Assessment of Pedestrians' Head and Lower Limb Injuries in Tram-Pedestrian Collisions

Analysis of pedestrians' head and lower limb injuries at the tissue level is lacking in studies of tram-pedestrian collisions. The purpose of this paper therefore to investigate the impact response process and severity of pedestrians' injuries in tram-pedestrian collisions, using the Total Human Model for Safety (THUMS) pedestrian human body model together with the tram FE model. Two full-scale tram-pedestrian dummy crash tests were performed to validate the FE model, and the total correlation and analysis (CORA) score of head acceleration yielded values of 0.840 and 0.734, confirming a strong agreement between the FE-simulated head responses and the experimental head kinematics. The effects of different tram speeds and impact angles on pedestrians' impact response injuries and the differences were further analyzed. The results indicate that direct impact of the lower limb with the tram's obstacle deflector leads to lower limb bone shaft fractures and knee tissue damage. Neck fling contributed to worsened head injury. Coup contusions were the predominant type of brain contusion, surpassing contrecoup contusions, while diffuse axonal injury was mainly concentrated in the collision-side region of the brain. Pedestrians' injuries are influenced by tram velocity and impact angle: higher tram velocities increase the risk of lower limb and head injuries. The risk of head injury for pedestrians is higher when the impact angle is negative, while lower limb injuries are more significant when the impact angle is 0°. This study provides practical guidance for enhancing tram safety and protecting pedestrians.

An MCL internal brace can withstand cyclic fatigue loading and produce a valgus load to failure similar to that of intact knees

PURPOSE

The purpose of this study is to report on the biomechanical durability and strength of an MCL internal brace construct. The null hypothesis is that there will be no difference between this construct and the intact MCL in terms of deflection during fatigue testing and the ultimate failure load.

METHODS

Eight cadaver knees were used. A grade 3 equivalent MCL tear was created with both the superficial and deep femoral MCL severed. An internal brace was created by placing a cortical button and loop through the center of the femoral MCL origin and secured on the lateral cortex of the distal femur. A FiberTape (Arthrex, Naples, FL) was looped through the cortical button loop and was secured in the center of the tibial insertion of the MCL. After pre-cycling, the specimens underwent 1000 cycles of compressive load between 100 and 300 N, using four point bending testing into direct valgus. Pre and post testing deflection was measured using three dimensional motion data from two sets of reflective markers. A load-to-failure test was then conducted with failure defined as the first significant decrease in the load-displacement curve.

RESULTS

The mean increase in deflection between pre- and post-testing was 0.6° (SD ± 0.3°). The mean failure bending moment was 122.4 Nm (SD ± 29 Nm).

CONCLUSION

The internal brace construct employed in this study was able to withstand cyclic fatigue loading and recorded a valgus load to failure similar to that of intact knees. It is important for clinicians who are considering using this commercially available technique to be aware of how the construct performs under cyclic loading compared to the intact MCL.

Influence of walking on knee ligament response in car-to-pedestrian collisions

Pedestrians are likely to experience walking before accidents. The walking process imposes cyclic loading on knee ligaments and increases knee joint temperature. Both cyclic loading and temperature affect the material properties of ligaments, which further influence the risk of ligament injury. However, the effect of such walking-induced material property changes on pedestrian ligament response has not been considered. Therefore, in this study, we investigated the influence of walking on ligament response in car-to-pedestrian collisions. Using Total Human Model for Safety (THUMS) model, knee ligament responses (i.e., cross-sectional force and local strain) were evaluated under several crash scenarios (i.e., two impact speeds, two knee contact heights, and three pedestrian postures). In worst case scenarios, walking-induced changes in ligament material properties led to a 10% difference in maximum local strain and a 6% difference in maximum cross-sectional force. Further considering the material uncertainty caused by experimental dispersion, the ligament material property changes due to walking resulted in a 28% difference in maximum local strain and a 26% difference in maximum cross-sectional force. This study demonstrates the importance of accounting for walking-induced material property changes for the reliability of safety assessments and injury analysis.

Effect of Tissue Erosion Modeling Techniques on Pedestrian Impact Kinematics

The pedestrian is one of the most vulnerable road users and has experienced increased numbers of injuries and deaths caused by car-to-pedestrian collisions over the last decade. To curb this trend, finite element models of pedestrians have been developed to investigate pedestrian protection in vehicle impact simulations. While useful, modeling practices vary across research groups, especially when applying knee/ankle ligament and bone failure. To help better standardize modeling practices this study explored the effect of knee ligament and bone element elimination on pedestrian impact outcomes. A male 50th percentile model was impacted by three European generic vehicles at 30, 40, and 50 km/h. The pedestrian model was set to three element elimination settings: the "Off-model" didn't allow any element erosion, the "Lig-model" allowed lower-extremity ligament erosion, and the "All-model" allowed lower-extremity ligament and bone erosion. Failure toggling had a significant effect on impact outcomes (0 < p ≤ 0.03). The head impact time response was typically the smallest for the "Off-model" while the wrap around distance response was always largest for the All-model. Moderate differences in maximum vehicle-pedestrian contact forces across elimination techniques were reported in this study (0.1 - 1.7 kN). Future work will examine additional failure modelling approaches, model anthropometries and vehicles to expand this investigation.

A validated lower extremity model to investigate the effect of stabilizing knee components in pedestrian collisions

Lower extremity injuries account for over 50% of pedestrian orthopedic injuries in car-to-pedestrian collisions. Pedestrian finite element models are useful tools for studying pedestrian safety, but current models use simplified knee models that exclude potentially important stabilizing knee components. The effect of these stabilizing components in pedestrian impacts is currently unknown. The goal of this study was to develop a detailed lower-extremity model to investigate the effect of these stabilizing components on pedestrian biomechanics. In this study the Global Human Body Model Consortium male 50th percentile pedestrian model lower body was updated to include various stabilizing knee components, enhance geometric anatomical accuracy of previously modeled soft tissue structures, and update hard and soft tissue material models. The original and updated models were compared across 13 validation tests and the updated model reported significantly ( p = 0.01) larger CORA scores (0.73 ± 0.15) than the original model (0.56 ± 0.20). To investigate the effect of the new stabilizing knee components the updated model had its stabilizing components severed. The severed and intact models were impacted by the EuroNCAP SUV and family car models at 30 and 40 km/h. The intact and severed models reported nearly identical head impact times, wrap around distances, and lower-extremity injury outcomes in all four impacts, but the stabilizing components reduced the varus knee angle of the secondarily impacted leg by up to 4.9°. The stabilizing components may prevent secondary impacted leg injuries in lower intensity impacts but overall had little effect on pedestrian biomechanical outcomes.

Knee ligament injuries in U.S. pedestrian crashes

OBJECTIVE

Projectile legform tests are used to evaluate pedestrian lower extremity injury risk, including risk of injury to the cruciate and collateral ligaments. However, it has been suggested that cruciate ligament injuries rarely occur without collateral ligament injuries, making a cruciate ligament injury requirement unnecessary in pedestrian test procedures. Therefore, the current study examines cruciate ligament injuries among U.S. pedestrians with and without other injuries that are evaluated in pedestrian test procedures.

METHODS

Injury data for pedestrians treated in U.S. trauma centers from 2007 to 2017 were drawn from the National Trauma Data Bank (NTDB) Research Data Set (RDS) and from its successor, the Trauma Quality Program (TQP) Participant User Files (PUF). Crash and demographic details for individual cases with documented knee ligament injuries were obtained from the Pedestrian Crash Data Study (PCDS).

RESULTS

Among pedestrians aged 16 and older with knee ligament injuries, 38% had only collateral injuries, 31% had only cruciate injuries and 31% were documented with injuries to both. Younger pedestrians also sustained cruciate injuries without collateral injuries, with 36% of the 0-15 year-old pedestrians diagnosed with knee ligament injuries having isolated cruciate injuries. Given that injuries to the left and right knee could not be distinguished in NTDB cases, these estimates of isolated ligament injuries are likely conservative, so that at least 31% of pedestrians aged 16 and older and at least 36% of younger pedestrians sustained cruciate ligament injuries without collateral ligament injuries in the same knee. A PCDS case study illustrated how cruciate injury can occur without collateral injury in a lateral bumper impact below the knee.

CONCLUSIONS

Cruciate ligament injuries can occur in pedestrian crashes, with or without other injuries that are evaluated in pedestrian test procedures. Isolated cruciate injuries may be more likely in impacts above or below the knee and in impacts with a component of anterior-posterior loading. The frequency of cruciate injury in the absence of collateral injury in lateral and non-lateral impact supports inclusion of injury measures correlating to cruciate injury risk in pedestrian legform test procedures.

The Influence of Gait Stance and Vehicle Type on Pedestrian Kinematics and Injury Risk

Pedestrians are one of the most vulnerable road users. In 2019, the USA reported the highest number of pedestrian fatalities number in nearly three decades. To better protect pedestrians in car-to-pedestrian collisions (CPC), pedestrian biomechanics must be better investigated. The pre-impact conditions of CPCs vary significantly in terms of the characteristics of vehicles (e.g., front-end geometry, stiffness, etc.) and pedestrians (e.g., anthropometry, posture, etc.). The influence of pedestrian gait posture has not been well analyzed. The purpose of this study was to numerically investigate the changes in pedestrian kinematics and injuries across various gait postures in two different vehicle impacts. Five finite element (FE) human body models, that represent the 50th percentile male in gait cycle, were developed and used to perform CPC simulations with two generic vehicle FE models representing a low-profile vehicle and a high-profile vehicle. In the impacts with the high-profile vehicle, a sport utility vehicle, the pedestrian models usually slide above the bonnet leading edge and report shorter wrap around distances than in the impacts with a low-profile vehicle, a family car/sedan (FCR). The pedestrian postures influenced the postimpact rotation of the pedestrian and consequently, the impacted head region. Pedestrian posture also influenced the risk of injuries in the lower and upper extremities. Higher bone bending moments were observed in the stance phase posture compared to the swing phase. The findings of this study should be taken into consideration when examining pedestrian protection protocols. In addition, the results of this study can be used to improve the design of active safety systems used to protect pedestrians in collisions.

A detailed finite element model of a mid-sized male for the investigation of traffic pedestrian accidents

The pedestrian is one of the most vulnerable road users and comprises approximately 23% of the road crash-related fatalities in the world. To protect pedestrians during Car-to-Pedestrian Collisions (CPC), subsystem impact tests are used in regulations. These tests provide insight but cannot characterize the complex vehicle-pedestrian interaction. The main purpose of this study was to develop and validate a detailed pedestrian Finite Element (FE) model corresponding to a 50th percentile male to predict CPC induced injuries. The model geometry was reconstructed using a multi-modality protocol from medical images and exterior scan data corresponding to a mid-sized male volunteer. To investigate injury response, this model included internal organs, muscles and vessels. The lower extremity, shoulder and upper body of the model were validated against Post Mortem Human Surrogate (PMHS) test data in valgus bending, and lateral/anterior-lateral blunt impacts, respectively. The whole-body pedestrian model was validated in CPC simulations using a mid-sized sedan and simplified generic vehicles bucks and previously unpublished PMHS coronal knee angle data. In the component validations, the responses of the FE model were mostly within PMHS test corridors and in whole body validations the kinematic and injury responses predicted by the model showed similar trends to PMHS test data. Overall, the detailed model showed higher biofidelity, especially in the upper body regions, compared to a previously reported simplified pedestrian model, which recommends using it in future pedestrian automotive safety research.

KINEMATICS AND INJURY MECHANISM OF CYCLIST LOWER LIMB IN VEHICLE-TO-BICYCLE COLLISIONS

Accident data show that lower limb is one of the most frequently injured body parts for cyclists in vehicle collisions. However, studies of cyclist lower limb injuries and protection are still sparse. Therefore, the purpose of this study is to investigate the kinematics and injury mechanism of cyclist lower limb in vehicle-to-bicycle collisions considering different impact boundary conditions. To achieve this, the finite element (FE) modeling approach and an FE human body lower limb model with detailed muscles were employed, and impact boundary conditions with different vehicle front-end shapes and cycling postures were considered. Predictions of lower limb kinematics, knee ligament elongation and bending moment of upper and lower leg were used for analysis. The simulation results show that cycling posture has a significant influence on cyclist lower limb kinematics and injury risk, lateral bending toward the direction of vehicle or vehicle moving combining with lateral shearing is the main mechanism for cyclist knee ligament injuries, and injuries to long bones of cyclist leg in vehicle impacts could form lateral bending at both directions. The findings suggest that the influence of cycling posture and distinct difference in injury mechanism between cyclist and pedestrian should be considered in the assessment of vehicle safety design for cyclist lower limb protection.

Crash Injury Analysis of Knee Joint Considering Pedestrian Safety

Background:

Lower extremity injuries are frequently observed in car-to-pedestrian accidents and due to the bumper height of most cars, knee joint is one of the most damaged body parts in car-to-pedestrian collisions.

Objective:

The aim of this paper is first to provide an accurate Finite Element model of the knee joint and second to investigate lower limb impact biomechanics in car-to-pedestrian accidents and to predict the effect of parameters such as collision speed and height due to the car speed and bumper height on knee joint injuries, especially in soft tissues such as ligaments, cartilages and menisci.

Materials and Methods:

In this analytical study, a 3D finite element (FE) model of human body knee joint is developed based on human anatomy. The model consists of femur, tibia, menisci, articular cartilages and ligaments. Material properties of bones and soft tissues were assumed to be elastic, homogenous and isotropic.

Results:

FE model is used to perform injury reconstructions and predict the damages by using physical parameters such as Von-Mises stress and equivalent elastic strain of tissues.

Conclusion:

The results of simulations first show that the most vulnerable part of the knee is MCL ligament and second the effect of speed and height of the impact on knee joint. In the critical member, MCL, the damage increased in higher speeds but as an exception, smaller damages took place in menisci due to the increased distance of two bones in the higher speed.

A Computationally Efficient Finite Element Pedestrian Model for Head Safety: Development and Validation

Head injuries are often fatal or of sufficient severity to pedestrians in vehicle crashes. Finite element (FE) simulation provides an effective approach to understand pedestrian head injury mechanisms in vehicle crashes. However, studies of pedestrian head safety considering full human body response and a broad range of impact scenarios are still scarce due to the long computing time of the current FE human body models in expensive simulations. Therefore, the purpose of this study is to develop and validate a computationally efficient FE pedestrian model for future studies of pedestrian head safety. Firstly, a FE pedestrian model with a relatively small number of elements (432,694 elements) was developed in the current study. This pedestrian model was then validated at both segment and full body levels against cadaver test data. The simulation results suggest that the responses of the knee, pelvis, thorax, and shoulder in the pedestrian model are generally within the boundaries of cadaver test corridors under lateral impact loading. The upper body (head, T1, and T8) trajectories show good agreements with the cadaver data in vehicle-to-pedestrian impact configuration. Overall, the FE pedestrian model developed in the current study could be useful as a valuable tool for a pedestrian head safety study.

Biomechanical Responses and Injury Characteristics of Knee Joints under Longitudinal Impacts of Different Velocities

Background and Objective

Knee joint collision injuries occur frequently in military and civilian scenarios, but there are few studies assessing longitudinal impacts on knee joints. In this study, the mechanical responses and damage characteristics of knee longitudinal collisions were investigated by finite element analysis and human knee impact tests.

Materials and methods

Based on a biocollision test plateau, longitudinal impact experiments were performed on 4 human knee joints (2 in the left knee and 2 in the right knee) to measure the impact force and stress response of the bone. And then a finite element model of knee joint was established from the Chinese Visible Human (CVH), with which longitudinal impacts to the knee joint were simulated, in which the stress response was determined. The injury response of the knee joint-sustained longitudinal impacts was analyzed from both the experimental model and finite element analysis.

Results

The impact experiments and finite element simulation found that low-speed impact mainly led to medial injuries and high-speed impact led to both medial and lateral injuries. In the knee joint impact experiment, the peak flexion angles were 13.8° ± 1.2, 30.2° ± 5.1, and 92.9° ± 5.45 and the angular velocities were 344.2 ± 30.8 rad/s, 1510.8 ± 252.5 rad/s, and 9290 ± 545 rad/s at impact velocities 2.5 km/h, 5 km/h, and 8 km/h, respectively. When the impact velocity was 8 km/h, 1 knee had a femoral condylar fracture and 3 knees had medial tibial plateau fractures or collapse fractures. The finite element simulation of knee joints found that medial cortical bone stress appeared earlier than the lateral peak and that the medial bone stress concentration was more obvious when the knee was longitudinally impacted.

Conclusion

Both the experiment and FE model confirmed that the biomechanical characteristics of the injured femur and medial tibia are likely to be damaged in a longitudinal impact, which is of great significance for the prevention and treatment of longitudinal impact injuries of the knee joint.

Development and Validation of an Age-Specific Lower Extremity Finite Element Model for Simulating Pedestrian Accidents

The objective of the present study is to develop an age-specific lower extremity finite element model for pedestrian accident simulation. Finite element (FE) models have been used as a versatile tool to simulate and understand the pedestrian injury mechanisms and assess injury risk during crashes. However, current computational models only represent certain ages in the population, the age spectrum of the pedestrian victims is very large, and the geometry of anatomical structures and material property of the lower extremities changes with age for adults, which could affect the injury tolerance, especially in at-risk populations such as the elderly. The effects of age on the material mechanical property of bone and soft tissues of the lower extremities as well as the geometry of the long bone were studied. Then an existing 50th percentile male pedestrian lower extremity model was rebuilt to depict lower extremity morphology for 30- to 70-year-old (YO) individuals. A series of PMHS tests were simulated to validate the biofidelity and stability of the created age-specific models and evaluate the lower extremity response. The development of age-specific lower extremity models will lead to an improved understanding of the pedestrian lower extremity injury mechanisms and injury risk prediction for the whole population in vehicle-pedestrian collision accidents.

A Finite Element Model of a Midsize Male for Simulating Pedestrian Accidents

Pedestrians represent one of the most vulnerable road users and comprise nearly 22% the road crash-related fatalities in the world. Therefore, protection of pedestrians in car-to-pedestrian collisions (CPC) has recently generated increased attention with regulations involving three subsystem tests. The development of a finite element (FE) pedestrian model could provide a complementary component that characterizes the whole-body response of vehicle–pedestrian interactions and assesses the pedestrian injuries. The main goal of this study was to develop and to validate a simplified full body FE model corresponding to a 50th male pedestrian in standing posture (M50-PS). The FE model mesh and defined material properties are based on a 50th percentile male occupant model. The lower limb-pelvis and lumbar spine regions of the human model were validated against the postmortem human surrogate (PMHS) test data recorded in four-point lateral knee bending tests, pelvic\abdomen\shoulder\thoracic impact tests, and lumbar spine bending tests. Then, a pedestrian-to-vehicle impact simulation was performed using the whole pedestrian model, and the results were compared to corresponding PMHS tests. Overall, the simulation results showed that lower leg response is mostly within the boundaries of PMHS corridors. In addition, the model shows the capability to predict the most common lower extremity injuries observed in pedestrian accidents. Generally, the validated pedestrian model may be used by safety researchers in the design of front ends of new vehicles in order to increase pedestrian protection.

A finite element model of a six-year-old child for simulating pedestrian accidents

Child pedestrian protection deserves more attention in vehicle safety design since they are the most vulnerable road users who face the highest mortality rate. Pediatric Finite Element (FE) models could be used to simulate and understand the pedestrian injury mechanisms during crashes in order to mitigate them. Thus, the objective of the study was to develop a computationally efficient (simplified) six-year-old (6YO-PS) pedestrian FE model and validate it based on the latest published pediatric data. The 6YO-PS FE model was developed by morphing the existing GHBMC adult pedestrian model. Retrospective scan data were used to locally adjust the geometry as needed for accuracy. Component test simulations focused only the lower extremities and pelvis, which are the first body regions impacted during pedestrian accidents. Three-point bending test simulations were performed on the femur and tibia with adult material properties and then updated using child material properties. Pelvis impact and knee bending tests were also simulated. Finally, a series of pediatric Car-to-Pedestrian Collision (CPC) were simulated with pre-impact velocities ranging from 20km/h up to 60km/h. The bone models assigned pediatric material properties showed lower stiffness and a good match in terms of fracture force to the test data (less than 6% error). The pelvis impact force predicted by the child model showed a similar trend with test data. The whole pedestrian model was stable during CPC simulations and predicted common pedestrian injuries. Overall, the 6YO-PS FE model developed in this study showed good biofidelity at component level (lower extremity and pelvis) and stability in CPC simulations. While more validations would improve it, the current model could be used to investigate the lower limb injury mechanisms and in the prediction of the impact parameters as specified in regulatory testing protocols.

The influence of lower extremity postures on kinematics and injuries of cyclists in vehicle side collisions

OBJECTIVE

A cyclist assumes various cyclic postures of the lower extremities while pushing the pedals in a rotary motion while pedaling. In order to protect cyclists in collisions, it is necessary to understand what influence these postures have on the global kinematics and injuries of the cyclist.

METHOD

Finite element (FE) analyses using models of a cyclist, bicycle, and car were conducted. In the simulations, the Total Human Model of Safety (THUMS) occupant model was employed as a cyclist, and the simulation was set up such that the cyclist was hit from its side by a car. Three representative postures of the lower extremities of the cyclist were examined, and the kinematics and injury risk of the cyclist were compared to those obtained by a pedestrian FE model. The risk of a lower extremity injury was assessed based on the knee shear displacement and the tibia bending moment.

RESULTS

When the knee position of the cyclist was higher than the hood leading edge, the hood leading edge contacted the leg of the cyclist, and the pelvis slid over the hood top and the wrap-around distance (WAD) of the cyclist's head was large. The knee was shear loaded by the hood leading edge, and the anterior cruciate ligament (ACL) ruptured. The tibia bending moment was less than the injury threshold. When the cyclist's knee position was lower than the hood leading edge, the hood leading edge contacted the thigh of the cyclist, and the cyclist rotated with the femur as the pivot point about the hood leading edge. In this case, the head impact location of the cyclist against the car was comparable to that of the pedestrian collision. The knee shear displacement and the tibia bending moment were less than the injury thresholds.

CONCLUSION

The knee height of the cyclist relative to the hood leading edge affected the global kinematics and the head impact location against the car. The loading mode of the lower extremities was also dependent on the initial positions of the lower extremities relative to the car structures. In the foot up and front posture, the knee was loaded in a lateral shear direction by the hood leading edge and as a result the ACL ruptured. The bicycle frame and the struck-side lower extremity interacted and could influence the loadings on lower extremities.

The influence of gait stance on pedestrian lower limb injury risk

The effect of pedestrian gait on lower limb kinematics and injuries has not been analyzed. The purpose of this paper was therefore to investigate the effect of pedestrian gait on kinematics and injury risk to the lower limbs using the Total Human Model for Safety adult male pedestrian model together with FE models of vehicle front structures. The modeling results indicate that the tibia and femur cortical bone von-Mises stress and the lateral knee bending angle of an adult pedestrian are strongly dependent on the gait stance when struck by both a sedan car and an SUV at 40km/h. The gait analysis shows that generally the leg of an adult pedestrian has lower injury risk when the knee is flexed and linear regressions show high negative correlation between knee flexion angle during impact and knee lateral bending angle and also high negative correlation between lower leg axial rotation during impact and knee lateral bending angle. Furthermore, in some gait stances a self-contact between the legs occurs, and the peak bones stresses and knee shearing displacement in the leg are then increased. Assessment of pedestrian lower limb injury should take account of these gait stance effects.

The tolerance of the human body to automobile collision impact - a systematic review of injury biomechanics research, 1990-2009

Road traffic injuries account for 1.3 million deaths per year world-wide. Mitigating both fatalities and injuries requires a detailed understanding of the tolerance of the human body to external load. To identify research priorities, it is necessary to periodically compare trends in injury tolerance research to the characteristics of injuries occurring in the field. This study sought to perform a systematic review on the last twenty years of experimental injury tolerance research, and to evaluate those results relative to available epidemiologic data. Four hundred and eight experimental injury tolerance studies from 1990-2009 were identified from a reference index of over 68,000 papers. Examined variables included the body regions, ages, and genders studied; and the experimental models used. Most (20%) of the publications studied injury to the spine. There has also been a substantial volume of biomechanical research focused on upper and lower extremity injury, thoracic injury, and injury to the elderly - although these injury types still occur with regularity in the field. In contrast, information on pediatric injury and physiological injury (especially in the central nervous system) remains lacking. Given their frequency of injury in the field, future efforts should also include improving our understanding of tolerances and protection of vulnerable road users (e.g., motorcyclists, pedestrians).

Coupling lateral bending and shearing mechanisms to define knee injury criteria for pedestrian safety

OBJECTIVE

In car-pedestrian accidents, lateral bending and shearing kinematics have been identified as principal injury mechanisms causing permanent disabilities and impairments to the knee joint. Regarding the combined lateral bending and shearing contributions of knee joint kinematics, developing a coupled knee injury criterion is necessary for improving vehicle countermeasures to mitigate pedestrian knee injuries.

METHODS

The advantages of both experimental tests and finite element (FE) simulations were combined to determine the reliable injury tolerances of the knee joint. First, 7 isolated lower limb tests from postmortem human subjects (PMHS) were reported, with dynamic loading at a velocity of 20 km/h. With the intention of replicating relevant injury mechanisms of vehicle-pedestrian impacts, the experimental tests were categorized into 3 groups by the impact locations on the tibia: the distal end to prioritize pure bending, the middle diaphysis to have combined bending and shearing effects, and the proximal end to acquire pure shearing. Then, the corresponding FE model was employed to provide an additional way to determine exact injury occurrences and develop a robust knee injury criterion by the variation in both the lateral bending and shearing contributions through a sensitivity analysis of impact locations.

RESULTS

Considering the experimental test results and the subsequent sensitivity analysis of FE simulations, both the tolerances and patterns of knee joint injuries were determined to be influenced by impact locations due to various combined contributions of lateral bending and shearing. Both medial collateral ligament and cruciate ligament failures were noted as the onsets of knee injuries, namely, initial injuries. Finally, a new injury criterion categorized by initial injury patterns of knee joint was proposed by coupling lateral bending and shearing levels.

CONCLUSIONS

The developed injury criterion correlated the combined joint kinematics to initial knee injuries based on subsegment tests and FE simulations conducted with a biofidelic lower limb model. This provides a valuable way of predicting the risk of knee injury associated with vehicle-pedestrian crashes and thereby represents a further step to promote the design of vehicle countermeasures for pedestrian safety.

Osteochondral microdamage from valgus bending of the human knee

BACKGROUND

Valgus bending of the knee is promoted as an anterior cruciate ligament injury mechanism and is associated with a characteristic "footprint" of bone bruising. The hypothesis of this study was that during ligamentous failure caused by valgus bending of the knee, high tibiofemoral contact pressures induce acute osteochondral microdamage.

METHODS

Four knee pairs were loaded in valgus bending until gross injury with or without a tibiofemoral compression pre-load. The peak valgus moment and resultant motions of the knee joint were recorded. Pressure sensitive film documented the magnitude and location of tibiofemoral contact. Cartilage fissures were documented on the tibial plateau, and microcracks in subchondral bone were documented from micro-computed tomography scans.

FINDINGS

Injuries were to the anterior cruciate ligament in three knees and the medial collateral ligament in seven knees. The mean (standard deviation) peak bending moment at failure was 107 (64)Nm. Valgus bending produced regions of contact on the lateral tibial plateau with average maximum pressures of approximately 30 (8)MPa. Cartilage fissures and subchondral bone microcracks were observed in these regions of high contact pressure.

INTERPRETATION

Combined valgus bending and tibiofemoral compression produce slightly higher contact pressures, but do not alter the gross injury pattern from isolated valgus bending experiments. Athletes who sustain a severe valgus knee bending moment, may be at risk of acute osteochondral damage especially if the loading mechanism occurs with a significant tibiofemoral compression component.

A new approach to multibody model development: pedestrian lower extremity

OBJECTIVE

The goal of this study was to develop a mathematical model of the 50th percentile male lower extremity capable of predicting injury risk and simulating the kinetic and kinematic response of the pedestrian lower extremity under vehicle impact loading.

METHODS

The hip-to-foot multibody model was developed for the MADYMO software platform using exterior and interior geometry and inertial properties from a detailed finite element model (FEM) of the human lower extremity and stiffness and failure tolerance data from the literature. The leg and thigh models' structural and contact parameters were simultaneously optimized to validate model response in simulations replicating previous dynamic bending experiments. The aggregate model's full-scale kinematic response was verified by comparing 3-D local (knee bending angles) and global (linear accelerations and velocities) frame leg and thigh kinematics from vehicle impact simulations with data generated from seven vehicle-pedestrian (PMHS) impact experiments.

RESULTS

By optimizing contact and structural response variables, the applied moment vs. deflection response of the leg and thigh showed excellent correlation with the experimental corridor averages in component-level bending simulations. The full-scale kinematic response of the 50th percentile male model showed good correlation with the PMHS response data in both the rate of valgus knee bending (approximately 3 degress/ms) and in the timing and magnitude of the peak thigh and leg accelerations (250 g and 400 g). Additionally, as a result of vehicle interaction, both the model and the experiments showed that the thigh and leg are initially accelerated upward (100 g) and downward (100 g), respectively, and then downward (60 g) and upward (100 g), respectively. The model also predicted a valgus knee injury and a tibia fracture similar to those seen in the PMHS.

CONCLUSIONS

The use of a facet surface model of the lower extremity skin and simultaneous optimization of the model's structural response and contact parameters resulted in a model capable of accurately predicting the detailed kinematic response of the lower extremity under vehicle impact loading at 40 km/h. The model can be scaled to represent varying pedestrian anthropometries and can assess the risks associated with sustaining the most common pedestrian injuries. As a vehicle design tool, the model can be used to optimize front-end designs, or it can be used in combination with a detailed FEM to reduce the vast design space prior to FE simulations. Additionally, the model can be used as a tool to study pedestrian impact kinematics, real-world case reconstructions, or particular vehicle countermeasures.

A comparative analysis of the pedestrian injury risk predicted by mechanical impactors and post mortem human surrogates

The objective of this study is to compare the risk of injury to pedestrians involved in vehicle-pedestrian impacts as predicted by two different types of risk assessment tools: the pedestrian subsystem impactors recommended by the European Enhanced Vehicle-Safety Committee (EEVC) and post-mortem human surrogates (PMHS). Seven replicate full-scale vehicle-pedestrian impact tests were performed with PMHS and a mid-sized sedan travelling at 40 km/h. The PMHS were instrumented with six-degree-of-freedom sensor cubes and sensor data were transformed and translated to predict impact kinematics at the head center of gravity, proximal tibiae, and knee joints. Single EEVC WG 17/EuroNCAP adult headform, upper legform and lower legform impactor tests of the same vehicle were selected for comparison based on the proximity of their impact locations to that of the PMHS. The PMHS experienced higher HIC values (1830/2160) and lower impact velocities (8.5/7.5 m/s) than the impactor (1532 and 11.1 m/s) in impacts at the lower fourth of the windshield. The lower legform impactor (31 degrees) and PMHS (right: 25-40 degrees, and left: 24-39 degrees) predicted similar maximum knee bending angles. Some PMHS tibial accelerations (114-613 g) exceeded the proposed acceptance criteria (150-200 g) in both the absence and presence of distal tibial fracture, with the impactor predicting a similar result (335 g). The upper legform impactor test resulted in bending moments (361 Nm) and forces (6.3 kN) exceeding the acceptance criteria, while PMHS sustained pelvic injuries in 6 out of 7 tests.