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A systematic video analysis of National Hockey League (NHL) concussions, part I: who, when, where and what?

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A systematic video analysis of National Hockey League (NHL) concussions, part I: who, when, where and what?
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  doi: 10.1136/bjsports-2013-092235  published online May 1, 2013 Br J Sports Med   Michael G Hutchison, Paul Comper, Willem H Meeuwisse, et al.  how concussions occur in the NHLHockey League (NHL) concussions, part II: A systematic video analysis of National   http://bjsm.bmj.com/content/early/2013/06/12/bjsports-2013-092235.full.html Updated information and services can be found at: These include:  References   http://bjsm.bmj.com/content/early/2013/06/12/bjsports-2013-092235.full.html#ref-list-1 This article cites 17 articles, 5 of which can be accessed free at: P<P Published online May 1, 2013 in advance of the print journal. serviceEmail alerting the box at the top right corner of the online article.Receive free email alerts when new articles cite this article. Sign up in Notes (DOIs) and date of initial publication. publication. Citations to Advance online articles must include the digital object identifier citable and establish publication priority; they are indexed by PubMed from initialtypeset, but have not not yet appeared in the paper journal. Advance online articles are Advance online articles have been peer reviewed, accepted for publication, edited and   http://group.bmj.com/group/rights-licensing/permissions To request permissions go to:  http://journals.bmj.com/cgi/reprintform To order reprints go to:  http://group.bmj.com/subscribe/ To subscribe to BMJ go to:  group.bmj.comon October 3, 2013 - Published by bjsm.bmj.comDownloaded from   A systematic video analysis of National HockeyLeague (NHL) concussions, part II: how concussionsoccur in the NHL Michael G Hutchison, 1,2 Paul Comper, 1,3 Willem H Meeuwisse, 4 Ruben J Echemendia 5,6 1 David L. MacIntosh SportMedicine Clinic, Faculty of Kinesiology & PhysicalEducation, University of Toronto, Toronto, Ontario,Canada 2 Injury Prevention ResearchOf  fi ce, Keenan ResearchCentre, St. Michael ’ s Hospital,Toronto, Ontario, Canada 3 Graduate Department of Rehabilitation Science, Facultyof Medicine, University of Toronto, Toronto, Ontario,Canada 4 Faculty of Kinesiology,Hotchkiss Brain Institute,Sport Injury PreventionResearch Centre, University of Calgary, Calgary, Alberta,Canada 5 Psychological andNeurobehavioral Associates,Inc., State College,Pennsylvania, USA 6 University of Missouri — Kansas City, Kansas City,Missouri, USA Correspondence to Dr Michael Hutchison,David L. MacIntosh SportMedicine Clinic, Faculty of Kinesiology & PhysicalEducation, University of Toronto, 55 Harbord Street,Toronto, Ontario,Canada M5S 2W6;michael.hutchison@utoronto.caAccepted 29 March 2013 To cite:  Hutchison MG,Comper P, Meeuwisse WH, et al  .  Br J Sports Med  Published Online First:[  please include  Day MonthYear] doi:10.1136/bjsports-2013-092235 ABSTRACTBackground  Concussions in sports are a growingcause of concern, as these injuries can have debilitatingshort-term effects and little is known about the potentiallong-term consequences. This work aims to describe  how   concussions occur in the National Hockey League. Methods  Case series of medically diagnosed concussionsfor regular season games over a 3.5-year period during the2006 – 2010 seasons. Digital video records were coded andanalysed using a standardised protocol. Results  88% (n=174/197) of concussions involvedplayer-to-opponent contact. 16 diagnosed concussions werea result of   fi ghting. Of the 158 concussions that involvedplayer-to-opponent body contact, the most commonmechanisms were direct contact to the head initiated by theshoulder 42% of the time (n=66/158), by the elbow 15%(n=24/158) and by gloves in 5% of cases (n=8/158). Whenthe results of anatomical location are combined with initialcontact, almost half of these events (n=74/158) wereclassi fi ed as direct contact to the lateral aspect of the head. Conclusions  The predominant mechanism of concussionwas consistently characterised by player-to-opponentcontact, typically directed to the head by the shoulder,elbow or gloves. Also, several important characteristics wereapparent: (1) contact was often to the lateral aspect of thehead; (2) the player who suffered a concussion was oftennot in possession of the puck and (3) no penalty was calledon the play. INTRODUCTION In the past decade, there has been a considerableattention on the issue of concussions in hockey, asit is one of the most common injuries in the sport,occurring at all levels of play and age groups. 1 – 7 In a previous paper, we described  ‘ the four W ’ s ’ of concussions sustained by National HockeyLeague (NHL) players, namely:  Who, When, Where and What? 8 Building on our previous work, thepurpose of the present paper was to describe  how concussions occur in the NHL. In addition to iden-tify the principal mechanisms associated with con-cussions, two speci fi c contextual issues (ie, puckpossession and penalty) will be addressed. METHODS NHL players suspected of having a concussion wereinitially identi fi ed by team athletic trainers or thera-pists and then evaluated by team physicians who diag-nosed concussion according to the Zurich (2008)Concussion in Sport de fi nition. 9 Digital video recordsof diagnosed concussions from the NHL injury sur-veillance system were provided to the researchers byNHL Operations for regular season games occurringfrom 4 October 2006 to 31 December 2009. Thestudy was approved by Ethics Review Board of the Of  fi ce of Research Services at the University of Toronto (protocol reference #23882). Heads up checklist The Heads Up Checklist (HUC) provides a standar-dised framework for coding injury mechanisms of concussion using digital video records. 10 The HUCcontains 17 speci fi c factors of interest organisedinto three broad sections: (1) Event, (2) GameSituation and (3) Equipment. The majority of thispaper will focus on the analysis of factors related tothe Event section. See table 1 for summary of oper-ational de fi nitions from the HUC Event Section.Two additional HUC factors of interest and rele-vance to the present paper were puck possessionand penalty. Puck possession refers to the situationin which a player had control of  — although was notnecessarily in direct contact with — the puck whileattempting a hockey skill (eg, skating or passing).Consequently, a player deemed to be in possessionof the puck at the time of contact with anotherplayer was coded as  ‘ puck possession — yes ’ . A player deemed not to have possession of the puckat the time of contact was coded as,  ‘ puck posses-sion — no ’ . The situation in which a player com-pleted a pass or a shot following the possession of the puck was coded as  ‘ just released ’ . Time tocontact (ms) was documented post hoc in caseswhere puck possession was classi fi ed as just released. Procedure Two raters independently viewed the digital videorecords of events associated with physician-diagnosed concussions. Raters viewed each eventusing Quicktime Player Pro V.7.6.6 software resid-ing on an Apple MacBook Pro 4.1 (operating soft-ware Mac OS X V.10.5.8). 11 Each category of theHUC was completed for each distinct concussionevent. Raters were allowed to view the event asmany times as required, at any playback speeddeemed necessary to complete all categories on theHUC. In cases where there was initial disagreementbetween raters, video records of events werereviewed to determine consensus. If consensus wasnot reached between the two raters, a third raterforced the consensus. Outcome measures Digital video records of concussions were codedusing the HUC. The following factors from the Hutchison MG,  et al  .  Br J Sports Med   2013; 00 :1 – 5. doi:10.1136/bjsports-2013-092235 1 Original article   BJSM Online First, published on June 13, 2013 as 10.1136/bjsports-2013-092235 Copyright Article author (or their employer) 2013. Produced by BMJ Publishing Group Ltd under licence. group.bmj.comon October 3, 2013 - Published by bjsm.bmj.comDownloaded from group.bmj.comon October 3, 2013 - Published by bjsm.bmj.comDownloaded from group.bmj.comon October 3, 2013 - Published by bjsm.bmj.comDownloaded from group.bmj.comon October 3, 2013 - Published by bjsm.bmj.comDownloaded from group.bmj.comon October 3, 2013 - Published by bjsm.bmj.comDownloaded from   Event section of the HUC were analysed: scenario (eg, oppon-ent, team-mate, fall, other); initial contact with (eg, shoulder,elbow, stick, etc); region (eg, head, neck, torso or below waist);anatomical location (eg, anterior, posterior or lateral); and accel-eration of head (eg, sagittal or coronal, transverse or multi-plane). The two additional factors analysed from the HUC werepuck possession (eg, yes, no or just released) and penalty (eg,yes or no). Statistical analyses Descriptive statistics of the outcome measures of interest werelimited to coded events leading to concussion (n=197) or thesubset of concussions that involved contact with an opponent,but did not due to  fi ghting (n=158). All analyses were per-formed using Statistical Analysis Software, V.9.2. RESULTS  A total of 260 concussions occurred in 4299 NHL regularseason games from the beginning of the 2006 – 2007 season tothe end of December 2009 (6.05/100 games). Seventy-six percent (197 of the 260 concussions) were identi fi ed on video andanalysed for the present study. Of the events that were notcoded by the raters, 19 were excluded because of poor imagequality or lack of appropriate camera angles. The remainingevents (n=44) were not included in the present study becausethe video record could not be matched to the concussion event,or the concussion occurred outside of game play, for example,during a warm-up or a practice setting. Scenario The greatest proportion of events associated with concussioninvolved contact with an opponent (n=174/197, 88%). Of the 174 events involving contact with an opponent, 9.2%(n=16/174) were due to  fi ghting. With respect to the 16 eventsclassi fi ed as  fi ghts, all involved direct contact to the head and75% (n=12/16) involved secondary contact, most often bycontact to the head by an opponent ’ s  fi st or by the player ’ s headstriking the ice surface. Those concussions involving contact withan opponent, but not involving  fi ghting (174 – 16( fi ghts)=158),were used for the majority of the analyses that follow. Initial contact with In order to describe the mechanisms of injury leading to concus-sion, each event was analysed according to its component ele-ments. The  fi rst step was to describe the body part of the ‘ hitter ’  that initiated contact with the concussed player, referredto as  initial contact with . As the aggregate data illustrate in fi gure 1, the most common initial contact to any part of theplayer ’ s body leading to a concussion was by a hitter ’ s shoulder(55%), followed by the elbow (21%) and gloves (12%), for atotal of 88%. The remaining 12% of initial contacts were classi- fi ed as stick, puck, helmet, knee or inconclusive. Region The next stage in the analysis was to identify the region or partof the body on the concussed player that was initially contactedby the hitter, broadly classi fi ed as head, neck, torso or belowthe waist. The most common body part initially contacted wasthe player ’ s head, 68% (n=108/158), while the torso regionaccounted for approximately 28% (n=44/158). The remainingpercentage (4%, n=6) was classi fi ed as below the waist, belowthe neck or inconclusive.With respect to contacts that occurred by hitters directly to aplayer ’ s head, the contact was initiated by the shoulder 42% of the time (n=66/158), by the elbow 15% (n=24/158) and bygloves in 5% of cases (n=8/158; see  fi gure 1). In summary, 62%(n=98) of the concussions in the sample of 158 were directlyattributed to shoulders, elbows or gloves delivered by the hitterto the head of an opponent during the  fl ow of the game. Body location and acceleration of head  A further re fi nement was made to identify the speci fi c anatom-ical aspect (ie, anterior, posterior or lateral) of the region of body of the concussed player  fi rst contacted. For example, if aplayer was struck directly in the mouth by an opponent ’ s elbow,then the body location would be classi fi ed as  ‘ anterior. ’  Table 2provides a breakdown of events identi fi ed as contact to thetorso or head, strati fi ed by body location (anterior, posterior or Table 1  Operational definitions of terms from the Heads Up Checklist — Event section Scenario Identifies the context that precipitated the eventual injury. For example, did the scenario involve another player (eg, with team-mate or withopponent) or an unprecipitated trip or fall (other)Initial contact with Identifies the body part (eg, head, elbow, shoulder, gloves/fist) or object (eg, stick or puck) that first contacted the injured player in the scenarioRegion Identifies the anatomical region of the player receiving the contact (eg, head/face, neck, torso or below waist)Body location Refers to the anatomical aspect of the region struck (ie, anterior, posterior or lateral). For example, if a player is struck directly in the mouth by anopponent ’ s stick, then it would be classified as anteriorAcceleration of head Identifies the biomechanical plane(s) of the player ’ s head motion that might have occurred during the Event. For example, sagittal, coronal ortransverse Figure 1  Initial contact with:  fi rst body part of the hitter thatinitiated contact with the concussed player. 2 Hutchison MG,  et al  .  Br J Sports Med   2013; 00 :1 – 5. doi:10.1136/bjsports-2013-092235 Original article  lateral), from the subset of 158 events involving an opponent.The lateral aspect of the head or torso was the most commonarea of initial contact (n=92/158, 58%), while initial contact of the anterior and posterior aspects of the head or torsoaccounted for 22% (34/158) and 16% (n=25/158), respectively.When the results of anatomical aspect are combined withinitial contact, almost half of these events (n=74/158) were clas-si fi ed as direct contact to the lateral aspect of the head. Of importance, a large proportion of these were by shoulder, elbowor gloves (n=71/158). Taken together, approximately 35%(n=71/197) of all concussions during the three and half seasonswere classi fi ed as occurring by direct impact to the lateral aspectof the head by shoulders, elbows or gloves.In addition to the anatomical aspect, raters also documentedobservable head motion during events that resulted in diagnosedconcussions. Head acceleration frequently occurred in multipleplanes, typically in the sagittal and transverse planes(n=62/158). There was a relatively even distribution of eventsclassi fi ed as sagittal or coronal plane (n=40/158) and transverseplane (n=42/158). Of note, 12% of the events were deemed tohave no observable head motion or were inconclusive forobservable head motion (n=18/158). Puck possession When considering the events (excluding  fi ghting) that involvedan opponent (n=158), the concussed player was in possessionof the puck approximately 23% of the time (n=37), while 34%(n=54) of the time the player had no possession of the puck. In42% (n=67) of the events, the player who suffered a concussionhad  ‘ just released ’  the puck; that is, the player had been in pos-session of the puck during the play, but was no longer in posses-sion of it when the player was contacted by an opponent. Of those classi fi ed as  ‘ just released ’ , 49 events permitted quanti fi ca-tion of time-frames to analyse the time from puck release tocontact. In over 70% of these events, the time from puckrelease to contact was less than 0.5 s. Although not clearly speci- fi ed in the rules of hockey, this time  ‘ lag ’  for delivering a hit toan opponent is generally considered to be acceptable. Penalty  A  fi nal point of interest was to determine if the on-ice of  fi cialscalled a penalty on the play for the events that resulted in con-cussions. Of the events evaluated, there was suf  fi cient informa-tion on the digital video records to determine whether a penaltywas called for 168 events. Of these, 29% (n=49) were consid-ered infractions according to on-ice of  fi cials. When lookingspeci fi cally at direct contact to the head by shoulder, elbowor gloves, 22% (n=37) were deemed to be rule violations. Inother words, applying the then-current rules to the player-to-opponent contacts that resulted in concussions, less than one-quarter of the direct contacts to the head were considered penal-ties by on-ice of  fi cials. DISCUSSION For three and half NHL regular seasons evaluated as part of thisstudy, the predominant mechanism of concussion was consistentlycharacterised byplayer-to-opponent-playercontact, typicallydirec-ted to the head by the shoulder, elbow or gloves. When this mech-anism was elucidated further, several important characteristicswere apparent: (1) contact was often to the lateral aspect of thehead; (2) the player who suffered a concussion was often not inpossession of the puck and (3) no penalty was called on the play.With the combination of speed, hard surfaces and frequentcollisions in hockey, it is reasonable to expect that a proportionof hockey concussions might result from a collision with a team-mate or by accidental falls or trips. The present data indicatethat accidental falls or trips and collisions with team-matesaccounted for only 10% of concussions analysed and are there-fore a relatively rare occurrence.More than three quarters of all events involving player-to-player contact occurred when neither player had possessionof the puck, suggesting a lack of situational awareness orvulnerability as a signi fi cant contributing factor to injury.Consequently, educating athletes and coaches that there is a highprobability that concussions can occur even when the player isnot handling the puck is imperative. Applying the rules of play during the study period, on-iceof  fi cials did not penalise the majority of the events leading toconcussion. The  fi nding of a clear mechanism of concussionidenti fi ed in the majority of events analysed combined with fewon-ice penalties provides evidence for the inclusion of a rule-based approach to help reduce the occurrence of the behaviourand safeguard players from playing situations that could lead toconcussions. A rule-based approach to ensure player safety haspreviously been successful (eg,  ‘ spearing ’  in football, hittingfrom behind in hockey) and is a common method to de fi neunacceptable behaviour and ensure player safety. Since the studyperiod, the NHL introduced Rule 48  ‘ Illegal Check to theHead ’ , which states that  ‘ a lateral or blind side hit to an oppon-ent where the head is targeted and/or the principal point of contact is not permitted ’ . 12 This rule — introduced in 2010 — was revised in 2011 to encompass targeted contact to the head.In addition to speci fi c rules and additional sanctions, changesto equipment standards are also potential avenues to reduce thefrequency of concussions in hockey. The present study identi fi eda common mechanism of injury and the results may informfuture research and area of focus for equipment manufacturers.Helmet manufacturers are attempting to design helmets thatincorporate distinct features meant to improve energy attenu-ation in response to lateral blows. 13 Moreover, the high propor-tion of shoulders and elbows as the principal point of contactinitiation may warrant the investigation of equipment improve-ments to lessen the forces of impact upon contact.The  fi ndings from this study revealed that a particular injurymechanism, that is, a direct blow to the head, accounted for alarge numberof concussions. However, those familiar with hockeyhave witnessed collisions that appear to involve signi fi cant forcesapplied directly to a player ’ s head, yet with no adverse outcome(ie, concussion). Meeuwisse 14 has suggested that it is important tomeasure and understand this  ‘ mechanism of no injury ’ , to re fi nethe understanding of which component(s) of the apparent mech-anism of concussion may be responsible for injury. In addition,capturing and analysing direct hits to the head that do not result inconcussion will allow for a more comprehensive understanding of the relative risk of such actions, thereby providing valuable infor-mation regarding this potentially debilitating injury. Table 2  Contacts to the head or torso stratified by bodylocation, % (n) Anterior Posterior Lateral Head 18 (29) 3 (4) 47 (74)Torso 3 (5) 13 (21) 11 (18) Percentages in table 2 were calculated from the denominator n=158; 4% (7 events)were classified as either  ‘ other ’  or  ‘ inconclusive ’ . Hutchison MG,  et al  .  Br J Sports Med   2013; 00 :1 – 5. doi:10.1136/bjsports-2013-092235 3 Original article  Limitations Structured comprehensive video analysis is a promising tool toanalyse the mechanisms of speci fi c injury types, successfullyapplied in a variety of sports. 15 – 18 However, video analysis isnot without limitations. Although this study concurs with previ-ous work identifying the possibly signi fi cant contribution of rotational acceleration, 19 – 21 the limitations of video recordingsdid not allow for a detailed biomechanical analysis that quanti- fi ed linear and rotational accelerations.Second, the present results were restricted to a dataset arisingfrom video records corresponding to NHL players diagnosed withconcussions. Although these data are thought to accurately repre-sent the mechanism of injury in the NHL, they may not be repre-sentative of other leagues with players of different ages, skill levelsand physical characteristics. Furthermore, it is not clear how thesedata relate to leaguesthat have different rulesthanthe NHL. CONCLUSION Professional hockey carries an inherent risk of concussion. Toour knowledge, this is the  fi rst study that has systematicallyassessed the antecedent events leading to concussions usingvideo analysis. We were able to identify that the majority of con-cussions during the study period occurred by direct contacts tothe head by the shoulder, elbow or gloves. The results from thepresent study should be considered in the development andimplementation of future prevention measures and strategies.Reducing the frequency of concussions in the NHL will requirea multisystems approach that includes a number of educationand prevention strategies (eg, rules, education, discipline, etc). What are the new  fi ndings? ▸  The study identi fi ed a predominant mechanism of concussionin the NHL over a 3.5-year period during the 2006 – 2010seasons. The mechanism of concussion was consistentlycharacterised by player-to-opponent-player contact, typicallydirected to the head by the shoulder, elbow or gloves. ▸  When this mechanism was elucidated further, severalimportant characteristics were apparent: •  Contact was often to the lateral aspect of the head; •  The player who suffered a concussion was often not inpossession of the puck; •  No penalty was called on the play. How might it impact on clinical practice in the nearfuture? ▸  Medical professionals should be cognizant of thepredominant mechanism associated with concussions inprofessional hockey and thoroughly evaluate and monitorathletes with suspected concussions. ▸  The  fi nding of a clear mechanism of concussion identi fi ed inthe majority of events analysed combined with few on-icepenalties provides evidence for the inclusion of a rule-basedapproach to help reduce the occurrence of the behaviourand safeguard players from playing situations that couldlead to concussions. Correction notice  This article has been corrected since it was published OnlineFirst. In the Results section, 'The remaining events (n=43)' has been changed to'The remaining events (n=44)'. Acknowledgements  The authors are grateful to members of the NHL/NHLPAConcussion Working Group: Dr Mark Aubry, Mr Bill Daly, Ms Maria Dennis, Ms JulieGrand, Dr John Rizos, Mr Rob Zamuner and also Mr Jim Ramsay for their insightthroughout the research study. We would also like to thank Ms Cynthia Lichter of NHLOperations for her ongoing assistance with the videos. PC and MGH would like toacknowledge Dr Angela Colantonio and Dr Doug Richards of the University of Toronto for their ongoing advice and support through the development of themanuscript. Contributors  MGH and PC had full access to all of the data in the study and takeresponsibility for the integrity of the data and the accuracy of the data analyses.WHM and RJE were also main contributors to the content of this manuscript andwere involved in the study ’ s design. MGH mainly contributed to the statisticalanalysis. All authors interpreted the results, drafted the manuscript, decided tosubmit the manuscript and involved in the critical revision of the manuscript. Funding  This study received funding by Ontario Neurotrauma Foundation (ONF)and The Pashby Sports Safety Fund. The organisations that contributed funds to theresearch had no role in the design of the study, the collection, analysis andinterpretation of the data. Competing interests  All authors have completed and submitted the ICMJE Formfor Disclosure of Potential Con fl icts of Interest. PC is a member of the ConcussionWorking Group and a clinical neuropsychologist consultant with the NHLPA, forwhich he receives remuneration, but he did not receive any funding from the NHL orthe NHLPA to conduct the present research. WHM is a member of the ConcussionWorking Group and medical consultant to the NHL, for which he receivesremuneration, but did not receive any funding from the NHL or NHLPA to conductthe present research. RJE is a consultant to the NHL, MLS and US SoccerFederation for which he receives  fi nancial remuneration. No  fi nancial remunerationwas received for activities speci fi cally related to this research. MGH receivedgraduate training funding from Ontario Neurotrauma Foundation and The PashbySports Safety Fund. Ethics approval  Ethics Review Board of the Of  fi ce of Research Services at theUniversity of Toronto. Provenance and peer review  Not commissioned; externally peer reviewed. REFERENCES 1 Agel J, Dompier TP, Dick R,  et al  . 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