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.

Interaction of contact velocity and cord compression in determining the severity of spinal cord injury.

Rate, depth, and duration of compression are the principal determinants of experimental spinal cord injury (SCI) severity. Since existing models do not allow independent control of these variables, the interaction of these factors has not been fully elucidated. The purpose of this study was to define the interactive relation of velocity (V) and compression (C) in SCI using a constrained stroke pneumatic impactor that allowed independent control of these variables. Computer simulation of previous weight-drop experiments using a lumped-mass model were compared with this series of impacts. After rigid stabilization of adjacent cervical vertebrae, the spinal cord (SC) in 48 male ferrets was compressed through the C6-C7 interspace. Maximum compression was 25%, 35%, 50%, or 65% of the SC diameter. Impacts were delivered at five velocities from 1.5 m/s to 6 m/s. Severity of injury was determined by pre and postinjury measurement of somatosensory evoked potentials (SEP) and blinded quantitation of histopathologic findings. Twenty-three of 48 animals (48%) had measurable SEP at 4 hs. No animal recovered SEP at 65% compression at any velocity, or at a velocity of 6 m/s for any level of compression. Recovery of SEP and histologic severity score correlated better with velocity-compression product, or maximum viscous response (VC) than with either V or C alone. The mean histologic severity score was higher in animals exhibiting no recovery of SEP. Modeling the viscoelastic elements of the SC using existing force-time and force-deflection data suggests that estimates of compression from current weight-drop techniques may be inaccurate. At low contact velocity, functional and anatomic damage is best predicted by maximum SC compression. However, as velocity increases, SCI severity becomes a function of the viscous response (VC), demonstrating the rate sensitivity of spinal cord tissue. Tolerance to SC compression decreases as the rate of deformation increases. This helps to explain apparent discrepancies between compression and severity of experimental SCI.

A viscous tolerance criterion for soft tissue injury assessment.

Experiments in our laboratory have documented that high-speed impact can cause severe injury to internal organs before either of the currently accepted chest injury criteria, which are based on spinal acceleration or chest compression, approach their tolerance limit. Those studies demonstrate an interdependence between the velocity of deformation and compression of the body on injury risk. A tolerable level of chest compression at a low velocity can prove to be fatal at higher velocities of deformation. The observation of a rate-sensitive tolerable compression led to the introduction of the Viscous criterion, VCmax, which accounts for the importance of both parameters. VCmax is the maximum of the product of velocity of deformation (V) and compression (C), and is derivable from the chest deflection response. This paper presents the empirical evidence and theoretical basis supporting the Viscous criterion, and shows it to be an indicator of the energy dissipated by soft tissue deformation. The Viscous criterion accurately predicts the risk of vital organ and soft tissue injury when other criteria fail.

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.

Injury biomechanics research: an essential element in the prevention of trauma.

The central aspects of injury biomechanics research are defined and research approaches described. These aspects include the identification and definition of impact injury mechanisms, the quantification of biomechanical response to impact, the determination of impact tolerance levels, and the development and use of injury assessment devices and techniques for evaluating injury prevention systems. The current status of knowledge and technology is then reviewed for the head, cervical spine, thorax, abdomen, and lower extremity. Important gaps are identified, and research priorities emphasizing functional impairment are proposed.

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.

A blueprint for injury control in the United States.

In a 1988 appraisal of the status and progress of the injury control program at the Centers for Disease Control (CDC), a National Academy of Sciences' Review Committee applauded the rapid progress made by CDC in 3 years, including the competitive evaluation of research proposals and funding of 5 injury prevention research centers and 31 demonstration projects. CDC also made progress in forming the Division of Injury Epidemiology and Control, which has developed an intramural cooperative program with other Federal agencies and an outreach effort to State and local public health departments. The Review Committee felt that, by all measures, the CDC response to the recommendations of the Academy's 1985 report, "Injury in America," has been a success, and a national program for injury control is underway. However, the Committee made the following recommendations for further development and maturing of the CDC program: The CDC effort needs to gain institute status (National Institute for Injury Control) and appropriate funding to address research needs adequately. As the program grows, the organizational structure of the Institute should attain a balance of the five principal areas of injury control (epidemiology, prevention, biomechanics, acute care, and rehabilitation), assuring that CDC programs go beyond traditional public health approaches and identify the causes of injury as the key step toward effective control. CDC should continue the competitive evaluation and selection of research centers and demonstration projects, including State and local outreach programs, and should direct a major part (80 percent) of its injury control funds in this area. CDC should continue its cooperation with other Federal agencies and consider formal interagency coordination and joint funding of research. An advisory council should be formed to help guide the further development of the CDC program and devise a blueprint for future programs.

Limits and challenges of crash protection.

The objective of this paper is to present information on fatal motor vehicle crashes, the effectiveness of lap-shoulder belts in preventing these deaths, and the limitations on their lifesaving capabilities. With this perspective, an evaluation is made of the potential for further reductions in crash fatalities if advanced safety systems are included in the standard occupant protection package. These systems might include additional lap-shoulder belt technologies, such as pretensioners, webbing locks or grabbers, load limiters, and adjustable anchors, as well as belt supplements, such as air bags and energy-absorbing interiors. Difficulties encountered in evaluating the effectiveness of these systems in the laboratory are then described. Finally, the potential for precrash and postcrash safety technologies in combination with crash-phase technology is discussed as an effective use of resources to improve occupant protection.

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.

Injury impairment and disability scales to assess the permanent consequences of trauma.

Impairment and disability caused by injury are major public health costs in terms of monetary losses and personal suffering. Currently, there is no satisfactory method of measuring these losses. Impairment is the loss of function after injury healing. The level of impairment depends on the type and severity of injury in conjunction with medical-social factors. An Injury Impairment Scale (IIS) similar to the Abbreviated Injury Scale (AIS) is proposed, with severity codes of 0-6 like the AIS. The criteria of Mobility/Dexterity, Cognitive/Psychological, Cosmetic/Disfigurement, Sensory, Pain, and Sexual/Reproduction are used for coding impairment resulting from injury. Methods for determining whole body impairment (WBI) are discussed. Use of the highest impairment code on any criterion is suggested at this time to assign WBI. Disability depends on a patient's impairment and ability to accommodate the impairment. Factors such as education, past employment, family and community support, and personal and community resources play a role in the patient's ability to accommodate an impairment, fulfill the activities of daily living, socialize, and be productively employed. An Injury Disability Scale (IDS) and method of determining disability from impairment is proposed. Three patient case studies utilizing the proposed coding systems are presented. Validation of the injury impairment and disability scales will require in-depth evaluation by several institutes and medical facilities with large databases that include adequate follow-up examination information. This paper addresses the concepts for injury, impairment, and disability scaling and establishes a framework to undertake injury control research.

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.

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.

Biomechanics of injury in lateral impacts.

Fourteen anesthetized swine were subjected to blunt lateral impact at velocities of 4.3, 6.7, or 8.2 m/s with a 15 cm flat pendulum weighing 23.4 kg accelerated to impact speed by a power-assisted pneumatic impactor. Injuries consisted of laceration of the liver and spleen resulting in severe hemoperitoneum and death by ventricular fibrillation and respiratory arrest in the highest severity impacts. Logist analysis of the biomechanical responses and serious or fatal injury indicated that the maximum Viscous response (VC) had the best correlation with injury risk. A tolerance level of VC = 0.89 m/s was determined for a 25% probability of serious injury. In contrast, maximum chest compression did not correlate with injury. The experiments indicate that internal organ and soft tissue injury may occur by a Viscous mechanism during the rapid phase of compression of the body. The Viscous response is an effective measure of injury risk in side impacts.

Involvement of older drivers in multivehicle side-impact crashes.

Side impacts were studied using three separate analyses. National Accident Sampling System (NASS) and National Crash Severity Study (NCSS) cases were reviewed on multivehicle crashes involving fatal chest and abdominal injury by interior contact. Twenty-five cases were analyzed and showed an unusually high involvement of older occupants. Analyses of the 1975-1986 FARS confirmed an overinvolvement. Sixty-four percent of near-side seated occupants were over 50 years old and 36% over 70 in fatal multivehicle side impacts. In contrast, 26% of victims in single-vehicle frontal crashes were over 50 and 8% over 70 years old. Analysis of the 1982-1986 NASS showed that single-vehicle side impacts are not an important injury risk for older drivers, except on icy or wet roads. In contrast, the risk of injury in multivehicle side impacts increases steadily with age and is a major problem for older drivers. The individual NASS and NCSS cases also showed that 88% of the multivehicle side crashes took place at an intersection and that the driver of the struck vehicle frequently caused the crash by driving error (48%) or traffic violation (16%). The majority of cases occurred in daylight hours, on dry roads, and without alcohol involvement. Changes in visual perception, judgment and attention of the older driver may be factors in their missing a traffic signal or turning in front of traffic under the right-of-way. In addition, a reduced tolerance to impact force probably contributes to the injury. Although an analysis of photographs of the side-impacted vehicle indicated that 44% had side-structure deformation that was similar to that produced in the National Highway Traffic Safety Administration (NHTSA) moving deformable barrier test, only 24%-32% of the cases actually addressed the proposed NHTSA dynamic side-impact test. The results of this analysis bear on the agency's preliminary regulatory impact analysis.

Biomechanics of the human chest, abdomen, and pelvis in lateral impact.

Fourteen unembalmed cadavers were subjected to 44 blunt lateral impacts at velocities of approximately 4.5, 6.7, or 9.4 m/s with a 15 cm flat circular interface on a 23.4 kg pendulum accelerated to impact speed by a pneumatic impactor. Chest and abdominal injuries consisted primarily of rib fractures, with a few cases of lung or liver laceration in the highest severity impacts. There were two cases of pubic ramus fracture in the pelvic impacts. Logist analysis of the biomechanical responses and injury indicated that the maximum Viscous response had a slightly better correlation with injury than maximum compression for chest and abdominal impacts. A tolerance level of VC = 1.47 m/s for the chest and VC = 1.98 m/s for the abdomen were determined for a 25% probability of critical injury. Maximum compression was similarly set at C = 38% for the chest and at C = 44% for the abdomen. The experiments indicate that chest and abdominal injury may occur by a viscous mechanism during the rapid phase of body compression, and that the Viscous and compression responses are effective, complementary measures of injury risk in side impact. Although serious pelvic injury was infrequent, lateral public ramus fracture correlated with compression of the pelvis, not impact force or pelvic acceleration. Pelvic tolerance was set at 27% compression.

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.

Cardiovascular injury from blunt thoracic impact of epinephrine and isoproterenol injected rabbits.

Nonpenetrating thoracic impact of 10 anesthetized rabbits injected with epinephrine and experiencing transient hypertension resulted in 4 incidents of traumatic rupture of the left ventricle. Impact of similar severity did not produce ventricular injury (p less than 0.01) in either 11 control or 10 animals injected with isoproterenol and experiencing transient hypotension. Immediate death (p less than 0.001) and aortic rupture (p less than 0.05) were most frequent in epinephrine injected animals. Impact during cardiac systole produced more frequent cardiovascular lesions in the epinephrine injected animals than during diastolic loading (p less than 0.001), whereas the cardiac phase was not a significant factor in the thoracic injuries of the control or isoproterenol injected animals. The experiments indicate that the precondition of the myocardium is an important factor in the incidence of ventricular and major vascular rupture in nonpenetrating thoracic impact.

Evaluation of biomechanical response and potential injury from thoracic impact.

An analytical model for the anteroposterior thoracic impact response of the human thorax is investigated to: 1) establish a comparison between the model and available cadaver data for blunt impacts, 2) demonstrate typical force, deflection, and acceleration impact response characteristics as well as additional parameters, such as stored and dissipated energies and associated powers, and 3) develop biomechanical response characteristics for frontal impacts of varying severity (i.e., mass: 2-26 kg and velocity: 2-24 m/s) within the range of model applicability. The analysis provides fundamental relationships between thoracic impact characteristics and biomechanical response and human injury potential.