Concussions Amongst Youth Ice Hockey Players

Concussions amongst youth ice hockey players

- A retrospective survey in Västerbotten and Västernorrland amongst teenagers 13-15 years of age

Hjärnskaknngar bland hockeyspelande ungdomar

- En retrospektiv enkätstudie i Västerbotten och Västernorrland bland tonåringar 13-15 år

Amanda Mattsson

Examensarbete, 30 hp Magisterprogram i Idrottsmedicin, 60 hp VT 2020

Avdelningen för idrottsmedicin, Inst. för samhällsmedicin och rehabilitering Umeå universitet, 901 87 Umeå

Abstract Sports-related concussions are one of the most complex injuries in the sports medicine field since head traumas are hard to recognize, discover and manage. Adolescent brains are under development and therefore more sensitive to concussions. Even though it is well established that concussions are a frequently occuring injury amongst youths, research on concussions on the youth ice hockey level in Sweden have not been previously investigated. Therefore, the primary aim of the present study was to investigate the cumulative prevalence of concussions amongst ice hockey players 13-15 years of age. A total of 188 players were invited to participate. The response rate was 40% whereas 61 players (girls n=6, boys n= 55) met the inclusion criteria. More than one-third (41%) reported at least one concussion, the majority of them hockey related. The study did not only investigate the prevalence of concussions, the understanding on concussions have also been examined, which revealed that half of the participants recognized Hjärntrappan. Although the study could not detect any significant relationship regarding potential risk factors and reported concussions, the investigation have illuminated a complex injury. In conclusion, the prevalence of concussions in the cohort was relatively high since more than one-third (41%) reported at least one concussion. Further, half of the participants recognized Hjärntrappan. The result emphasizes more education regarding head traumas for players, coaches and parents in youth ice hockey in order to prevent disastrous consequences such as premature career ending, future cognitive dysfunction and mental illness.

Key words: Adolescents, Brain Injury, Hjärntrappan, Questionnaire

Table of contents

ABSTRACT ...... 0

TABLE OF CONTENTS ...... 1

INTRODUCTION ...... 2

AIM ...... 5

METHOD ...... 6

PARTICIPANTS ...... 6 PROCEDURES ...... 7 SURVEY INSTRUMENT ...... 7 STATISTICAL METHODS ...... 7 ETHICAL CONSIDERATIONS ...... 8

RESULT ...... 8

DISCUSSION ...... 12

METHODOLOGICAL DISCUSSION ...... 15 LIMITATIONS ...... 17 ETHICAL AND SOCIAL CONSIDERATIONS ...... 17 PRACTICAL APPLICATIONS ...... 18

CONCLUSION ...... 18

REFERENCES ...... 20

APPENDICES ...... 23

Introduction

Sports-related concussions (SRC) are one of the most complex injuries in the sports medicine field since head traumas are hard to recognize, discover and manage (King, Hume & Gissane, 2014; McCrory et al., 2017; Register-Mihalik et al., 2018). SRC is a growing public health concern (Emery 2010; Kroshus, Garnett, Hawrilenko, Baugh & Calzo, 2015) and is considered as a ‘silent’ injury (King et al., 2014). Concussion is a functional injury and usually developing which means that symptoms can occur minutes to hours after the injury sequence. The symptoms can develop in minutes or up to hours after the injury sequence (McCrory et al., 2017). The symptoms are regularly not visible in the same extension as for example a bone fracture (McGuine et al., 2019), but can for instance include headache, concentration difficulties or nausea (McCrory et al., 2017). Further, concussions is a challenge to administer since every injury is unique (McCrory et al., 2017; Schneider et al., 2018) with a wide variety of clinical signs and symptoms (Covassin, Swanik & Sachs, 2003). Another aspect that adds to the injury complexity is underreporting (Kroshus et al., 2015; Pfister, Pfister, Hagel, Ghali, & Ronksley, 2016). According to Chrisman, Schiff, Chung, Herring and Rivara (2014), little is known about factors that might influence concussion identification and management amongst players younger than 15 years of ange. However, previous studies have focused on coaches and guardians attitudes as well as knowledge regarding concussions rather than on the affected youths (Register-Mihalik et al., 2018). Underreporting is a well established issue on all levels of ice hockey participation (Kroshus et al., 2015; Pfister, Pfister, Hagel, Ghali, & Ronksley, 2016). Athletes might try to minimize their symptoms in order to continue playing (Abbassi & Sirmon-Taylor, 2017; Mrazik, Perra, Brooks & Naidu, 2015) or they might continue because of insufficient knowledge of what a concussion is (Meehan & Bachur, 2009; Mrazik et al., 2015; Pfister et al., 2016).

Historically, unconsciousness has been a criterion for diagnosing concussions (Ruhe, Gänsslen & Klein, 2014). However, over the last five decades the definition for SRC has been revised (Guay et al., 2016). The present study defines concussion in accordance with Berlin Consensus Statement on Concussions in Sport, which is a joint statement represented by 11 national and international sports organisations (McCrory et al., 2017) as following: Concussion is the result of a traumatic brain injury due to a direct and hard impact to the

upper torso or other body parts that can result in a sudden movement of the neck or head (McCrory et al., 2017). The statement provides potential explanations as to why SRC can occur with frequent development both short term as well as long term consesequences. Furthermore it also includes clinical signs and symptoms that could be valuable while evaluating SRC (McCrory et al., 2017; Patricios et al., 2018). The Swedish method return-to- sport strategy ’Hjärntrappan’ (Tegner, Gustafsson, Forssblad, Lundgren & Sölveborn, 2007) is a well established guideline for management of concussions. At least 24 hours or longer have to pass without any symptoms for each step to continue to the next progression level. If any symptoms worsen, the athlete should go back to the previous step. Hjärntrappan consists of six steps, in which the first is called “brain rest” and refers to physical as well as cognitive rest. The guidelines continue with gradual activity level increase until the final step, where the athlete can return to sport with full body contact (Tegner et al., 2007; McCrory et al., 2017). Several concussions are considered as minor, but the cumulative effects of repeated head traumas (Covassin et al., 2003) can lead to long-term consequences (McCrory et al., 2017; Manley et al., 2017). For example chronic headache, depression, suicide or second-impact syndrome which means that the brain swells and in worst case scenario causes death (Jordan, 2013).

Adolescents brains are structurally different compared to adults (Bloodgood et al., 2013: Krolikowski et al., 2017). Therefore, the susceptibility to incur concussions increases amongst youths since they have reduced neck strength and musculature with a limited capacity to decrease head accelerations (Campolettano et al., 2020). Furthermore, an injury to a developing brain could result in a longer recovery time and interfere with brain progress which can cause long-term consequences later in life (Krolikowski et al., 2017). At the age of five, childrens heads have grown to more than 90% of full-size. The full-size is reached between 10 to 16 years of age meanwhile the body development lags behind, which causes an increased head-body ratio for children relative to adults (Campolettano et al., 2020; Pfister et al., 2016).

Players in contact sports are four times more likely to be injured compared to non-contact (Houghton & Emery, 2012; Lin, Casey, Herman, Katz & Tenforde, 2018). Contact sports also tend to result in an increased risk of SRC because it generally involves high speed (Register-

Mihalik et al., 2018; Schneider et al., 2018). American football (Pfister et al., 2016), ice hockey (Pauelsen, Nyberg, Tegner & Tegner, 2017) and soccer (Roudriges, Lasmar & Caramelli, 2016) are examples of sports with a high risk of SRC, since contact with high impact occurs frequently (Lin et al., 2018; Pfister et al., 2016). Ice hockey is a physical high- speed sport and lots of body contact while playing on ice surrounded by hard boards (Pauelsen et al., 2017). There is a central difference between boys and girls ice hockey since intentional body checking is prohibited at all female ice hockey levels (Reed, Taha, Greenwald & Keightley, 2017). However, body checking is considered as a central part of the game amongst boys (Houghton & Emery, 2012; Hutchison, Comper, Meeuwisse & Echemendia, 2015; Pauelsen et al., 2017). In Sweden, boys are allowed to body check from the age of 12 years old (Svenska ishockeyförbundet, 2018). Body checking can be defined as an individual defensive skill to separate the puck carrier from the puck (Black, Hagel, Palacios-Derflingher, Schneider, & Emery, 2017; Brooks et al., 2014). In order to prevent the injury frequency, players wear protective gears such as gloves, helmets and shoulder pads. Despite these precautions, the injury rate is still significant (Hutchison et al., 2015; Pauelsen et al., 2017).

Concussion is a frequently occurring injury in adolescent sports 12-16 years of age (McGuine et al., 2019; Mrazik et al., 2015) and the most reported injury in youth ice hockey 9-16 years of age (Kriz et al., 2016; Schneider et al., 2018). The injury incidence increases 4-fold when the hockey players are allowed to body check their opponent (Asplund, Bettcher & Borchers, 2009; Schneider et al., 2018). Body checking is considered as the main cause of trauma in ice hockey, representing up to 86% of all injuries amongst players 9-15 years of age (Emery et al., 2011; Malenfant, Nadeau, Hamel, & Emery, 2012; Pfister et al., 2016). Further, the severity and frequency of sustained concussions are influenced by several factors such as differences in size amongst children, age gender, previous brain injuries and player position (Emery, Hagel, Decloe, & Carly, 2010; Reed et al., 2017). Large discrepancies in relative age and body composition may result in an increased injury prevalence in players who are smaller and less physically developed (Brooks et al., 2014; Reed et al., 2017; Wattie et al., 2007). Emery et al., (2010) suggest that the risk of injury rises with increased age, which is in line with Reed et al., (2017). Gender are reported to play a role in injury rate because of biological sex differences (Lin et al., 2018). A previous history of concussions might also have

an impact on future brain injuries (Marklund, Bellander, Godbolt, Levin, McCrory & Thelin 2019) and runs six times higher risk for future concussions (Chiang Colvin, Mullen, Lovell, Vereeke West, Collins & Groh, 2009). Forwards and defensemen are highly exposed for concussions in senior ice hockey level (Hutchison et al., 2015). Player position has also been identified as a risk factor amongst youths. Forwards are at greater risk of contracting concussions than defensemen and goalies (Emery et al., 2010).

Frequency of concussions amongst ice hockey players on senior level are well studied (Paulsen et al., 2017; Pfister et al., 2016). However, the prevalence is missing on youth level in Sweden. In order to minimize concussions it is necessary to identify risk groups (Covassin et al., 2003; Mihalik, Wasserman, Teel, & Marshall, 2020). If the prevalence of concussions is shown to be high, the present study will pay attention to it and moreover give grounds for implementing preventive intervention strategies. Prevention strategies amongst sports organizations, leaders, and referees as well as game changing rules could increase the awareness and decrease the injury frequency.

Aim The main purpose of the present study was to investigate the prevalence of concussions amongst ice hockey players 13-15 years of age, through a retrospective cohort in the Västerbotten and Västernorrland country, Sweden. Further, a secondary aim was to examine the player’s awareness regarding Hjärntrappan. Research questions:

- What is the cumulative prevalence of concussions amongst ice hockey players 13-15 years of age in the Västerbotten and Västernorrland country?

- Which awareness about Hjärntrappan exists amongst the young ice hockey players, and from which sources does the players receive information about concussions?

- Could potential risk factors for concussions be identified in the present cohort?

Method

Participants Three ice hockey associations in Västerbotten and Västernorrland were contacted by phone during January 2020 with information regarding the aim of the study and an enquiry to participate (Appendix 1). Since the study sample contained minors, at least one guardian was asked to sign a written concession. With the written concession signed, the youts were willing to take a stand in their own participation. In order to participate, the inclusion criteria was established. Players were included if they (1) had a approval from at least one guardian (2) voluntarily agreed to participate (3) signed a written consent form and (4) were ice hockey players between 13-15 years of age. The exclusion criteria stated (1) written approval but did not complete the survey.

A total of 188 players were invited to participate and 76 individuals accepted the written information. A flowchart for the sample selection are presented in figure 1.

Procedures A questionnaire regarding concussions was created in consultation with a supervisor during November and December 2019. The majority of the questions were closed-ended questions, demanding a yes or no answer. Further, a selection of the questions also had multiple choice options and free text alternatives to enable more elaborate answers. In order to examine if the adolescents in the selected group understood the questions, a pilot survey for soccer players was implemented since the magister thesis would be carried out on hockey players. Soccer is a risk sport for concussions since close combats are frequently occurring (McCrory et al., 2017; Pfister et al., 2018). Data from the pilot study was collected in January 2020. The participants (n=12) were girls at 13 years of age from Umeå. Based on the results, minor changes was made to the magister thesis. Since the survey was retrospective and made demands on the participants memory, symptoms were removed from the questionnaire.

Prior to the survey, the participants received a letter with study information (Appendix 2). In order to confirm their attendance, a written consent was needed which could be filled in on the front page of the survey. The final questionnaire contained 25 questions (Appendix 3). Initially, background information about the player was requested, with following questions about the general perception of concussions. If the player filled in zero concussions, the questionnaire could be submitted. Players with at least one concussion continued to answer questions regarding their concussions in particular. The survey was conducted during March and April 2020. The estimated time to complete the survey was 5-10 minutes.

Survey instrument A digital survey was created using the web-based program Websurvey (Websurvey by Textalk, Göteborg). In consultation with the head coaches, the test leader sent an email containing information and a link to access the survey. The coaches forwarded the email to the guardians, who allowed participation when they handed over the email to their child.

Statistical methods The data collection was compiled in an Excel spreadsheet (Excel 2020, version 16.35, Redmond, Washington, USA). Body Mass Index (BMI) was calculated by weight / (height in

meter^2). The data analyses were made in JMP (JMP, 2020 version 14.3.0, Buckinghamshire, U.K). Through residuals and histograms, normal distribution of the data was controlled. Descriptive statistics for continuous variables are presented as means and standard deviations (SD). Binary variables are presented as counts and percentages. A one way analysis of variance (ANOVA) and Tukey’s post hoc test has been performed to examine differences in weight and concussions. ANOVA has also been performed to analyse the difference in BMI and concussions (Thomas, Nelson, & Silverman, 2018). In order to investigate the relationship between number of reported concussions and potential risk factors such as age, height and player position, Spearman’s rank correlation was performed. Statistical significance level for all analyses was set to α=0.05.

Ethical considerations The study has applied rules of research guidelines in accordance with the World Medical Association Declaration of Helsinki (2014). The participation was voluntary and the answers could not be linked to the individual since they were told not to write their name in the survey. The data collection was treated confidentially and the result was presented at a group level. All subjects were informed about their right to discontinue as well as withdraw their answers afterwards without any explanation. The physical risk to participate were none, but feelings of discomfort due to the questions could arise. The total sum of discomfort or risks were considered small compared to the potential benefits with the study.

Result

A total of 76 players consented to participate in the study which gives a response frequency at 40%. However, 61 players met the inclusion criteria and were included in the present study. Anthropometric data of the participants are presented in Table 1.

The main findings of the survey answers are summarized in Table 2.

Of the total reported concussions, 17 (50%) were diagnosed by a doctor. The remaining were reported as undiagnosed. Eight (40%) concussions induced on ice were diagnosed by a doctor. Amongst the players which has contracted atleast one concussion, 13 players (52%) had sustained their first concussion before the age of 12, the remaining 12 players (48%) has contracted a concussion at the age of 12 or later. The concussion situations inccured are presented in Figure 2.

Amongst the concussed players, 16 players out of 25 (64%) experienced support from teammates and coaches. Meanwhile, 8 individuals (32%) stated that the team had been unaware of the injury and 1 player (4%) reported no support from the team. Of those who did not inform the team about the concussion, the majority were undiagnosed (88%) and half of them occurred on ice. Over 90% considered concussion to be harmful (56/61; 91%). Two individuals (8%) who contracted concussions off ice did not thought it was harmful. Four players (16%) reported a recovery time of more than three weeks before they could return to play, 10 (40%) were recovered after one week and 2 players (8%) answered zero recovery days. Four players (16%) has experienced continued symptoms after their concussion. Of the concussed participants recognized 20 players (80%) Hjärntrappan. The sources where the participants received information about concussions are presented in Figure 3.

Seven players (11%) reported no general information about concussions and did not recognize Hjärntrappan. Amongst the 54 participants (89%) who has received information about concussions from different sources, 23 players (43%) were not aware of Hjärntrappan. Overall, 51% of the participants recognized Hjärntrappan.

Players with two concussions had an average weight of 64.7 kg ± 10.0. The average body weight for those who sustained one concussion was 58.4 kg ± 8.8 and zero concussions 57.7 kg ± 8.8. No statistical significance amongst weight and concussions were found based on the ANOVA-analyses (F= 2.2, P= 0.1). Through the ANOVA-test, a significant relationship between body mass index and numbers of concussions was noted (F= 3.3, P= 0.041). The Tukey’s post hoc analysis showed a difference between 0 and 2 concussions (p=0.032, p<0.05). For a visual overview of the result by box plots, see Figure 4.

Figure 4. The ANOVA-test devided in groups depending on numbers of concussions. The box plot illustrates the differences between BMI and numbers of reported concussions, where a difference between 0 and 2 concussions was noted.

Spearman’s rank correlation has been performed to investigate the relationship between potential risk factors - height, age and playing experience - and reported numbers of concussions. The result are presented in Table 3.

Discussion

Concussion is the most reported injury amongst ice hockey players 9-16 years of age (Kriz et al., 2016; Schneider et al., 2018). Further, Marar, Mcllvain, Fields and Comstock (2012) has investigated concussions amongst high school athletes in over 20 sports and found a concussion rate in boys ice hockey of 5.4 per 10 000 athlete exposures. One-third of all youths world wide are calculated to experience head traumas before the age of 16 years (Dahl & Emanuelsson, 2013). The prevalence of concussions amongst teenagers 13-15 years of age in Västerbotten and Västernorrland in the present study were relatively high since

almost half of the participants has sustained at least one concussion. It is a serious concern that several players have sustained at least one concussion at this young age. In total, nearly half of the participants reported at least one concussion, where the majority were hockey- related. Half of the reported concussions were clinically-diagnosed. It is interesting why players who suspected a concussion resisted to get the injury evaluated by a doctor. If players who reported concussions without confirmation by a doctor can be considered reliable is unsure, but it presumably exists undetected cases. The majority of participants in the present study has experienced a blow to the head or neck while playing ice hockey and over 90% considered concussions to be harmful. On the other hand, less than half of them sought medical attention after the hit which indicates an insufficient knowledge on how to manage head injuries. However, it is not clarified how comprehensive the hit was or if the players experienced symptoms afterwards. These conditions are likely associated with the decision to seek medical attention or not. A knowledge gap in how to manage concussions and how it is characterized is well established (Campolettano et al., 2020). Players with a potentially concussive impact after a blow to the head or neck often resists a medical evaluation (Kroshus et al., 2015). A previous study reported that more than 50% of 1 400 adolescents did not recognize symptoms for concussion after head traumas. This was referred to as a lack of awareness regarding symptoms that could arise as a consequence of sustaining a concussion, what a concussion is or in fear of missed playing time. Peer pressure from coaches, caretakers or teammates likely influence the players to avoid seeking medical help after head traumas (Mrazik et al., 2015; Kroshus et al., 2015). According to previous studies, youth sport coaches understanding has been improving over the recent years, but they still misunderstand how to manage the injury (Chrisman et al., 2014). Further, the attitude and knowledge amongst parents regarding the injury is insufficient (Chrisman et al., 2014). Moreover, this could contribute to underreporting of concussions (Campolettano et al., 2020; Kroshus et al., 2015; Register-Mihalik et al., 2018).

The higher concussion rates in contact sports might influence what adolescents know and believe about concussions (Register-Mihalik et al., 2018). Previous research revealed that a previous history of concussions did not affect the knowledge (P= 0.333) (Register-Mihalik, McLeod, Linnan, Guskiewicz & Marshall, 2017). Players with a concussion history had a worse attitude towards the importance of education on head injuries in comparison to those

who had not experienced a head injury (Register-Mihalik, McLeod, Linnan, Guskiewicz & Marshall, 2017). Even though four-fifths of the concussed players are conscious of Hjärntrappan (Tegner et al., 2007) the overall knowledge amongst the total participants indicates an insufficient understanding. Further, future studies should examine how many of the athletes that actually follows the guidelines. It is important since early RTS can result in long term consequences such as chronic headache, depression or premature career ending (Jordan, 2013). A longer recovery time indicates that the players may be aware of the consequences which comes with a short recovery time, since it is shown that a longer recovery time has been associated with an increased future knowledge (Register-Mihalik et al., 2018). The athletes have primarily received general information about the injury from family members, coaches or another person from the hockey team, which is in accordance with previous findings (Kroshus et al., 2015; Register-Mihalik et al., 2018). The attitude from adults may influence the youths understanding of concussions (Kroshus et al., 2015).

Body checking is identified as a risk factor for concussions with a summary odds ratio of 1.71 [95%, CI 1.2 to 2.4] (Emery et al., 2010). The majority of the sports related concussions has essentially incurred in situations involving body contact during games. This result is in accordance with previous findings (Abrahams et al., 2014; Kontos et al., 2016; Pfister et al., 2016). According to Malenfant et al., (2012) and Pfister et al., (2016), body checking can represent up to 86% of all injuries amongst hockey players 9-15 years of age. Similar studies has shown a four times greater risk to sustain a concussion when players are allowed to body check (Asplund et al., 2009; Schneider et al., 2018). Multiple players has experienced concussions before the age of 12, when body checking was prohibited. This may be explained by unintentional body checking (Darling, Schaubel, Baker, Leddy, Bisson & Willer, 2011), weaker neck musculature (Krolikowski et al., 2017) and reduced core stability which are also factors associated with increased injury risk (Pontillo, Hines & Sennett, 2020). Previous history of concussions has been noted as a risk factor to sustain future head traumas (Marklund et al., 2019). The survey has registered concussions off ice even though the purpose was to investigate the prevalence amongst youth in ice hockey, due to the increased sensibility for future concussions, regardless of the situation that induced the injury (Krolikowski et al., 2015; Marklund et al., 2019). Players with previous concussions runs a six times higher risk for future head traumas (Chiang Colvin et al., 2009). In addition

to this, players in contact sports are in general already four times as exposed to injuries and concussions compared to non-contact athletes (Houghton & Emery, 2012; Lin et al., 2018).

Several factors may have an impact on the concussion frequency, including age, gender, player position and body mass (Brooks et al., 2014; Reed et al., 2017). Despite the lack of a significant relationship between weight and number of sustained concussions, there is a tendency that heavier players are at greater risk to contract concussions. These findings are in contrast to previous studies who stated that lighter players are more vulnerable to injuries in general (Brooks et al., 2014; Emery et al., 2010; Reed et al., 2017). The divergences could possibly be explained by a larger amount of participants. Further, previous investigators has completed prospective studies during ongoing seasons (Brooks et al, 2014; Reed et al., 2017) while the present study is retrospective. Different stages in physical maturity are associated with increased injury rate in players who are smaller and less physically developed (Brooks et al., 2014; Emery et al., 2010; Reed et al., 2017; Wattie et al., 2007). The physical maturity can differ up to 41 cm and 48 kilograms amongst players playing at the same level and biological age of 13 and 14 years of age, therefore lighter players are more exposed to injuries than heavier (Emery et al., 2010). Reed et al., (2017) found that a higher BMI significantly predicted a greater number of head impacts per game (P= 0.008). A weak relationship between BMI and number of concussions was revealed in the current study. One individual had a great impact of the statistical analysis and accounted for the correlation. When the outlier was removed, the significance vanished. Prospectively, half of the players has sustained a concussion before body checking was permitted. This information indicates that body checking is not the only factor to cause concussions. The sample size was relatively small and homogenous in body compositions amongst the players. That could be a possible reason why no significant relationship between reported concussions and previously identified factors could be noted. It is not possible to draw any conclusions regarding potential risk factors and to sustain concussions based on the present study results.

Methodological discussion Three hockey collations in two districts were contacted for practical reasons since the test leader initially intended to visit their training facilities. The present study was dropout sensitive, in particular for girls since it is a male dominated sport (Abrahams et al., 2014). The sample size was small with a low response frequency. Furthermore, the survey is not 15

validated since the questionnaire is based on personal experiences and formulated in consultation with the supervisor. However, there is no previous survey for adolescents in the selected age group regarding concussions. In order to improve the reliability, the questionnaire has been tested through a pilot study amongst soccer players at the same age group. Future studies should develop the questionnaire, to get a greater overview of the problem with SRC.

At the beginning, the final survey was supposed to be implemented through paper and pen. This to ensure that the players would respond independently without any influences from external sources, for example family or friends. Another reason was to increase the probability of high response rate if the test leader was present during the investigation. Due to the coronavirus, the circumstances of the survey changed during the period of time that the study was supposed to take place. The survey was moved to a web-based platform due the hockey seasons early end. Therefore, there was no way for the test leader to ensure that the participants weren't affected by external factors when answering the questions. Further, a self reported survey with a retrospective design is considered recall bias since the questions rely on the participants memory. How the questions have been formulated and the probability of misinterpretation of the questions is a factor to take in consideration for the statistical analysis.

The statistical analysis has not been adjusted for confounders because of skewed group selection, boys compared to girls. Further, the limited amount of time resulted in a small sample size, too small to investigate gender as a potential risk factor regarding concussions (Lin et al., 2018). Therefore, the result has been presented on the whole group, not divided by sex since there were no difference for the statistical analyses when the relationships only was investigated amongst boys. The present study has only presented numbers of concussions while previous studies have reported concussion incidence ratio in relation to playing hours and per players (Darling et al., 2011; Kontos et al., 2016; Schneider et al., 2014). Future studies should register playing hours in order to increase the cumulative veracity to predict concussion risk over time.

If the study would be replicated the ambition should be to reach out to a lager selection and a more equal gender distribution which enables statistical analyses divided into boys and girls separately. Additionally, the survey should be distributed through paper and pen to enhance the answers frequency and reduce the risk to be affected by external sources. On the other hand, for practical reasons and for a wider population, web-based surveys are more flexible and does not require as much planning as a physical questionnaire. Future studies should approach prospective cohort studies and follow teams over one or several ongoing seasons, just like Pauelsen et al., (2017) did in the Swedish Hockey League over 29 seasons. Moreover, a shorter survey or interview should be carried out for coaches to evaluate their attitude and awareness regarding concussions. This is relevant because the communication between coaches and players can normalize or undermine the attitude towards concussions (Kroshus et al., 2015).

Limitations The low response rate (40%) and a relatively homogenous selection group is not representative for a whole population. The result is therefore not generalizable over the whole youth ice hockey population. Furthermore, the prevalence and knowledge of concussions are most likely varying depending on where in Sweden the players are located (Register-Mihalik et al, 2018). It is conceivable that the non-significant results regarding factors and risk to sustain a concussion could be a type-II error. The players who chose to participate in the survey might have been more interested or aware of concussions than those who did not. However, the result provides an overview for youth hockey players at 13- 15 years of age regarding concussions in Västerbotten and Västernorrland country, Sweden. Further, it would have been desirable with more follow up questions for a comprehensive investigation and therefore a more distinct analysis. On the other hand, the response frequency might have been even lower.

Ethical and social considerations Before inclusion, the subjects were informed about the purpose of the study. It was a central part of the information letter to clarify that the participation was voluntary. Further, the final decision to participate was with the players and not the caretakers or coaches. When the survey had to take place on the web-based platform, the participants were asked to fill in

their team belonging. The purpose was only for the test leader to keep track of the number of respondents from each team. The associations were left out in the results to minimize the risk that players would be identified in the study. The results are presented on a group level leaving individuals out of the report. All players are under 18 years of age which means that the caretaker had to authorize the participation.

Research is missing on the selected age groups even though it is well established that concussion is a complex injury with lots of underreporting and lack of knowledge (Campolettano et al., 2020). Further, the differences in physical maturity might have a great impact on the severity and frequency of concussions (Brooks et al, 2014). Therefore, in terms of social benefits, it is important to improve the awareness by illuminating the prevalence, in particular amongst adolescents since youths brains are under development (Krolikowski et al., 2017). The present study is the first to investigate the concussion occurrence amongst Swedish youth ice hockey players 13-15 years of age and could be useful as an indicator of the current situation for youth hockey players today, and hopefully inspire further studies on the subject.

Practical Applications It is crucial for coaches, parents and players to be aware of the potential consequences of contracting a concussion since early RTS can provoke long-term consequences such as chronic headache, depression or premature career ending (Jordan, 2013). In other words,to enhance the awareness and knowledge on how to manage head traumas, it is important to illuminate the prevalence. The result emphasizes implementation of more educational preventive strategies for coaches, parents and players in order to improve the youths mental as well as physical health.

Conclusion

The present study is the first to present the occurrence of concussions in Sweden amongst young ice hockey players. The prevalence of concussions in the cohort was relatively high since more than one-third (41%) reproted at least one concussion. It is a serious concern that almost half of the players had experienced at least one concussion at this young age, a

time-period in life were the brain is under significant development. The awareness of concussions revelad that half of the participants recognized Hjärntrappan. This information emphasizes the need of education about head traumas for players, coaches and guardians. Actions in order to prevent concussions are important. In case of concussions, increased understanding for the importance of medical care is crucial. In conclusion, the present study illuminates both a relative high prevalence and an inadequate awareness of concussions amongst young ice hockey players. If concussions are not managed in the right way or preventative actions are not considered, this could lead to premature career ending, lifelong cognitive dysfunction and mental illness.

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Appendices

Appendix 1. Information letter

Appendix 2. Background information

Appendix 3.The Questionnare