Concussion In Football Players Research Articles

Microstructural Alterations in Tract Development in College Football and Volleyball Players: A Longitudinal Diffusion MRI Study.

Repeated impacts in high-contact sports such as American football can affect the brain's microstructure, which can be studied using diffusion MRI. Most imaging studies are cross-sectional, do not include low-contact players as controls, or lack advanced tract-specific microstructural metrics. We aimed to investigate longitudinal changes in high-contact collegiate athletes compared with low-contact controls using advanced diffusion MRI and automated fiber quantification. We examined brain microstructure in high-contact (football) and low-contact (volleyball) collegiate athletes with up to 4 years of follow-up. Inclusion criteria included university and team enrollment. Exclusion criteria included history of neurosurgery, severe brain injury, and major neurologic or substance abuse disorder. We investigated diffusion metrics along the length of tracts using nested linear mixed-effects models to ascertain the acute and chronic effects of subconcussive and concussive impacts, and associations between diffusion changes with clinical, behavioral, and sports-related measures. Forty-nine football and 24 volleyball players (271 total scans) were included. Football players had significantly divergent trajectories in multiple microstructural metrics and tracts. Longitudinal increases in fractional anisotropy and axonal water fraction, and decreases in radial/mean diffusivity and orientation dispersion index, were present in volleyball but absent in football players (all findings |T-statistic|> 3.5, p value <0.0001). This pattern was present in the callosum forceps minor, superior longitudinal fasciculus, thalamic radiation, and cingulum hippocampus. Longitudinal differences were more prominent and observed in more tracts in concussed football players (n = 24, |T|> 3.6, p < 0.0001). An analysis of immediate postconcussion scans (n = 12) demonstrated a transient localized increase in axial diffusivity and mean/radial kurtosis in the uncinate and cingulum hippocampus (|T| > 3.7, p < 0.0001). Finally, within football players, those with high position-based impact risk demonstrated increased intracellular volume fraction longitudinally (T = 3.6, p < 0.0001). The observed longitudinal changes seen in football, and especially concussed athletes, could reveal diminished myelination, altered axonal calibers, or depressed pruning processes leading to a static, nondecreasing axonal dispersion. This prospective longitudinal study demonstrates divergent tract-specific trajectories of brain microstructure, possibly reflecting a concussive and repeated subconcussive impact-related alteration of white matter development in football athletes.

Serum microRNAs associated with concussion in football players.

Mild Traumatic Brain Injury (mild TBI)/concussion is a common sports injury, especially common in football players. Repeated concussions are thought to lead to long-term brain damage including chronic traumatic encephalopathy (CTE). With the worldwide growing interest in studying sport-related concussion the search for biomarkers for early diagnosis and progression of neuronal injury has also became priority. MicroRNAs are short, non-coding RNAs that regulate gene expression post-transcriptionally. Due to their high stability in biological fluids, microRNAs can serve as biomarkers in a variety of diseases including pathologies of the nervous system. In this exploratory study, we have evaluated changes in the expression of selected serum miRNAs in collegiate football players obtained during a full practice and game season. We found a miRNA signature that can distinguish with good specificity and sensitivity players with concussions from non-concussed players. Furthermore, we found miRNAs associated with the acute phase (let-7c-5p, miR-16-5p, miR-181c-5p, miR-146a-5p, miR-154-5p, miR-431-5p, miR-151a-5p, miR-181d-5p, miR-487b-3p, miR-377-3p, miR-17-5p, miR-22-3p, and miR-126-5p) and those whose changes persist up to 4 months after concussion (miR-17-5p and miR-22-3p).

Targeting Rule Implementation Decreases Concussions in High School Football: A National Concussion Surveillance Study.

Background:Concussions occur at higher rates in high school football as compared with all other high school sports. In 2014, the National Federation of State High School Associations implemented rules defining illegal contact against a defenseless player above the shoulders to reduce concussions in football players in the United States. To the best of our knowledge, rates of emergency department (ED)—diagnosed concussions of high school football players before and after the 2014 rule implementation have not been compared.Hypothesis:It was hypothesized that (1) there would be lower rates of helmet-to-helmet and helmet-to-body-part concussions after rule implementation and (2) alternative mechanisms of concussion would not differ, as these would be less influenced by rule implementation.Study Design:Cohort study; Level of evidence, 3.Methods:Data from the National Electronic Injury Surveillance System (NEISS) were analyzed for high school football players 14 to 18 years old sustaining a concussion from January 1, 2009, to December 31, 2019. Data were collected on mechanism of injury, setting, and loss of consciousness. Raw data were used to calculate national estimates based on the assigned statistical sample weight of each hospital by the NEISS.Results:A total of 4983 (national estimate = 154,221) high school football concussions were diagnosed in US EDs; 58.8% of concussions occurred during competition and 41.2% during practice. Between 2009 and 2013 the rate of concussions diagnosed in EDs rose 10.7% as compared with a 6.2% decrease between 2015 and 2019 (P = .04). Between 2009 and 2013, the rate of helmet-to-helmet concussions rose 17.6% as compared with a 5.6% decrease between 2015 and 2019 (P = .03). There were no significant changes between other mechanisms of concussion before and after the 2014 rule implementation.Conclusion:We identified a decreased trend in overall and helmet-to-helmet high school football concussions diagnosed in the ED after implementation of the targeting rule. This study adds to the growing literature regarding the importance and efficacy of rule implementation in reducing sports-related concussions.

Positive association between serum quinolinic acid and functional connectivity following concussion

The molecular mechanisms underlying the diverse psychiatric and neuropathological sequalae documented in subsets of athletes with concussion have not been identified. We have previously reported elevated quinolinic acid (QuinA), a neurotoxic kynurenine pathway metabolite, acutely following concussion in football players with prior concussion. Similarly, work from our group and others has shown that increased functional connectivity strength, assessed using resting state fMRI, occurs following concussion and is associated with worse concussion-related symptoms and outcome. Moreover, other work has shown that repetitive concussion may have cumulative effects on functional connectivity and is a risk factor for adverse outcomes. Understanding the molecular mechanisms underlying these cumulative effects may ultimately be important for therapeutic interventions or the development of prognostic biomarkers. Thus, in this work, we tested the hypothesis that the relationship between QuinA in serum and functional connectivity following concussion would depend on the presence of a prior concussion. Concussed football players with prior concussion (N = 21) and without prior concussion (N = 16) completed a MRI session and provided a blood sample at approximately 1 days, 8 days, 15 days, and 45 days post-injury. Matched, uninjured football players with (N = 18) and without prior concussion (N = 24) completed similar visits. The association between QuinA and global connectivity strength differed based on group (F(3, 127) = 3.46, p = 0.019); post-hoc analyses showed a positive association between QuinA and connectivity strength in concussed athletes with prior concussion (B = 16.05, SE = 5.06, p = 0.002, 95%CI[6.06, 26.03]), but no relationship in concussed athletes without prior concussion or controls. Region-specific analyses showed that this association was strongest in bilateral orbitofrontal cortices, insulae, and basal ganglia. Finally, exploratory analyses found elevated global connectivity strength in concussed athletes with prior concussion who reported depressive symptoms at the 1-day visit compared to those who did not report depressive symptoms (t(15) = 2.37, mean difference = 13.50, SE = 5.69, p = 0.032, 95%CI[1.36, 25.63], Cohen’s d = 1.15.). The results highlight a potential role of kynurenine pathway (KP) metabolites in altered functional connectivity following concussion and raise the possibility that repeated concussion has a “priming” effect on KP metabolism.

A Prospective Study of Acute Blood-Based Biomarkers for Sport-Related Concussion.

Prospectively characterize changes in serum proteins following sport-related concussion and determine whether candidate biomarkers discriminate concussed athletes from controls and are associated with duration of symptoms following concussion. High school and collegiate athletes were enrolled between 2015 and 2018. Blood was collected at preinjury baseline and within 6 hours (early acute) and at 24 to 48 hours (late acute) following concussion in football players (n = 106), matched uninjured football players (n = 84), and non-contact-sport athletes (n = 50). Glial fibrillary acidic protein, ubiquitin c-terminal hydrolase-L1, S100 calcium binding protein B, alpha-II-spectrin breakdown product 150, interleukin 6, interleukin 1 receptor antagonist, and c-reactive protein were measured in serum. Linear models assessed changes in protein concentrations over time. Receiver operating curves quantified the discrimination of concussed athletes from controls. A Cox proportional hazard model determined whether proteins were associated with symptom recovery. All proteins except glial fibrillary acidic protein and c-reactive protein were significantly elevated at the early acute phase postinjury relative to baseline and both control groups and discriminated concussed athletes from controls with areas under the curve of 0.68 to 0.84. The candidate biomarkers also significantly improved the discrimination of concussed athletes from noncontact controls compared to symptom severity alone. Glial fibrillary acidic protein was elevated postinjury relative to baseline in concussed athletes with a loss of consciousness or amnesia. Finally, early acute levels of interleukin 1 receptor antagonist were associated with the number of days to symptom recovery. Brain injury and inflammatory proteins show promise as objective diagnostic biomarkers for sport-related concussion, and inflammatory markers may provide prognostic value. ANN NEUROL 2020;87:907-920.

Psychosocial experiences of concussed collegiate athletes: The role of emotional support in the recovery process

Objective: Understand from whom concussed football players seek and receive emotional support, and whether this support is associated with injury perceptions. Participants: Football players (N = 26) from three NCAA Division I programs. Methods: With approval from the head athletic trainer, concussed athletes (2017 season) completed short surveys within 4–6 days of diagnosis and when cleared to return. Results: Concussed athletes perceived their injury as a normal consequence of playing football, not serious, and reported little, if any, depression and anxiety. Athletes reported the most support from athletic trainers; the least from coaches and teammates. Emotional support was associated with fewer adverse psychosocial reactions, more sport-injury related growth, and greater intentions to report future concussion symptoms. Conclusion: Results from this pilot study suggest that emotional support during the concussion recovery process should be understood and fostered by university officials charged with the health and well-being of collegiate football players.

Functional brain effects of acute concussion in Australian rules football players

Aim To determine whether acute sport-related concussion is associated with functional brain changes in Australian rules footballers. Methods Twenty acutely concussed professional Australian footballers were studied with 3 T magnetic resonance imaging and compared to 20 age-matched control subjects. We statistically compared whole-brain local functional magnetic resonance imaging connectivity between acutely concussed footballers and controls using voxel-wise permutation testing. Results The acutely concussed football players had significantly decreased local functional magnetic resonance imaging connectivity in the right dorsolateral prefrontal cortex, right inferior parietal lobe, and right anterior insula, compared to controls. No functional brain changes between groups within the default mode network were observed. Discussion Acutely concussed footballers had in common decreased functional connectivity within the right lateralized “cognitive control network” of the brain that is involved in executive functions, and the “salience network” involved in switching between tasks. Dysfunction of these brain regions is a plausible explanation for typical clinical features of concussion.

Concussion Characteristics in High School Football by Helmet Age/Recondition Status, Manufacturer, and Model

Background: Football helmets used by high school athletes in the United States should meet the National Operating Committee on Standards for Athletic Equipment performance standards. Despite differences in interior padding and exterior shells, all football helmets should provide comparable protection against concussions. Yet, debate continues on whether differences in the rates or severity of concussions exist based on helmet age/recondition status, manufacturer, or model. Purpose: To investigate whether high school football concussion characteristics varied by helmet age/recondition status, manufacturer, and model. Study Design: Descriptive epidemiological study. Methods: High school football concussion and helmet data were collected from academic years 2008-2009 through 2012-2013 as part of the National High School Sports-Related Injury Surveillance Study. The certified athletic trainers of participating schools submitted athlete-exposure (AE) and injury information weekly. Results: Participating schools reported 2900 football concussions during 3,528,790 AEs for an overall rate of 8.2 concussions per 10,000 AEs. Concussion rates significantly increased from 2008-2009 through 2012-2013 overall (P = .006) as well as in competition (P = .027) and practice (P = .023). Characteristics of concussed football players (ie, mean number of symptoms, specific concussion symptoms, symptom resolution time, and time until return to play) were similar among players wearing new helmets when compared with reconditioned helmets. Fewer players wearing an old/not reconditioned helmet had concussion symptoms resolve within 1 day compared with players wearing a new helmet. Despite differences in the manufacturers and models of helmets worn by all high school football players compared with players who sustained a concussion, the mean number of concussion symptoms, specific concussion symptoms, symptom resolution time, and time until return to play were similar for concussions sustained by football players wearing the most common helmet manufacturers and models. Conclusion: Overall, for new and reconditioned football helmets, the most common helmet manufacturers and models on the market today appear to provide high school football players with similar protection against concussions. Clinical Relevance: Concussions can have serious acute and long-term effects. An understanding of concussion patterns in high school athletes can drive targeted preventive measures, including improvements to and/or better use of protective equipment, to reduce the incidence and/or severity of sports-related concussions.

Cerebral Blood Flow Alterations in Acute Sport-Related Concussion.

Sport-related concussion (SRC) is a major health problem, affecting millions of athletes each year. While the clinical effects of SRC (e.g., symptoms and functional impairments) typically resolve within several days, increasing evidence suggests persistent neurophysiological abnormalities beyond the point of clinical recovery after injury. This study aimed to evaluate cerebral blood flow (CBF) changes in acute SRC, as measured using advanced arterial spin labeling (ASL) magnetic resonance imaging (MRI). We compared CBF maps assessed in 18 concussed football players (age, 17.8 ± 1.5 years) obtained within 24 h and at 8 days after injury with a control group of 19 matched non-concussed football players. While the control group did not show any changes in CBF between the two time-points, concussed athletes demonstrated a significant decrease in CBF at 8 days relative to within 24 h. Scores on the clinical symptom (Sport Concussion Assessment Tool 3, SCAT3) and cognitive measures (Standardized Assessment of Concussion [SAC]) demonstrated significant impairment (vs. pre-season baseline levels) at 24 h (SCAT, p < 0.0001; SAC, p < 0.01) but returned to baseline levels at 8 days. Two additional computerized neurocognitive tests, the Automated Neuropsychological Assessment Metrics and Immediate Post-Concussion and Cognitive Testing, showed a similar pattern of changes. These data support the hypothesis that physiological changes persist beyond the point of clinical recovery after SRC. Our results also indicate that advanced ASL MRI methods might be useful for detecting and tracking the longitudinal course of underlying neurophysiological recovery from concussion.

Mood symptoms correlate with kynurenine pathway metabolites following sports-related concussion

ObjectiveAn imbalance of neuroactive kynurenine pathway metabolites has been proposed as one mechanism behind the neuropsychiatric sequelae of certain neurological disorders. We hypothesized that concussed football players would have elevated...

Recovery of static stability following a concussion

The purpose of this study was to use centre of pressure (COP) measurements to determine if static balance deficits had recovered when concussed athletes were cleared to return to play. Nine concussed varsity football players were matched with nine teammates who served as controls. Static balance in the anterior–posterior (A/P) and medial–lateral (M/L) directions was assessed during quiet stance with eyes open and eyes closed. Results showed that concussed football players displayed greater A/P COP displacements in the acute phase, which recovered by RTP; however, COP velocity remained elevated compared to controls even at RTP, particularly in the A/P direction. This balance control deficit in the A/P direction may suggest vestibular impairment, likely due to poor sensorimotor integration of the lateral vestibulospinal tract. The observed persistence of balance control deficits in concussed football players at RTP are usually undetected by traditional assessments because the current study used higher-order COP analysis. Future RTP balance measures may want to incorporate higher-order measures of balance.

Functionally-detected cognitive impairment in high school football players without clinically-diagnosed concussion.

Head trauma and concussion in football players have recently received considerable media attention. Postmortem evidence suggests that accrual of damage to the brain may occur with repeated blows to the head, even when the individual blows fail to produce clinical symptoms. There is an urgent need for improved detection and characterization of head trauma to reduce future injury risk and promote development of new therapies. In this study we examined neurological performance and health in the presence of head collision events in high school football players, using longitudinal measures of collision events (the HIT(™) System), neurocognitive testing (ImPACT(™)), and functional magnetic resonance imaging MRI (fMRI). Longitudinal assessment (including baseline) was conducted in 11 young men (ages 15-19 years) participating on the varsity and junior varsity football teams at a single high school. We expected and observed subjects in two previously described categories: (1) no clinically-diagnosed concussion and no changes in neurological behavior, and (2) clinically-diagnosed concussion with changes in neurological behavior. Additionally, we observed players in a previously undiscovered third category, who exhibited no clinically-observed symptoms associated with concussion, but who demonstrated measurable neurocognitive (primarily visual working memory) and neurophysiological (altered activation in the dorsolateral prefrontal cortex [DLPFC]) impairments. This new category was associated with significantly higher numbers of head collision events to the top-front of the head, directly above the DLPFC. The discovery of this new category suggests that more players are suffering neurological injury than are currently being detected using traditional concussion-assessment tools. These individuals are unlikely to undergo clinical evaluation, and thus may continue to participate in football-related activities, even when changes in brain physiology (and potential brain damage) are present, which will increase the risk of future neurological injury.

High School Concussions in the 2008-2009 Academic Year

Background An estimated 136 000 concussions occur per academic year in high schools alone. The effects of repetitive concussions and the potential for catastrophic injury have made concussion an injury of significant concern for young athletes. Purpose The objective of this study was to describe the mechanism of injury, symptoms, and management of sport-related concussions using the High School Reporting Information Online (HS RIO) surveillance system. Study Design Descriptive epidemiology study. Methods All concussions recorded by HS RIO during the 2008-2009 academic year were included. Analyses were performed using SPSS software. Chi-square analysis was performed for all categorical variables. Statistical significance was considered for P < .05. Results A total of 544 concussions were recorded. The most common mechanism (76.2%) was contact with another player, usually a head-to-head collision (52.7%). Headache was experienced in 93.4%; 4.6% lost consciousness. Most (83.4%) had resolution of their symptoms within 1 week. Symptoms lasted longer than 1 month in 1.5%. Computerized neuropsychological testing was used in 25.7% of concussions. When neuropsychological testing was used, athletes were less likely to return to play within 1 week than those for whom it was not used (13.6% vs 32.9%; P < .01). Athletes who had neuropsychological testing appeared less likely to return to play on the same day (0.8% vs 4.2%; P = .056). A greater proportion of injured, nonfootball athletes had computerized neuropsychological testing than injured football players (23% vs 32%; P = .02) Conclusion When computerized neuropsychological testing is used, high school athletes are less likely to be returned to play within 1 week of their injury. Concussed football players are less likely to have computerized neuropsychological testing than those participating in other sports. Loss of consciousness is relatively uncommon among high school athletes who sustain a sport-related concussion. The most common mechanism is contact with another player. Some athletes (1.5%) report symptoms lasting longer than 1 month.

MEASUREMENT OF HEAD IMPACTS IN COLLEGIATE FOOTBALL PLAYERS

It has been speculated that a theoretical injury threshold of 70 to 75 g may exist for concussions in football players. We aimed to investigate acute balance and neurocognitive performance after head impacts exceeding a theoretical injury threshold in the absence of both self-reported symptoms and a concussion diagnosis 24 hours before testing. Forty-three Division I collegiate football players participated in this double-blind, repeated-measures study. Subjects participated in three test sessions (baseline, low impact, and high impact) separated by at least 2 weeks. The Head Impact Telemetry System (Simbex, Lebanon, NH) recorded real-time head impacts sustained during practices and games. The Automated Neuropsychological Assessment Metrics assessed neurocognitive performance. The NeuroCom Sensory Organization Test (NeuroCom International Inc., Clackamas, OR) assessed postural stability. The Graded Symptom Checklist evaluated symptom presence and severity in our participants. After the low-impact test session (<60 g), we observed improvements in the Math Processing (F(1, 26) = 9.797; P = 0.004), Matching to Sample (F(1, 26) = 6.504; P = 0.017), and Sternberg Procedure (F(1, 26) = 5.323; P = 0.030) Automated Neuropsychological Assessment Metrics test modules. Statistically significant differences were also observed after the high-impact test session (>90 g) with improvements in Math Processing (F(1, 22) = 16.629; P < 0.001), Procedural Reaction Time (F(1, 22) = 14.668; P < 0.001), and the total number of symptoms reported (F(1, 22) = 10.267; P = 0.004). Neurocognitive improvements were likely attributed to a learning effect. Our findings suggest that sustaining an impact greater than 90 g does not result in acute observable balance and neurocognitive deficits within 24 hours of sustaining the impact. Although previous studies have suggested a theoretical injury threshold, none have been founded on empirical data collected on the playing field in real-time. Future studies should consider the cumulative effects of impacts of varying magnitudes.

Recent Neuroimaging Techniques in Mild Traumatic Brain Injury

Recent Neuroimaging Techniques in Mild Traumatic Brain Injury

Incidence of cerebral concussions associated with type of mouthguard used in college football.

Controversy exists among sports dentists as to whether or not a 'custom made' mouthguard is more effective in reducing the incidence of cerebral concussion than the boil-and-bite 'non-custom made' mouthguard. While members on each side remain steadfast in their opinion, not a single epidemiological study has been conducted to investigate the effect of type of mouthguard worn on the incidence of cerebral concussion. The aim of this study was to determine if there was a difference between the type of mouthguard worn and the incidence of cerebral concussions among National Collegiate Athletic Association (NCAA) Division I-A football players. During the 15-week 2001 college football season, trainers entered, via an interactive web site, weekly data for each game and practice sessions for the preceding week. Eighty-seven (76%) out of a possible 114 Division I teams participated. A total of 506 297 athletic exposures were recorded; 369 brain concussions were reported. The incidence of cerebral concussions per 1000 exposures was 0.73. Utilizing a risk ratio with a 95% confidence interval, no statistical difference occurred in the incidence of cerebral concussions between football players wearing custom made versus non-custom made mouthguards (0.990,1.750). In this study, there was no advantage of wearing a custom made mouthguard over a boil-and-bite mouthguard to reduce the risk of cerebral concussion in football players.

Does the use of artificial turf contribute to head injuries?

A number of high-profile professional football players have suffered career-ending concussions. The purpose of this article is to test the surfaces used by a professional team to determine their impact-attenuating properties. An accelerometer was dropped from a height of 48 inches onto three different playing fields in the St. Louis area: an indoor artificial turf practice field, a grass outdoor practice field, and the artificial turf field at a domed stadium. The accelerometer was dropped 20 times from a height of 48 inches onto each surface. Statistical analysis of the peak Gs for impacts onto each surface indicate all three are statistically different. The artificial surface of the domed stadium was the hardest surface, with an average peak acceleration of 261 Gs compared with 183 Gs for the indoor artificial turf practice field and 246 Gs for the outdoor grass field. The surface used to play league games has the least impact attenuation of any field tested and may contribute to the high incidence of concussion in football players.

Incidence of concussion in high school football players of Ohio and Pennsylvania.

Football injuries account for more concussions than any other sport in North America. A 1977 survey of high school football players in Minnesota found that 19% of players reported at least one concussion (characterized by loss of awareness) during a season. These results have not been confirmed in subsequent studies. This study sought to estimate the incidence of concussion among high school football players in our region, establish the frequency of the most common symptoms, and determine the duration of subsequent restriction from participation in the sport. The athletic boards of area high schools distributed a three-page survey to 450 high school football players. Of the 450 surveys distributed, 234 (52%) were returned, only 1 of which was excluded because of contradictory information. The incidence of concussion in football players was 47.2% (110/233, P < .001 versus a previously determined rate of 19%). Eighty-one of 233 players (34.9%) had multiple concussions. A total of 376 concussions were reported. The distribution of severity of the 376 reported concussive events was grade I, 87.8%; grade II, 9.9%; and grade III, 2.4%. Only 12 athletes were required to stop play for one or more games. The incidence of high school football players sustaining a concussion is much higher than previously established. The majority of these are mild (grade I) concussions. Further research is needed since multiple low-grade concussions may incur cumulative neuropsychologic impairments.

THE INCIDENCE OF CONCUSSION IN COLEGE FOOTBALL PLAYERS

889 Concussions occur commonly during football participation and can produce a variety of symptoms. Many players, coaches and medical personnel are not fully aware of the actual symptoms that can be associated with a concussion. This has led many to suspect that the incidence of concussions in football players has been underestimated. This study was done to more precisely define the actual incidence of football - related concussions. A survey was conducted among 279 football players from 6 Division III college football teams during the 1997 season. The survey revealed that 230 players (or 82%) reported they had previously suffered symptoms consistent with a grade I concussion during their football career. 93% of these 230 players reported having recurrent symptoms of grade I concussion. 86 players (or 31%) reported previous symptoms of grade II concussion, while 28 players (or 10%) previously had symptoms of grade III concussion. When asked specifically about their last game, 37 players (13%) reported they had grade I symptoms; 4 players (1%) had grade II symptoms; and no players reported grade III concussion symptoms. Of the 41 players (15%) reporting concussion symptoms in their last game, only 6 informed their coach, trainer or team physician of these symptoms, and 4 were removed from the game. Only 85 (30%) of the players surveyed, said they had previously been diagnosed with a concussion related to football. This data confirms that the incidence of concussion among college football players is greatly underestimated. More research is needed to assess the significance of these more mild concussive injuries that are so frequently seen.

Second impact syndrome.

Diffuse cerebral swelling with delayed catastrophic deterioration, a known complication of brain trauma, has been postulated to occur after repeated concussive brain injury in sports--the "second impact syndrome" (SIS). Certain current concussion management guidelines are contingent upon this assumption. We established criteria for definite, probable, and possible SIS and analyzed all published cases. A total of 17 cases were identified in which the reports described the cases as being consistent with SIS. Of these, only five probable cases of SIS were found based on our diagnostic criteria. We also studied the accuracy of recalled episodes of minor concussion in football players by their teammates because the diagnosis of SIS is usually based on such accounts. We found overreporting of recalled episodes of concussion in teammates when compared with self reports and videotape analysis. Based on case reports, the claim that SIS is a risk factor for diffuse cerebral swelling is not established. Prevention strategies for sports-related cerebral swelling are difficult to implement in the absence of established risk factors.