Concussion in professional football: comparison with boxing head impacts--part 10

A Season of American Football Is Not Associated with Changes in Plasma Tau

American football athletes are routinely exposed to sub-concussive impacts over the course of the season. This study sought to examine the effect of a season of American football on plasma tau, a potential marker of axonal damage. Nineteen National Collegiate Athletic Association (NCAA) football athletes underwent serial blood sampling over the course of the 2014-2015 season at those times in which the number and magnitude of head impacts likely changed. Non-contact sport controls (NCAA men's swim athletes; n = 19) provided a single plasma sample for comparison. No significant differences were observed between control swim athletes and football athletes following a period of non-contact (p = 0.569) or a period of contact (p = 0.076). Football athletes categorized as starters (n = 11) had higher tau concentrations than non-starters (n = 8) following a period of non-contact (p = 0.039) and contact (p = 0.036), but not higher than swimmers (p = 1.000 and p = 1.000, respectively). No difference was noted over the course of the season in football athletes, irrespective of starter status. Despite routine head impacts common to the sport of American football, no changes were observed over the course of the season in football athletes, irrespective of starter status. Further, no difference was observed between football athletes and non-contact control swim athletes following a period of non-contact or contact. These data suggest that plasma tau is not sensitive enough to detect damage associated with repetitive sub-concussive impacts sustained by collegiate-level football athletes.

The Current Status of Research on Chronic Traumatic Encephalopathy

Chronic traumatic encephalopathy (CTE) evolved from the term dementia pugilistica describing the dementia found in many boxers to its current use in describing the dementia and depression sometimes found in athletes subjected to multiple concussions or subconcussive blows to the head. Concurrently, the neuropathology evolved to specify a unique type of tauopathy found in perivascular spaces at the depth of sulci and other features not typically seen in neurodegenerative tauopathies. Four stages of CTE have been proposed, with 4 corresponding clinical syndromes of traumatic encephalopathy syndrome. However, it remains unclear whether this is a syndrome unique to repetitive head trauma, especially in contact sports, because the epidemiology has been difficult to establish. In particular, research to date has had a denominator problem in not establishing the total number of potential cases at risk for developing CTE. The current review examines the evidence to date for these syndromes and contributing or complicating factors affecting the neuropathology, neuroimaging, and clinical presentations associated with them.

Cervical Injury Assessments for Concussion Evaluation: A Review

BACKGROUND

A concussion is a complex pathophysiologic process that is induced by biomechanical forces and affects the brain. Cervical injuries and concussion can share similar mechanisms and nearly identical symptoms or causes. Therefore, symptoms or causes alone may be insufficient to differentiate between patients with a concussion and patients with cervical injuries.

OBJECTIVE

To demonstrate the homogeneous causes and symptoms observed in patients with a concussion and patients with cervical injury and to provide information on clinical tests that can differentiate cervical injury from pathologic conditions of vestibular or central origin.

SUMMARY

Given that concussion and cervical injury share similar causes and symptoms, this information alone may be insufficient to diagnose a concussion. Clinical assessments, such as the cervical joint-reposition error test, smooth-pursuit neck-torsion test, head-neck differentiation test, cervical flexion-rotation test, and physical examination of the cervical spine, can be performed after a head and neck pathomechanical event to identify the presence of cervical injury. Differentiating between a concussion and cervical injury is clinically vital for timely and appropriate evidence-based treatment.

CONCLUSIONS

Specific clinical tests should be used after a head and neck pathomechanical event to differentiate between symptoms due to a concussion and cervical injury. Continued research on the clinical utility of the 5 identified cervicogenic tests is also recommended.

Effect of the Suboccipital Musculature on Symptom Severity and Recovery after Mild Traumatic Brain Injury

BACKGROUND AND PURPOSE

Neck musculature mass has been suggested as a biomechanical contributor to injury severity in mild traumatic brain injury. We sought to determine how the cross-sectional areas of the suboccipital muscles affect symptom severity, neurocognitive performance, and recovery time in patients with mild traumatic brain injury.

MATERIALS AND METHODS

Sixty-four consecutive patients with mild traumatic brain injury underwent MR imaging and serial neurocognitive testing with the Immediate Post-Concussion Assessment and Cognitive Test. Cross-sectional areas of the rectus capitis posterior musculature were retrospectively obtained at C1, and cross-sectional areas of the remaining 7 suboccipital muscles were measured at C2. Cross-sectional area reproducibility was evaluated. Overall and individual muscle cross-sectional areas were correlated with symptom severity, neuropsychological testing, recovery time, and headache.

RESULTS

Sixty-four patients with mild traumatic brain injury had imaging through C1, and 43 had imaging through C2. Reproducibility of cross-sectional area measurements was substantial (correlation coefficients = 0.9517-0.9891). Lower cross-sectional area of the rectus capitis posterior minor was correlated with greater symptom severity (r = 0.596, P < .0001), longer recovery time (r = 0.387, P = .002), poor verbal memory performance (r = 0.285, P = .02), and headache (r = 0.39, P = .001). None of the other cross-sectional areas were associated with symptom severity, recovery time, neurocognitive testing, or headache.

CONCLUSIONS

In mild traumatic brain injury, the rectus capitis posterior minor is the only suboccipital muscle whose cross-sectional area is associated with symptom severity and worse outcome. Given the unique connection of this muscle to the dura, this finding may suggest that pathology of the myodural bridge contributes to symptomatology and prognosis in mild traumatic brain injury.

Resultant linear acceleration of an instrumented head form does not differ between junior and collegiate taekwondo athletes' kicks

OBJECTIVE

The purpose of this study was to compare the effects of various taekwondo kicks and age (school level) in absolute terms and relative body mass on the resultant linear acceleration (RLA) of an instrumented head form.

METHODS

Forty-eight male (middle school: 16; high school: 16; university: 16) taekwondo athletes were recruited for this study. Subjects performed 10 turning, 10 jump spinning hook, and 10 jump back kicks on a Hybrid II head mounted on a height-adjustable frame.

RESULTS

A 2-way (School × Kick) MANOVA was used to determine the differences in RLA between schools (age groups) by type of kick. There was no univariate School main effect for absolute RLA (η ² = 0.06) and RLA relative to body mass (η ² = 0.06). No univariate Kick main effects were found for absolute (η ² = 0.06) and relative RLA (η ² = 0.06).

CONCLUSION

It is of concern that RLA did not significantly differ between school levels, implying that young taekwondo athletes generate similar forces to their adult counterparts, possibly exposing young athletes to an increased risk for head injuries.

The Ability of Men's Lacrosse Helmets to Reduce the Dynamic Impact Response for Different Striking Techniques in Women's Field Lacrosse

BACKGROUND

Women's field lacrosse is described as a noncontact game relying primarily on rules to decrease the risk of head injuries. Despite not allowing head contact, however, concussions continue to be reported in women's field lacrosse.

PURPOSE

To assess the ability of men's lacrosse helmets to decrease linear and angular acceleration for different striking techniques in women's field lacrosse.

STUDY DESIGN

Controlled laboratory study.

METHODS

A helmeted and unhelmeted Hybrid III 50th Percentile headform was attached to a Hybrid III neckform and were subjected to impacts by 8 striking techniques. Eleven athletic females completed 5 slashing techniques, while physical reconstruction equipment was used to simulate falls and shoulder and ball impacts to the head. Three trials were conducted for each condition, and peak resultant linear and angular accelerations of the headform were measured.

RESULTS

Falls produced the highest linear and angular acceleration, followed by ball and high-velocity stick impacts. Low-velocity stick impacts were found to produce the lowest linear and angular accelerations. Men's lacrosse helmets significantly decreased linear and angular accelerations in all conditions, while unhelmeted impacts were associated with high accelerations.

CONCLUSION

If women's field lacrosse is played within the rules, only falls were found to produce high linear and angular acceleration. However, ball and high-velocity stick impacts were found to produce high linear and angular accelerations. These linear and angular accelerations were found to be within the ranges reported for concussion. When the game is not played within the rules, men's lacrosse helmets provide an effective method of reducing linear and angular accelerations. Thus, women's field lacrosse may be able to reduce the occurrence of high linear and angular acceleration impacts by having governing bodies improving rules, implementing the use of helmets, or both.

CLINICAL RELEVANCE

Identifying striking techniques that produce high linear and angular acceleration specific to women's lacrosse and measuring the capacity of a men's lacrosse helmet to reduce linear and angular acceleration.

Chronic Traumatic Encephalopathy and Movement Disorders: Update

Association of repetitive brain trauma with progressive neurological deterioration has been described since the 1920s. Punch drunk syndrome and dementia pugilistica (DP) were introduced first to explain symptoms in boxers, and more recently, chronic traumatic encephalopathy (CTE) has been used to describe a neurodegenerative disease in athletes and military personal with a history of multiple concussions. Although there are many similarities between DP and CTE, a number of key differences are apparent especially when comparing movement impairments. The aim of this review is to compare clinical and pathological aspects of DP and CTE with a focus on disorders of movement.

Serum Neurofilament Light in American Football Athletes over the Course of a Season

Despite being underreported, American football boasts the highest incidence of concussion among all team sports, likely due to exposure to head impacts that vary in number and magnitude over the season. This study compared a biological marker of head trauma in American football athletes with non-contact sport athletes and examined changes over the course of a season. Baseline serum neurofilament light polypeptide (NFL) was measured after 9 weeks of no contact and compared with a non-contact sport. Serum NFL was then measured over the course of the entire season at eight time-points coincident with expected changes in likelihood of increased head impacts. Data were compared between starters (n = 11) and non-starters (n = 9). Compared with non-starters (mean ± standard deviation) (7.30 ± 3.57 pg•mL^-1) and controls (6.75 ± 1.68 pg•mL^-1), serum NFL in starters (8.45 ± 5.90 pg•mL^-1) was higher at baseline (mean difference; ±90% confidence interval) (1.69;  ± 1.96 pg•mL^-1 and 1.15;  ± 1.4 pg•mL^-1, respectively). Over the course of the season, an increase (effect size [ES] = 1.8; p < 0.001) was observed post-camp relative to baseline (1.52 ± 1.18 pg•mL^-1), which remained elevated until conference play, when a second increase was observed (ES = 2.6; p = 0.008) over baseline (4.82 ± 2.64 pg•mL^-1). A lack of change in non-starters resulted in substantial differences between starters and non-starters over the course of the season. These data suggest that a season of collegiate American football is associated with elevations in serum NFL, which is indicative of axonal injury, as a result of head impacts.

Chronic traumatic encephalopathy: contributions from the Boston University Center for the Study of Traumatic Encephalopathy

OBJECTIVE

Chronic Traumatic Encephalopathy (CTE) is a neurodegenerative disease associated with repetitive brain trauma (RBT). Initially described in boxers, CTE has now been found in other contact sport athletes with a history of RBT. In recent years, there has been tremendous media attention regarding CTE, primarily because of the deaths of high profile American football players who were found to have CTE upon neuropathological examination. However, the study of CTE remains in its infancy. This review focuses on research from the Centre for the Study of Traumatic Encephalopathy (CSTE) at Boston University.

METHODS

This study reviews the formation of the CSTE, major CSTE publications and current ongoing research projects at the CSTE.

RESULTS

The neuropathology of CTE has been well-described. Current research focuses on: methods of diagnosing the disease during life (including the development of biomarkers), examination of CTE risk factors (including genetic susceptibility and head impact exposure variables); description of the clinical presentation of CTE; development of research diagnostic criteria for Traumatic Encephalopathy Syndrome; and assessment of mechanism and pathogenesis.

CONCLUSIONS

Current research at the BU CSTE is aimed at increasing understanding of the long-term consequences of repetitive head impacts and attempting to begin to answer several of the unanswered questions regarding CTE.

Clinical features of repetitive traumatic brain injury and chronic traumatic encephalopathy

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease characterized by a distinct pattern of hyperphosphorylated tau (p-tau). Thought to be caused by repetitive concussive and subconcussive injuries, CTE is considered largely preventable. The majority of neuropathologically confirmed cases have occurred in professional contact sport athletes (eg, boxing, football). A recent post-mortem case series has magnified concerns for the public's health following its identification in six high school level athletes. CTE is diagnosed with certainty only following a post-mortem autopsy. Efforts to define the etiology and clinical progression during life are ongoing. The goal of this article is to characterize the clinical concepts associated with short- and long-term effects of repetitive traumatic brain injury, with a special emphasis on new clinical diagnostic criteria for CTE. Utilizing these new diagnostic criteria, two cases of neuropathologically confirmed CTE, one in a professional football player and one in a professional boxer, are reported. Differences in cerebellar pathology in CTE confirmed cases in boxing and football are discussed.

Merging pathology with biomechanics using CHIMERA (Closed-Head Impact Model of Engineered Rotational Acceleration): a novel, surgery-free model of traumatic brain injury

Background

Traumatic brain injury (TBI) is a major health care concern that currently lacks any effective treatment. Despite promising outcomes from many preclinical studies, clinical evaluations have failed to identify effective pharmacological therapies, suggesting that the translational potential of preclinical models may require improvement. Rodents continue to be the most widely used species for preclinical TBI research. As most human TBIs result from impact to an intact skull, closed head injury (CHI) models are highly relevant, however, traditional CHI models suffer from extensive experimental variability that may be due to poor control over biomechanical inputs. Here we describe a novel CHI model called CHIMERA (Closed-Head Impact Model of Engineered Rotational Acceleration) that fully integrates biomechanical, behavioral, and neuropathological analyses. CHIMERA is distinct from existing neurotrauma model systems in that it uses a completely non-surgical procedure to precisely deliver impacts of prescribed dynamic characteristics to a closed skull while enabling kinematic analysis of unconstrained head movement. In this study, we characterized head kinematics as well as functional, neuropathological, and biochemical outcomes up to 14d following repeated TBI (rTBI) in adult C57BL/6 mice using CHIMERA.

Results

Head kinematic analysis showed excellent repeatability over two closed head impacts separated at 24h. Injured mice showed significantly prolonged loss of righting reflex and displayed neurological, motor, and cognitive deficits along with anxiety-like behavior. Repeated TBI led to diffuse axonal injury with extensive microgliosis in white matter from 2-14d post-rTBI. Injured mouse brains also showed significantly increased levels of TNF-α and IL-1β and increased endogenous tau phosphorylation.

Conclusions

Repeated TBI using CHIMERA mimics many of the functional and pathological characteristics of human TBI with a reliable biomechanical response of the head. This makes CHIMERA well suited to investigate the pathophysiology of TBI and for drug development programs.

Electronic supplementary material

The online version of this article (doi:10.1186/1750-1326-9-55) contains supplementary material, which is available to authorized users.

Chronic traumatic encephalopathy: clinical-biomarker correlations and current concepts in pathogenesis

Background

Chronic traumatic encephalopathy (CTE) is a recently revived term used to describe a neurodegenerative process that occurs as a long term complication of repetitive mild traumatic brain injury (TBI). Corsellis provided one of the classic descriptions of CTE in boxers under the name “dementia pugilistica” (DP). Much recent attention has been drawn to the apparent association of CTE with contact sports (football, soccer, hockey) and with frequent battlefield exposure to blast waves generated by improvised explosive devices (IEDs). Recently, a promising serum biomarker has been identified by measurement of serum levels of the neuronal microtubule associated protein tau. New positron emission tomography (PET) ligands (e.g., [¹⁸ F] T807) that identify brain tauopathy have been successfully deployed for the in vitro and in vivo detection of presumptive tauopathy in the brains of subjects with clinically probable CTE.

Methods

Major academic and lay publications on DP/CTE were reviewed beginning with the 1928 paper describing the initial use of the term CTE by Martland.

Results

The major current concepts in the neurological, psychiatric, neuropsychological, neuroimaging, and body fluid biomarker science of DP/CTE have been summarized. Newer achievements, such as serum tau and [¹⁸ F] T807 tauopathy imaging, are also introduced and their significance has been explained.

Conclusion

Recent advances in the science of DP/CTE hold promise for elucidating a long sought accurate determination of the true prevalence of CTE. This information holds potentially important public health implications for estimating the risk of contact sports in inflicting permanent and/or progressive brain damage on children, adolescents, and adults.

Is There Chronic Brain Damage in Retired NFL Players? Neuroradiology, Neuropsychology, and Neurology Examinations of 45 Retired Players

BACKGROUND

Neuropathology and surveys of retired National Football League (NFL) players suggest that chronic brain damage is a frequent result of a career in football. There is limited information on the neurological statuses of living retired players. This study aimed to fill the gap in knowledge by conducting in-depth neurological examinations of 30- to 60-year-old retired NFL players.

HYPOTHESIS

In-depth neurological examinations of 30- to 60-year-old retired players are unlikely to detect objective clinical abnormalities in the majority of subjects.

STUDY DESIGN

A day-long medical examination was conducted on 45 retired NFL players, including state-of-the-art magnetic resonance imaging (MRI; susceptibility weighted imaging [SWI], diffusion tensor imaging [DTI]), comprehensive neuropsychological and neurological examinations, interviews, blood tests, and APOE (apolipoprotein E) genotyping.

LEVEL OF EVIDENCE

Level 3.

METHODS

Participants' histories focused on neurological and depression symptoms, exposure to football, and other factors that could affect brain function. The neurological examination included Mini-Mental State Examination (MMSE) evaluation of cognitive function and a comprehensive search for signs of dysarthria, pyramidal system dysfunction, extrapyramidal system dysfunction, and cerebellar dysfunction. The Beck Depression Inventory (BDI) and Patient Health Questionnaire (PHQ) measured depression. Neuropsychological tests included pen-and-paper and ImPACT evaluation of cognitive function. Anatomical examination SWI and DTI MRI searched for brain injuries. The results were statistically analyzed for associations with markers of exposure to football and related factors, such as body mass index (BMI), ethanol use, and APOE4 status.

RESULTS

The retired players' ages averaged 45.6 ± 8.9 years (range, 30-60 years), and they had 6.8 ± 3.2 years (maximum, 14 years) of NFL play. They reported 6.9 ± 6.2 concussions (maximum, 25) in the NFL. The majority of retired players had normal clinical mental status and central nervous system (CNS) neurological examinations. Four players (9%) had microbleeds in brain parenchyma identified in SWI, and 3 (7%) had a large cavum septum pellucidum with brain atrophy. The number of concussions/dings was associated with abnormal results in SWI and DTI. Neuropsychological testing revealed isolated impairments in 11 players (24%), but none had dementia. Nine players (20%) endorsed symptoms of moderate or severe depression on the BDI and/or met criteria for depression on PHQ; however, none had dementia, dysarthria, parkinsonism, or cerebellar dysfunction. The number of football-related concussions was associated with isolated abnormalities on the clinical neurological examination, suggesting CNS dysfunction. The APOE4 allele was present in 38% of the players, a larger number than would be expected in the general male population (23%-26%).

CONCLUSION

MRI lesions and neuropsychological impairments were found in some players; however, the majority of retired NFL players had no clinical signs of chronic brain damage.

CLINICAL RELEVANCE

These results need to be reconciled with the prevailing view that a career in football frequently results in chronic brain damage.

Current understanding of chronic traumatic encephalopathy

OPINION STATEMENT

Chronic traumatic encephalopathy (CTE) is a unique neurodegenerative disease found in individuals with a history of repetitive head impacts. The neuropathology of CTE is increasingly well defined. Prospective, longitudinal studies with post-mortem neuropathologic validation as well as in vivo diagnostic techniques are needed in order to advance the understanding of CTE clinically. Given the large number of individuals who incur concussions and other forms of brain trauma, this is an important area for scientific and public health inquiry.

Animal models of sports-related head injury: bridging the gap between pre-clinical research and clinical reality

Sports-related head impact and injury has become a very highly contentious public health and medico-legal issue. Near-daily news accounts describe the travails of concussed athletes as they struggle with depression, sleep disorders, mood swings, and cognitive problems. Some of these individuals have developed chronic traumatic encephalopathy, a progressive and debilitating neurodegenerative disorder. Animal models have always been an integral part of the study of traumatic brain injury in humans but, historically, they have concentrated on acute, severe brain injuries. This review will describe a small number of new and emerging animal models of sports-related head injury that have the potential to increase our understanding of how multiple mild head impacts, starting in adolescence, can have serious psychiatric, cognitive and histopathological outcomes much later in life. Sports-related head injury (SRHI) has emerged as a significant public health issue as athletes can develop psychiatric and neurodegenerative disorders later in life. Animal models have always been an integral part of the study of human TBI but few existing methods are valid for studying SRHI. In this review, we propose criteria for effective animal models of SRHI. Movement of the head upon impact is judged to be of primary importance in leading to concussion and persistent CNS dysfunction.

Biomechanics of head injury in olympic taekwondo and boxing

Objective

The purpose was to examine differences between taekwondo kicks and boxing punches in resultant linear head acceleration (RLA), head injury criterion (HIC15), peak head velocity, and peak foot and fist velocities. Data from two existing publications on boxing punches and taekwondo kicks were compared.

Methods

For taekwondo head impacts a Hybrid II Crash Dummy (Hybrid II) head was instrumented with a tri-axial accelerometer mounted inside the Hybrid II head. The Hybrid II was fixed to a height-adjustable frame and fitted with a protective taekwondo helmet. For boxing testing, a Hybrid III Crash Dummy head was instrumented with an array of tri-axial accelerometers mounted at the head centre of gravity.

Results

Differences in RLA between the roundhouse kick (130.11±51.67 g) and hook punch (71.23±32.19 g, d = 1.39) and in HIC15 (clench axe kick: 162.63±104.10; uppercut: 24.10±12.54, d = 2.29) were observed.

Conclusions

Taekwondo kicks demonstrated significantly larger magnitudes than boxing punches for both RLA and HIC.

Clinical presentation of chronic traumatic encephalopathy

OBJECTIVE

The goal of this study was to examine the clinical presentation of chronic traumatic encephalopathy (CTE) in neuropathologically confirmed cases.

METHODS

Thirty-six adult male subjects were selected from all cases of neuropathologically confirmed CTE at the Boston University Center for the Study of Traumatic Encephalopathy brain bank. Subjects were all athletes, had no comorbid neurodegenerative or motor neuron disease, and had next-of-kin informants to provide retrospective reports of the subjects' histories and clinical presentations. These interviews were conducted blind to the subjects' neuropathologic findings.

RESULTS

A triad of cognitive, behavioral, and mood impairments was common overall, with cognitive deficits reported for almost all subjects. Three subjects were asymptomatic at the time of death. Consistent with earlier case reports of boxers, 2 relatively distinct clinical presentations emerged, with one group whose initial features developed at a younger age and involved behavioral and/or mood disturbance (n = 22), and another group whose initial presentation developed at an older age and involved cognitive impairment (n = 11).

CONCLUSIONS

This suggests there are 2 major clinical presentations of CTE, one a behavior/mood variant and the other a cognitive variant.

A systematic review of diffusion tensor imaging findings in sports-related concussion

Sports-related concussion (SRC) is typically associated with functional, as opposed to structural, injury. The results of traditional structural neuroimaging techniques used to assess SRC tend to be normal in many athletes, and are only clinically helpful in ruling out a more serious injury. Diffusion tensor imaging (DTI) has increasingly been touted as a method offering greater clinical potential in mild traumatic brain injury (mTBI). Despite this, the utility of DTI as a clinical tool for diagnosing and managing SRC has received considerably less attention than it has in the general TBI research literature. The aim of this article is to conduct a systematic review of DTI in SRC, and to provide a focus and overview of research findings using this MRI technique in SRC. A systematic review of articles published in the English language, up to February 2012, was retrieved via PsycINFO(®), MEDLINE(®), EMBASE, SPORTDiscus(™), Scopus, Web of Science, and Informit; using the key search terms: diffusion tensor imaging, diffusion magnetic resonance imaging, diffusion weighted MRI, diffusion MRI, fractional anisotropy, tractography, apparent diffusion coefficient, magnetic resonance imaging, mild traumatic brain injury, mTBI, traumatic brain injury, concussion, sport, athletic and athlete. Observational, cohort, correlation, cross-sectional and longitudinal studies were all included in the current review. Results of the review found eight articles that met inclusion criteria, which included data on 214 athletes and 96 controls. Seven of eight studies reported some type of DTI abnormality, although the neuroanatomical sites involved varied. Although considerable methodological variations exist across studies, the current review suggests that DTI may possess adequate diagnostic sensitivity to detect SRC in affected athletes. Further longitudinal studies are required to demonstrate its discriminate validity and prognostic capacity within this field.

Olympic boxing is associated with elevated levels of the neuronal protein tau in plasma

OBJECTIVES

The aim of this study was to investigate if olympic (amateur) boxing is associated with elevation of brain injury biomarkers in peripheral blood compared to controls.

MATERIALS AND METHODS

Thirty olympic boxers competing in at least 47 bouts were compared to 25 controls. Blood was collected from the controls at one occasion and from the boxers within 1-6 days after a bout and after a rest period of at least 14 days. Tau concentration in plasma was determined using a novel single molecule ELISA assay and S-100B, glial fibrillary acidic protein, brain-derived neurotrophic factor and amyloid β 1-42 were determined using standard immunoassays.

RESULTS

None of the boxers had been knocked-out during the bout. Plasma-tau was significantly increased in the boxers after a bout compared to controls (mean ± SD, 2.46 ± 5.10 vs. 0.79 ± 0.961 ng L(-1), p = 0.038). The other brain injury markers did not differ between the groups. Plasma-tau decreased significantly in the boxers after a resting period compared to after a bout (p = 0.030).

CONCLUSIONS

Olympic boxing is associated with elevation of tau in plasma. The repetitive minimal head injury in boxing may lead to axonal injuries that can be diagnosed with a blood test.

The neuropathology and neurobiology of traumatic brain injury

The acute and long-term consequences of traumatic brain injury (TBI) have received increased attention in recent years. In this Review, we discuss the neuropathology and neural mechanisms associated with TBI, drawing on findings from sports-induced TBI in athletes, in whom acute TBI damages axons and elicits both regenerative and degenerative tissue responses in the brain and in whom repeated concussions may initiate a long-term neurodegenerative process called dementia pugilistica or chronic traumatic encephalopathy (CTE). We also consider how the neuropathology and neurobiology of CTE in many ways resembles other neurodegenerative illnesses such as Alzheimer's disease, particularly with respect to mismetabolism and aggregation of tau, β-amyloid, and TDP-43. Finally, we explore how translational research in animal models of acceleration/deceleration types of injury relevant for concussion together with clinical studies employing imaging and biochemical markers may further elucidate the neurobiology of TBI and CTE.

Hybrid III anthropomorphic test device (ATD) response to head impacts and potential implications for athletic headgear testing

The Hybrid III 50th percentile male anthropomorphic test device (ATD) is the most widely used human impact testing surrogate and has historically been used in automotive or military testing. More recently, this ATD is finding use in applications evaluating athletic helmet protectivity, quantifying head impact dosage and estimating injury risk. But ATD head-neck response has not been quantified in omnidirectional athletic-type head impacts absent axial preload. It is probable that headgear injury reduction that can be quantified in a laboratory, including in American football, boxing, hockey, lacrosse and soccer, is related to a number of interrelated kinetic and kinematic factors, such as head center of gravity linear acceleration, head angular acceleration, head angular velocity, occipito-cervical mechanics and neck stiffness. Therefore, we characterized ATD head-neck dynamic response to direct head impacts in a series of front, oblique front and lateral head impacts. Key findings were: (1) impacts producing highest ATD resultant center of gravity linear acceleration resulted in the lowest resultant occipito-cervical spine bending moment/force. (2) Resultant ATD head angular velocity and angular acceleration did not appear coupled to impact direction at lower impact energy levels; these parameters were coupled at higher energy levels. (3) The ATD had progressively increasing occipito-cervical stiffness in extension, torsion and lateral bending, respectively. Because the ATD neck influenced head and neck impact dosage parameters, testing agencies, manufacturers and researchers should consider using the Hybrid III head form attached to a neck as a means to quantify head and neck injury risks as opposed to systems that do not utilize a neck. This heightened understanding of Hybrid III ATD head-neck response, and consideration of order of stiffest axes in the lateral, oblique and extension directions, respectively, should aid in the development of head and neck injury impact testing standards.

Effects of Olympic-style taekwondo kicks on an instrumented head-form and resultant injury measures

OBJECTIVE

The objective of this study was to assess the effect of taekwondo kicks and peak foot velocity (FVEL) on resultant head linear acceleration (RLA), head injury criterion (HIC15) and head velocity (HVEL).

METHODS

Each subject (n=12) randomly performed five repetitions of the turning kick (TK), clench axe kick (CA), front leg axe kick, jump back kick (JB) and jump spinning hook kick (JH) at the average standing head height for competitors in their weight division. A Hybrid II Crash Test Dummy head was fitted with a protective taekwondo helmet and instrumented with a triaxial accelerometer and fixed to a height-adjustable frame. Resultant head linear acceleration, HVEL, FVEL data were captured and processed using Qualysis Track Manager.

RESULTS

The TK (130.11 ± 51.67 g) produced a higher RLA than the CA (54.95 ± 20.08 g, p<0.001, d=1.84) and a higher HIC15 than the JH (672.74 ± 540.89 vs 300.19 ± 144.35, p<0.001, ES=0.97). There was no difference in HVEL of the TK (4.73 ± 1.67 m/s) and that of the JB (4.43 ± 0.78 m/s; p=0.977, ES<0.01).

CONCLUSIONS

The TK is of concern because it is the most common technique and cause of concussion in taekwondo. Future studies should aim to understand rotational accelerations of the head.

Boxing and mixed martial arts: preliminary traumatic neuromechanical injury risk analyses from laboratory impact dosage data

Object

In spite of ample literature pointing to rotational and combined impact dosage being key contributors to head and neck injury, boxing and mixed martial arts (MMA) padding is still designed to primarily reduce cranium linear acceleration. The objects of this study were to quantify preliminary linear and rotational head impact dosage for selected boxing and MMA padding in response to hook punches; compute theoretical skull, brain, and neck injury risk metrics; and statistically compare the protective effect of various glove and head padding conditions.

Methods

An instrumented Hybrid III 50th percentile anthropomorphic test device (ATD) was struck in 54 pendulum impacts replicating hook punches at low (27–29 J) and high (54–58 J) energy. Five padding combinations were examined: unpadded (control), MMA glove–unpadded head, boxing glove–unpadded head, unpadded pendulum–boxing headgear, and boxing glove–boxing headgear. A total of 17 injury risk parameters were measured or calculated.

Results

All padding conditions reduced linear impact dosage. Other parameters significantly decreased, significantly increased, or were unaffected depending on padding condition. Of real-world conditions (MMA glove–bare head, boxing glove–bare head, and boxing glove–headgear), the boxing glove–headgear condition showed the most meaningful reduction in most of the parameters. In equivalent impacts, the MMA glove–bare head condition induced higher rotational dosage than the boxing glove–bare head condition. Finite element analysis indicated a risk of brain strain injury in spite of significant reduction of linear impact dosage.

Conclusions

In the replicated hook punch impacts, all padding conditions reduced linear but not rotational impact dosage. Head and neck dosage theoretically accumulates fastest in MMA and boxing bouts without use of protective headgear. The boxing glove–headgear condition provided the best overall reduction in impact dosage. More work is needed to develop improved protective padding to minimize linear and rotational impact dosage and develop next-generation standards for head and neck injury risk.

Coupled left-shift of Nav channels: modeling the Na⁺-loading and dysfunctional excitability of damaged axons

Injury to neural tissue renders voltage-gated Na⁺ (Nav) channels leaky. Even mild axonal trauma initiates Na⁺-loading, leading to secondary Ca²⁺-loading and white matter degeneration. The nodal isoform is Nav1.6 and for Nav1.6-expressing HEK-cells, traumatic whole cell stretch causes an immediate tetrodotoxin-sensitive Na⁺-leak. In stretch-damaged oocyte patches, Nav1.6 current undergoes damage-intensity dependent hyperpolarizing- (left-) shifts, but whether left-shift underlies injured-axon Nav-leak is uncertain. Nav1.6 inactivation (availability) is kinetically limited by (coupled to) Nav activation, yielding coupled left-shift (CLS) of the two processes: CLS should move the steady-state Nav1.6 "window conductance" closer to typical firing thresholds. Here we simulated excitability and ion homeostasis in free-running nodes of Ranvier to assess if hallmark injured-axon behaviors--Na⁺-loading, ectopic excitation, propagation block--would occur with Nav-CLS. Intact/traumatized axolemma ratios were varied, and for some simulations Na/K pumps were included, with varied in/outside volumes. We simulated saltatory propagation with one mid-axon node variously traumatized. While dissipating the [Na⁺] gradient and hyperactivating the Na/K pump, Nav-CLS generated neuropathic pain-like ectopic bursts. Depending on CLS magnitude, fraction of Nav channels affected, and pump intensity, tonic or burst firing or nodal inexcitability occurred, with [Na⁺] and [K⁺] fluctuating. Severe CLS-induced inexcitability did not preclude Na⁺-loading; in fact, the steady-state Na⁺-leaks elicited large pump currents. At a mid-axon node, mild CLS perturbed normal anterograde propagation, and severe CLS blocked saltatory propagation. These results suggest that in damaged excitable cells, Nav-CLS could initiate cellular deterioration with attendant hyper- or hypo-excitability. Healthy-cell versions of Nav-CLS, however, could contribute to physiological rhythmic firing.

CSF-biomarkers in Olympic boxing: diagnosis and effects of repetitive head trauma

Background

Sports-related head trauma is common but still there is no established laboratory test used in the diagnostics of minimal or mild traumatic brain injuries. Further the effects of recurrent head trauma on brain injury markers are unknown. The purpose of this study was to investigate the relationship between Olympic (amateur) boxing and cerebrospinal fluid (CSF) brain injury biomarkers.

Methods

The study was designed as a prospective cohort study. Thirty Olympic boxers with a minimum of 45 bouts and 25 non-boxing matched controls were included in the study. CSF samples were collected by lumbar puncture 1–6 days after a bout and after a rest period for at least 14 days. The controls were tested once. Biomarkers for acute and chronic brain injury were analysed.

Results

NFL (mean ± SD, 532±553 vs 135±51 ng/L p = 0.001), GFAP (496±238 vs 247±147 ng/L p<0.001), T-tau (58±26 vs 49±21 ng/L p<0.025) and S-100B (0.76±0.29 vs 0.60±0.23 ng/L p = 0.03) concentrations were significantly increased after boxing compared to controls. NFL (402±434 ng/L p = 0.004) and GFAP (369±113 ng/L p = 0.001) concentrations remained elevated after the rest period.

Conclusion

Increased CSF levels of T-tau, NFL, GFAP, and S-100B in >80% of the boxers demonstrate that both the acute and the cumulative effect of head trauma in Olympic boxing may induce CSF biomarker changes that suggest minor central nervous injuries. The lack of normalization of NFL and GFAP after the rest period in a subgroup of boxers may indicate ongoing degeneration. The recurrent head trauma in boxing may be associated with increased risk of chronic traumatic brain injury.

A novel animal model of closed-head concussive-induced mild traumatic brain injury: development, implementation, and characterization

Closed-head concussive injury is one of the most common causes of traumatic brain injury (TBI). While single concussions result in short-term neurologic dysfunction, multiple concussions can result in cumulative damage and increased risk for neurodegenerative disease. Despite the prevalence of concussion, knowledge about what occurs in the brain following this injury is limited, in part due to the limited number of appropriate animal research models. To study clinically relevant concussion we recently developed a simple, non-invasive rodent model of closed-head projectile concussive impact (PCI) TBI. For this purpose, anesthetized rats were placed on a platform positioned above a torque-sealed microcentrifuge tube packed with fixed amounts of dry ice. Upon heating, rapid sublimation of the dry ice produced a build-up of compressed CO(2) that triggered an eruptive force causing the cap to launch as an intact projectile, resulting in a targeted PCI head injury. A stainless steel helmet was implemented to protect the head from bruising, yet allowing the brain to sustain a mild PCI event. Depending on the injury location and the application of the helmet, PCI-induced injuries ranged from severe (i.e., head injury with subdural hematomas, intracranial hemorrhage, and brain tissue damage), to mild (no head injury, intracranial hemorrhage, or gross morphological pathology). Although no gross pathology was evident in mild PCI-induced injury, the following protein changes and behavioral abnormalities were detected between 1 and 24 h after PCI injury: (1) upregulation of glial fibrillary acidic protein (GFAP) in hippocampal regions; (2) upregulation of ubiquitin carboxyl-terminal hydrolase L1 (UCHL-1) in cortical tissue; and (3) significant sensorimotor abnormalities. Overall, these results indicated that this PCI model was capable of replicating salient pathologies of a clinical concussion, and could generate reproducible and quantifiable outcome measures.

Injury predictors for traumatic axonal injury in a rodent head impact acceleration model

A modified Marmarou impact acceleration injury model was developed to study the kinematics of the rat head to quantify traumatic axonal injury (TAI) in the corpus callosum (CC) and brainstem pyramidal tract (Py), to determine injury predictors and to establish injury thresholds for severe TAI. Thirty-one anesthetized male Sprague-Dawley rats (392±13 grams) were impacted using a modified impact acceleration injury device from 2.25 m and 1.25 m heights. Beta-amyloid precursor protein (β-APP) immunocytochemistry was used to assess and quantify axonal changes in CC and Py. Over 600 injury maps in CC and Py were constructed in the 31 impacted rats. TAI distribution along the rostro-caudal direction in CC and Py was determined. Linear and angular responses of the rat head were monitored and measured in vivo with an attached accelerometer and angular rate sensor, and were correlated to TAI data. Logistic regression analysis suggested that the occurrence of severe TAI in CC was best predicted by average linear acceleration, followed by power and time to surface righting. The combination of average linear acceleration and time to surface righting showed an improved predictive result. In Py, severe TAI was best predicted by time to surface righting, followed by peak and average angular velocity. When both CC and Py were combined, power was the best predictor, and the combined average linear acceleration and average angular velocity was also found to have good injury predictive ability. Receiver operator characteristic curves were used to assess the predictive power of individual and paired injury predictors. TAI tolerance curves were also proposed in this study.

A mouse model of human repetitive mild traumatic brain injury

A novel method for the study of repetitive mild traumatic brain injury (rmTBI) that models the most common form of head injury in humans is presented. Existing animal models of TBI impart focal, severe damage unlike that seen in repeated and mild concussive injuries, and few are configured for repetitive application. Our model is a modification of the Marmarou weight drop method and allows repeated head impacts to lightly anesthetized mice. A key facet of this method is the delivery of an impact to the cranium of an unrestrained subject allowing rapid acceleration of the free-moving head and torso, an essential characteristic known to be important for concussive injury in humans, and a factor that is missing from existing animal models of TBI. Our method does not require scalp incision, emplacement of protective skull helmets or surgery and the procedure can be completed in 1-2 min. Mice spontaneously recover the righting reflex and show no evidence of seizures, paralysis or impaired behavior. Skull fractures and intracranial bleeding are very rare. Minor deficits in motor coordination and locomotor hyperactivity recover over time. Histological analyses reveal mild astrocytic reactivity (increased expression of GFAP) and increased phospho-tau but a lack of blood-brain-barrier disruption, edema and microglial activation. This new animal model is simple and cost-effective and will facilitate characterization of the neurobiological and behavioral consequences of rmTBI. It is also ideal for high throughput screening of potential new therapies for mild concussive injuries as experienced by athletes and military personnel.

Boxing injuries presenting to U.S. emergency departments, 1990-2008

BACKGROUND

Boxing injuries can have serious consequences.

PURPOSE

To examine the epidemiology of boxing injuries in the U.S. with attention to head injuries and children.

METHODS

National estimates of boxing injuries were calculated using data from the National Electronic Injury Surveillance System. Injury rates per 1000 participants for the year 2003 were calculated using boxing participation data. Data analysis was conducted in 2009-2010.

RESULTS

An estimated 165,602 individuals (95% CI=134891, 196313) sustained boxing injuries that resulted in a visit to a U.S. hospital emergency department from 1990 through 2008. An average of 8716 (95% CI=7078, 10354) injuries occurred annually, and there was a statistically significant increase in the annual number of injuries during the 19-year study period (slope=610, p<0.001). The rate of injury was 12.7 per 1000 participants. Those injured were predominately male (90.9%). The most common diagnosis was fracture (27.5%), and the most common body regions injured were the hand (33.0%) and head and neck (22.5%). Punching bag-related injuries accounted for 36.8% of boxing injuries. The percentage of injuries that were concussions/closed head injuries in the group aged 12-17 years (8.9%) was similar to that in the group aged 18-24 years (8.1%) and the group aged 25-34 years (8.5%).

CONCLUSIONS

These findings, based on a nationally representative sample, indicate that injuries related to boxing are increasing in number. Increased efforts are needed to prevent boxing injuries.

Chronic traumatic encephalopathy: a potential late effect of sport-related concussive and subconcussive head trauma

Chronic traumatic encephalopathy (CTE) is a form of neurodegeneration believed to result from repeated head injuries. Originally termed dementia pugilistica because of its association with boxing, the neuropathology of CTE was first described by Corsellis in 1973 in a case series of 15 retired boxers. CTE has recently been found to occur after other causes of repeated head trauma, suggesting that any repeated blows to the head, such as those that occur in American football, hockey, soccer, professional wrestling, and physical abuse, can also lead to neurodegenerative changes. These changes often include cerebral atrophy, cavum septi pellucidi with fenestrations, shrinkage of the mammillary bodies, dense tau immunoreactive inclusions (neurofibrillary tangles, glial tangles, and neuropil neurites), and, in some cases, a TDP-43 proteinopathy. In association with these pathologic changes, disordered memory and executive functioning, behavioral and personality disturbances (eg, apathy, depression, irritability, impulsiveness, suicidality), parkinsonism, and, occasionally, motor neuron disease are seen in affected individuals. No formal clinical or pathologic diagnostic criteria for CTE currently exist, but the distinctive neuropathologic profile of the disorder lends promise for future research into its prevention, diagnosis, and treatment.

Prevalence and risk factors of Parkinson's disease in retired Thai traditional boxers

Boxing is often believed to be a frequent cause for parkinsonism caused by chronic repetitive head injury, with Muhammad Ali frequently cited as an example. The purpose of this study is to determine the prevalence of Parkinson's disease (PD) in retired Thai traditional boxers. Two standardized screening questionnaires were sent to all registered Thai traditional boxers. Subjects who screened positive for parkinsonism were invited for clinical examinations by two independent neurologists. Among 704 boxers (70%) who completed the questionnaires, 8 boxers (1.14%) had parkinsonism: 5 with PD, 1 with progressive supranuclear palsy and 2 with vascular parkinsonism. Boxers with PD were found to have an older mean age than those without PD (P = 0.003). The analysis of probable risk factors disclosed an association between the number of professional bouts (>100 times) and PD (P = 0.01). The crude prevalence of PD in Thai boxers was 0.71% (95% CI: 0.09-1.33), with a significant increase with age. The prevalence rate of PD in those aged 50 and above was 0.17% (95% CI: 0.15-0.20), age-adjusted to the USA 1970 census, which is comparable to that of the general populations. The analysis determined that the number of professional bouts is a risk factor among these boxers, supporting the notion that repetitive head trauma may pose an additional risk to certain individuals who are already susceptible to PD.

Brain injury in boxing

Clinical decision making for injured boxers follows the same therapeutic principles as the treatment plan for other injured athletes. Just as surgical techniques have improved, so has the scientific basis for implementing therapeutic exercises progressed to return the athletes to their former level of competition.

Boxing-related head injuries

Fatalities in boxing are most often due to traumatic brain injury that occurs in the ring. In the past 30 years, significant improvements in ringside and medical equipment, safety, and regulations have resulted in a dramatic reduction in the fatality rate. Nonetheless, the rate of boxing-related head injuries, particularly concussions, remains unknown, due in large part to its variability in clinical presentation. Furthermore, the significance of repeat concussions sustained when boxing is just now being understood. In this article, we identify the clinical manifestations, pathophysiology, and management of boxing-related head injuries, and discuss preventive strategies to reduce head injuries sustained by boxers.