Incidence,Risk,and Protective Factors of Mild Traumatic Brain Injury in a Cohort of Australian Nonprofessional Male Rugby Players

Abstract

Background

Mild traumatic brain injury (mTBI) is an emerging public health issue in high-contact sports. Understanding the incidence along with the risk and protective factors of mTBI in high-contact sports such as rugby is paramount if appropriate preventive strategies are to be developed.

Purpose

To estimate the incidence and identify the risk and protective factors of mTBI in Australian nonprofessional rugby players.

Study Design

Cohort study; Level of evidence, 2.

Methods

A cohort of 3207 male nonprofessional rugby players from Sydney, Australia, was recruited and followed over 1 or more playing seasons. Demographic information, history of recent concussion, and information on risk and protective factors were collected. The incidence of mTBI was estimated and the putative risk and protective factors were modeled in relation to mTBI.

Results

The incidence of mTBI was 7.97 per 1000 player game hours, with 313 players (9.8%) sustaining 1 or more mTBIs during the study. Players who reported always wearing protective headgear during games were at a reduced risk (incident rate ratio [IRR], 0.57; 95% confidence interval [CI], 0.40–0.82) of sustaining an mTBI. In contrast, the likelihood of mTBI was almost 2 times higher among players who reported having sustained either 1 (IRR, 1.75; 95% CI, 1.11–2.76) or more mTBIs (IRR, 1.65; 95% CI, 1.11–2.45) within the 12 months before recruitment.

Conclusion

Nonprofessional rugby has a high incidence of mTBI, with the absence of headgear and a recent history of mTBI associated with an increased risk of subsequent mTBI. These findings highlight that both use of headgear and the management of prior concussion would likely be beneficial in reducing the likelihood of mTBI among nonprofessional rugby players, who compose more than 99% of rugby union players in Australia.

Keywords

brain concussion incidence risk factors football head injuries athletic injuries

Rugby union (hereafter referred to as rugby) is an international sport, with many countries reporting increasing rates of participation, particularly at the nonprofessional level. In Australia the number of nonprofessional registered players has increased by 22% over the past 6 years, almost half of whom are school-aged players.¹ Similar increases have also been observed in the United States (35%). Despite its popularity, the high-contact sport of rugby has the potential for serious injury. Recent research has reported a high incidence of injuries in rugby players,^7,16,24 with more than one quarter of these being head injuries and the majority being mild traumatic brain injuries (mTBIs).²³

The reported incidence of mTBI in rugby varies, in part because studies do not always take account of the players’ exposure,¹⁴ but also because of variation in injury definitions and study design. Rugby studies that have taken exposure into account,^27,35 and more specifically, systematic reviews of the incidence of mTBI in a number of contact sport studies,^7,24 report that rugby has a high incidence of mTBI, ranging from 0.62 to 9.05 per 1000 player game hours. Moreover, when the incidence is stratified by competition level, the incidence of mTBI for professional rugby players ranges from 2.9 to 9.1 per 1000 player game hours, while among nonprofessional players it ranges from 0.6 to 5.0 per 1000 player game hours.^7,24 For school-level players the incidence of mTBI is approximately 1.03 per 1000 player game hours.²⁴

The use of headgear in rugby to reduce the likelihood and severity of contusions and lacerations is increasing rapidly.³⁴ Although there are some studies pointing to the effectiveness of both headgear and mouthguards in reducing the incidence of mTBI,^4,28,31 the evidence is not conclusive. For example, a recent Australian study has found no protective benefit of padded headgear in rugby.³³ For sports such as rugby, soccer, and Australian football, no sport-specific headgear has been proven to be beneficial in reducing the rates of mTBI, or of head injury in general.¶ In contrast, there are studies suggesting that certain aspects of a player’s personality may predispose them to injury,¹⁷ and the wearing of protective gear may encourage a more reckless style of play leading to injury. For example, a player’s tendency to act impulsively, particularly during the tackle phase in rugby, may increase the risk of injury.¹³

Other purported risk or protective factors for mTBI include the player’s training regimen, the player’s experience, the playing position, and a history of concussion. This latter finding has been reported to be either a risk factor^12,21,36 or have no effect^5,10 on future mTBI.

To date, there are no studies, using a longitudinal study design, that have investigated the incidence and risk and protective factors for mTBI in rugby players. The aims of the current study, therefore, are to estimate the incidence of mTBI in Australian nonprofessional rugby players, and to identify the potential risk and protective factors of mTBI across a range of player characteristics. The findings from the research will assist with the prevention and future management of mTBI in one of the largest community-based contact sports in Australia.

METHODS

A cohort of 3207 male nonprofessional rugby players aged 15 years and over from the Sydney metropolitan area (population approximately 4.5 million) was recruited. Players were recruited preseason from school, suburban, and grade competition levels. School players aged 15 to 18 years were recruited from nongovernment (private) schools that entered teams into school-based competitions. Players 19 years and older were recruited from suburban and grade competitions, each of which includes multiple levels of player ability. Grade-level competition feeds into professional-level competition (which includes provincial teams from Australia, New Zealand, and South Africa). Informed consent was obtained from all players or from parents if players were school-aged. Institutional Review Board approval was secured before commencing recruitment.

Each recruited player completed a 15-minute self-administered questionnaire (see online Appendix 1 for this article at http://ajs.sagepub.com/supplemental/) that included questions relating to demographic data such as age, height, weight, parents’ ancestry, and education; a 19-question sensation-seeking scale⁴⁴ assessing impulsivity; and questions relating to player characteristics such as competition level, previous rugby experience, principle playing position(s), training patterns, and use of protective equipment (headgear and mouthguards). Players were also asked whether they had a history of recent concussion and whether they had any diagnoses that may present similar symptoms to those resulting from a head injury, such as migraines or attention deficit hyperactivity disorder.

All players were followed between 1 and 3 winter playing seasons (playing seasons comprised 20 weeks) over a 3-year period from 2005 to 2007, with the median observational period being 1 season (85% of players). The outcome of interest was mTBI defined as a traumatically induced physiological disruption of brain function that involves at least 1 of the following: a period of loss of consciousness 30 minutes or less, any loss of memory for events immediately before or after the incident, or any alteration in mental state such as feeling dazed or confused. Players were recorded as sustaining an mTBI if they left the field during a game because of dizziness, confusion, loss of coordination, and/or loss of consciousness; stoppage of play was required; or they received medical attention because of a blow to the head during a game. For the purposes of this study, we use “mTBI” and “concussion” interchangeably.

Data related to the mTBI were collected either by a trained injury recorder (n = 12) who attended school games each season, or by a nominated suburban or grade club doctor, physical therapist, or coach (n = 18). Training was provided for all recorders, with greater focus on the injury recorders who were predominantly medical, physical therapy, or sports and exercise science students. The recorders attended a formal training session, were observed undertaking injury observations in the field, and received feedback on the quality and completeness of the work they submitted. Individual player’s game exposure was extracted from team player lists each week throughout the observational period. Players who sustained an mTBI during the game were allocated 50% of the total game playing time; this estimate was based on our pilot data, which highlighted that approximately 65% of players sustained an mTBI in the second half of the game.

The main outcome measure was the incidence of mTBI per 1000 player game hours. The incidence of mTBI was calculated as the number of mTBIs incurred divided by the total number of hours of player game exposure. All incidence rates were presented per 1000 player game hours.

Statistical Analyses

Descriptive statistics were calculated using SPSS version 15.0 software (SPSS Science Inc, Chicago, Illinois), and univariate associations between the incidence of mTBI and potential risk or protective factors were examined (95% confidence intervals were calculated using the method for a Poisson distribution).⁴³ Differences in the incidence of mTBI between player characteristics were analyzed by conducting a chi-square test for the comparison of rates. Statistical significance was accepted at P < .05 in all cases. Individual risk and protective factors associated with the incidence of mTBI were modeled using Poisson regression. The regression analyses were performed using the backward stepwise method using the SAS GENMOD procedure (SAS statistical software, SAS Institute, Cary, North Carolina). For the multivariate analyses, the number of mTBIs was used as the outcome in a Poisson regression, adjusted for age, and with exposure time offset using the log of player exposure time. Interactions and collinearity were then examined between the covariates. Incidence rate ratios (IRRs) and 95% confidence intervals (CIs) were calculated for the covariates that remained in the most parsimonious model.

RESULTS

Twenty-six nonprofessional rugby clubs and 8 schools participated in the study. A total of 3207 male players were recruited from these clubs and schools into the study, with a mean age of 22.7 years (standard deviation [SD], 5.5; range, 15–49 years). The mean body mass index of the players was 27.4 (SD, 4.2; range, 18–60). Seventy-seven percent (n = 2275) of players reported participating in rugby training for more than 3 hours per week; 36% (n = 1034) reported wearing protective headgear; and 80% (n = 1816) reported wearing a mouthguard during the game. Overall, 78% (n = 524) of players had completed high school education and 58% (n = 360) had completed, or were completing, higher education.

Almost 15% (n = 326) of cohort players had sustained a concussion in the 12 months before recruitment, with 25% (n = 81) of these players sustaining a concussion in the previous 3 months. Interestingly, 64% of recent concussions were among those players with more than 8 years of playing experience. A total of 347 mTBIs was sustained by a total of 313 players (9.8% of the cohort) over the observational period, with 29 of these 313 players (9.3%) sustaining multiple mTBIs over the same period. Of these 29 players, 25 sustained 2 mTBIs, 3 players sustained 3 mTBIs, and 1 player sustained 4 mTBIs over the observational period.

Appendix 2 (see online Appendix 2 for this article at http://ajs.sagepub.com/supplemental/) presents the incidence of mTBI per 1000 player game hours, stratified by demographic and key risk and protective factors for mTBI. The overall incidence of mTBI in the cohort was 7.97 per 1000 player game hours (95% CI, 6.94–9.11), with the incidence among players participating at suburban and grade levels being almost twice that of school-level players. When the incidence of mTBI was stratified by age group, the incidence was highest in the under-21 age group (incidence ratio [IR] = 10.54/1000 player game hours; 95% CI, 8.34–13.13). There was a linear relationship between the players’ height and the incidence of mTBI as well as the players’ weight and the incidence of mTBI. The incidence of mTBI was also higher among players reporting high impulsivity scores (IR = 9.91; 95% CI, 7.40–13.01) compared with those with low to medium scores (IR = 7.12; 95% CI, 6.00–8.39). Players training for 3 or more hours per week had a much lower incidence of mTBI (IR = 6.83; 95% CI, 5.74–8.06) compared with those training for less than 3 hours per week.

Players who reported they rarely wear protective gear had a much higher incidence of mTBI than those in other groups. The incidence of mTBI for players who reported that they rarely wear headgear during games (IR = 12.62; 95% CI, 8.38–18.27) was almost twice that of players who reported that they always wear headgear (IR = 7.39; 95% CI, 5.55–9.65). The incidence of mTBI for players who reported they rarely wear a mouthguard during games (IR = 13.36; 95% CI, 5.70–26.44) was also almost twice that of players who always wear a mouthguard (IR = 7.45; 95% CI, 6.31–8.74).

Players reporting a recent history of concussion showed a large variation in their incidence of mTBI. The incidence of mTBI was highest among those players with a history of concussion in the previous 3 months (IR = 16.99/1000 player hours; 95% CI, 9.26–28.58), almost 3 times the incidence of those without a recent history of concussion (IR = 6.55/1000 player hours; 95% CI, 5.52–7.71). Furthermore, those players who reported having 2 or more recent concussions (IR = 18.80; 95% CI, 13.36–25.71) had an incidence of mTBI 3 times that of players with no recent concussion.

After adjusting for age and offsetting exposure in the multivariate model (Table 1), there were 2 significant (P < .05) predictors of mTBI, namely, the use of headgear during games and the number of recent concussions reported by the player. Players who reported they always wear headgear during games were 43% (IRR = 0.57; 95% CI, 0.40–0.82) less likely to sustain an mTBI compared with players who reported they never wear headgear during games. In contrast, players sustaining 2 or more concussions in the 12 months before recruitment were almost 2 times more likely to sustain an mTBI during the season (IRR = 1.65; 95% CI, 1.11–2.45) compared with those without a history of concussion over the same period. The other important finding was that players sustaining only 1 concussion in the 12 months before recruitment were also almost 2 times more likely to sustain an mTBI during the season (IRR = 1.75; 95% CI, 1.11–2.76) compared with those without a history of concussion over the same period.

DISCUSSION

The incidence of mTBI observed in the current study is consistent with a recent Australian study of rugby players.³⁵ However, our reported incidence is higher than in recent meta-analyses of nonprofessional rugby players, which reported an incidence of mTBI ranging from 0.6 to 5.0 per 1000 player game hours.^7,24 The difference in the reported incidence of mTBI between the current study and other similar studies may be due to the variation between study designs, as well as the difference in the age distribution of the players in the various studies. The high incidence of mTBI in the current study could be attributed merely to our definition of mTBI. However, we believe that the observed incidence is a valid estimate of the incidence of mTBI among nonprofessional rugby players as we removed the likelihood of self-reported bias by using trained recorders and club medical staff to identify an mTBI and relied on player registrations for the game, obtained from the rugby association, to enumerate the exposure data; again, reducing the likelihood for overestimating or underestimating player participation.

The incidence of mTBI in the current study varied across a number of player characteristics. Players younger than 21 years of age were found to have almost twice the incidence of mTBI in older players. This may be partly because many of the players in this group had recently entered a higher level of competition, encountering an increase in player size, skill level, and speed of play—all factors well documented to increase a player’s risk of injury (Bird et al³; D. Williams and S. Blake, unpublished data, 1983).

There was a U-shaped relationship between a player’s rugby experience and the incidence of mTBI; players who were either inexperienced (0 to 3 years playing the game) or very experienced (>8 years of playing experience) were found to have a higher incidence of mTBI compared with players with between 4 and 8 years of experience. This association between limited previous experience and injury incidence is consistent with trends found in general sports injury studies^9,15,42 as well as in other rugby-specific studies.^39,42 However, the elevated risk to players with more than 8 years of experience is a new finding. It is not clear why there is such an increased incidence among experienced players, although one important observation is that 64% of recent concussions were among this subgroup; therefore, such a history may have predisposed these players to further injury.

Competition level plays a major part in the incidence of sporting injury because of variations in the size of the players, skill level, and the speed of the game. The incidence of mTBI was higher among players in suburban and grade levels than among those in school-level competition. Although there are few studies of mTBI in nonprofessional rugby with which to compare these data,^24,35 these trends are consistent with general sporting injury rates among varying grades.^3,6,9,15,40 Higher rates of injury were reported when levels of skill, fitness, and game intensity were highest,³ and when player size, strength, aggression, and competitiveness were also increased (D. Williams and S. Blake, unpublished data, 1983). Although fewer mTBIs were found in school-level players, studies have found that adolescents retain more ongoing postconcussion symptoms than adults,³⁸ even though they may sustain fewer mTBIs.

The protective benefits of headgear for rugby players, and those involved in other contact sports, continues to remain a moot point. In the current study, rugby players who always wore headgear during games were found to be at a significantly reduced risk of sustaining an mTBI throughout the season. This may be because of the type of players who choose to always wear headgear during games (fewer risk-takers wore headgear); however, in contrast, it may also encourage some players to feel more protected and, as a result, play more aggressively and therefore place themselves at greater risk for injury. Although this is not the research design to investigate the efficacy of such an intervention, it does point to the need to rigorously assess the benefits (or lack thereof) of appropriate headgear in contact sports.

Players with a history of 2 or more recent mTBIs were almost 2 times more likely to sustain a subsequent mTBI than players without a recent history of mTBI. Additionally, the likelihood of sustaining a mTBI was almost the same for players with a history of only 1 recent mTBI. This finding suggests that a recently sustained mTBI may be a significant predictor for recurrent mTBI.

There is no conclusive evidence that prior concussion is a precursor to a future mTBI. Many studies^20,25,37 indicate it is not a precursor to mTBI, and other studies^11,18 have found that high school and collegiate athletes suffering 3 or more concussions are more vulnerable to a subsequent concussion. The literature highlighting that recent mTBI is a precursor to subsequent mTBI stress that this finding may be an indicator that there has not been full recovery from the prior injury. For example, it is postulated that the increase in lactate production after injury to the brain leads to secondary ischemic injury, which may predispose the brain to repeat injury.² Unfortunately, in this study we were unable to determine whether inadequate recovery may have contributed to the repeat incidence of concussion, but a recent study of mTBI found no relationship between first and subsequent mTBI.²⁶

With recent history of 1 or more concussions being a significant predictor of mTBI in this Australian nonprofessional rugby cohort, the need for medically trained support staff for effective recognition of mTBI and the importance of preventing premature return to play is highlighted. The current lack of medical support to many nonprofessional rugby teams may have contributed to the predisposition of this group to further mTBI.

CONCLUSION

Nonprofessional rugby has a high incidence of mTBI, with the absence of headgear and a recent history of mTBI associated with an increased risk of subsequent mTBI. The findings from this cohort highlight that both use of headgear and the management of prior mTBI would likely be beneficial in reducing the likelihood of mTBI among non-professional rugby players, who compose more than 99% of rugby union players in Australia.

Footnotes

Table

ACKNOWLEDGMENT

This study would not have been possible without the willing cooperation and support of New South Wales community rugby clubs and schools and their players.

One or more authors has declared a potential conflict of interest: This study was supported by the U.S. Centers for Disease Control and Prevention grant 5R49CE323155 to the University of Pittsburgh Center for Injury Research and Control. Mark Stevenson is supported by funding from the Australian Government’s National Health and Medical Research Council. Stephanie Hollis is supported by postgraduate scholarship funding from the Australian Government’s National Health and Medical Research Council.

¶

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