TACKLING CONCUSSIONS IN SPORTS

Biomechanics of the toddler head during low-height falls: an anthropomorphic dummy analysis

OBJECT

Falls are the most common environmental setting for closed head injuries in children between 2 and 4 years of age. The authors previously found that toddlers had fewer skull fractures and scalp/facial soft-tissue injuries, and more frequent altered mental status than infants for the same low-height falls (<or=3 ft).

METHODS

To identify potential age-dependent mechanical load factors that may be responsible for these clinical findings, the authors created an instrumented dummy representing an 18-month-old child using published toddler anthropometry and mechanical properties of the skull and neck, and they measured peak angular acceleration during low-height falls (1, 2, and 3 ft) onto carpet pad and concrete. They compared these results from occiput-first impacts to previously obtained values measured in a 6-week-old infant dummy.

RESULTS

Peak angular acceleration of the toddler dummy head was largest in the sagittal and horizontal directions and increased significantly (around 2-fold) with fall height between 1 and 2 ft. Impacts onto concrete produced larger peak angular accelerations and smaller impact durations than those onto carpet pad. When compared with previously measured infant drops, toddler head accelerations were more than double those of the infant from the same height onto the same surface, likely contributing to the higher incidence of loss of consciousness reported in toddlers. Furthermore, the toddler impact forces were larger than those in the infant, but because of the thicker toddler skull, the risk of skull fracture from low-height falls is likely lower in toddlers compared with infants.

CONCLUSIONS

If similar fracture limits and brain tissue injury thresholds between infants and toddlers are assumed, it is expected that for impact events, the toddler is likely less vulnerable to skull fracture but more vulnerable to neurological impairment compared with the infant.

Potential for head injuries in infants from low-height falls

OBJECT

Falls are the most common accident scenario in young children as well as the most common history provided in child abuse cases. Understanding the biomechanics of falls provides clinicians with objective data to aid in their diagnosis of accidental or inflicted trauma. The objective of this study was to determine impact forces and angular accelerations associated with low-height falls in infants.

METHODS

An instrumented anthropomorphic infant surrogate was created to measure the forces and 3D angular accelerations associated with falls from low heights (0.3-0.9 m) onto a mattress, carpet pad, or concrete.

RESULTS

Although height significantly increased peak angular acceleration (alpha(p)), change in peak-to-peak angular velocity, time duration associated with the change in velocity, and peak impact force (F(p)) for head-first drops onto a carpet pad or concrete, none of these variables were significantly affected by height when dropped onto a mattress. The alpha(p) was not significantly different for drops onto a carpet pad and concrete from 0.6 or 0.9 m due to compression of the carpet pad. Surprisingly, sagittal alpha(p) was equaled or surpassed by axial alpha(p).

CONCLUSIONS

These are the first 3D angular acceleration and impact force data available for head impact in infants from low-height falls. A future study involving a computational model of the infant head will use the loads measured in this study to predict the probability of occipital skull fracture on impact from head-first low-height falls. Together, these studies will provide data that will aid clinicians in the evaluation of accidental and inflicted head injuries, and will contribute to the design of safer environments for children.

Head impact severity measures for evaluating mild traumatic brain injury risk exposure

OBJECTIVE

The aims of this study were to quantify the sensitivity of various biomechanical measures (linear acceleration, rotational acceleration, impact duration, and impact location) of head impact to the clinical diagnosis of concussion in United States football players and to develop a novel measure of head impact severity combining these measures into a single score that better predicts the incidence of concussion.

METHODS

On-field head impact data were collected from 449 football players at 13 organizations (n = 289,916) using in-helmet systems of six single-axis accelerometers. Concussions were diagnosed by medical staff and later associated with impact data. Principal component analysis and a weighting coefficient based on impact location were used to transform correlated head impact measures into a new composite variable, weighted principal component score (wPCS). The predictive power of linear acceleration, rotational acceleration, head injury criterion, and wPCS was quantified using receiver operating characteristic curves. The null hypothesis, that a measure was no more predictive than guessing, was tested (alpha = 0.05). In addition, receiver operating characteristic curves for wPCS and classical measures were directly compared to test the hypothesis that wPCS was more predictive of concussion than were classic measures (alpha = 0.05).

RESULTS

When all of the impacts were considered, every biomechanical measure evaluated was statistically more predictive of concussion than guessing (P < 0.005). However, for the top 1 and 2% of impacts based on linear acceleration, a subset that consisted of 82% of all diagnosed concussions, only wPCS was significantly more predictive of concussion than guessing (P < 0.03); when compared with each other, wPCS was more predictive of concussion than were classical measures for the top 1 and 2% of all of the data (P < 0.04).

CONCLUSION

A weighted combination of several biomechanical inputs, including impact location, is more predictive of concussion than a single biomechanical measure. This study is the first to the authors' knowledge to quantify improvements in the sensitivity of a biomechanical measure to incidence of concussion when impact location is considered.

Measurement of head impacts in collegiate football players: relationship between head impact biomechanics and acute clinical outcome after concussion

OBJECTIVE

To determine the relationship between recorded head accelerations and impact locations and acute clinical outcome of symptomatology, neuropsychological, and postural stability tests after cerebral concussion in Division I collegiate football players.

METHODS

A prospective field study was used in which accelerometers were embedded in the football helmets of 88 collegiate football players. Linear and rotational accelerations of all head impacts sustained over the course of 2004 to 2006 National Collegiate Athletic Association football seasons were collected in real-time. Change scores were calculated on clinical measures from the players' preseason baseline to postinjury (within 48 h) and regressed against the recorded linear and rotational accelerations of the head at the time of the concussion.

RESULTS

Thirteen concussions were recorded ranging in impact magnitudes of 60.51 to 168.71 g. Linear regression showed no significant relationships between impact magnitude (linear or rotational acceleration) or impact location and change scores for symptom severity, postural stability, or neurocognitive function (P > 0.05).

CONCLUSION

Our findings suggest that football players are concussed by impacts to the head that occur at a wide range of magnitudes and that clinical measures of acute symptom severity, postural stability, and neuropsychological function all appear to be largely independent of impact magnitude and location. Because of the varying magnitudes and locations of impacts resulting in concussion as well as other factors such as the frequency of subconcussive impacts and number of previous concussions, it may be difficult to establish a threshold for concussive injury that can be applied to all football players.

Measurement of head impacts in collegiate football players: clinical measures of concussion after high- and low-magnitude impacts

OBJECTIVE

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

Measurement of head impacts in collegiate football players: an investigation of positional and event-type differences

OBJECTIVE

There exists a need to better understand the biomechanical forces associated with head impacts in American football. The purpose of this study was to investigate whether or not differences in head accelerations existed between different player positions and different event types in collegiate football. We also sought to identify whether or not any associations existed between high-magnitude impacts and location of head impacts.

METHODS

We conducted a prospective field study in which accelerometers were embedded in the football helmets of 72 collegiate football players. Linear accelerations of all head impacts sustained over the course of the 2005 and 2006 National Collegiate Athletic Association football seasons were collected. One-way analyses of variance and chi tests of association assessed positional, event type, and location of head impact differences.

RESULTS

Football players consistently sustained head impacts between 21 and 23 g. Positional differences were identified within our sample. Impacts sustained during helmets-only practices were greater than those sustained in games or scrimmages. There was an association between position and high-magnitude impacts, as well as between high-magnitude impacts and location of head impact, with the likelihood of impacts to the top of the head much higher than those to the front, back, left, and right sides.

CONCLUSION

Less than 0.35% of impacts exceeding theoretical injury thresholds resulted in concussion. More injury data are required before any theoretical thresholds for injury can be confirmed. Coaches and sports medicine professionals should recognize that head impacts sustained in helmets-only practices are as severe as games or scrimmages; there seem to be no "light" days for football players.

CONCUSSION IN PROFESSIONAL FOOTBALL

OBJECTIVE

Impacts causing concussion in professional football were simulated in laboratory tests to determine collision mechanics. This study focuses on the biomechanics of concussion in the struck player.

METHODS

Twenty-five helmet impacts were reconstructed using Hybrid III dummies. Head impact velocity, direction, and helmet kinematics-matched game video. Translational and rotational accelerations were measured in both players' heads; 6-axis upper neck responses were measured in all striking and five struck players. Head kinematics and biomechanics were determined for concussed players. Head displacement, rotation, and neck loads were determined because finite element analysis showed maximum strains occurring in the midbrain after the high impact forces. A model was developed of the helmet impact to study the influence of neck strength and other parameters on head responses.

RESULTS

The impact response of the concussed player's head includes peak accelerations of 94 +/- 28 g and 6432 +/- 1813 r/s2, and velocity changes of 7.2 +/- 1.8 m/s and 34.8 +/- 15.2 r/s. Near the end of impact (10 ms), head movement is only 20.2 +/- 6.8 mm and 6.9 +/- 2.5 degrees. After impact, there is rapid head displacement involving a fourfold increase to 87.6 +/- 21.2 mm and 29.9 +/- 9.5 degrees with neck tension and bending at 20 ms. Impacts to the front of the helmet, the source of the majority of National Football League concussions, cause rotation primarily around the z axis (superior-inferior axis) because the force is forward of the neck centerline. This twists the head to the right or left an average of 17.6 +/- 12.7 degrees, causing a moment of 17.7 +/- 3.3 Nm and neck tension of 1704 +/- 432 N at 20 ms. The head injury criterion correlates with concussion risk and is proportional to deltaV(4)/d(1.5) for half-sine acceleration. Stronger necks reduce head acceleration, deltaV, and displacement. Even relatively small reductions in deltaV have a large effect on head injury criterion that may reduce concussion risks because changes in deltaV change head injury criterion through the 4th power.

CONCLUSION

This study addresses head responses causing concussion in National Football League players. Although efforts are underway to reduce impact acceleration through helmet padding, further study is needed of head kinematics after impact and their contribution to concussion, including rapid head displacement, z-axis rotation, and neck tension up to the time of maximum strain in the midbrain. Neck strength influences head deltaV and head injury criterion and may help explain different concussion risks in professional and youth athletes, women, and children.

In vivo study of head impacts in football: a comparison of National Collegiate Athletic Association Division I versus high school impacts

OBJECTIVE

To compare the frequency and magnitude of head impacts between National Collegiate Athletic Association Division I and American high school football players. The long-term goal is to correlate impact forces with injury patterns, leading to improvements in protective headgear.

METHODS

The helmets of football players at the University of Oklahoma (n = 40) and Casady High School (n = 16) were instrumented with the Head Impact Telemetry System (Simbex, Lebanon, NH). Data were collected for practices and games for the 2005 football season and were analyzed by player position and school. Player positions were separated into two groups (skill and line) for analysis. Two case studies of athletes who sustained a concussion are also presented.

RESULTS

A total of 54,154 impacts were recorded at the University of Oklahoma and 8326 at Casady High School. College players sustained high-level impacts greater than 98 g more frequently than high school players. The mean linear accelerations for the top 1, 2, and 5% of all impacts were also higher for college players (P < 0.02). Skill position players received 24.6% of all impacts and sustained an impact greater than 98 g once every 70 impacts. In contrast, linemen sustained the highest number of impacts, but most were relatively low-magnitude (20-30 g). Linemen sustained an impact greater than 98 g once every 125 impacts.

CONCLUSION

Differences in the frequency and magnitude of head acceleration after impact exist between a Division I college team and a high school team. Compared with linemen, skill position players typically sustain the highest-level impacts. Additional data collection and analysis are required to correlate concussion diagnosis with acceleration magnitude and impact location.

CHRONIC TRAUMATIC ENCEPHALOPATHY IN A NATIONAL FOOTBALL LEAGUE PLAYER

OBJECTIVE

We present the second reported case of autopsy-confirmed chronic traumatic encephalopathy in a retired professional football player, with neuropathological features that differ from those of the first reported case. These differing pathological features underscore the need for further empirical elucidation of the pathoetiology and pathological cascades of long-term neurodegenerative sequelae of professional football.

METHODS

A psychological autopsy was performed with the next-of-kin and wife. Medical and hospital records were reviewed. A complete autopsy was accompanied by a comprehensive forensic neuropathological examination. Restriction fragment length polymorphism analysis was performed to determine apolipoprotein-E genotype.

RESULTS

Pertinent premortem history included a 14-year span of play in organized football starting from the age of 18 years. The subject was diagnosed with severe major depressive disorder without psychotic features after retirement, attempted suicide multiple times and finally committed suicide 12 years after retirement by ingestion of ethylene glycol. Autopsy revealed cardiomegaly, mild to moderate coronary artery disease, and evidence of acute ethylene glycol overdose. The brain showed no atrophy, a cavum septi pellucidi was present, and the substantia nigra showed mild pallor. The hippocampus and cerebellum were not atrophic. Amyloid plaques, cerebral amyloid angiopathy, and Lewy bodies were completely absent. Sparse to frequent tau-positive neurofibrillary tangles and neuropil threads were present in all regions of the brain. Tufted and thorn astrocytes, as well as astrocytic plaques, were absent. The apolipoprotein-E genotype was E3/E4.

CONCLUSION

Our first and second cases both had long careers without multiple recorded concussions. Both manifested Major Depressive Disorder after retirement. Amyloid plaques were present in the first case and completely absent in the second case. Both cases exhibited neurofibrillary tangles, neuropil threads, and coronary atherosclerotic disease. Apolipoprotein-E4 genotypes were different. Reasons for the contrasting features in these two cases are not clear. Further studies are needed to identify and define the neuropathological cascades of chronic traumatic encephalopathy in football players, which may form the basis for prophylaxis and therapeutics.

Examining Concussion Rates and Return to Play in High School Football Players Wearing Newer Helmet Technology: A Three-Year Prospective Cohort Study

OBJECTIVE

The purpose of this study was to compare concussion rates and recovery times for athletes wearing newer helmet technology compared to traditional helmet design.

METHODS

This was a three-year, prospective, naturalistic, cohort study. Participants were 2,141 high school athletes from Western Pennsylvania. Approximately half of the sample wore the Revolution helmet manufactured by Riddell, Inc. (n = 1,173) and the remainder of the sample used standard helmets (n = 968). Athletes underwent computerized neurocognitive testing through the use of ImPACT at the beginning of the study. Following a concussion, players were reevaluated at various time intervals until recovery was complete.

RESULTS

In the total sample, the concussion rate in athletes wearing the Revolution was 5.3% and in athletes wearing standard helmets was 7.6% [chi (1, 2, 141) = 4.96, P < 0.027]. The relative risk estimate was 0.69 (95% confidence interval = 0.499- 0.958). Wearing the Revolution helmet was associated with approximately a 31% decreased relative risk and 2.3% decreased absolute risk for sustaining a concussion in this cohort study. The athletes wearing the Revolution did not differ from athletes wearing standard helmets on the mechanism of injury (e.g., head-to-head strike), on-field concussion markers (e.g., amnesia or loss of consciousness), or on-field presentation of symptoms (e.g., headaches, dizziness, or balance problems).

CONCLUSION

Recent sophisticated laboratory research has better elucidated injury biomechanics associated with concussion in professional football players. This data has led to changes in helmet design and new helmet technology, which appears to have beneficial effects in reducing the incidence of cerebral concussion in high school football players.

Concussion in Professional Football: Recovery of NFL and High School Athletes Assessed by Computerized Neuropsychological Testing—Part 12

OBJECTIVE

Acute recovery from concussion (mild traumatic brain injury) is assessed in samples of NFL and high school athletes evaluated within days of injury.

METHODS

All athletes were evaluated within days of injury using a computer-based neuropsychological test and symptom inventory protocol. Test performance was compared to preinjury baseline levels of a similar but not identical group of athletes who had undergone preseason testing. Statistical analyses were completed using Multivariate Analysis of Variance (MANOVA).

RESULTS

NFL athletes demonstrated a rapid neuropsychological recovery. As a group, NFL athletes returned to baseline performance in a week with the majority of athletes having normal performance two days after injury. High school athletes demonstrated a slower recovery than NFL athletes.

CONCLUSION

Computer-based neuropsychological testing was used within the overall medical evaluation and care of NFL athletes. As found in a prior study using more traditional neuropsychological testing, NFL players did not demonstrate decrements in neuropsychological performance beyond one week of injury. High school players demonstrated more prolonged neuropsychological effects of concussion.

Chronic Traumatic Encephalopathy in a National Football League Player

OBJECTIVE

We present the results of the autopsy of a retired professional football player that revealed neuropathological changes consistent with long-term repetitive concussive brain injury. This case draws attention to the need for further studies in the cohort of retired National Football League players to elucidate the neuropathological sequelae of repeated mild traumatic brain injury in professional football.

METHODS

The patient's premortem medical history included symptoms of cognitive impairment, a mood disorder, and parkinsonian symptoms. There was no family history of Alzheimer's disease or any other head trauma outside football. A complete autopsy with a comprehensive neuropathological examination was performed on the retired National Football League player approximately 12 years after retirement. He died suddenly as a result of coronary atherosclerotic disease. Studies included determination of apolipoprotein E genotype.

RESULTS

Autopsy confirmed the presence of coronary atherosclerotic disease with dilated cardiomyopathy. The brain demonstrated no cortical atrophy, cortical contusion, hemorrhage, or infarcts. The substantia nigra revealed mild pallor with mild dropout of pigmented neurons. There was mild neuronal dropout in the frontal, parietal, and temporal neocortex. Chronic traumatic encephalopathy was evident with many diffuse amyloid plaques as well as sparse neurofibrillary tangles and tau-positive neuritic threads in neocortical areas. There were no neurofibrillary tangles or neuropil threads in the hippocampus or entorhinal cortex. Lewy bodies were absent. The apolipoprotein E genotype was E3/E3.

CONCLUSION

This case highlights potential long-term neurodegenerative outcomes in retired professional National Football League players subjected to repeated mild traumatic brain injury. The prevalence and pathoetiological mechanisms of these possible adverse long-term outcomes and their relation to duration of years of playing football have not been sufficiently studied. We recommend comprehensive clinical and forensic approaches to understand and further elucidate this emergent professional sport hazard.

Concussion in Professional Football: Epidemiological Features of Game Injuries and Review of the Literature—Part 3

OBJECTIVE

A 6-year study was performed to determine the circumstances, causes, and outcomes of concussions in the National Football League.

METHODS

Between 1996 and 2001, the epidemiological features of concussions were recorded by National Football League teams with a standardized reporting form. Symptoms were reported and grouped as general symptoms, cranial nerve symptoms, memory or cognitive problems, somatic complaints, and loss of consciousness. The medical actions taken were recorded. In total, 787 game-related cases were reported, with information on the players involved, type of helmet impact, symptoms, medical actions, and days lost. Concussion risks were calculated according to player game positions.

RESULTS

There were 0.41 concussions per National Football League game. The relative risk was highest for quarterbacks (1.62 concussions/100 game-positions), followed by wide receivers (1.23 concussions/100 game-positions), tight ends (0.94 concussion/100 game-positions), and defensive secondaries (0.93 concussion/100 game-positions). The majority of concussions (67.7%) involved impact by another player's helmet. The remainder involved impact by other body regions of the striking player (20.9%) or ground contact (11.4%). The three most common symptoms of mild traumatic brain injury were headaches (55.0%), dizziness (41.8%), and blurred vision (16.3%). The most common signs noted in physical examinations were problems with immediate recall (25.5%), retrograde amnesia (18.0%), and information-processing problems (17.5%). In 58 of the reported cases (9.3%), the players lost consciousness; 19 players (2.4%) were hospitalized. A total of 92% of concussed players returned to practice in less than 7 days, but that value decreased to 69% with unconsciousness.

CONCLUSION

The professional football players most vulnerable to concussions are quarterbacks, wide receivers, and defensive secondaries. Concussions involved 2.74 symptoms/injury, and players were generally removed from the game. More than one-half of the players returned to play within 1 day, and symptoms resolved in a short time in the vast majority of cases.