CJSM Blog Journal Club — Brain Changes After a Single Season in Youth vs. High School Football

November 6, 2019 by sportingjim

The November 2019 Clinical Journal of Sport Medicine has just published, and as always the new edition is full of interesting and original research.

One of the studies that already is getting some buzz is one by a team of researchers (full disclosure: including myself) headed by Dr. Kim Barber-Foss entitled Relative Head Impact Exposure and Brain White Matter Alterations After a Single Season of Competitive Football: A Pilot Comparison of Youth Versus High School Football.

This is a perfect study for a journal club, as the subject of cumulative exposure to head impacts, most especially in our youngest athletes, has been a hot, hot topic in sports medicine for several years. The sport in question here is American gridiron football.

Our intrepid Blog Journal Club author and Junior Associate Editor Jason Zaremski MD leads the charge, as ever, in his most recent post. Thanks Dr. Zaremski for your insightful analysis of this new research.

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Title: Barber Foss KD, et al. Relative Head Impact Exposure and Brain White Matter Alterations After a Single Season of Competitive Football: A Pilot Comparison of Youth Versus High School Football. Clin J Sport Med 2019;29:442–450.

Introduction: The pre-holiday CJSM journal club brings you an innovative new study from expert researchers related to potential white matter changes in the brain in adolescent football players. As has been discussed in the CJSM journal club as well as throughout the media, there are many consequences to sustaining a sport related concussion (SRC). One question yet to be answered, with advances in neuroimaging techniques, can structural alterations of the brain be observed using magnetic resonance diffusion tensor imaging (DTI)? According to the authors, DTI can evaluate microscale white matter (WM) changes. This is potentially important as WM changes may be detected even without clinical signs of a SRC. More specifically, the measurable metrics include fractional anisotropy (FA), radial diffusivity (RD), axial diffusivity (AD), and mean diffusivity (MD). According to prior research, RD, AD, and MD are sensitive to detect WM changes in athletes participating in contact sports. Hence, we present “Relative Head Impact Exposure and Brain White Matter Alterations After a Single Season of Competitive Football: A Pilot Comparison of Youth Versus High School Football.”

Purpose: To determine preseason to postseason changes in WM integrity from repetitive head impacts for youth football (YFB) players compared with HS football players during a competitive football season.

Hypothesis(es): The magnitude of WM changes would be greater for YFB than for HS football players.

Methods/Design: Prospective study with IRB approval and consent and assent obtained.

Participants : Twelve YFB (13.08 +/- 0.64 years) and 21 HS (17.5 +/- 0.78 years) football athletes from the midwest. Of note, the DTI data for the 21 HS football players have been reported in a previous study (Myer GD, Yuan W, Barber Foss KD, et al. Analysis of head impact exposure and brain microstructure response in a season-long application of a jugular vein compression collar: a prospective, neuroimaging investigation in American football. Br J Sports Med. 2016;50:1276–1285.)

Interventions : Participants completed 2 magnetic resonance imaging (MRI) sessions: preseason and postseason. MRIs were completed with 3 Tesla magnetic strength. A board-certified neuroradiologist evaluated all images. Preseason testing took place before the start of the first practice. The postseason testing took place after the last competitive event, with the interval between the last competitive event and postseason imaging between 1 and 20 days (median 5 +/- 7.0 days) for the HS group and 1 to 59 days (median 5 +/- 4.5 days) for the YFB group.

Data Acquisition : Head impact exposure was recorded during practice and games using a helmet-mounted accelerometer (GForce Tracker). Placement of the device was to the inside of each football helmet in the same position and orientation. All data were collected for all practices and games. The accelerometers recorded peak linear acceleration and rotational velocity of the head. Before the initial exposure each accelerometer was calibrated according to device specifications and relative to the placement of the sensor in each helmet.

During the study period, 50 practices and 10 regular season games were completed for the HS group, whereas 28 practices and 9 games were completed for the YFB group. Athlete attendance was tracked by an athletic trainer for every practice and game session to calculate athlete exposures (AEs). The athletic trainer was also responsible for the assessment of any suspected SRC. YFB participants amassed a total of 438 AEs (105 game and 333 practice exposures) versus HS 1425 AEs (272 game and 1153 practice exposures). The YFB group had one reported SRC (2.28 per 1000 AEs). There were 3 SRC among HS (2.02 per 1000 AEs). It should be noted the average total number of impacts > 25 gs as well as > 100s in games and practice was significantly greater in the HS group compared to the YFB group.

Athletes who sustained concussions were all cleared to return to participation by their medical physician and completed a return-to-play protocol before the postseason scan. One concussed athlete (out of 3) from the HS group did not complete the MRI and was excluded from the final imaging analysis.

Outcome Measures: Group differences were evaluated from preseason to postseason using DTI, including FA, MD, AD, and RD.

Inclusion and Exclusion Criteria: There is no specific exclusion or inclusion criteria listed other than all participants play contact football and are an average age of 13 versus 17.5.

Statistical Measures/Analysis: Due to the complexity of the statistical analyses used analyzing data, I will refer the readers to page 445 of the manuscript for full statistical measures and analysis. However, summarizing the statistical analyses from the manuscript, the authors performed preseason to postseason DTI measures, in both HS and YFB group. The authors also used a within-group longitudinal change between the 2 time points at each voxel along the WM skeleton as generated in the TBSS analysis. All the t tests were performed 2-sided at significance level of p <0.05. For each participant, a difference map between the 2 time points was calculated for each DTI measure and used in a one-sample t-test to assess the longitudinal change for each group. Independent t tests were used to determine whether there was a significant group difference in the preseason to postseason DTI alteration. The time interval between the last game or practice and the postseason imaging was also included as a covariate in the analysis because of its large variability, although there was no statistically significant group difference in this parameter. All analyses with the athletes who had concussion during the season excluded.

Results/Outcomes: In the HS group, there were significant preseason to postseason reductions in MD, AD, and RD found in extensive WM areas. In the YFB group, there was significant preseason to postseason AD reduction but on a more limited extent. However, there were no significant findings observed in MD or RD in the YFB group.

Strengths:

Prospective

Novel Study idea and design

Provide important data in a microscopic level that could provide more information related to SRC

Weaknesses:

Small Sample Size

1 out of the 3 HS group participants that sustained a concussion was excluded from the final imaging analysis.

Need longer/longitudinal data

No mention of exclusion criteria. It is important to note if any of the participants have sustained a concussion in the past, history of neck injury, or other neurological insult they may have sustained. Additionally, did study participants participate in other contact or collision sports such as ice hockey, soccer, rugby, or diving (as an example) during the football season?

Increased number of days between last head impact exposure and postseason scan for the YFB group compared to the HS group (which the authors state)

Significantly less head impact exposure in YFB compared to HS group. This is important, as the authors mention, evidence indicates that the cumulative number of head impacts during a competitive season increases with the level of play. Thus, it is reasonable to ask if it is a fair comparison to analyze data between the two groups as the study is currently constructed.

Is this type of an evaluation clinically implementable?

Conclusion: There was a significant change from the preseason to postseason in AD reduction was found after one session of play in both groups. However, this study did not confirm that younger children are more susceptible to the effects of repetitive head impacts compared with their older counterparts in this cohort of subjects. Of note, after adjusting for head impact exposure, the extent of brain involvement was greater in the HS group than the YFB group.

Clinical Relevance: While this study was certainly interesting and presented novel data, given the lack of impact exposure and no mention of exclusion criteria, it is hard to draw strong conclusions when comparing groups and using this data to affect or change clinical management or recommendations at this time. However, it is important to note that the study results did suggest that WM changes may be related to volume and severity of head impacts but not age of the athlete when exposed. Thus, consideration for studying volume and magnitude over age of exposure may be more advantageous for future studies in this area of research.