Comparative multibody dynamics analysis of falls from playground climbing frames

Impact forces in backward falls: Subject-specific video-based rigid body simulation of backward falls

A critical missing component in the study of real-world falls is the ability to accurately determine impact forces resulting from the fall. Subject-specific rigid body dynamic (RBD) models calibrated to video captured falls can quantify impact forces and provide additional insights into injury risk factors. RBD models were developed based on five backward falls captured on surveillance video in long-term care facilities in British Columbia, Canada. Model joint stiffness and initial velocities were calibrated to match the kinematics of the fall and contact forces were calculated. The effect of joint stiffnesses (neck, lumbar spine, hip, and knee joint) on head contact forces were determined by modifying the calibrated stiffness values ±25%. Fall duration, fall trajectories, and maximum velocities showed a close match between fall events and simulations. The maximum value of pelvic velocity difference between Kinovea (an open-source software 2D digitization software) and Madymo multibody modeling was found to be 6% ± 21.58%. Our results demonstrate that neck and hip stiffness values have a non-significant yet large effect on head contact force (t(3) = 1, p = 0.387 and t(3) = 2, p = 0.138), while lower effects were observed for knee stiffness, and the effect of lumbar spine stiffness was negligible. The subject-specific fall simulations constructed from real world video captured falls allow for direct quantification of force outcomes of falls and may have applications in improving the assessment of fall-induced injury risks and injury prevention methods.

Slip and tilt: modeling falls over railings

Falls over railings are frequent case scenarios forensic experts are confronted with. An important issue is the differentiation of accidental and non-accidental falling scenarios. From a biomechanical point of view, this is a challenging task and should be addressed in a multifactorial approach. This work presents a simplified mechanical model in terms of a cranked rod that can be used in cases without relevant dynamic components in terms of pushing or jumping. If the anti-slip and the anti-tilt condition are violated, the possibility for a person to get over a railing should be assumed and investigated in more detail. Because our approach also involves uncertainties, the formulae should be understood to be part of a multifactorial approach. Numerical simulation, experimental reconstruction, injury pattern, and trace analysis can yield additional substantial connecting facts.

Characteristic analysis and fuzzy simulation of falls-from-height mechanics, and case studies

In this paper, methods for scientifically inferring the causes of the falls-from-height accidents, that is, the initial fall postures, and reconstructing the fall accident are presented. For this purpose, the general types of fall were subdivided into eight, and the characteristics of each fall type were analyzed. An initial posture estimation tool based on Fuzzy method was developed utilizing the massive amount of quantitative database that was constructed by repeating the simulation program for all types of falls. In addition, the initial conditions for each type were standardized with the experimental results and simulation data to reconstruct the fall behavior using the estimated fall accident type. The results of four carefully selected case studies were presented to verify the reliability and practicality of the developed fall analysis program and the reconstruction method.

The Strain Rates in the Brain, Brainstem, Dura, and Skull under Dynamic Loadings

Knowing the precise material properties of intracranial head organs is crucial for studying the biomechanics of head injury. It has been shown that these biological tissues are significantly rate-dependent; hence, their material properties should be determined with respect to the range of deformation rate they experience. In this paper, a validated finite element human head model is used to investigate the biomechanics of the head in impact and blast, leading to traumatic brain injuries (TBI). We simulate the head under various directions and velocities of impacts, as well as helmeted and unhelmeted head under blast shock waves. It is demonstrated that the strain rates for the brain are in the range of 36 to 241 s−1, approximately 1.9 and 0.86 times the resulting head acceleration under impacts and blast scenarios, respectively. The skull was found to experience a rate in the range of 14 to 182 s−1, approximately 0.7 and 0.43 times the head acceleration corresponding to impact and blast cases. The results of these incident simulations indicate that the strain rates for brainstem and dura mater are respectively in the range of 15 to 338 and 8 to 149 s−1. These findings provide a good insight into characterizing the brain tissue, cranial bone, brainstem and dura mater, and also selecting material properties in advance for computational dynamical studies of the human head.

Rate-dependent constitutive modeling of brain tissue

In this paper, the dynamic behavior of bovine brain tissue, measured from a set of in vitro experiments, is investigated and represented through a nonlinear viscoelastic constitutive model. The brain samples were tested by employing unconfined compression tests at three different deformation rates of 10, 100, and 1000 mm/s. The tissue exhibited a significant rate-dependent behavior with different compression speeds. Based on the parallel rheological framework approach, a nonlinear viscoelastic model that captures the key aspects of the rate dependency in large-strain behavior was introduced. The proposed model was numerically calibrated to the tissue test data from three different deformation rates. The determined material parameters provided an excellent constitutive representation of tissue response in comparison with the test results. The obtained material parameters were employed in finite element simulations of tissue under compression loadings and successfully verified by the experimental results, thus demonstrating the computational compatibility of the proposed material model. The results of this paper provide groundwork in developing a characterization framework for large-strain and rate-dependent behavior of brain tissue at moderate to high strain rates which is of the highest importance in biomechanical analysis of the traumatic brain injury.

Prediction of injury risks and features among scooter riders through MADYMO reconstruction of a scooter-microvan accident: Identifying the driver and passengers

In dealing with a scooter-related traffic accident with rider death, it is necessary to identify the driver responsible for the accident. This study aimed to reconstruct the kinematics of a scooter-microvan accident involving three riders and explored the differences in injury risks and characteristics of the scooter driver and passengers. We reconstructed a real accident by using MADYMO multi-body simulation software. Moreover, we designed two-variable simulation experiments to analyze how the velocity and impact angle of the microvan are related to the injuries of the three riders. When the microvan speed is set at 18 km/h and that of the scooter is set at 28.8 km/h, the simulated kinematics correlates well with real accident data, and the impact positions and injury parameters correlate well with the actual injuries. When the impact angle is smaller than 30° and the microvan impact velocity is lower than 40 km/h, the head injury of the driver is more life-threatening than the corresponding injuries of the rear passengers. When the impact angle is 15° and the microvan impact velocity is in the range of 0-20 km/h, the femur fracture risk is higher for the driver than for passengers. As the impact angle increases to 45°, passengers have a higher risk of femur fracture than the driver in the velocity range of 0-10 km/h. This impact velocity range becomes 0-30 km/h at an impact angle of 60° and then 40-70 km/h at an impact angle of 90°. Our study shows that the multibody method can reconstruct accidents and predict the different injury features and risks between the driver and passengers, which is useful in identifying the driver.

Multi-Scale Modeling of Head Kinematics and Brain Tissue Response to Blast Exposure

Injuries resulting from blast exposure have been increasingly prevalent in recent conflicts, with a particular focus on the risk of head injury. In the current study, a multibody model (GEBOD) was used to investigate the gross kinematics resulting from blast exposure, including longer duration events such as the fall and ground impact. Additionally, detailed planar head models, in the sagittal and transverse planes, were used to model the primary blast wave interaction with the head, and resulting tissue response. For severe blast load cases (scaled distance less than 2), the translational head accelerations during primary blast were found to increase as the height-of-burst (HOB) was lowered, while the HOB was found to have no effect for cases with scaled distance greater than 2. The HOB was found to affect both the magnitude and direction of rotational accelerations, with increasing magnitudes as the HOB deviated from the height of the head. The choice of ground contact stiffness was found to greatly affect the predicted head accelerations during ground impact. For a medium soil ground material, the kinematics during ground impact were greater for scaled distances exceeding 1.5, below which the primary blast produced greater kinematic head response.

Femur loading in feet-first fall experiments using an anthropomorphic test device

BACKGROUND

Femur fractures are a common orthopedic injury in young children. Falls account for a large portion of accidental femur fractures in young children, but there is also a high prevalence of femur fractures in child abuse, with falls often provided as false histories. Objective information regarding fracture potential in short distance fall scenarios may aid in assessing whether a child's injuries are the result of abuse or an accidental fall. Knowledge of femur loading is the first step towards understanding likelihood of fracture in a fall.

OBJECTIVE

Characterize femur loading during feet-first free falls using a surrogate representing a 12-month-old child.

METHODS

The femur and hip joint of a surrogate representing a 12-month-old were modified to improve biofidelity and measure femur loading; 6-axis load cells were integrated into the proximal and distal femur. Femur modification was based upon CT imaging of cadaveric femurs in children 10-14 months of age. Using the modified 12-month-old surrogate, feet-first free falls from 69 cm and 119 cm heights onto padded carpet and linoleum were conducted to assess fall dynamics and determine femur loading. Femur compression, bending moment, shear and torsional moment were measured for each fall.

RESULTS

Fall dynamics differed across fall heights, but did not substantially differ by impact surface type. Significant differences were found in all loading conditions across fall heights, while only compression and bending loads differed between carpet and linoleum surfaces. Maximum compression, bending, torsion and shear occurred in 119 cm falls and were 572 N, 23 N-m, 11 N-m and 281 N, respectively.

CONCLUSIONS

Fall dynamics play an important role in the biomechanical assessment of falls. Fall height was found to influence both fall dynamics and femur loading, while impact surface affected only compression and bending in feet-first falls; fall dynamics did not differ across carpet and linoleum. Improved pediatric thresholds are necessary to predict likelihood of fracture, but morphologically accurate representation of the lower extremity, along with accurate characterization of loading in falls are a crucial first step.

Identification of pre-impact conditions of a cyclist involved in a vehicle-bicycle accident using an optimized MADYMO reconstruction combined with motion capture

The aim of the present study was to develop an improved method, using MADYMO multi-body simulation software combined with an optimization method and three-dimensional (3D) motion capture, for identifying the pre-impact conditions of a cyclist (walking or cycling) involved in a vehicle-bicycle accident. First, a 3D motion capture system was used to analyze coupled motions of a volunteer while walking and cycling. The motion capture results were used to define the posture of the human model during walking and cycling simulations. Then, cyclist, bicycle and vehicle models were developed. Pre-impact parameters of the models were treated as unknown design variables. Finally, a multi-objective genetic algorithm, the nondominated sorting genetic algorithm II, was used to find optimal solutions. The objective functions of the walk parameter were significantly lower than cycle parameter; thus, the cyclist was more likely to have been walking with the bicycle than riding the bicycle. In the most closely matched result found, all observed contact points matched and the injury parameters correlated well with the real injuries sustained by the cyclist. Based on the real accident reconstruction, the present study indicates that MADYMO multi-body simulation software, combined with an optimization method and 3D motion capture, can be used to identify the pre-impact conditions of a cyclist involved in a vehicle-bicycle accident.

Homemade zipline and playground track ride injuries in children

BACKGROUND/PURPOSE

Playground track ride and homemade zipline-related injuries are increasingly common in the emergency department, with serious injuries and even deaths reported.

METHODS

Retrospective review of the National Electronic Injury Surveillance System (NEISS) database (2009-2015), followed by review of our academic pediatric trauma center's prospectively-maintained database (2005-2013). We included children ages 0-17years of age with zipline-related injuries. We recorded annual incidence of zipline-related injury, zipline type (homemade or playground), injuries and mechanism.

RESULTS

In the NEISS database, 9397 (95%CI 6728-12,065) total zipline-related injuries were reported (45.9% homemade, 54.1% playground). Homemade but not playground injuries increased over time. Common injuries were fracture (49.8%), contusion/laceration (21.2%) and head injury (12.7%). Fall was predominant mechanism (83%). Age 5-9 was most frequently affected (59%). Our center database (n=35, 40% homemade, 1 fatality) revealed characteristics concordant with NEISS data. Head injury was related to fall height>5ft and impact with another structure.

CONCLUSIONS

Homemade zipline injuries are increasing. Children ages 5-9 are at particular risk and should be carefully supervised. Despite protective surfaces, playground ziplines cause significant head injury, extremity fracture and high rates of hospital admission. Playground surface standards should be reviewed and revised as needed.

LEVEL OF EVIDENCE

Prognosis Study, Level III.

A biomechanical analysis of traumatic brain injury for slips and falls from height

Background

Falls are a common cause of morbidity and mortality in society, particularly among the aged and young. There has been research to describe the epidemiology of these types of events, but to date there has been few correlations of clinical brain injury outcomes and metrics used in biomechanical research; parameters often used to help develop protective devices and environments. The purpose of this research was to examine the kinematic characteristics of falls from standing and higher heights in an effort to understand how clinical brain injury is predicted by biomechanical injury metrics.

Methods

Computer simulations of nine traumatic brain injury events from falling were conducted to determine the biomechanical metrics associated with each injury case.

Results

Many of the impacts were to the occipital region of the head, as would be expected from backward falls or from slipping from ladders. These falls resulted in low rotational acceleration values and high linear accelerations, suggesting linear acceleration may be an important characteristic of this injury mechanism. In addition, even though each case resulted in severe head injury, the HIC15 (Head Injury Criterion) values did not consistently predict injury when the kinematic output was lower than 300 g. This result suggests that HIC15 may have limited value as a predictor for high energy short duration direct impacts to the head. The results supported a relationship between fall height and duration of loss of consciousness, with the higher fall heights producing longer times of unconsciousness.

Conclusion

Linear acceleration may be the metric that should be focused on to develop further strategies to protect against severe TBI for fall cases similar to those in this research. In addition, the HIC15 may not be suitable as a predictive metric for TBI and future development of protective devices for the prevention of head injury should take this into account.

Pediatric concussion: biomechanical differences between outcomes of transient and persistent (> 4 weeks) postconcussion symptoms

OBJECTIVE Currently, little is known about the biomechanics of head impact for concussion in youths (ages 5 to 18 years). Even less is known about the biomechanical characteristics and variables related to head impacts that may be useful in differentiating between transient and persistent postconcussion symptoms in a youth population. The purpose of this research was to examine the differences in biomechanics of youth head impact for transient postconcussion symptoms (TPCSs) and persistent postconcussion symptoms (PPCSs) by using data from a hospital population. METHODS In a laboratory setting and using physical, computational, and finite element models, the authors reconstructed falling events in a large cohort of patients who had sustained a brain injury that resulted in transient or persistent postconcussion symptoms. The falling events and resulting concussions for the TPCS and PPCS patient groups were analyzed in terms of force, energy, peak resultant linear and rotational accelerations, and maximum principal strain in the gray and white matter of the brain, as well as measurements of cumulative strain damage. RESULTS The results indicated that there were no significant differences between the groups for any of the variables analyzed. CONCLUSIONS With methods derived for use in an adult population, the magnitudes of peak linear acceleration for the youth data set were determined to be above the 50% risk of injury. The youth data set showed higher brain tissue strain responses for lower energy and impact velocities than measured in adults, suggesting that youths are at higher risk of concussive injury at lower event severities. A trend shown by some variables indicated that larger magnitudes of response were associated with PPCSs, but no single measurement variable consistently differentiated between the TPCS and PPCS groups. It is possible that using the biomechanics of head and brain responses to predict a subjective symptom load may not be appropriate. To enhance future biomechanical analyses, further investigations should include the use of quantifiable measures of brain injury linked to clinical outcomes and possible confounding factors such as history of brain injury and patient predisposition.

A comparison in a youth population between those with and without a history of concussion using biomechanical reconstruction

OBJECTIVE Concussion is a common topic of research as a result of the short- and long-term effects it can have on the affected individual. Of particular interest is whether previous concussions can lead to a biomechanical susceptibility, or vulnerability, to incurring further head injuries, particularly for youth populations. The purpose of this research was to compare the impact biomechanics of a concussive event in terms of acceleration and brain strains of 2 groups of youths: those who had incurred a previous concussion and those who had not. It was hypothesized that the youths with a history of concussion would have lower-magnitude biomechanical impact measures than those who had never suffered a previous concussion. METHODS Youths who had suffered a concussion were recruited from emergency departments across Canada. This pool of patients was then separated into 2 categories based on their history of concussion: those who had incurred 1 or more previous concussions, and those who had never suffered a concussion. The impact event that resulted in the brain injury was reconstructed biomechanically using computational, physical, and finite element modeling techniques. The output of the events was measured in biomechanical parameters such as energy, force, acceleration, and brain tissue strain to determine if those patients who had a previous concussion sustained a brain injury at lower magnitudes than those who had no previously reported concussion. RESULTS The results demonstrated that there was no biomechanical variable that could distinguish between the concussion groups with a history of concussion versus no history of concussion. CONCLUSIONS The results suggest that there is no measureable biomechanical vulnerability to head impact related to a history of concussions in this youth population. This may be a reflection of the long time between the previous concussion and the one reconstructed in the laboratory, where such a long period has been associated with recovery from injury.

The dynamics of electric powered wheelchair sideways tips and falls: experimental and computational analysis of impact forces and injury

Background

To reduce the occurrence of wheelchair falls and to develop effective protection systems, we aimed to quantify sideways tip and fall dynamics of electric power wheelchairs (EPWs). We hypothesized that driving speed, curb height and angle of approach would affect impact forces and head injury risk for wheelchair riders. We further expected that fall dynamics and head injury risk would be greater for unrestrained riders compared to restrained riders.

Methods

Sideways wheelchair tip and fall dynamics were reconstructed using a remotely operated rear wheel drive EPW and a Hybrid III test dummy driving at different approach angles (5 to 63°) over an adjustable height curb (0.30 to 0.41 m) at speeds of 0.6–1.5 m/s. Rigid body dynamics models (Madymo, TASS International, Livonia, MI) were developed in parallel with the experiments to systematically study and quantify the impact forces and the sideways tip or fall of an EPW user in different driving conditions.

Results

Shallower approach angles (25°) (p < 0.05) and higher curbs (0.4 m) (p < 0.05) were the most significant predictors of tipping for restrained passengers. Unrestrained passengers were most affected by higher curbs (0.4 m) (p < 0.005) and fell forward from the upright wheelchair when the approach angle was 60°. Head impact forces were greater in unrestrained users (6181 ± 2372 N) than restrained users (1336 ± 827 N) (p = 0.00053). Unrestrained users had significantly greater head impact severities than restrained users (HIC = 610 ± 634 vs HIC = 29 ± 38, p = 0.00013) and several tip events resulted in HICs > 1000 (severe head injury) in unrestrained users.

Conclusions

Sideways tips and forward falls from wheelchairs were most sensitive to curb height and approach angle but were not affected by driving speed. Sideways tips and falls resulted in impact forces that could result in concussions or traumatic brain injury and require injury prevention strategies. Seat belts eliminated the risk of falling from an upright chair and reduced head impact forces in sideways wheelchair tips in this study; however, their use must be considered within the ethical and legal definitions of restraints.

Bicycle helmet use to reduce the impact of head injuries in ladder users

BACKGROUND

The aim of this study was to determine if wearing a bicycle helmet during ladder use could reduce the incidence and severity of head injury in the event of a fall.

METHODS

A headform model with inbuilt accelerometers was used to determine the Head Injury Criterion (HIC) score of head impact by dropping 41 helmeted and unhelmeted headforms from eight heights. These results were compared.

RESULTS

There was a statistically significant difference between averaged HIC scores in helmeted and unhelmeted drops (P < 0.001). Unhelmeted HIC scores ranged from 387 at 0.25 m to 2121 at 0.6 m. Helmeted HIC scores ranged from 29 at 0.25 m to 1199 at 2.5 m. At a height of 0.5 m, the risk of severe brain injury (AIS ≥4) from direct frontal head impact is predicted to reduce from >50% to <5% with helmet use.

CONCLUSION

There was a significant decrease in the HIC scores when helmets are used and it is likely that the benefits would be seen in the clinical setting. These results provide an argument for the use of a bicycle helmets by all ladder users, in particular those over age 50 who are at increased risk of head injuries. We recommend that bicycle helmet use be incorporated into ladder injury prevention strategies.

The dynamic response characteristics of traumatic brain injury

Traumatic brain injury (TBI) continues to be a leading cause of morbidity and mortality throughout the world. Research has been undertaken in order to better understand the characteristics of the injury event and measure the risk of injury to develop more effective environmental, technological, and clinical management strategies. This research used methods that have limited applications to predicting human responses. This limits the current understanding of the mechanisms of TBI in humans. As a result, the purpose of this research was to examine the characteristics of impact and dynamic response that leads to a high risk of sustaining a TBI in a human population. Twenty TBI events collected from hospital reports and eyewitness accounts were reconstructed in the laboratory using a combination of computational mechanics models and Hybrid III anthropometric dummy systems. All cases were falls, with an average impact velocity of approximately 4.0m/s onto hard impact surfaces. The results of the methodology were consistent with current TBI research, describing TBI to occur in the range of 335-445g linear accelerations and 23.7-51.2krad/s(2) angular accelerations. More significantly, this research demonstrated that lower responses in the antero-posterior direction can cause TBI, with lateral impact responses requiring larger magnitudes for the same types of brain lesions. This suggests an increased likelihood of sustaining TBI for impacts to the front or back of the head, a result that has implications affecting current understanding of the mechanisms of TBI and associated threshold parameters.

Traumatic Brain Injuries

BACKGROUND:

Head impact direction has been identified as an influential risk factor in the risk of traumatic brain injury (TBI) from animal and anatomic research; however, to date, there has been little investigation into this relationship in human subjects. If a susceptibility to certain types of TBI based on impact direction was found to exist in humans, it would aid in clinical diagnoses as well as prevention methods for these types of injuries.

OBJECTIVE:

To examine the influence of impact direction on the presence of TBI lesions, specifically, subdural hematomas, subarachnoid hemorrhage, and parenchymal contusions.

METHODS:

Twenty reconstructions of falls that resulted in a TBI were conducted in a laboratory based on eyewitness, interview, and medical reports. The reconstructions involved impacts to a Hybrid III anthropometric dummy and finite element modeling of the human head to evaluate the brain stresses and strains for each TBI event.

RESULTS:

The results showed that it is likely that increased risk of incurring a subdural hematoma exists from impacts to the frontal or occipital regions, and parenchymal contusions from impacts to the side of the head. There was no definitive link between impact direction and subarachnoid hemorrhage. In addition, the results indicate that there is a continuum of stresses and strain magnitudes between lesion types when impact location is isolated, with subdural hematoma occurring at lower magnitudes for frontal and occipital region impacts, and contusions lower for impacts to the side.

CONCLUSION:

This hospital data set suggests that there is an effect that impact direction has on TBI depending on the anatomy involved for each particular lesion.

The influence of dynamic response and brain deformation metrics on the occurrence of subdural hematoma in different regions of the brain

Object

The purpose of this study was to examine how the dynamic response and brain deformation of the head and brain—representing a series of injury reconstructions of which subdural hematoma (SDH) was the outcome—influence the location of the lesion in the lobes of the brain.

Methods

Sixteen cases of falls in which SDH was the outcome were reconstructed using a monorail drop rig and Hybrid III headform. The location of the SDH in 1 of the 4 lobes of the brain (frontal, parietal, temporal, and occipital) was confirmed by CT/MR scan examined by a neurosurgeon.

Results

The results indicated that there were minimal differences between locations of the SDH for linear acceleration. The peak resultant rotational acceleration and x-axis component were larger for the parietal lobe than for other lobes. There were also some differences between the parietal lobe and the other lobes in the z-axis component. Maximum principal strain, von Mises stress, shear strain, and product of strain and strain rate all had differences in magnitude depending on the lobe in which SDH was present. The parietal lobe consistently had the largest-magnitude response, followed by the frontal lobe and the occipital lobe.

Conclusions

The results indicated that there are differences in magnitude for rotational acceleration and brain deformation metrics that may identify the location of SDH in the brain.

Pediatric bed fall computer simulation model: parametric sensitivity analysis

Falls from beds and other household furniture are common scenarios that may result in injury and may also be stated to conceal child abuse. Knowledge of the biomechanics associated with short-distance falls may aid clinicians in distinguishing between abusive and accidental injuries. In this study, a validated bed fall computer simulation model of an anthropomorphic test device representing a 12-month-old child was used to investigate the effect of altering fall environment parameters (fall height, impact surface stiffness, initial force used to initiate the fall) and child surrogate parameters (overall mass, head stiffness, neck stiffness, stiffness for other body segments) on fall dynamics and outcomes related to injury potential. The sensitivity of head and neck injury outcome measures to model parameters was determined. Parameters associated with the greatest sensitivity values (fall height, initiating force, and surrogate mass) altered fall dynamics and impact orientation. This suggests that fall dynamics and impact orientation play a key role in head and neck injury potential. With the exception of surrogate mass, injury outcome measures tended to be more sensitive to changes in environmental parameters (bed height, impact surface stiffness, initiating force) than surrogate parameters (head stiffness, neck stiffness, body segment stiffness).

Finite element analysis of pedestrian lower limb fractures by direct force: the result of being run over or impact?

The elucidation and prediction of the biomechanics of lower limb fractures could serve as a useful tool in forensic practices. Finite element (FE) analysis could potentially help in the understanding of the fracture mechanisms of lower limb fractures frequently caused by car-pedestrian accidents. Our aim was (1) to develop and validate a FE model of the human lower limb, (2) to assess the biomechanics of specific injuries concerning run-over and impact loading conditions, and (3) to reconstruct one real car-pedestrian collision case using the model created in this study. We developed a novel lower limb FE model and simulated three different loading scenarios. The geometry of the model was reconstructed using Mimics 13.0 based on computed tomography (CT) scans from an actual traffic accident. The material properties were based upon a synthesis of data found in published literature. The FE model validation and injury reconstruction were conducted using the LS-DYNA code. The FE model was validated by a comparison of the simulation results of three-point bending, overall lateral impact tests and published postmortem human surrogate (PMHS) results. Simulated loading scenarios of running-over the thigh with a wheel, the impact on the upper leg, and impact on the lower thigh were conducted with velocities of 10 m/s, 20 m/s, and 40 m/s, respectively. We compared the injuries resulting from one actual case with the simulated results in order to explore the possible fracture bio-mechanism. The peak fracture forces, maximum bending moments, and energy lost ratio exhibited no significant differences between the FE simulations and the literature data. Under simulated run-over conditions, the segmental fracture pattern was formed and the femur fracture patterns and mechanisms were consistent with the actual injury features of the case. Our study demonstrated that this simulation method could potentially be effective in identifying forensic cases and exploring of the injury mechanisms of lower limb fractures encountered due to inflicted lesions. This model can also help to distinguish between possible and impossible scenarios.

Mechanical characterization of brain tissue in tension at dynamic strain rates

Mechanical characterization of brain tissue at high loading velocities is crucial for modeling Traumatic Brain Injury (TBI). During severe impact conditions, brain tissue experiences compression, tension and shear. Limited experimental data is available for brain tissue in extension at dynamic strain rates. In this research, a High Rate Tension Device (HRTD) was developed to obtain dynamic properties of brain tissue in extension at strain rates of ≤90/s. In vitro tensile tests were performed to obtain properties of brain tissue at strain rates of 30, 60 and 90/s up to 30% strain. The brain tissue showed a stiffer response with increasing strain rates, showing that hyperelastic models are not adequate. Specifically, the tensile engineering stress at 30% strain was 3.1±0.49kPa, 4.3±0.86kPa, 6.5±0.76kPa (mean±SD) at strain rates of 30, 60 and 90/s, respectively. Force relaxation tests in tension were also conducted at different strain magnitudes (10-60% strain) with the average rise time of 24ms, which were used to derive time dependent parameters. One-term Ogden, Fung and Gent models were used to obtain material parameters from the experimental data. Numerical simulations were performed using a one-term Ogden model to analyze hyperelastic behavior of brain tissue up to 30% strain. The material parameters obtained in this study will help to develop biofidelic human brain finite element models, which can subsequently be used to predict brain injuries under impact conditions and as a reconstruction and simulation tool for forensic investigations.

Paediatric bed fall computer simulation model development and validation

Falls from beds and other household furniture are common scenarios stated to conceal child abuse. Knowledge of the biomechanics associated with short-distance falls may aid clinicians in distinguishing between abusive and accidental injuries. Computer simulation is a useful tool to investigate injury-producing events and to study the effect of altering event parameters on injury risk. In this study, a paediatric bed fall computer simulation model was developed and validated. The simulation was created using Mathematical Dynamic Modeling(®) software with a child restraint air bag interaction (CRABI) 12-month-old anthropomorphic test device (ATD) representing the fall victim. The model was validated using data from physical fall experiments of the same scenario with an instrumented CRABI ATD. Validation was conducted using both observational and statistical comparisons. Future parametric sensitivity studies using this model will lead to an improved understanding of relationships between child (fall victim) parameters, fall environment parameters and injury potential.

Height, fun and safety in the design of children's playground equipment

The study reported in this paper adopted a holistic design approach to investigate issues associated with height related playground injuries from a users' perspective. The main objective was to gain an understanding of the relationship between height and fun so as to establish practical guidelines for addressing the causes of height related injuries whilst maintaining the attributes of playground equipment that children find fun and challenging. Results show that, on the one hand, the risk of injury increases when height is coupled with the use of upper body strength and, on the other hand, that coordination is a greater source of fun and challenge than height for children. Accordingly, it is suggested that the level of risk of injury attached to children's playground equipment can be reduced when the use of lower body strength and coordination are combined with lower free fall heights.