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Funk J.R.,5711 University Heights Blvd | Rowson S.,Wake forest University | Daniel R.W.,Wake forest University | Duma S.M.,Wake forest University
Annals of Biomedical Engineering | Year: 2012

For several years, Virginia Tech and other schools have measured the frequency and severity of head impacts sustained by collegiate American football players in real time using the Head Impact Telemetry (HIT) System of helmet-mounted accelerometers. In this study, data from 37,128 head impacts collected at Virginia Tech during games from 2006 to 2010 were analyzed. Peak head acceleration exceeded 100 g in 516 impacts, and the Head Injury Criterion (HIC) exceeded 200 in 468 impacts. Four instrumented players in the dataset sustained a concussion. These data were used to develop risk curves for concussion as a function of peak head acceleration and HIC. The validity of this biomechanical approach was assessed using epidemiological data on concussion incidence from other sources. Two specific aspects of concussion incidence were addressed: the variation by player position, and the frequency of repeat concussions. The HIT System data indicated that linemen sustained the highest overall number of head impacts, while skill positions sustained a higher number of more severe head impacts (peak acceleration > 100 g or HIC > 200). When weighted using injury risk curves, the HIT System data predicted a higher incidence of concussion in skill positions compared to linemen at rates that were in strong agreement with the epidemiological literature (Pearson's r = 0.72-0.87). The predicted rates of repeat concussions (21-39% over one season and 33-50% over five seasons) were somewhat higher than the ranges reported in the epidemiological literature. These analyses demonstrate that simple biomechanical parameters that can be measured by the HIT System possess a high level of power for predicting concussion. © 2011 Biomedical Engineering Society. Source

Funk J.R.,5711 University Heights Blvd
Clinical Anatomy | Year: 2011

The biomechanics of ankle injury have been studied extensively, primarily through mechanical testing of human cadavers. Cadaveric testing is an invaluable methodology in biomechanics, because the magnitude and direction of the loading can be measured precisely and correlated with the resulting injury pattern. Clinical and epidemiological studies provide useful descriptions of injury patterns that occur in the real world, but their retrospective nature precludes a definitive analysis of the forces that caused the injury. Understanding the mechanism of ankle injuries is essential for developing countermeasures to prevent injury and for reconstructing injurious events. Knowledge of an injury's mechanism can also suggest potential associated injuries, which is helpful in diagnosis and treatment. The purpose of this review is to summarize the published research on ankle injury mechanisms with an emphasis on biomechanical experiments on human cadavers. Injury patterns are described based on the principal axis of force or torque producing the injury in conjunction with off-axis forces and out-of-plane foot positions. A mechanistic description of ankle injuries is complicated by the fact that the same mechanism can sometimes produce different injuries and the same injury can sometimes be caused by multiple mechanisms. Nonetheless, a framework for relating injury mechanisms and injury patterns is a valuable tool in the understanding, prevention, and treatment of ankle injuries. © 2011 Wiley-Liss, Inc. Source

Funk J.,5711 University Heights Blvd | Wirth J.,5711 University Heights Blvd | Bonugli E.,5711 University Heights Blvd | Watson R.,5711 University Heights Blvd
SAE Technical Papers | Year: 2012

Rollover crashes are often difficult to reconstruct in detail because of their chaotic nature. Historically, vehicle speeds in rollover crashes have been calculated using a simple slide-to-stop formula with empirically derived drag factors. Roll rates are typically calculated in an average sense over the entire rollover or a segment of it in which vehicle roll angles are known at various positions. A unified model to describe the translational and rotational vehicle dynamics throughout the rollover sequence is lacking. We propose a pseudo-cylindrical model of a rolling vehicle in which the rotational and translational dynamics are coupled to each other based on the average frictional forces developed during ground contacts. We describe the model as pseudo-cylindrical because vertical motion is ignored but the ground reaction force is not constrained to act directly underneath the center of gravity of the vehicle. The tumbling phase of a rollover is modeled in three distinct phases: an initial brief airborne phase between roll initiation and the first ground contact, an early phase in which relative sliding between the perimeter of the vehicle and the ground causes the roll rate to increase, and a later phase in which the vehicle rolls without sliding and the roll rate decreases. In the early phase, the average vehicle deceleration is higher and is governed by sliding friction. In the later phase, the average vehicle deceleration is lower and is governed by geometric factors. Model predictions were fit to data from 12 well-documented rollover crashes in order to derive empirical values for the model parameters. In 11 out of the 12 rollovers studied, the model predictions matched the actual results with good accuracy. The results validate the underlying physical principles of the model and provide data that can be used to apply the model to real world rollovers. The proposed model provides a physical basis for understanding vehicle dynamics in rollovers and may be used in certain cases to improve the accuracy of a rollover reconstruction. Copyright © 2012 SAE International. Source

Funk J.R.,5711 University Heights Blvd | Cormier J.M.,5711 University Heights Blvd | Manoogian S.J.,5711 University Heights Blvd
Accident Analysis and Prevention | Year: 2012

Previous epidemiological studies of rollover crashes have focused primarily on serious and fatal injuries in general, while rollover crash testing has focused almost exclusively on cervical spine injury. The purpose of this study was to examine and compare the risk factors for cervical spine, head, serious, and fatal injury in real world rollover crashes. Rollover crashes from 1995-2008 in the National Automotive Sampling System-Crashworthiness Data System (NASS-CDS) were investigated. A large data set of 6015 raw cases (2.5 million weighted) was generated. Nonparametric univariate analyses, univariate logistic regression, and multivariate logistic regression were conducted. Complete or partial ejection, a lack of seatbelt use, a greater number of roof inversions, and older occupant age significantly increased the risk of all types of injuries studied (p < 0.05). Far side seating position increased the risk of fatal, head, and cervical spine injury (p < 0.05), but not serious injury in general. Higher BMI was associated with an increased risk of fatal, serious, and cervical spine injury (p < 0.05), but not head injury. Greater roof crush was associated with a higher rate of fatal and cervical spine injury (p < 0.05). Vehicle type, occupant height, and occupant gender had inconsistent and generally non-significant effects on injury. This study demonstrates both common and unique risk factors for different types of injuries in rollover crashes. © 2011 Elsevier Ltd. All rights reserved. Source

Scott W.R.,5711 University Heights Blvd | Bonugli E.,5711 University Heights Blvd | Guzman H.,5711 University Heights Blvd | Swartzendruber D.,5711 University Heights Blvd
SAE International Journal of Passenger Cars - Mechanical Systems | Year: 2012

The purpose of this study was to determine if quasi-static (QS) bumper force-deformation (F-D) data could be used in a low-speed bumper-to-bumper simulation model (1) in order to reconstruct low-speed crashes. In the simulation model, the bumpers that make contact in a crash are treated as a system. A bumper system is defined as the two bumpers that interact in a crash positioned in their orientation at the time of the crash. A device was built that quasi-statically crushes the bumpers of a bumper system into each other and measures the compression force and the deformation of the bumper system. Three bumper systems were evaluated. Two QS F-D measurements were performed for each bumper system in order to demonstrate the repeatability of the QS F-D measurement. These measurements had a compression phase and a rebound phase. A series of crash tests were performed using each bumper system. In each crash test, a stationary target vehicle was struck on the rear bumper by the front bumper of a bullet vehicle. Both vehicles were instrumented with accelerometers. The bullet vehicle had load cells at the front that measured crash forces and a displacement sensor that measured the deformation of the bumper system during the crash. The crash tests were performed over a range of impact speeds for the bullet vehicle. The compression QS F-D data were used as an input to the simulation model in order to reconstruct the vehicle motions in the crash tests. The other inputs required to simulate a crash test were the impact speed of the bullet vehicle, the vehicle masses and the coefficient of restitution measured in the crash test. The study demonstrated that the simulation model with the QS F-D data accurately recreated the velocities of the target and bullet vehicle in the crash tests. © 2012 SAE International. Source

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