscles in people with recurrent low back pain. J Electromyogra Kinesiol 2009;19:763–73. Hodges PW, Hoorn V, Wrigley TV. The relationship between muscle activation and rate of progression of cartilage loss in knee osteoarthritis. International Federation of Manipulative Physical Therapists Congress. Quebec City, Canada, 2012. Hodges PW, Tucker K. Moving differently in pain: a new theory to explain the adaptation to pain. Pain 2011;152(3 Suppl):S90–8.



Risk factors for groin injury in sport: an updated systematic review Jackie L Whittaker, Claire Small, Lorrie Maffey and Carolyn A Emery Br J Sports Med published online April 1, 2015

Updated information and services can be found at: http://bjsm.bmj.com/content/early/2015/04/01/bjsports-2014-094287

These include:

Supplementary Supplementary material can be found at: Material http://bjsm.bmj.com/content/suppl/2015/04/02/bjsports-2014-094287. DC1.html

References Email alerting service

Topic Collections

This article cites 51 articles, 21 of which you can access for free at: http://bjsm.bmj.com/content/early/2015/04/01/bjsports-2014-094287 #BIBL Receive free email alerts when new articles cite this article. Sign up in the box at the top right corner of the online article.

Articles on similar topics can be found in the following collections BJSM Reviews with MCQs (66) Health education (415) Injury (857)

Notes

To request permissions go to: http://group.bmj.com/group/rights-licensing/permissions To order reprints go to: http://journals.bmj.com/cgi/reprintform To subscribe to BMJ go to: http://group.bmj.com/subscribe/