Animal model for sport-related concussion; ICP and cognitive function.

BACKGROUND: We have recently developed and characterized a rat model of mild traumatic brain injury which simulates the concussive injuries frequently encountered by players in American professional football. OBJECTIVES: To study the effect of multiple impacts to the head on intracranial pressure, cognitive function, and exploratory behavior. MATERIALS AND METHODS: The model was employed to cause concussion. Intracranial pressure, cognitive function, and exploratory behavior were examined following the multiple impacts of a 50 or 100 g projectile at a velocity of 9.3 or 11.2 m/s to the helmet protected head. RESULTS: Intracranial pressure measured at 6 and 10 h, and 1, 2, 3, 5, and 7 days. It was maximally elevated 10 h after impact and returned to the control levels 7 days later. Morris Water Maze assessment, 48 h after impact, revealed impaired cognitive function. Open field testing 2-4 days and 1 and 2 weeks after impacts indicated consistently reduced spontaneous exploratory activity. CONCLUSION: Multiple impacts to the head raise intracranial pressure and impair cognitive function and exploratory activity in this animal model.

Biomechanics of the head for Olympic boxer punches to the face.

OBJECTIVE: The biomechanics of the head for punches to the jaw and the risk of head injury from translational and rotational acceleration were studied. [figure: see text] METHODS: Seven Olympic boxers from five weight classes delivered 18 straight punches to the frangible face of the Hybrid III dummy. Translational and rotational head acceleration, neck responses, and jaw pressure distribution were measured. High speed video recorded each blow and was used to determine punch velocity. Equilibrium was used to determine punch force, energy transfer, and power. RESULTS: Punch force averaged 3427 (standard deviation (SD) 811) N, hand velocity 9.14 (SD 2.06) m/s, and effective punch mass 2.9 (SD 2.0) kg. Punch force was higher for the heavier weight classes, due primarily to a higher effective mass of the punch. Jaw load was 876 (SD 288) N. The peak translational acceleration was 58 (SD 13) g, rotational acceleration was 6343 (SD 1789) rad/s(2), and neck shear was 994 (SD 318) N. CONCLUSIONS: Olympic boxers deliver straight punches with high impact velocity and energy transfer. The severity of the punch increases with weight class.

Head kinematics in mini-sled tests of foam padding: relevance of linear responses from free motion headform (FMH) testing to head angular responses.

The revised Federal Motor Vehicle Safety Standard (FMVSS) No. 201 specifies that the safety performance of vehicle upper interiors is determined from the resultant linear acceleration response of a free motion headform (FMH) impacting the interior at 6.7 m/s. This study addresses whether linear output data from the FMH test can be used to select an upper interior padding that decreases the likelihood of rotationally induced brain injuries. Using an experimental setup consisting of a Hybrid III head-neck structure mounted on a mini-sled platform, sagittal plane linear and angular head accelerations were measured in frontal head impacts into foam samples of various stiffness and density with a constant thickness (51 mm) at low (approximately 5.0 m/s), intermediate (approximately 7.0 m/s), and high (approximately 9.6 m/s) impact speeds. Provided that the foam samples did not bottom out, recorded peak values of angular acceleration and change in angular velocity increased approximately linearly with increasing peak resultant linear acceleration and value of the Head Injury Criterion (HIC36). The results indicate that the padding that produces the lowest possible peak angular acceleration and peak change in angular velocity without causing high peak forces is the one that produces the lowest possible HIC36 without bottoming out in the FMH test.

Influence of the lateral ventricles and irregular skull base on brain kinematics due to sagittal plane head rotation.

Two-dimensional physical models of the human head were used to investigate how the lateral ventricles and irregular skull base influence kinematics in the medial brain during sagittal angular head dynamics. Silicone gel simulated the brain and was separatedfrom the surrounding skull vessel by paraffin that provided a slip interface between the gel and vessel. A humanlike skull base model (HSB) included a surrogate skull base mimicking the irregular geometry of the human. An HSBV model added an elliptical inclusion filled with liquid paraffin simulating the lateral ventricles to the HSB model. A simplified skull base model (SSBV) included ventricle substitute but approximated the anterior and middle cranial fossae by a flat and slightly angled surface. The models were exposed to 7600 rad/s2 peak angular acceleration with 6 ms pulse duration and 5 deg forced rotation. After 90 deg free rotation, the models were decelerated during 30 ms. Rigid body displacement, shear strain and principal strains were determined from high-speed video recorded trajectories of grid markers in the surrogate brains. Peak values of inferior brain surface displacement and strains were up to 10.9X (times) and 3.3X higher in SSBV than in HSBV. Peak strain was up to 2.7X higher in HSB than in HSBV. The results indicate that the irregular skull base protects nerves and vessels passing through the cranial floor by reducing brain displacement and that the intraventricular cerebrospinal fluid relieves strain in regions inferior and superior to the ventricles. The ventricles and irregular skull base are necessary in modeling head impact and understanding brain injury mechanisms.

The effectiveness of active head restraint in preventing whiplash.

BACKGROUND: Whiplash injury claims have increased for two decades and manual head restraints are often incorrectly adjusted. A Self-Aligning Head Restraint (SAHR) was designed to move upward and forward by occupant motion in a rear crash providing earlier neck support, even when the head restraint is positioned low. This study determines its field effectiveness. METHODS: Insurance records were analyzed for consecutive Saab rear crashes in Sweden over 18 months. The Saab 9000/900 had standard head restraints and Saab 9-5/9-3 had SAHR. A questionnaire was mailed to the occupants, insurance and medical records were reviewed, and phone interviews were conducted. RESULTS: SAHR reduced whiplash injury risks by 75 +/- 11% from an 18 +/- 5% incidence in 85 occupants with standard head restraints to 4 +/- 3% in 92 occupants with SAHR. No SAHR seat required repair or replacement after the crashes. CONCLUSION: SAHR is effective in reducing whiplash injury in rear crashes and is a passive public-health approach that works irrespective of manual head-restraint adjustment.

Simulation of acute subdural hematoma and diffuse axonal injury in coronal head impact.

Coronal head impacts were simulated in a physical model, based on the hypothesis that acute subdural hematoma (ASDH) is related to cerebral vertex displacement and diffuse axonal injury (DAI) to local Green-Lagrange strain. The geometry of the 2D model was based on anatomical measurements taken from the MRI scans of 10 adult males. Silicone gel modelled the cerebrum, paraffin the CSF and elastic membranes the trabeculae of the sulci. Pendulum impacts gave peak angular acceleration of 7800 rad s(-2) in models with and without sulci. The motion of the gel and Green-Lagrange strain were calculated from tracked coordinates of Patrick markers. Worst-case bridging vein strains are produced on the contrecoup side and are approximately doubled by adding sulci. Given that axons in the corpus callosum are highly oriented, Green-Lagrange strain was resolved in the fibre direction. It is found to be close to the minimum principal strain, indicating a degree of natural, teleological protection for the axons. The data support the use of delta0peak as a suitable descriptor for the risk of DAI but not for ASDH.

Prevention of commotio cordis in baseball: an evaluation of chest protectors.

BACKGROUND: In a recent study of fatal chest impacts by baseballs, 28% of the children were wearing a chest protector. This study evaluates the effectiveness of chest protectors in reducing the risk of commotio cordis. METHODS: Five commercially available chest protectors were placed on a three-rib structure simulating the chest and impacted at 40, 50, 60, and 70 miles per hour by a standard baseball. Ten repeated tests were conducted on each vest in random order, and on the control (unprotected chest). The viscous response (or viscous criterion [VC]) was used to assess differences in fatality risk. RESULTS: One vest had a statistically lower VC (average, 50.6%, p < 0.05) for all impact speeds. Three averaged 18.7% to 27.7% lower VC, but were significantly different only at higher speeds. One vest had an average 34.2% higher VC, and was significantly higher at 40 to 50 miles per hour (p < 0.05). A method was proposed linking laboratory test results to real-world incidents of ventricular fibrillation. CONCLUSIONS: The majority of commercially available chest protectors fail to provide consistent reductions in commotio cordis risk. Nonetheless, there are benefits from their use in baseball until improved safety equipment is developed and standard tests are established to assess sport equipment effectiveness.

Strain relief from the cerebral ventricles during head impact: experimental studies on natural protection of the brain.

Physical models of the parasagittal human skull/brain have been tested to investigate whether the cerebral ventricles provide natural protection of the brain by relieving strain during head rotation. A sophisticated model included anatomical structures, and a semicircular model consisted of a cylinder divided into two semicircles. Silicone gel simulated the brain and was detached from the vessel by a layer of liquid paraffin simulating the cerebrospinal fluid. Both models were run with and without an elliptical inclusion filled with liquid paraffin simulating a cerebral ventricle. The 2D models were exposed to angular acceleration by a pendulum impact causing 7600 rad/s2 peak rotational acceleration with 6 ms pulse duration. After rotating 100 degrees, the models were decelerated during 30 ms. The trajectory of grid markers was analyzed from high-speed video (1000 frames/s). Rigid-body displacement, shear strain and principal strain were determined from the displacement of three-point sets inferior and superior to the ventricle. For the subventricular (inferior) region in the sophisticated model, approximately 40% lower peak strain values were obtained in the model with ventricle than in the one without. Subcortical displacement was reduced by 12%. Corresponding strain reduction in the subcortical (superior) region was approximately 40% following the acceleration and 25% following the deceleration. Similar but less pronounced effects were found for the semicircular model. The lateral ventricles play an important role as strain relievers and provide natural protection against brain injury.

Biomechanical predictor of commotio cordis in high-speed chest impact.

BACKGROUND: Commotio cordis is a term used to describe cases of blunt thoracic impact causing fatality without gross structural damage of the heart and internal organs. Death is attributed to ventricular fibrillation or cardiac arrhythmia aggravated by traumatic apnea. The biomechanical response related to the risk of commotio cordis has not been determined. METHODS: Reanalysis of previously published experimental data was performed to determine which biomechanical parameter predicts the occurrence of commotio cordis. Logistic regression was used to determine the risk for commotio cordis with the level of chest compression, rate of chest deformation, and viscous criterion. RESULTS: By using only cases without serious tissue injury (Abbreviated Injury Scale score < 4), viscous criterion was the best predictor of commotio cordis or ventricular fibrillation (chi2 = 7.69, p = 0.006). It was also the best predictor of heart rupture (chi2 = 13.19,p = 0.0003) and severe cardiac injury with Abbreviated Injury Scale score > or = 4 (chi2 = 25.03, p = 0.0001). CONCLUSION: Based on this in-depth analysis, the viscous criterion is the relevant biomechanical response to assess the risk of commotio cordis and more severe thoracic injury in high-speed blunt impact.

Car occupant safety in frontal crashes: a parameter study of vehicle mass, impact speed, and inherent vehicle protection.

A new mathematical model was developed to estimate average injury and fatality rates in frontal car-to-car crashes for changes in vehicle fleet mass, impact speed distribution, and inherent vehicle protection. The estimates were calculated from injury fatality risk data, delta-V distribution and collision probability of two vehicles, where delta V-depends on impact speed and mass of the colliding vehicles. The impact speed distribution was assumed to be unaffected by a change in fleet mass distribution. The results showed that safety in frontal crashes would improve 27-35% by a 10% increase in fatality risk parameters, which reflected substantial improvement in inherent vehicle protection. A 40% safety improvement was attained by a 10% impact speed reduction. Consequences of vehicle fleet mass were not as strong, but depended on the average mass ratio of the fleet. A reduction in mass range would be the most beneficial, while a uniform mass reduction of 20% would increase the fatality rate by 5.4%. The model estimates trends in traffic safety and may help to identify priorities in active and passive safety.

Injury probability and risk in frontal crashes: effects of sorting techniques on priorities for offset testing.

Front occupant exposure, MAIS2+ and MAIS3+ injury risk, and maximum-injured body regions were studied in frontal offset impacts. The effect of overlap amount was evaluated in three data subsets from 9,902 accident-involved Volvo cars with at least SEK35,000 (= US$5,000) damage. The subsets were selected by a MAIS2+ or MAIS3+ injured co-occupant or by an equivalent barrier speed (EBS) > 20 mph, and consisted of 661 or 249 cases and 654 cases, respectively. Age and gender effects were minimized. Collisions with 1/3 to 2/3 overlap were most frequent, but the most injurious crash type was influenced by the data sorting technique. The EBS criterion seemed to select crashes of more comparable severity and this dataset may be most appropriate to evaluate overlap effects. With EBS > 20 mph, the highest injury risk occurred in 1/3 overlap crashes, at 62% for MAIS2+ and 44% for MAIS3+ injury. This was two to three times higher than the corresponding risk in full frontal crashes. Head and chest were the most severely injured body regions, but lower-extremity injuries became more important as overlap decreased.

Biomechanical properties of human cadaveric ankle-subtalar joints in quasi-static loading.

The biomechanical properties of human ankle-subtalar joints have been determined in a quasi-static loading condition. The moving center of rotation was determined and approximated by a fixed point. The moment-angle characteristics of the ankle-subtalar joints about the fixed center of rotation have been measured under four basic movements: dorsiflexion, plantarflexion, inversion, and eversion. The method linearly increases rotation of the calcaneus until failure, and measures the moments, forces, and linear and rotational displacements. Failure was identified as the initial drop of moment on plot showing the moment representing gross injury or microfilament damage. In this study, 32 human ankle-subtalar joints have been tested to failure. The center of rotation of the ankle-subtalar joints was determined for a pure dorsiflexion (9 specimens), plantarflexion (7 specimens), inversion (8 specimens), and eversion (8 specimens). Failure in the joints occurred at an average moment of -33.1 +/- 16.5 Nm in dorsiflexion, 40.1 +/- 9.2 Nm in plantarflexion, -34.1 +/- 14.5 Nm in inversion, and 48.1 +/- 12.2 Nm in eversion. The failure angle was also determined in all four motions. Failure was best predicted by an angle of -44.0 +/- 10.9 deg in dorsiflexion, 71.6 +/- 5.7 deg in plantarflexion, -34.3 +/- 7.5 deg in inversion, and 32.4 +/- 7.3 deg in eversion. Injury was identified in every preparation tested in inversion and eversion, while it resulted in five of the nine preparations in dorsiflexion, and in three of the seven in plantarflexion. Injury occurred at -47.0 +/- 5.3 deg and -36.2 +/- 14.8 Nm in dorsiflexion, and at 68.7 +/- 5.9 deg and 36.7 +/- 2.5 Nm in plantarflexion. The results obtained in this study provide basic information of the ankle-subtalar joint kinematics, biomechanics, and injury. The data will be used to form a basis for corridors of the ankle-subtalar joint responses.

Blunt chest impacts: assessing the relative risk of fatal cardiac injury from various baseballs.

OBJECTIVE: To compare various soft-core baseballs for their ability to reduce the risk of fatal chest-impact injury. DESIGN: This study used a three-rib biomechanical surrogate to quantitatively analyze chest impacts from nine soft-core baseballs and one standard baseball, which served as the control. Impacts were achieved with an air cannon system, with the velocity of impact being 40, 50, and 60 mph. MATERIALS AND METHODS: The deflection of the three-rib structure at the sternum was measured and used to calculate the viscous criterion, which correlates with risk of chest-impact injury. MEASUREMENTS AND MAIN RESULTS: Analysis showed that baseballs with lighter mass had a significantly lower viscous criterion (p < 0.05). Those with a similar mass had no change in the viscous criterion, and the heaviest soft-core baseball had a significantly higher viscous criterion at an impact velocity of 60 mph. CONCLUSION: The results of this study indicate that soft-core baseballs may not differ from a standard baseball with regard to the risk of fatal chest-impact injury while playing baseball. Other techniques, such as preventive coaching, need to be implemented when trying to improve baseball safety.

Headrest position during normal driving: implication to neck injury risk in rear crashes.

The gap and relative height of headrest behind drivers were determined for 1915 vehicles approaching an intersection on a two lane road. Vehicle type and headrest adjustment were also evaluated using film of normal driving taken by the Insurance Institute for Highway Safety. Only 10% of drivers had headrests in the most favorable position to prevent neck extension during a rearend crash. 73% of cars had adjustable headrests, but only a quarter were placed in the up position. 83% of the adjustable headrests could have been raised to better protect the driver. Hyge sled tests were run to determine biomechanical responses for the various conditions observed in normal driving. This included three headrest heights and three gaps behind the head. Neck extension from the Hybrid III dummy was normalized to the response for a high, close headrest, and injury risk was assumed to be proportional to neck extension. The current driving situation has a relative injury risk of 3.4 in rearend crashes, compared to 1.0 for the favorable condition. If all adjustable headrests were placed in the up position, the relative risk would be lowered to 2.4, a 28.3% reduction in whiplash injury risk. Public education and vehicle design should address the importance of proper headrest placement for driving safety.

Foot-ankle injuries: influence of crash location, seating position and age.

Foot-ankle injuries have increased in relative importance in recent years. As a basis for future countermeasures, an epidemiology study has been undertaken using Swedish accident data from Folksam Insurance. The database consists of 805 foot-ankle injuries out of 57,949 car occupant injuries reported from 1985 to 1991. The influence of crash location, seating position and occupant age is determined for the frequency, incidence and rate of foot-ankle injury in car crashes. Frontal car crashes produce 76% of the AIS 2-3 foot-ankle injuries with 13% in side impacts and 8% in roll-overs. The rate of AIS 2-3 foot-ankle injury is 24.7 per 1000 occupants injured in all crash locations and is similar irrespective of seating positions. Ankle fractures and sprains both occur at an incidence of 3.7 per 1000 injuries, followed by malleolus fractures at 2.7 and midtarsal fractures at 2.4. The foot-ankle injury incidence and rate are significantly greater (p < 0.01) in near oblique-frontal crashes than for 12 o'clock frontals. For drivers in 11 o'clock and front passengers in 12 o'clock, the incidence is 27.8 per 1000 injuries as compared to 17.5 for drivers and front passengers in 12 o'clock crashes. Occupant age is not as significant as seating position and crash location; however, there are higher incidences for rear occupants > or = 60 years old in oblique frontal crashes. Using the new AAAM Impairment Injury Scale (IIS), 48% of the foot-ankle injuries are rated with residual impairment IIS 1-2. The incidence in near-seated occupants is 1.5 times greater in oblique frontal crashes than in frontals. The incidence for IIS 1-2 impairment in near oblique-frontal crashes is 12.8 per 1000 occupant injuries as compared to 8.3 in frontal crashes.

Restraint effectiveness, availability and use in fatal crashes: implications to injury control.

The effectiveness and benefits of occupant restraint systems are compared by seating position in motor vehicles. While safety belts are 42% effective in preventing fatalities, the addition of the driver side airbag provides a 12% increase in effectiveness. The implications of safety belt use and airbag availability over the next decade are considered for fatal injury prevention. The analysis includes theoretical relationships and forecasts fatality prevention as lap-shoulder belt use increases and airbags phase into the vehicle fleet.

Humanitarian benefits of cadaver research on injury prevention.

This paper discusses the value of human cadaveric subjects in injury biomechanics research. Published data were used to estimate the number of cadavers used in the past 30 years and to show that, as a benefit to society, over 60 lives were saved and countless injuries prevented for each cadaver used in the development and validation of safety improvements. Ethical and religious concerns regarding the use of cadavers are also addressed. Because of the substantial humanitarian value of cadaver research and the lack of suitable specimens, it is proposed that cadaver resources be pooled and that institutions with surplus specimens supply the few cadaver testing laboratories with specimens each year. This approach will enable further development of safety systems and facilitate achieving the national goals for injury control.

Comparison of arm up and down in side impacts with BioSID and different armrests.

BioSID dummy tests were run with the arm down at the side during loading of different armrests in simulated side impact crashes. The Hyge sled tests duplicated previous studies of BioSID with the arm up, SID, and animals. When the BioSID arm is against the side, the arm extends from the shoulder to the bottom of the third rib and has a steel shank covered by foam and vinyl. Loading through the arm transfers force to the three chest ribs and shoulder. In comparison, direct armrest loading of the chest or abdomen primarily involves a single rib and substantial rib deflection, when the armrest crush-force exceeds the strength of the rib. The Viscous response in BioSID showed the greatest difference of all criteria for the arm up or down. The response of the third rib correlated with injury risks determined from animal tests using the different armrest designs in a simulated high position. While injury data are not available for the arm at the side or for the armrest in the low position, the STIFF armrest may cause injury when the arm is not at the side and the armrest loads the liver and spleen. Rib deflection in BioSID showed the protrusion of the STIFF armrest into the abdominal region in both arm positions, because the loading was below the arm even in the down position. However, the arm extends laterally so it involves the upper ribs earlier than in the arm-up condition where more space is available.(ABSTRACT TRUNCATED AT 250 WORDS)

Computing body segment trajectories in the Hybrid III dummy using linear accelerometer data.

An analytical method was developed and tested using several mini-sled and Hyge sled tests to calculate the planar trajectory of a Hybrid III dummy head. Aimed at expediting the Hybrid III test analyses, it may provide an opportunity for cost savings through reduced hardware and manpower on film analyses. Transformation from the moving coordinate to the laboratory coordinate is based on the angular positions integrated from the derived angular accelerations. Gravitational correction of the linear accelerometers was found to be insignificant. The computed head trajectories were compared to the ones obtained from the high speed film images. Accuracy of the calculated head trajectory relies heavily on the accuracy of the computed angular acceleration. Strain-gaged accelerometers are not dependable at all times during an impact and an ill-behaved signal for a very short period may create a significant drift in computed displacement due to double integrations. Accuracy of the currently available accelerometers is not high enough for an angular displacement calculation. A new generation of accelerometers with higher accuracy, or an angular velocity sensor may provide more accurate angular displacement for trajectory analyses. The redundancy of the in-line accelerations helps improve the isolation of erroneous outputs and improve accuracy of the procedure.

Mechanism of injury from air bag deployment loads.

Loadings induced by deploying currently representative air bags were studied with driver surrogates (anesthetized swine) leaning against the system during inflation. Torso injury mechanisms were studied in a physiologic model, supported against a static steering wheel-mounted air bag system. Severe and extensive chest and abdominal injuries to the swine were observed in the tests. Loading caused by air bag deployment can occur in either of two phases. The first phase represents the initial punch out of the bag from the module; the second phase represents the membrane force of the inflating bag. Statistical analysis indicated that punch out induced injury because of the high rate of loading to the surrogate body region in direct contact with the air bag module. Membrane forces induced injury by high compression over a larger area. Punch-out loading might be reduced by allowing the bag to escape from other parts of the container not in contact with the driver during deployment. Loading by the inflating bag might be reduced by using a compliant steering system to support the module. The amount and rate of generated gas had only marginal effect on the cumulative injury. Even an inflator with inadequate gas output to protect a properly seated occupant had sufficient energy to induce severe injuries in a surrogate in contact with the inflating module. Analysis of the field relevance of the results must consider not only the injury potential given that a driver is in direct contact with the air bag module at the time of deployment, but also the expected field frequency of such an event. Analysis of the field relevance of the results must also consider the correlation of the laboratory test environment with real-world exposure.