Brain morphometry in former American football players: Findings from the DIAGNOSE CTE research project.

Exposure to repetitive head impacts (RHIs) in contact sports is associated with neurodegenerative disorders including chronic traumatic encephalopathy (CTE) which currently can be diagnosed only at postmortem. American football players are at higher risk of developing CTE given their exposure to RHIs. One promising approach for diagnosing CTE in vivo is to explore known neuropathological abnormalities at postmortem in living individuals using structural magnetic resonance imaging (MRI). MRI brain morphometry was evaluated in 170 male former American football players ages 45-74 years (n = 114 professional; n = 56 college) and 54 same-age unexposed asymptomatic male controls (n = 58 age range 45-74). Cortical thickness and volume of regions of interest were selected based on established CTE pathology findings and were assessed using FreeSurfer. Group differences and interactions with age and exposure factors were evaluated using a generalized least squares model. A separate logistic regression and independent multinomial model were performed to predict each Traumatic Encephalopathy Syndrome (TES) diagnosis core clinical features and provisional level of certainty for CTE pathology using brain regions of interest. Former college and professional American football players (combined) showed significant cortical thickness and/or volume reductions compared to unexposed asymptomatic controls in the hippocampus amygdala entorhinal cortex parahippocampal gyrus insula temporal pole and superior frontal gyrus. Post-hoc analyses identified group-level differences between former professional players and unexposed asymptomatic controls in the hippocampus amygdala entorhinal cortex parahippocampal gyrus insula and superior frontal gyrus. Former college players showed significant volume reductions in the hippocampus amygdala and superior frontal gyrus compared to the unexposed asymptomatic controls. We did not observe age-by-group interactions for brain morphometric measures. Interactions between morphometry and exposure measures were limited to a single significant positive association between the age of first exposure to organized tackle football and right insular volume. We found no significant relationship between brain morphometric measures and the TES diagnosis core clinical features and provisional level of certainty for CTE pathology outcomes. These findings suggest that MRI morphometrics detects abnormalities in individuals with a history of RHI exposure that resemble the anatomic distribution of pathological findings from postmortem CTE studies. The lack of findings associating MRI measures with exposure metrics (except for one significant relationship) or TES diagnosis and core clinical features suggests that brain morphometry must be complemented by other types of measures to characterize individuals with RHIs.

ENIGMA's simple seven: Recommendations to enhance the reproducibility of resting-state fMRI in traumatic brain injury.

Resting state functional magnetic resonance imaging (rsfMRI) provides researchers and clinicians with a powerful tool to examine functional connectivity across large-scale brain networks, with ever-increasing applications to the study of neurological disorders, such as traumatic brain injury (TBI). While rsfMRI holds unparalleled promise in systems neurosciences, its acquisition and analytical methodology across research groups is variable, resulting in a literature that is challenging to integrate and interpret. The focus of this narrative review is to address the primary methodological issues including investigator decision points in the application of rsfMRI to study the consequences of TBI. As part of the ENIGMA Brain Injury working group, we have collaborated to identify a minimum set of recommendations that are designed to produce results that are reliable, harmonizable, and reproducible for the TBI imaging research community. Part one of this review provides the results of a literature search of current rsfMRI studies of TBI, highlighting key design considerations and data processing pipelines. Part two outlines seven data acquisition, processing, and analysis recommendations with the goal of maximizing study reliability and between-site comparability, while preserving investigator autonomy. Part three summarizes new directions and opportunities for future rsfMRI studies in TBI patients. The goal is to galvanize the TBI community to gain consensus for a set of rigorous and reproducible methods, and to increase analytical transparency and data sharing to address the reproducibility crisis in the field.

Preinjury Measures Do Not Predict Future Concussion Among Collegiate Student-Athletes: Findings From the CARE Consortium.

ABSTRACT: This prospective cohort study aimed to determine whether preinjury characteristics and performance on baseline concussion assessments predicted future concussions among collegiate student-athletes. Participant cases (concussed = 2529; control = 30,905) completed preinjury: demographic forms (sport, concussion history, sex), Immediate Post-Concussion Assessment and Cognitive Test, Balance Error Scoring System, Sport Concussion Assessment Tool symptom checklist, Standardized Assessment of Concussion, Brief Symptom Inventory-18 item, Wechsler Test of Adult Reading, and Brief Sensation Seeking Scale. We used machine-learning logistic regressions with area under the curve, sensitivity, and positive predictive values statistics for univariable and multivariable analyses. Primary sport was determined to be the strongest univariable predictor (area under the curve = 64.3% ± 1.4, sensitivity = 1.1% ± 1.4, positive predictive value = 4.9% ± 6.5). The all-predictor multivariable model was the strongest (area under the curve = 68.3% ± 1.6, sensitivity = 20.7% ± 2.7, positive predictive value = 16.5% ± 2.0). Despite a robust sample size and novel analytical approaches, accurate concussion prediction was not achieved regardless of modeling complexity. The strongest positive predictive value (16.5%) indicated only 17 of every 100 individuals flagged would experience a concussion. These findings suggest preinjury characteristics or baseline assessments have negligible utility for predicting subsequent concussion. Researchers, healthcare providers, and sporting organizations therefore should not use preinjury characteristics or baseline assessments for future concussion risk identification at this time.

School-level determinants of incidence of sports-related concussion: Findings from the CARE Consortium.

OBJECTIVE: Epidemiologic research on sports-related concussion (SRC) has focused on individual risk factors, with limited research on institutional risk factors and variability in concussion rates. METHODS: This study used data from 53,822 athletes-seasons collected at 30 United States sites (26 civilian institutions and 4 military service academies), from 2014/15 to 2018/19 academic years, by the Concussion Assessment, Research, and Education Consortium. School-level risk factors included competitive division (DI, DII, DIII), school type (military/civilian) and a Sport Risk Index (SRI; Low, Medium, High). For comparability between civilian institutions and military academies, only NCAA athletes and concussions in sports games and practices were included. Random intercepts log-binomial regression was used to estimate Risk Ratios (RRs) and model variability in SRC risk. RESULTS: A total of 2,503 SRCs were observed during the study period, including 829 competition SRCs (33%) and 1,674 practice SRCs (67%). Most variability in SRC risk was at the level of athlete or team (within-school), rather than at the school-level. Specifically, across the three SRC outcomes (all [competition and practice combined], competition-only, and practice-only), within-school variability was 5 to 7 times greater than between-school variability. Three school-level risk factors (Division, School Type, and SRI) accounted for over one-third (36%) of between-school variability. SRI was the strongest school-level predictor of SRC risk (RR = 5.7; 95%CI: 4.2, 7.6 for High vs. Low). SRC risk was higher for Division I compared to Divisions II/III (RR = 1.6; 95%CI: 0.9, 2.9 for DI vs. DIII), and military academies had a moderately elevated risk of SRC (RR = 1.4; 95%CI: 0.7, 2.7). CONCLUSION: A large portion of the apparent variability between schools was attributable to structural factors (sport risk and competitive level), suggesting that there were minimal systemic differences in concussion identification between schools. While most variability is within-school, understanding school-level determinants of concussion risk may still be important in providing the implementation science context for individual-level interventions.

Current and Emerging Techniques in Neuroimaging of Sport-Related Concussion.

SUMMARY: Sport-related concussion (SRC) affects an estimated 1.6 to 3.8 million Americans each year. Sport-related concussion results from biomechanical forces to the head or neck that lead to a broad range of neurologic symptoms and impaired cognitive function. Although most individuals recover within weeks, some develop chronic symptoms. The heterogeneity of both the clinical presentation and the underlying brain injury profile make SRC a challenging condition. Adding to this challenge, there is also a lack of objective and reliable biomarkers to support diagnosis, to inform clinical decision making, and to monitor recovery after SRC. In this review, the authors provide an overview of advanced neuroimaging techniques that provide the sensitivity needed to capture subtle changes in brain structure, metabolism, function, and perfusion after SRC. This is followed by a discussion of emerging neuroimaging techniques, as well as current efforts of international research consortia committed to the study of SRC. Finally, the authors emphasize the need for advanced multimodal neuroimaging to develop objective biomarkers that will inform targeted treatment strategies after SRC.

Altered brain functional connectivity in the frontoparietal network following an ice hockey season.

Sustaining sports-related head impacts has been reported to result in neurological changes that potentially lead to later-life neurological disease. Advanced neuroimaging techniques have been used to detect subtle neurological effects resulting from head impacts, even after a single competitive season. The current study used resting-state functional magnetic resonance imaging to assess changes in functional connectivity of the frontoparietal network, a brain network responsible for executive functioning, in collegiate club ice hockey players over one season. Each player was scanned before and after the season and wore accelerometers to measure head impacts at practices and home games throughout the season. We examined pre- to post-season differences in connectivity within the frontoparietal and default mode networks, as well as the relationship between the total number of head impacts sustained and changes in connectivity. We found a significant interaction between network region of interest and time point (p = .016), in which connectivity between the left and right posterior parietal cortex seed regions increased over the season (p < .01). Number of impacts had a significant effect on frontoparietal network connectivity, such that more impacts were related to greater connectivity differences over the season (p = .042). Overall, functional connectivity increased in ice hockey athletes over a season between regions involved in executive functioning, and sensory integration, in particular. Furthermore, those who sustained more impacts had the greatest changes in connectivity. Consistent with prior findings in resting-state sports-related head impact literature, these findings have been suggested to represent brain injury.Highlights Functional connectivity of the frontoparietal network significantly increased between the pre- and post-season, which may be a compensatory mechanism driven by neural tissue injury caused by repetitive head impacts.Changes in frontoparietal network connectivity are related to head impact exposure, measured as the number of head impacts sustained in a single season.Functional connectivity of the default mode network did not change over an ice hockey season.

King-Devick testing and concussion recovery time in collegiate athletes.

OBJECTIVES: To assess whether the King-Devick (KD) test is useful as a prognostic test for prolonged concussion symptoms by examining the relationship between a) change in performance on KD test from baseline to within two days post-injury and b) the absolute KD time at post-concussion testing, with an outcome of time to return to play (RTP). DESIGN: Prospective Cohort Study. METHODS: Collegiate varsity athletes in the Concussion Assessment, Research, and Education (CARE) Consortium completed baseline and post-injury King-Devick tests from 2014 to 2018. Two exposures were evaluated: 1) change in KD score from baseline to within two days post-injury and 2) absolute KD score within two days post-injury, adjusted for baseline KD. We used Cox proportional hazards models to analyze the relationships between these exposures and time to RTP post-concussion. RESULTS: A total of 309 concussion injuries were included. Median baseline KD score was 40.0 s (IQR: 35.8, 45.2). Median post-injury KD score was 45.8 s (IQR: 39.8, 57.1). Median number of days until RTP in this cohort was 11 (IQR: 8, 17). Post-injury KD score adjusted for baseline KD had a stronger association with time to RTP duration (HR: 0.99 (0.98, 1.00), p = 0.03) than the difference in KD score from baseline to post-injury (HR: 0.99 (0.99, 1.00), p = 0.07). CONCLUSIONS: Higher post-injury KD scores are associated with longer RTP. The association between KD post-concussion test and longer RTP warrants further investigation to assess the utility of the KD for prognostication in a clinical setting.

Relationships between aggression, sensation seeking, brain stiffness, and head impact exposure: Implications for head impact prevention in ice hockey.

OBJECTIVES: The objectives of this study were to (1) examine the relationship between the number of head impacts sustained in a season of men's collegiate club ice hockey and behavioral traits of aggression and sensation seeking, and (2) explore the neural correlates of these behaviors using neuroimaging. DESIGN: Retrospective cohort study. METHODS: Participants (n = 18) completed baseline surveys to quantify self-reported aggression and sensation-seeking tendencies. Aggression related to playing style was quantified through penalty minutes accrued during a season. Participants wore head impact sensors throughout a season to quantify the number of head impacts sustained. Participants (n = 15) also completed baseline anatomical and magnetic elastography neuroimaging scans to measure brain volumetric and viscoelastic properties. Pearson correlation analyses were performed to examine relationships between (1) impacts, aggression, and sensation seeking, and (2) impacts, aggression, and sensation seeking and brain volume, stiffness, and damping ratio, as an exploratory analysis. RESULTS: Number of head impacts sustained was significantly related to the number of penalty minutes accrued, normalized to number of games played (r = .62, p < .01). Our secondary, exploratory analysis revealed that number of impacts, sensation seeking, and aggression were related to stiffness or damping ratio of the thalamus, amygdala, hippocampus, and frontal cortex, but not volume. CONCLUSIONS: A more aggressive playing style was related to an increased number of head impacts sustained, which may provide evidence for future studies of head impact prevention. Further, magnetic resonance elastography may aid to monitor behavior or head impact exposure. Researchers should continue to examine this relationship and consider targeting behavioral modification programs of aggression to decrease head impact exposure in ice hockey.

Evaluating Adult Decision-Making Modifiers in Support of Youth Contact-Sport Participation.

CONTEXT: Nearly 44 million youth participate in organized youth sports programs in the United States each year. However, approximately 25% of parents have considered removing their children from sports due to the fear of concussion. OBJECTIVE: To determine which adult decision-making modifiers (eg, gender, educational attainment, career type) influenced support for youth contact-sports participation. DESIGN: Cross-sectional study. SETTING: Midwestern university and medical center. PATIENTS OR OTHER PARTICIPANTS: Convenience sample of staff and faculty (N = 5761; 73.9% female) from 2017 to 2018. MAIN OUTCOME MEASURE(S): Support for youth contact-sports participation using multivariate binary logistic regression to calculate odds ratios and 95% CIs. RESULTS: The sample was split between adults with children (AWCs; n = 3465, age = 45.39 ± 13.27 years, 76.72% female) and adults without children (AWOCs; n = 2296, age = 30.84 ± 9.01 years, 70.26% female). Among AWCs, those who obtained a bachelor's degree or higher were more likely to support contact-sports participation. Females were more inclined to allow all contact sports, specifically football (odds ratio [OR] = 2.22; 95% CI = 1.64, 3.01) and ice hockey (OR = 1.98; 95% CI = 1.42, 2.78). Overall, previous adult sport participation, increasing number of children, and child gender were significant modifying variables in greater support of youth contact-sports participation among AWCs (P < .001). Among AWOCs, previous sport participation in football (OR = 3.27; 95% CI = 2.14, 4.87), ice hockey (OR = 4.26; 95% CI = 2.23, 8.17), or soccer (OR = 2.29; 95% CI = 1.48, 3.54) increased the likelihood of an adult supporting contact-sports participation. Lastly, all adults were less inclined to support a daughter participating in any contact sport than a son. CONCLUSIONS: These results reveal adult- and child-specific variables that may influence youth contact-sports participation. These decisions may be developed through the lens of certain gender role beliefs and may lead adults to perceive certain sports as more appropriate for sons than daughters.

Mechanical characterization of athletic helmet shells.

Our purpose was to compare the mechanical properties of the protective outer shells of various athletic helmets in their final, fully manufactured form. Sections were taken from 3 different helmet shells (Bauer RE-AKT hockey helmet, Cascade R lacrosse helmet, and Riddell Speedflex football helmet) at 4 different locations (front, side, top, and rear) for a total of 12 test specimens. The 4 specimens from each helmet shell were potted together in epoxy resin moulds and mechanically polished. The hardness, elastic modulus and phase angle were measured using dynamic nanoindentation performed at 100 Hz with an oscillation amplitude of 1 nm (rms). Repeated ANOVA analysis was used to compare each of the dependent variables for each of the 3 helmets across the 4 different locations. The interaction between helmet type and location was significant for hardness (F6,63 = 2.84, P = 0.032, Pη2 = 0.21), elastic modulus (F6,63 = 6.412, P < 0.001, Pη2 = 0.38), and phase angle (F6,63 = 7.65, P < 0.001, Pη2 = 0.42). Polycarbonate has a higher ability to dissipate mechanical energy making it the recommended superior choice for helmet shells. In addition, the results lead us to speculate that manufacturing causes changes in the molecular weight or the distribution of fillers across locations for polyethylene but not for polycarbonate since mechanical properties are fairly uniform over the surface of football helmets, at least within a given helmet.

Evaluation of Musculoskeletal Re-Injury Occurrence in Previously Concussed National Football League Athletes.

INTRODUCTION: Increased risk of musculoskeletal (MSK) injury post-concussion has been reported in collegiate athletes, yet it is unknown if professional football athletes are at the same risk of secondary injury. The objective of this study was to determine if the risk of MSK injury in National Football League (NFL) athletes increases after concussion. METHODS: NFL injury reports from 2013 to 2017 were collected from public websites. Concussed athletes (n=91) were equally matched to a non-injured control and an athlete with an incident of musculoskeletal (MSK) injury. RESULTS: Following their return to sport, concussed athletes were 2.35 times more likely to have a subsequent MSK injury relative to non-injured controls (95% CI: 2.35 [1.25, 4.44], P = 0.01), but were no more likely than athletes with an incident MSK injury (P = 0.55). Likewise, athletes with an incident MSK injury were no more likely to have a subsequent MSK injury than controls (P = 0.08). DISCUSSION: Increased odds of MSK injury in the 12-week period following a concussion in professional football athletes warrants future research on the acute effects of concussion and the relationship to MSK injury risk.

Associations Between Neurochemistry and Gait Performance Following Concussion in Collegiate Athletes.

OBJECTIVE: To evaluate the strength of associations between single-task and dual-task gait measures and posterior cingulate gyrus (PCG) neurochemicals in acutely concussed collegiate athletes. SETTING: Participants were recruited from an NCAA Division 1 University. PARTICIPANTS: Nineteen collegiate athletes acutely (<4 days) following sports-related concussion. DESIGN: We acquired magnetic resonance spectroscopy (MRS) in the PCG and gait performance measurements in the participants, acutely following concussion. Linear mixed-effects models were constructed to measure the effect of gait performance, in the single- and dual-task settings, and sex on the 6 neurochemicals quantified with MRS in mmol. Correlation coefficients were also calculated to determine the direction and strength of the relationship between MRS neurochemicals and gait performance, postconcussion symptom score, and number of previous concussions. MAIN MEASURES: Average gait speed, average cadence, N-acetyl aspartate, choline, myo-inositol, glutathione, glutamate plus glutamine, and creatine. RESULTS: Single-task gait speed (P = .0056) and cadence (P = .0065) had significant effects on myo-inositol concentrations in the PCG, independent of sex, in concussed collegiate athletes. Single-task cadence (P = .047) also had a significant effect on glutathione in the PCG. No significant effects were observed between dual-task gait performance and PCG neurochemistry. CONCLUSIONS: These findings indicate that increased concentrations of neuroinflammatory markers in the PCG are associated with slower single-task gait performance within 4 days of sports-related concussion.

Investigating the Range of Symptom Endorsement at Initiation of a Graduated Return-to-Play Protocol After Concussion and Duration of the Protocol: A Study From the National Collegiate Athletic Association-Department of Defense Concussion, Assessment, Research, and Education (CARE) Consortium.

BACKGROUND: Organizations recommend that athletes should be asymptomatic or symptom-limited before initiating a graduated return-to-play (GRTP) protocol after sports-related concussion, although asymptomatic or symptom-limited is not well-defined. HYPOTHESES: (1) There will be a range (ie, beyond zero as indicator of "symptom-free") in symptom severity endorsement when athletes are deemed ready to initiate a GRTP protocol. (2) Baseline symptom severity scores and demographic/preinjury medical history factors influence symptom severity scores at the commencement of the GRTP protocol. (3) Greater symptom severity scores at GRTP protocol initiation will result in longer protocol duration. (4) Symptom severity scores will not differ between those who did and did not sustain a repeat injury within 90 days of their initial injury. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: Across 30 universities, athletes (N = 1531) completed assessments at baseline and before beginning the GRTP protocol, as determined by local medical staff. Symptom severity scores were recorded with the symptom checklist of the Sport Concussion Assessment Tool-3rd Edition. Nonparametric comparisons were used to examine the effect of medical, demographic, and injury factors on symptom endorsement at GRTP protocol initiation, as well as differences in symptom severity scores between those who did and did not sustain a repeat injury within 90 days. A Cox regression was used to examine the association between symptom severity scores at GRTP protocol initiation and protocol duration. RESULTS: Symptom severity scores at the time when the GRTP protocol was initiated were as follows: 0 to 5 (n = 1378; 90.0%), 6 to 10 (n = 76; 5.0%), 11 to 20 (n = 42; 3.0%), and ≥21 (n = 35; 2.0%). Demographic (sex and age), medical (psychiatric disorders, attention-deficit/hyperactivity disorder, learning disorder), and other factors (baseline symptom endorsement and sleep) were significantly associated with higher symptom severity scores at the GRTP initiation (P < .05). The 4 GRTP initiation time point symptom severity score groups did not significantly differ in total time to unrestricted RTP, χ2(3) = 1.4; P = .73. When days until the initiation of the GRTP protocol was included as a covariate, symptom severity scores between 11 and 20 (P = .02; hazard ratio = 1.44; 95% CI, 1.06-1.96) and ≥21 (P < .001; hazard ratio = 1.88; 95% CI, 1.34-2.63) were significantly associated with a longer GRTP protocol duration as compared with symptom severity scores between 0 and 5. Symptom severity scores at GRTP initiation did not significantly differ between those who sustained a repeat injury within 90 days and those who did not (U = 29,893.5; P = .75). CONCLUSION: A range of symptom severity endorsement was observed at GRTP protocol initiation, with higher endorsement among those with higher baseline symptom endorsement and select demographic and medical history factors. Findings suggest that initiation of a GRTP protocol before an absolute absence of all symptoms is not associated with longer progression of the GRTP protocol, although symptom severity scores >10 were associated with longer duration of a GRTP protocol. Results can be utilized to guide clinicians toward optimal GRTP initiation (ie, balancing active recovery with avoidance of premature return to activity).

Sex differences in mechanisms of head impacts in collegiate soccer athletes.

BACKGROUND: There has been growing interest in head impacts related to sports participation due to potential long- and short-term consequences of head injuries. Our purpose was to compare head impact magnitude and frequency between men's and women's intercollegiate soccer players based on head impact mechanism. METHODS: 28 collegiate soccer players (16 women: age = 19.94 (1.06) years, height = 163.75 (5.15) cm, mass = 61.21 (5.09) kg; 12 men: age = 20.25 (1.14) years, height = 180.34 (6.03) cm, mass = 74.09 (9.32) kg) wore xPatch (X2 Biosystems, Seattle, WA) head impact sensors. Each practice and game was video recorded in order to confirm head impacts. The independent variable was impact mechanism (head to head, head to body (other than head), head to ground, ball to head, goal to head, and combination). Sensors collected linear and rotational accelerations and frequency of head impacts per 1000 athlete exposures. FINDINGS: Men were more likely to sustain head impacts than women (IRR = 1.74, CI95 = 1.59-1.92). The highest head impact incidence rate for men was head to body (IR = 611.68, CI95 = 553.11-670.25) while the highest impact incidence rate for women was ball to head (IR = 302.29, CI95 = 270.93-333.64). The interaction between sex and mechanism was significant for rotational accelerations (F4, 1720 = 3.757, P = .005, ω2 = 0.013) but not for linear accelerations (F4,1720 = 0.680, P = .606, ω2 < 0.001, 1 - ß = 0.223). INTERPRETATION: To reduce the frequency of head impacts in men, perhaps rules governing player to player contact should be more strictly enforced as these data confirm frequent player-to-head contact during soccer practices and games. Prevention efforts for women should be focused on limiting the amount of purposeful heading (planned contact between the head and ball) occurring during play especially since these impacts had higher magnitudes compared to men.

Impact Mitigation Properties of Women's Lacrosse Headgear.

Recently, protective headgear has been released for women's lacrosse despite the fact that contact to the head is illegal. The purposes of this study were to (1) compare the linear and rotational impact attenuation properties of 2 brands of lacrosse headgear at 4 different locations during laboratory pendulum impacts and (2) determine impact dissipation of new and used lacrosse headgear. We measured peak rotational acceleration (PRA; rad/s2) and linear acceleration (PLA; g) at 4 impact locations (side, rear boss non-centric (NC), front boss, and front) in two headgear brands (Cascade LX, Hummingbird). Two headgear service lives (new headgear, used headgear) were included for the second analysis. During the slower speed, there was a significant interaction between impact location and helmet brand (p = 0.002) for PLA. No other findings were significant. While the Hummingbird headgear reduced linear and rotational accelerations of the headform better than the Cascade headgear during slow velocity impacts to the front and front boss locations, it did so due to extreme motion of the helmet upon impact that we believe may compromise protection of the head and face from lacerations and other injuries.

King-Devick Test Reliability in National Collegiate Athletic Association Athletes: A National Collegiate Athletic Association-Department of Defense Concussion Assessment, Research and Education Report.

CONTEXT: The King-Devick (KD) test has received considerable attention in the literature as an emerging concussion assessment. However, important test psychometric properties remain to be addressed in large-scale independent studies. OBJECTIVE: To assess (1) test-retest reliability between trials, (2) test-retest reliability between years 1 and 2, and (3) reliability of the 2 administration modes. DESIGN: Cross-sectional study. SETTING: Collegiate athletic training facilities. PATIENTS OR OTHER PARTICIPANTS: A total of 3248 intercollegiate student-athletes participated in year 1 (male = 55.3%, age = 20.2 ± 2.3 years, height = 1.78 ± 0.11 m, weight = 80.7 ± 21.0 kg) and 833 participated in both years. MAIN OUTCOME MEASURE(S): Time, in seconds, to complete the KD error free. The KD test reliability was assessed between trials and between annual tests over 2 years and stratified by test modality (spiral-bound cards [n = 566] and tablet [n = 264]). RESULTS: The KD test was reliable between trials (trial 1 = 43.2 ± 8.3 seconds, trial 2 = 40.8 ± 7.8 seconds; intraclass correlation coefficient [ICC] (2,1) = 0.888, P < .001), between years (year 1 = 40.8 ± 7.4 seconds, year 2 = 38.7 ± 7.7 seconds; ICC [2,1] = 0.827, P < .001), and for both spiral-bound cards (ICC [2,1] = 0.834, P < .001) and tablets (ICC [2,1] = 0.827, P < .001). The mean change between trials for a single test was -2.4 ± 3.8 seconds. Although most athletes improved from year 1 to year 2, 27.1% (226 of 883) of participants demonstrated worse (slower) KD times (3.2 ± 3.9 seconds) in year 2. CONCLUSIONS: The KD test was reliable between trials and years and when stratified by modality. A small improvement of 2 seconds was identified with annual retesting, likely due to a practice effect; however, 27% of athletes displayed slowed performance from year 1 to year 2. These results suggest that the KD assessment was a reliable test with modest learning effects over time and that the assessment modality did not adversely affect baseline reliability.

Differences in the Mechanism of Head Impacts Measured Between Men's and Women's Intercollegiate Lacrosse Athletes.

BACKGROUND: Lacrosse is a rapidly growing sport in the United States. Comparing the magnitude and frequency of head impact mechanisms between sexes will provide data for injury prevention techniques and risk reduction of head injuries. PURPOSE: To compare sex-specific differences in the magnitude and frequency of head impact mechanisms in National Collegiate Athletic Association (NCAA) Division III intercollegiate lacrosse athletes. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: A total of 31 NCAA Division III intercollegiate lacrosse athletes (16 men [mean age, 21 ± 1 years; mean height, 179.70 ± 5.82 cm; mean weight, 80.71 ± 6.33 kg] and 15 women [mean age, 20 ± 1 years; mean height, 165.43 ± 5.25 cm; mean weight, 64.08 ± 7.59 kg]) voluntarily participated in this study. Participants wore xPatch sensors at every event during the 2015 spring season. Sensors recorded the magnitude, frequency, and location of head impacts over 10g. Linear (g) and rotational (deg/s2) acceleration determined impact magnitudes. We calculated incidence rates (IRs; per 1000 athlete-exposures [AEs]) and incidence rate ratios (IRRs) with 95% CIs to determine frequency differences. Film footage from each event was synchronized with the time of each head impact for verification and mechanism coding. Sex and impact mechanism served as the independent variables. RESULTS: A significant interaction was found between impact mechanism and sex (P < .001) and main effects for impact mechanism (P < .001) and sex (P < .001). The most common mechanism in men's lacrosse was head to body (IR, 970.55/1000 AEs [95% CI, 266.14-331.98]), and in women's lacrosse, stick to head (IR, 289.87/1000 AEs [95% CI, 124.32-184.55]) was most common. Only 9 of 419 impermissible head impacts in men's lacrosse games were classed as penalties (2%); 7 of 25 impermissible head impacts in women's lacrosse games were called as penalties (28%). CONCLUSION: The impact mechanisms of head to body in men's lacrosse and stick to head in women's lacrosse are penalties but occur frequently, suggesting that a focus on stressing rule enforcement is warranted. Because mechanism and sex affect the magnitude of head impacts, proper offensive and defensive techniques against opponents should be encouraged to reduce head impacts.

The effect of football helmet facemasks on impact behavior during linear drop tests.

Football helmet certification tests are performed without a facemask attached to the helmet; however, the facemask is expected to contribute substantially to the structure and dynamics of the helmet through the effects of added mass and added stiffness. Facemasks may increase the peak acceleration and severity index; therefore, as-used helmets may not mitigate head impacts as effectively as certification tests indicate. Furthermore, the effect is expected to depend on the helmet design as well as the orientation and speed of the impact. This study examined the influence of the facemask on impact behavior in a NOCSAE-style linear drop test and the interactions with location, velocity, and helmet model. Increases in peak acceleration and severity index of up to 36% were observed when helmets were tested with the facemask.

Effect of Impact Mechanism on Head Accelerations in Men's Lacrosse Athletes.

Quantifying head impacts is a vital component to understanding and preventing head trauma in sport. Our objective was to establish the frequency and magnitude of head impact mechanisms in men's lacrosse athletes. Eleven male lacrosse athletes wore xPatch sensors during activity. Video footage of practices and games was analyzed to verify impacts and code them with impact mechanisms. The authors calculated incidence rates (IRs) per 1000 exposures with corresponding 95% confidence intervals (CIs) and used multivariate analysis of variances to compare the linear (g) and rotational (rad/s2) accelerations between mechanisms. A total of 167 head impacts were successfully verified and coded with a mechanism using video footage during 542 total exposures. The highest IR was head to body (IR = 118.08; 95% CI, 89.15-147.01), and the lowest was head to ball (IR = 3.69; 95% CI, 0-8.80) (incidence rate ratio = 32.00; 95% CI, 67.83-130.73). Analysis indicated that impact mechanism failed to significantly alter the combined dependent variables (multivariate F10,306 = 1.79, P = .06, η2 = .06, 1-ß = 0.83). While head to head, body to head, and stick to head mechanisms are penalty-inducing offenses in men's lacrosse, head to ground, head to ball, and combination impacts have similar head accelerations. If penalties and rules are created to protect players from traumatic head injury, the authors recommend stricter enforcement.

The Ability of an Aftermarket Helmet Add-On Device to Reduce Impact-Force Accelerations During Drop Tests.

CONTEXT: The Guardian Cap provides a soft covering intended to mitigate energy transfer to the head during football contact. Yet how well it attenuates impacts remains unknown. OBJECTIVE: To evaluate the changes in the Gadd Severity Index (GSI) and linear acceleration during drop tests on helmeted headforms with or without Guardian Caps. DESIGN: Crossover study. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: Nine new football helmets sent directly from the manufacturer. INTERVENTION(S): We dropped the helmets at 3 velocities on 6 helmet locations (front, side, right front boss, top, rear right boss, and rear) as prescribed by the National Operating Committee on Standards for Athletic Equipment. Helmets were tested with facemasks in place but no Guardian Cap and then retested with the facemasks in place and the Guardian Cap affixed. MAIN OUTCOME MEASURE(S): The GSI scores and linear accelerations measured in g forces. RESULTS: For the GSI, we found a significant interaction among drop location, Guardian Cap presence, and helmet brand at the high velocity (F10,50 = 3.01, P = .005) but not at the low (F3.23,16.15 = 0.84, P = .50) or medium (F10,50 = 1.29, P = .26) velocities. Similarly for linear accelerations, we found a significant interaction among drop location, Guardian Cap presence, and helmet brand at the high velocity (F10,50 = 3.01, P = .002, ω2 = 0.05) but not at the low (F10,50 = 0.49, P = .89, ω2 < 0.01, 1-ß = 0.16) or medium (F5.20,26.01 = 2.43, P = .06, ω2 < 0.01, 1-ß = 0.68) velocities. CONCLUSIONS: The Guardian Cap failed to significantly improve the helmets' ability to mitigate impact forces at most locations. Limited evidence indicates how a reduction in GSI would provide clinically relevant benefits beyond reducing the risk of skull fracture or a similar catastrophic event.