Journal of Science and Medicine in Sport (2009) 12, 12—19

OPINION PIECE

Epidemiological studies of injuries in rugbyleague: Suggestions for definitions, data collectionand reporting methods

D.A. Kinga,∗, T.J. Gabbettb, C. Gissanec, L. Hodgsond

a Emergency Department, Hutt Valley District Health Board, Lower Hutt, New Zealandb Brisbane Broncos Rugby League Club, Red Hill, Brisbane, Qld, Australiac Sports Rehabilitation Directorate, Department of Human Sciences, St Mary’s University College,Twickenham, Middlesex, TW1 4SX, UKd The Rugby Football League, Red Hall Leeds, UK

Received 18 December 2006; received in revised form 5 December 2007; accepted 11 December 2007

KEYWORDSInjury;Incidence;Methods;Definition;Rugby league

Summary Studies on rugby league injuries use a variety of definitions and method-ologies. Consequently, comparisons of published studies are difficult. Researcherswith an interest in understanding the epidemiology of rugby league injury partic-ipated in a majority agreement process. This paper provides suggestions for thedefinitions, data collection and reporting methods for future studies of rugby leagueinjuries. The proposed methods and definitions were developed through the use of amajority agreement process on draft versions by all authors. Recommended defini-tions for injury incidence, recurrence, severity and match exposure are provided as

well as injury site, type, diagnosis and causation. Suggestions for match and traininginjury incidence calculations are also provided for the purposes of comparison. Thispaper provides standard definitions that, if utilised, will enable meaningful com-parison of future rugby league injury surveillance data from different countries and

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Introduction

Studies on the incidence of sporting injuries have

varied in two main areas. These variations are(1) the definitions utilised and (2) the method-ologies undertaken.1—5 As a consequence of these

∗ Corresponding author.E-mail address: Douglas.King@huttvalleydhb.org.nz

(D.A. King).

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1440-2440/$ — see front matter © 2008 Sports Medicine Australia. Publishedoi:10.1016/j.jsams.2007.12.001

tralia. Published by Elsevier Ltd. All rights reserved.

ariations between studies, the results and con-lusions obtained often have some importantifferences.1,3—9 A fundamental process, and typ-cally the first step behind the injury preventionrocess, is ongoing injury surveillance.1,4,10,11 How-ver, inter-study comparisons may prove to be

ifficult due to the inconsistencies in the injuryefinitions utilised.

Studies on the incidence of injuries in rugbyeague have suffered from inconsistencies in the

d by Elsevier Ltd. All rights reserved.

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njury definitions for rugby league

njury definitions utilised. As a result of these incon-istencies, comparison and determination of thenjury incidence may be difficult to undertake.5,12

ariations reported in injury incidence are often theesult of data obtained from a relatively small num-ers of players and teams13,14 and, often over aimited time frame.12

Undertaking long term studies and incorporat-ng data collection from several teams increaseshe sample size and may assist in reducing any ran-om error that may occur.15 In addition, the use ofsimilar injury definition aids in inter-study com-

arisons. In a similar fashion to other professionalporting codes,10,16 the purpose of this paper waso address this problem by establishing definitions,ethodology and reporting standards that may be

dopted for the reporting of injuries in rugby leaguenabling comparison between future studies.

ethods

esearchers from Australia, United Kingdom andew Zealand who have an interest in rugby league

njury epidemiology participated in this project.ll researchers communicated by email and con-ributed to all discussions. Two Australian authorsubsequently withdrew from the paper as not alluthors could agree on the injury definition orts use in their future research.17,18 The resultinguggested methods and definitions paper was devel-ped through the use of email communication andraft reviews by the remaining authors. A majoritygreement was adopted for producing the sugges-ions for the definitions and methodological issueselated to the conducting of studies on rugby leaguenjuries. A working document was then producednd distributed to all authors for review and dis-ussion. Minor amendments were completed beforehe document was produced and submitted for pub-ication.

efinitions

ugby league injuries

n the study of sports injuries, definitions areypically provided as operational criteria for theecording and reporting of injuries rather than as

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theoretical definition. These definitions usuallyre broadly based around the concept that ‘‘bodilyamage caused by a transfer or absence of energy’’s the reason injuries occur.19 This concept is use-ul in the clarification of whether an incident in

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ugby league should be recorded as an injury. His-orically, the main focus of rugby league injuriesas been the recording and reporting of matchelated injuries.5,6,8,9,12—14 To enable standardiza-ion between future studies it is recommended thathe following definitions be utilised. This definitions similar to other consensus definitions16,19 and isesigned to enable comparisons to occur betweentudies.

njury definition

t is recommended that a rugby league injury beefined as:

‘Any pain or disability that occurs during participa-ion in rugby league match or training activities thats sustained by a player, irrespective of the need foratch or training time loss or for first aid or medical

ttention. An injury that results in a player requir-ng first aid or medical attention is referred to as amedical attention injury’ and an injury that resultsn the player being unable to partake in full part ofuture training and/or match activities is referredo a ‘time loss’ injury.’’

The definition is designed to capture all injuries,ncluding those that do, and do not result in missedatches. A match or training time loss injury is

‘any injury that causes a player to be unable toarticipate in a rugby league training activity or toe selected in a competitive match’’. The matchr training time loss definition has been popular inugby league injury research and is often used toompare between studies. However, it avoids doc-menting injuries that fall below this threshold,20

hich may account for as much as 70% of allreatments.21—23 This definition is designed to beimited in a way so that all researchers of rugbyeague injuries can apply it equally. Given that allnjuries may be associated with direct and/or indi-ect costs, data recorders that wish to record morenjury details than just missed match injuries arencouraged to do so.

atch injury

he rugby league match is any game undertakens part of any official competition. These injurieshould be reported utilising the suggested defini-ions for both an injury and for injury severity.

raining participation loss

ot all studies record or report injuries that occurs a result of players participating in training activ-

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ities. Also, not all studies record and report trainingtime loss as a result of injuries from either match ortraining participation. This is where match or train-ing related injuries result in loss of training timeand these can be recorded as part of any study onrugby league injuries. The loss of training time asa result of injuries sustained from match participa-tion needs to be identified separately from trainingtime loss from injuries that occur as a result ofparticipating in a training activity.

Injury recurrence

An injury is considered to have recovered once theplayer has returned to full participation in a rugbyleague match or training activity. It is, therefore,recommended that a rugby league recurrent injurybe defined as:

‘‘An injury of the same type, site, side and locationas the index injury which occurs after a player’sreturn to full participation in rugby league activitiesfrom the index injury. A recurrent injury occurringwithin 2 months of a player’s return to full partic-ipation is referred to as an ‘early recurrence’; oneoccurring 2—12 months after a player’s return to fullparticipation as a ‘late recurrence’; and one occur-ring more than 12 months after a player’s return tofull participation as a ‘delayed recurrence’.’’16,19

The recording of recurrent injuries can be under-taken for both match and training injuries. Thesecould be recorded and reported separately for bothmatch and training injuries to reduce the possibil-ity of confounding the results.2 Any injury that isrecurrent does not necessarily need to be identicalin severity to be considered recurrent.

Injury severity

The definition of injury severity for the purpose ofstudying rugby league match injuries is the actualnumber of matches missed per injury. As such, it isrecommended that the rugby league injury severitybe defined as:

‘‘Transient (no matches/trainings missed), Minor(1 missed match/training week), Moderate (2—4missed matches/training weeks), or Major (5 ormore missed matches/training weeks)’’.20

Studies that wish to include injuries that do not

result in time loss these should be recorded andreported under the term transient injuries. Forthe purpose of studies in rugby league, a tran-sient injury is defined as ‘‘any injury that causesa player to seek medical or first aid treatment

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D.A. King et al.

uring or after a rugby league activity but doesot lead to loss of further participation or non-election for matches’’. These include injuries thatre ongoing but not of sufficient severity to preventhe player from participating in match activities oreing selected for match participation.

A transient injury does not imply a quick recoveryrom an injury, simply that there is no loss of matchr training participation. Some injuries can last forong periods but if there are no missed matches orraining activities as a result of these injuries, theseransient injuries would be missing from the missedatch data set.

raining injury severity

f reporting training injuries, these may be reportedtilising the same time loss injury severity format.he use of missed training activities enables cap-ure across all levels of participation irrespectivef the number of trainings that the squad under-akes. The recording and reporting of training injuryeverity should be kept separate from match injuryeverity.2

atch exposure

t is recommended that match exposure be defineds:

‘The product of the number of players, the numberf matches between two different teams,16,19 andhe match duration for the period that the study iseing conducted. The recommended recording ofxposure time is the duration of the matches beingtudied in hours.’’

The recording of match exposure is best per-ormed without adjusting for technical aspects ofhe match such as golden point period (extra time)r when players are temporarily suspended or dis-issed from participation as a result of misconduct

r foul play (i.e. sin-bin or sent off). If the matcharticipation time is less than 80 min (1.33 h) thenhe time should be calculated to reflect the actualatch duration (e.g. 70 min = 1.17 h).

raining exposure

raining exposure should be used for those studiesncluding training aspects in studies on rugby leaguenjuries. Training exposure is defined as:

‘The product of the number of players, the num-er of training sessions, and the training durationor the period that the study is being conducted.he recommended recording of exposure time is

Injury definitions for rugby league 15

Table 1 Participation level classification

Main grouping Category Definition

1. Junior Mini modified Under 9 years of age and played under the mini-modifiedrules of the game

Modified From 9 years of age to 12 years of age and played undermodified rules of the game

2. Amateur Junior From 13 years or age and under 18 years of age as playedunder International competition rules as stipulated by localcompetitions

Senior From 18 years of age and played under internationalcompetition rules but not receiving any payment forparticipation

3. Sub Elite Semi-professional From 16 years of age and played under international rulesand receiving moderate remuneration for participation aswell as additional employment to generate incomeFromandsourc

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4. Elite Professional participants

he duration of the training sessions being studiedn hours.’’

njury onset

t is suggested that all injuries which satisfy thenjury definition be subdivided into: (1) overallnjuries (2) match injuries and (3) training injuries.his leads to five fundamental injury rates beingalculated: (1) overall injury incidence, (2) totalatch onset injuries, (3) match onset injuries

esulting in match time loss and training time loss,4) total training onset injuries and (5) trainingnset injuries leading to training time loss andissed matches.

tudy design

e recommend that most epidemiological stud-es in rugby league be undertaken as prospectiveohort studies. This minimises the occurrence ofrrors associated with recall bias as identified withetrospective study designs.16 Cohort designs allowhe examination of the relationship between expo-ure and injury risk, and permits the temporalequence between exposure and injury risk to bestablished.24 These studies would ideally be usedo establish the magnitude of the injury risk ando establish the aetiological risk factors associatedith participation in rugby league activities. It haseen suggested that they provide the best informa-ion and direct measurement of risk for developingn outcome.25 Other studies, such as interventiontudies, and controlled trials are encouraged.

articipation level

he level of participation may be categorised util-sing the categories listed in Table 1.

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16 years of age and played under international rulesreceiving remuneration for participation as their maine of income

njury incidence

atch injury incidenceore studies are now reporting the injury incidenceer 1000 match participation hours. Calculation ofhe match injury incidence may be undertaken byividing the number of recorded injuries by thexposure hours, then multiplying this value by 1000o obtain the injury incidence per 1000 playingours.20,26—29

njury incidence

=(

Number of injuries in the periodPlayers × hours × matches

)× 1000

raining injury incidence

raining injury incidence may be expressed as thenjury incidence per 1000 training hours. Calcu-ation of the training injury incidence may bendertaken by dividing the number of recordednjuries by the exposure hours, then multiplying thisalue by 1000 to obtain the injury incidence per000 training hours.20,26—29

njury incidence

=(

Number of Injuries in the periodPlayers × hours × training sessions

)× 1000

ctivity at time of injury

he activity at the time of injury may be recordedtilising the categories listed in Table 2.

16 D.A. King et al.

Table 2 Activity at the time of injury classification

Timing Primary activity Specific activity Specific activity

Acute Player contact Tackling TacklingBeing tackled

Other player contact CollisionScrumOther (e.g. fighting)

Other contact Fixture contactBall contactLanding on surface

Non contact Acute runningAcute kickingAcute passingAcute catchingOther

Gradual or unknown Contact e.g. TacklingNon contact Gradual running

Gradual kickingGradual weights

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Study population

Studies, whether utilising a single squad of play-ers or more, may be best conducted over noless than one season (including the preseason),12 months or the duration of any tournament beingstudied.16,19,30 Ideally, all injuries reported andexposures experienced would be documented forevery player in the cohort throughout the studyperiod to aid in the analysis.

Baseline information

Physiological31—36 and anthropometric31,33,34,37

studies in rugby league are becoming more estab-lished as other researchers become involvedin studying all physical aspects of participants.Although, no set guidelines have been establishedin regards to what anthropometric assessments orphysiological tests should be undertaken, basicdescriptive information relating to the person(i.e. age, gender, height and body mass) arerecommended to be included in the study as theseparameters help define the study population andmay be used for analysis of potential risk factors inrelation to injuries.24

Injury recording form

Preferably all injuries would be recorded on astandardised injury recording form. An exam-ple of a standardised injury reporting formthat has been developed for all sporting activ-

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ties, including rugby league, can be found atttp://sma.org.au/information/ssdownload.asp.his injury reporting form may include playeretails (name, age or player identifier), participa-ion level being studied (Table 1), injury location,njury type, activity at the time of injury (Table 2),njury time, and playing position. Ideally injuryeporting forms should be completed as soon asossible after the injury is sustained to avoidnaccuracies associated with recording informationetrospectively.16,19 In the case of injuries requir-ng further advanced medical assessment it may beecessary to await the results of the assessmentefore recording the injury.

eporting

iskshe epidemiologic incidence proportion (IP) maye included in epidemiological studies.21 The IP issed to enable identification of the average risk perlayer over a specified study period.21 The IP ide-lly would be reported as a percentage of risk fornjury from participation in rugby league. It is rec-mmended that when reporting the IP that the timeeriod that the IP defines is identified (i.e. season,ournament, year).21 Calculation of the IP may bendertaken by dividing the number of players thatave sustained an injury over the study period by

he number of players at risk of being injured.21

ncience proportion =(

Number of injured playersNumber of players at risk

)

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njury definitions for rugby league

iscussion

he injury definition was the most challengingspect for all authors to agree upon. Inclu-ion and exclusion criteria created the greatestebate with the definition focusing on whatan be fully complied with now and in theuture. For example, having an injury definitionith the inclusion of ‘‘seeking trainer/medicalssistance’’ or ‘‘presenting to medical staff,’’ay expose a study to bias as not all teams

nder study may have qualified trainers or med-cal staff present at all sessions.2,10 A biasay be introduced because injury rate will

ary according to the accessibility of thesetaff.2,10

The original group contributed to the debatebout the preferred definitions. Unfortunately, hav-ng several authors meant that it was difficult toake some decisions about some of the fundamen-

als of the project, including the actual definitionf an injury. Two of the authors strongly felt thathe fundamental injury definition in rugby leaguehould be based on match injuries and time lossarticipation only, while the remaining authorselt strongly that the fundamental injury definitionhould be broader. Many attempts were made toesolve this conflict in opinion by the use of email.he resulting injury definition led to two of theontributors requesting that they not to be nameds authors of the paper, on the grounds that theyid not support the proposed injury definition. Theesulting injury definition is similar to previous con-ensus definitions for rugby union19 and footballsoccer).16

Injury severity classification also created consid-rable discussion. Although time loss is identifieds the gold standard in reporting rugby leaguenjuries, transient injuries do create an impactn the financial resources of teams and participa-ion of players.14,21 As well, injuries that result inissed training sessions may be recorded as part

f the injury severity, although it is acknowledgedhat not all authors are present at training ses-ions and may not be able to record data for thesectivities.

Training injury inclusion also created discus-ion for the reasons above. Teams with dedicatedesearchers who, as part of their employmenthrough their role in the team, are present atraining sessions, will record a higher trainingnjury incidence than teams where players have

o travel to consult medical staff.10 Addition-lly, any retrospective review of injuries has beendentified to have some associated difficulties.38

layers are often unable to fully recall injury

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everity and only have an acceptable to goodevel of agreement for all details relating to thenjury.38

Transient injuries may be included in the studys this enables documentation of all injurieshat occur in matches but these should be iden-ified as such. If transient injuries were to bencluded, it is recommended that future stud-es on rugby league injury incidence includeata for both total (all injuries recorded)nd those injuries that resulted in time lossnjuries.

Although not all studies include training injuries,here are an increasing number of studies noweing published on this area of rugby league.29,39 Asuch, this paper aims to provide a suggested stan-ard injury definition for rugby league studies. Theurpose and setting of any study undertaken willetermine the inclusion or exclusion of aspects ofhis paper. Whatever recording regimen is adoptedor the study being undertaken, it is recommendedhat it is consistently used throughout the study.lthough the collection of transient injuries is

mportant in economic terms as they require aevel of input or treatment,14 it must be acknowl-dged that the recording of these injuries maylace a higher demand on personnel involved in thetudy.2

Data collectors for epidemiological studies inugby league would ideally be a single recorderhroughout the duration of the study. It is acknowl-dged that there will be different levels ofxpertise between the various participation levelsnd that this has an impact on the data collected,nterpretation of the definitions used and identifi-ation of the areas of interest in the study. It isecommended that identification of the data col-ectors’ qualifications be included in the studiesanuscript.Although, these definitions and methods outlined

re only suggestions, we recommend the use ofhese for all levels of rugby league participation. Its acknowledged that the definitions and methodsill need to be trialled and evaluated and that fur-

her consultations, feedback and amendments tohese may be required before a consensus amongstll rugby league researchers can be achieved. Theim of this paper is to promote discussion and torovide a standard that, if followed, will enableomparison of future rugby league injury epidemi-logical data from different countries, thereby

nhancing the body of information already estab-ished. As well, trends of and risk factors for injuriesn rugby league among countries could be identifiedfter establishing the injury incidence and causes.hese standards enable future researchers to inves-

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tigate the next stage in the sequence of preventionby establishing the aetiology and mechanism ofinjury in rugby league.11,40

Acknowledgements

John Orchard and Wayne Hoskins initially con-tributed in the paper but withdrew due to theirbelief that the proposed definition could not beutilised within the scope of their rugby leagueresearch.

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