Analysis of 6YO pediatric human body model kinematics and kinetics to determine submarining across naturalistic seating postures.

OBJECTIVES: The aim of this study was to analyze the kinematics and kinetics of a naturalistically seated 6-year-old (6YO) pediatric human body model and evaluate the metrics described by earlier studies for pediatric ATDs to indicate whether different postures and booster seats were more associated with submarining than others in a frontal impact. METHODS: The PIPER 6YO pediatric human body model was restrained on a lowback (LBB) and a highback (HBB) booster child restraint seat (CRS) in four naturalistic seating postures: leaning-forward, leaning-inboard, leaning-outboard, and a pre-submarining posture, and a baseline reference seating position as per the FMVSS No. 213 protocol. A 2012 mid-size sedan finite element (FE) model was used as the vehicle environment. A standard 3-point lap-shoulder belt system was modeled to restrain the child and the CRS in the left-rear vehicle seat. Additionally, a No-CRS condition was modeled in a reference posture and pre-submarining posture in which the occupant's legs bent over the edge of the rear seat. 12 conditions were simulated in LS-DYNA R10.1.0, and kinematics and kinetics were compared to metrics as per prior literature: 1) maximum femur displacement and pelvis rotation, 2) maximum knee-head excursion and maximum change in torso angle, 3) lap belt trajectory relative to pelvis's coordinate frame. RESULTS: The pre-submarining posture on the HBB depicted submarining in all metrics except for the lap belt trajectory. Only the pre-submarining posture in No-CRS depicted submarining through analysis of all metrics. For this pre-submarining No-CRS condition, the mid-abdominal compression was approximately 5 times greater than the average of the mid abdominal compression depths of all other cases and maximum abdominal pressure was at least 22.9 kPa higher than the rest of the conditions. CONCLUSIONS: The results of this study suggest that metrics used to assess submarining for 6YO pediatric occupants in frontal impacts may need to be updated so that they are more accurate for both simulated and physical studies. In addition, the results of this study could be used to design booster seats that discourage postures that could lead to an increased likelihood of submarining-like characteristics in a frontal crash impact.

Rearward-Facing Infant Child Restraint Systems with Support Legs in Frontal and Frontal-Oblique Impacts.

Previous studies of support legs in rearward-facing infant CRS models have focused on frontal impacts and have found that the presence of a support leg is associated with a reduction in head injury metrics. However, real-world crashes often involve an oblique principal direction of force. The current study used sled tests to evaluate the effectiveness of support legs in rearward-facing infant CRS models for frontal and frontal-oblique impacts with and without a simulated front row seatback. Frontal and frontal-oblique impact sled tests were conducted using the simulated Consumer Reports test method with and without the blocker plate, which was developed to represent a front row seatback. The Q1.5 anthropomorphic test device (ATD) was seated in rearward-facing infant CRS models, which were tested with and without support legs. The presence of a support leg was associated with significant reductions of head injury metrics below injury tolerance limits for all tests, which supports the findings of previous studies. The presence of a support leg was also associated with significant reductions of peak neck tensile force. The presence of the blocker plate resulted in greater head injury metrics compared to tests without the blocker plate, but the result was non-significant. However, the fidelity of the interaction between the CRS and blocker plate as an adequate representation of the interaction that would occur in a real vehicle is not well understood. The findings from the current study continue to support the benefit of support legs in managing the energy of impact for a child in a rearward-facing CRS.

Pediatric occupant human body model kinematic and kinetic response variation to changes in seating posture in simulated frontal impacts - with and without automatic emergency braking.

OBJECTIVE: The study quantifies the kinematics of children in booster child restraint systems (CRSs) in various naturalistic seating postures exposed to frontal impacts in a full-vehicle environment, with and without the application of pre-crash automatic emergency braking. METHODS: The PIPER 6YO and 10YO pediatric human body models were positioned in CRSs. The 6YO was restrained on a lowback (LBB) and highback (HBB) booster, while the 10YO was positioned on an LBB and in a NoCRS condition. All simulations used the 3-point seatbelt. The child models were pre-positioned (gravity settled, seatbelt tensioned) in four naturalistic seating postures: leaning-forward, leaning-forward-inward, leaning-forward-outward, and a pre-submarining position, along with a baseline reference seating position. A 2012 Toyota Camry finite element (FE) model was used as the vehicle environment. A standard 3-point lap-shoulder belt system was modeled to restrain the child and CRS in the left-rear vehicle seat. Two vehicle impact cases were considered: with and without a pre-crash AEB. For with-AEB cases, a pre-crash phase was run to incorporate postural changes due to the application of AEB. All seating positions were ultimately subjected to a full-frontal rigid-barrier impact at 35 MPH. A total of 40 conditions were simulated in LS-DYNA. RESULTS: Injury metrics varied widely for both occupants. Shoulder belt slippage was observed for the 6YO leaning-forward-inward on HBB. No head contact was observed for any simulated cases. Forward-leaning and forward-inward-leaning postures generally had greater head excursion across all seating postures. The lap belt rode over the pelvis for pre-submarining postures. Injury metrics for cases with pre-crash AEB were lower compared to their corresponding without-AEB cases. HIC15, head acceleration, upper neck tension force, and upper neck flexion moment were similar or lower for with-AEB scenarios. CONCLUSIONS: Pre-crash AEB reduces the effect of the impact despite the same collision speed as cases without-AEB. This is primarily due to the limited travel distance of the occupant, thus, starting an earlier ride-down during the crash. Moreover, different initial seating postures lead to a wide range of injury exposures. Vehicle and child restraint design should incorporate these seating postures to ensure robust protection of the occupant in a crash.

Near crash characteristics among risky drivers using the SHRP2 naturalistic driving study.

PROBLEM: Previous research have focused extensively on crashes, however near crashes provide additional data on driver errors leading to critical events as well as evasive maneuvers employed to avoid crashes. The Strategic Highway Research Program 2 (SHRP2) Naturalistic Driving Study contains extensive data on real world driving and offers a reliable methodology to study near crashes. The current study utilized the SHRP2 database to compare the rate and characteristics associated with near crashes among risky drivers. METHODS: A subset from the SHRP2 database consisting of 4,818 near crashes for teen (16-19 yrs), young adult (20-24 yrs), adult (35-54 yrs), and older (70+ yrs) drivers was used. Near crashes were classified into seven incident types: rear-end, road departure, intersection, head-on, side-swipe, pedestrian/cyclist, and animal. Near crash rates, incident type, secondary tasks, and evasive maneuvers were compared across age groups. For rear-end near crashes, near crash severity, max deceleration, and time-to-collision at braking were compared across age. RESULTS: Near crash rates significantly decreased with increasing age (p < 0.05). Young drivers exhibited greater rear-end (p < 0.05) and road departure (p < 0.05) near crashes compared to adult and older drivers. Intersection near crashes were the most common incident type among older drivers. Evasive maneuver type did not significantly vary across age groups. Near crashes exhibited a longer time-to-collision at braking (p < 0.01) compared to crashes. SUMMARY: These data demonstrate increased total near crash rates among young drivers relative to adult and older drivers. Prevalence of specific near crash types also differed across age groups. Timely execution of evasive maneuvers was a distinguishing factor between crashes or near crashes. Practical Applications: These data can be used to develop more targeted driver training programs and help OEMs optimize ADAS to address the most common errors exhibited by risky drivers.

Evaluation of Rotation Reduction Features in Infant and Extended-Use Convertible Child Restraint Systems during Frontal and Rear Impacts.

A correctly used child restraint system (CRS) is associated with a substantial reduction of injury and mortality risks in motor vehicle crashes and epidemiologic data suggests that toddlers are provided greater protection when restrained in a rearward-facing CRS compared to a forward-facing CRS. Some 'extended-use' European CRS models can accommodate children up to six years rearward-facing and have a support (load) leg and/or a pair of lower (Swedish) tethers to reduce rotation during frontal and rear impacts, respectively. Laboratory studies have found that a support leg reduces head and neck injury metrics of anthropomorphic test devices (ATDs) younger than three years in rearward-facing CRS models during frontal impacts. The objectives of the current study were to perform sled tests to: (1) evaluate the effects of using a support leg in rearward-facing infant and extended-use convertible CRS models during frontal impacts, (2) evaluate the effects of using a pair of lower tethers in a rearward-facing extended-use convertible CRS model during rear impacts and (3) compare responses of ATDs in an extendeduse convertible CRS with a support leg and a pair of lower tethers in rearward- and forward-facing configurations during frontal and rear impacts. The presence of a support leg in rearward-facing infant and extended-use convertible CRS models in frontal impacts was associated with reductions in head injury metrics across a range of pediatric ATDs and neck injury metrics were below injury tolerance values. Other strategies in the design of rearward-facing CRS and front row vehicle seatbacks may be available to further reduce head injury metrics. Lower tethers reduced the rearward rotation of an extended-use convertible CRS toward the vehicle seatback in rear impacts and were typically associated with reductions in head and neck injury metrics for the Q6 ATD, but not the Q3 ATD. For frontal impacts, neck injury metrics were typically greater for ATDs in the forward-facing extended-use convertible CRS, whereas head injury metrics were typically greater for the rearward-facing condition (with a support leg and a pair of lower tethers). Interactions of the ATD head and/or the rearward-facing extended-use convertible CRS with the blocker plate in rearward-facing frontal impacts need to be further investigated.

Responses of the scaled pediatric human body model in the rear- and forward-facing child seats in simulated frontal motor vehicle crashes.

Objective: The study presents the first-ever endeavor at developing 18-, 24-, 30-, 36-, 42-, and 48-month-old pediatric finite element models from the 6-year-old PIPER human body model as a baseline and comparing their responses systematically in rear-facing and forward-facing simulations across similar boundary conditions.Methods: A 6-year-old PIPER model was scaled down to create anthropometric models of the 18-, 24-, 30-, 36-, 42-, and 48-month-old child using the PIPER scaling tool. The models were installed on a convertible car seat (rear-facing and forward-facing configurations) installed with a 3-point lap-shoulder belt in the rear outboard seat of a 2012 Toyota Camry vehicle model finite element model and setup for full-frontal crash simulation (24 G, 120 ms pulse).Results: The forward-facing models showed higher head resultant accelerations for 24-, 36-, 42-, and 48-month-old models (reduction for rear-facing seats ranging from 10% to 32%). For the 18- and 30-month-old models, the maximum head acceleration showed similar values (difference of less than 10%). Upper neck forces and moments were consistently lower for rear-facing models compared to forward-facing. The neck forces were reduced by 83%-90% and the neck moments were reduced by 63%-85% in the rear-facing models compared to their respective forward-facing configurations. The reduction in head injury criterion (HIC36) for rear-facing models ranged from 14% to 51%. The neck injury criterion (Nij) for all forward-facing models was 6 to 9 times the values of their rear-facing counterpart.Conclusions: The study shows the potential benefit of rear-facing orientation compared to forward-facing for children up to 4 years of age in a controlled environment.

Age and gender differences in emergency takeover from automated to manual driving on simulator.

Objective: The objective of this study was to explore how age and sex impact the ability to respond to an emergency when in a self-driving vehicle.Methods: For this study, 60 drivers (male: 48%, female: 52%) of different age groups (teens: aged 16-19, 32%, adults: aged 35-54, 37%, seniors: aged 65+, 32%) were recruited to share their perspectives on self-driving technology. They were invited to ride in a driving simulator that mimicked a vehicle in autopilot mode (longitudinal and lateral control).Results: In a scenario where the automated vehicle unexpectedly drives toward a closed highway exit, 21% of drivers did not react at all. For this event, where drivers had 6.2 s to avoid a crash, 40% of drivers crashed. Adults aged 35-54 crashed less than other age groups (33% crash rate), whereas teens crashed more (47% crash rate). Seniors had the highest crash rate (50% crash rate). Males (38% crash rate) crashed less than females (43% crash rate). All participants with a reaction time less than 4 s were able to avoid the crash.Conclusions: The results from the simulation drives show that humans lose focus when they do not actively drive so that their response in an emergency does not allow them to reclaim control quickly enough to avoid a crash.

Evaluating the response of the PIPER scalable human body model across child restraining seats in simulated frontal crashes.

OBJECTIVE: Booster seats ensure appropriate belt fit for children that a traditional vehicle seat belt cannot offer to small occupants. In this study, the responses of the PIPER 6-year-old human body model are compared to the traditional Q6 anthropomorphic test dummy (ATD). METHODS: Eight frontal impact finite element simulations were run using 4 different child restraining systems on the FMVSS 213 test bench. Kinematics and kinetics were extracted and compared between the 2 child models. RESULTS: The PIPER 6-year-old showed variation by 11.2 ± 14.1% (head resultant acceleration, G), 20.4 ± 50.3% (chest resultant acceleration, G), 272.9 ± 188.4% (chest displacement, mm), 24.8 ± 17.5% (maximum head excursion, mm), -31.5 ± 5.1% (neck force, Fz, N), -73.8 ± 2.8% (neck moment, My, N.m), and -60.4 ± 7.2% (Nij) compared to the Q6. However, the kinematics of both models were nearly similar. CONCLUSIONS: The PIPER model has a flexible neck and shows higher chest displacement compared to the Q6. We hypothesize that this is due to the inherent anatomical and mechanical differences between the human body model and the ATD model. More research is needed to explore these differences systematically.

Comparison of crash rates and rear-end striking crashes among novice teens and experienced adults using the SHRP2 Naturalistic Driving Study.

OBJECTIVE: Motor vehicle crashes are the leading cause of death for teens. Previous teen and adult crash rates have been based upon fatal crashes, police-reported crashes, and estimated miles driven. Large-scale naturalistic driving studies offer the opportunity to compute crash rates using a reliable methodology to capture crashes and driving exposure. The Strategic Highway Research Program 2 (SHRP2) Naturalistic Driving Study contains extensive real-world data on teen and adult driving. This article presents findings on the crash rates of novice teen and experienced adult drivers in naturalistic crashes. METHODS: A subset from the SHRP2 database consisting of 539 crash events for novice teens (16-19 years, n = 549) and experienced adults (35-54 years, n = 591) was used. Onboard instrumentation such as scene cameras, accelerometers, and Global Positioning System logged time series data at 10 Hz. Scene videos were reviewed for all events to identify rear-end striking crashes. Dynamic variables such as acceleration and velocity were analyzed for rear-end striking events. Number of crashes, crash rates, rear-end striking crash severity, and rear-end striking impact velocity were compared between novice teens and experienced adults. RESULTS: Video review of the SHRP2 crashes identified significantly more crashes (P < 0.01) and rear-end striking crashes (P < 0.01) among the teen group than among the adult group. This yielded crash rates of 30.0 crashes per million miles driven for novice teens compared to 5.3 crashes per million miles driven for experienced adults. The crash rate ratio for teens vs. adults was 5.7. The rear-end striking crash rate was 13.5 and 1.8 per million miles driven for novice teens and experienced adults, respectively. The rear-end striking crash rate ratio for teens vs. adults was 7.5. The rear-end striking crash severity measured by the accelerometers was greater (P < 0.05) for the teen group (1.8 ± 0.9 g; median = 1.6 g) than for the adult group (1.1 ± 0.4 g; median = 1.0 g), suggesting that teen crashes tend to be more serious than adult crashes. Increased rear-end striking impact velocity (P < 0.01) was also observed for novice teens (18.8 ± 13.2 mph; median = 18.9 mph) compared to experienced adults (3.3 ± 1.2 mph; median = 2.8 mph). CONCLUSION: To our knowledge, this is the first study to compare crash rates between teens and adults using a large-scale naturalistic driving database. Unlike previous crash rates, the reported rates reliably control for crash type and driving exposure. These results conform to previous findings that novice teens exhibit increased crash rates compared to experienced adults.

Vehicular Causation Factors and Conceptual Design Modifications to Reduce Aortic Strain in Numerically Reconstructed Real World Nearside Lateral Automotive Crashes.

Aortic injury (AI) leading to disruption of the aorta is an uncommon but highly lethal consequence of trauma in modern society. Most recent estimates range from 7,500 to 8,000 cases per year from a variety of causes. It is observed that more than 80% of occupants who suffer an aortic injury die at the scene due to exsanguination into the chest cavity. It is evident that effective means of substantially improving the outcome of motor vehicle crash-induced AIs is by preventing the injury in the first place. In the current study, 16 design of computer experiments (DOCE) were carried out with varying levels of principal direction of force (PDOF), impact velocity, impact height, and impact position of the bullet vehicle combined with occupant seating positions in the case vehicle to determine the effects of these factors on aortic injury. Further, a combination of real world crash data reported in the Crash Injury Research and Engineering Network (CIREN) database, Finite Element (FE) vehicle models, and the Wayne State Human Body Model-II (WSHBM-II) indicates that occupant seating position, impact height, and PDOF, in that order play, a primary role in aortic injury.

Comparative performance of forward-facing child restraint systems on the C/FMVSS 213 bench and vehicle seats.

OBJECTIVE: The objective of this study was to evaluate the fidelity of the C/FMVSS 213 test bench, by comparing the dynamic performance of forward-facing child restraint systems (FFCRS) mounted on the C/FMVSS 213 sled bench versus mounted on a selection of production vehicle seats. METHODS: The C/FMVSS 213 bench or one of 3 second-row original equipment manufacturer vehicle seats was mounted to the deck of acceleration crash sled. An FFCRS with a restrained anthropomorphic test device (ATD) was secured by 3-point belt (3-PT) or LATCH lower anchor (LLA) on the C/FMVSS 213 bench or vehicle seat, with or without a tether. The sled was then exposed to a 48 km/h acceleration pulse. Three unique make and model vehicle seats and FFCRS were tested. Fifty-three sled tests were performed. RESULTS: When FFCRS were secured with LLA and no tether, little difference between the vehicle seats and 213 bench was observed. Similarly, when FFCRS were affixed with 3-PT and no tether, few kinematic variable differences achieved statistical significance; chest resultant acceleration was, on average, 9.1 g (SD=6.6, P=.006) higher on the vehicle seats compared to the bench, as was CRS seatback excursion (difference [Δ] of 39.8 mm, SD=32.7, P=.011) and ATD knee excursion (Δ=36.4 mm, SD=12.0, P<.001). However, when the tether was added to either the 3-PT or LLA attachment methods, the difference between the bench and vehicle seats was more pronounced. ATD kinematic measures such as head resultant acceleration (Δ=14.6 g, SD=7.2, P<.001) and pelvis resultant acceleration (Δ=8.6 g, SD=6.0, P=.005) were higher on the vehicle seats compared to the bench, as were the injury metrics for head and chest injury: ΔHIC15=162.2 (SD=87.4, P=.001) and ΔChest 3 ms clip=5.5 g (SD=6.2, P=.040). Of note, CRS (Δ=62.8 mm, SD=32.7, P=.000) and ATD head (Δ=66.3 mm, SD=30.9, P=.000) and knee (Δ=46.9 mm, SD=25.8, P=.001) forward excursion were all higher on the vehicle seats compared to the bench in 3-PT with tether condition. CONCLUSIONS: Without the tether attached, we observed few kinematic and kinetic differences between the vehicle seat and the C/FMVSS 213 bench, suggesting that the bench is an adequate surrogate for the vehicle seat in this condition. With the tether attached, we found significant differences between the C/FMVSS 213 bench and vehicle seats, suggesting that the fidelity of the bench could be improved in the tethered mode. When differences were statistically significant, excursion and injury metrics were generally greater on the vehicle seats than on the C/FMVSS 213 bench.

Pediatric occupant-vehicle contact maps in rollover motor vehicle crashes.

OBJECTIVE: Rollover crashes account for more than 33% of all motor vehicle-related fatalities and have the highest fatality risk of all crash types, at 1.37% in the United States. There is increased awareness of the high fatality rate associated with this crash type, but there is very limited pediatric-specific data related to rollover crashes in the United States. Recent focus on rollover mitigation has resulted in implementation of countermeasures, making it important to evaluate injury causation for child occupants in rollover crashes with a more current data set. METHODS: We queried the Crash Injury Research and Engineering Network (CIREN) from case years 1998 through 2013. Rollover crashes for passenger vehicles of model year 1998 or newer with at least one restrained occupant (excluding drivers) between 0 and 19 years of age were included. Vehicle-involved physical component and occupant-vehicle contact maps were developed with the CIREN data set. RESULTS AND CONCLUSIONS: Of the 20 CIREN cases that met the inclusion criteria, 15 had one or more injuries attributed to contact with some part of the vehicle structure. The CIREN analyses revealed that the head was the most common seriously injured body region, primarily due to contact with the roof side rail and/or vehicle interior. This finding was true for both adolescents and younger pediatric passengers in outboard seating positions. Fifty percent of head injury causation scenarios involving the vehicle interior had component intrusion of 20+ cm at the point of contact. Further exploration of pediatric rollover injury mechanisms using computational modeling and real-world testing is recommended in order to improve upon current mitigation strategies.

Injury risk for rear-seated occupants in small overlap crashes.

Small overlap crashes, where the primary crash engagement is outboard from the longitudinal energy absorbing structures of the vehicle, have received recent interest as a crash dynamic that results in high likelihood of injury. Previous analyses of good performing vehicles showed that 24% of crashes with AIS 3+ injuries to front seat occupants were small overlap crashes. However, similar evaluations have not been conducted for those rear seated. Vehicle dynamics suggest that rear seat occupants may be at greater risk due to lack of lateral seating support and a steering wheel to hold, making them more sensitive to lateral movement seen in these crashes. Thus, the objective was to calculate injury risk for rear-seated occupants in small overlap collisions. AIS 2+ and AIS 3+ injury risk was calculated from NASS-CDS data from 2000-2011. Inclusion criteria were vehicles of model year 2000 or later, with CDC codes of "FL" or "FR", and an occupant in the second or third row. AIS2+ injury risk was 5.1%, and AIS3+ injury risk was 2.4%. Of note, half of the occupants were <15 years of age indicating rear seat protection should emphasize the young. Occupants seated near side were nearly three times as likely to sustain an AIS2+ injury than occupants seated far side. Particular attention should be paid to the prominence of head injuries in this crash dynamic and consideration given to their mitigation. Additional research should determine whether countermeasures being implemented for front seat occupants can be beneficial to rear seat occupants.

Homogenization of vehicle fleet frontal crash pulses from 2000-2010.

Full-scale vehicle crash tests are performed globally to assess vehicle structure and restraint system performance. The crash pulse, captured by accelerometers mounted within the occupant compartment, measures the motion of the vehicle during the impact event. From an occupant's perspective, the crash pulse is the inertial event to which the vehicle's restraint systems must respond in order to mitigate the forces and accelerations that act on a passenger, and thus reduce injury risk. The objective of this study was to quantify the characteristics of crash pulses for different vehicle types in the contemporary North American fleet, and delineate current trends in crash pulse evolution. NHTSA and Transport Canada crash test databases were queried for full-frontal rigid barrier crash tests of passenger vehicles model year 2000-2010 with impact angle equaling zero degrees. Acceleration-time histories were analyzed for all accelerometers attached to the vehicle structure within the occupant compartment. Custom software calculated the following crash pulse characteristics (CPCs): peak deceleration, time of peak deceleration, onset rate, pulse duration, and change in velocity. Vehicle body types were classified by adapting the Highway Loss Data Institute (HLDI) methodology, and vehicles were assigned a generation start year in place of model year in order to more accurately represent structural change over time. 1094 vehicle crash tests with 2795 individual occupant compartment-mounted accelerometers were analyzed. We found greater peak decelerations and and shorter pulse durations across multiple vehicle types in newer model years as compared to older. For midsize passenger cars, large passenger cars, and large SUVs in 56 km/h rigid barrier tests, maximum deceleration increased by 0.40, 0.96, and 1.57 g/year respectively, and pulse duration decreased by 0.74, 1.87, and 2.51 ms/year. We also found that the crash pulse characteristics are becoming more homogeneous in the modern vehicle fleet; the range of peak deceleration values for all vehicle classes decreased from 17.1 g in 1997-1999 generation start years to 10.7 g in 2009-2010 generation years, and the pulse duration range decreased from 39.5 ms to 13.4 ms for the same generation year groupings. This latter finding suggests that the designs of restraint systems may become more universally applicable across vehicle body types, since the occupant compartment accelerations are not as divergent for newer vehicles.

Finite element aortic injury reconstruction of near side lateral impacts using real world crash data.

Traumatic rupture of the aorta (TRA) remains the second most common cause of death associated with motor vehicle crashes, only less prevalent than brain injury. On average, nearly 8000 people die annually in the United States due to blunt injury to the aorta. It is observed that over 80% of occupants who suffer an aortic injury die at the scene due to exsanguination into the chest cavity. In the current study, eight near side lateral impacts, in which TRA occurred, were reconstructed using a combination of real world crash data reported in the Crash Injury Research and Engineering Network (CIREN) database, finite element (FE) models of vehicles, and the Wayne State Human Body Model - II (WSHBM). For the eight CIREN cases reconstructed, the high strain regions in the aorta closely matched with the autopsy data provided. The peak average maximum principal strains in all of the eight CIREN cases were localized in the isthmus region of the aorta, distal to the left subclavian artery, and averaged at 22 ± 6.2% while the average maximum pressure in the aorta was found to be 117 ± 14.7 kPa.

Analysis of the mechanism of lateral impact aortic isthmus disruption in real-life motor vehicle crashes using a computer-based finite element numeric model: with simulation of prevention strategies.

INTRODUCTION: Despite advances in the surgical therapy of aortic injury (AI) using endovascular prostheses, more than 60% of motor vehicle crash (MVC) induced AIs die at the scene. In 80 cases of MVC AI, both change in velocity on impact (Delta V) and impact energy (IE) were correlated with autopsy or surgical findings. Of the 34 AIs due to lateral impact MVCs (LMVC), 91% had an aortic isthmus laceration. Computer simulation is used to study the cause of LMVC AI. METHODS: To delineate AI mechanism, 10 real life LMVCs (8 left, 2 right) were simulated using a computer-based finite element numerical model. Each began with the initial vehicle impact with another vehicle or fixed object, followed by the vehicle's compartment structures' impact with the patient's chest wall, causing a rise in intra-aortic pressure and the resulting location and pattern of aortic wall stresses and strains. In the real LMVCs, the Delta V ranged from 27.5 to 62 kph with impact energies of from 46,051 to 313,502 joules. In both real-life and the model, the main cause of the chest wall impact was intrusion of the car's B-pillar. Dynamic simulations delineate increased stress and strains at the aortic Isthmus. In some LMVCs, the B-pillar intrusion was also seen to impact the head in the AI cases. RESULTS: In the simulations, aortic pressure rose from 100 mm Hg precrash to as high as 1,322 mm Hg. Both the maximum aortic longitudinal tensile strain and the von Mises Stress were proportional to the maximum force impacted on the chest wall. Aortic isthmus maximum stresses ranged from 1.1 Mega Pascal (MPa) to 3.2 MPa, with longitudinal tensile strains ranging from 8.2% to 48.5%. The simulation dynamics demonstrated that the proximal pressurized turgid aorta initially moves toward the LMVC impact. As a result, the ascending aorta and aortic arch (proximal ascending aorta) rotate about the fulcrum of the great vessels, so that this aortic unit, acting as the long-arm of an Archimedes lever system, exerts the maximum stress and strain at the aortic isthmus or short-arm, where the real-life aortic rupture occurs. CONCLUSION: Simulation supports the lever hypothesis that the force on the short-arm aortic isthmus is proportionally greater than at the long-arm proximal aorta. Simulation also suggests improved vehicle construction techniques, which increase the strength and resistance to deformation of the B-pillar and vehicle side structure plus a B-pillar airbag will limit the intrusion forces causing LMVC AIs and reduce the incidence of associated head injuries.

Below Knee Impact Responses using Cadaveric Specimens.

Knee injuries represent about 10% of all injuries suffered during car crashes. Efforts to assess the injury risk to the posterior cruciate ligament (PCL) have been based on a study available in the literature (Viano et al., 1978), in which only two of the five knees tested had PCL ruptures. The aims of the current study were to repeat the study with a higher number of samples, study the effects of other soft tissues on knee response, and assess the adequacy of the experimental setup for the identification of a PCL tolerance. A total of 14 knees were tested using a high-speed materials testing machine. Eight were intact knees (with the patella and all the muscular and ligamentous structures), three were PCL-only knees (patella and all the muscular and ligamentous structures other than the PCL removed), and the last three were PCL-only knees with the tibia protected from bending fracture. Of the eight intact knees tested, only one had PCL mid substance rupture, one had a partial articular fracture of the tibia below the plateau, and six had simple transverse fracture of the tibial metaphysis. Of the three PCL-only knees without tibial protection, one had PCL mid substance rupture, one had avulsion at the posterior intercondylar attachment point, and the last one had a simple oblique fracture of the tibial metaphysis. Of the three PCL only knees with tibia protection, two had PCL mid-substance ruptures and the third one had an avulsion at the tibial insertion site with partial articular fracture of the lateral plateau. Overall, the results of the current study were similar to those observed by Viano et al. (1978). The average displacement at failure for all PCL related injuries was 17.2+/-2.8 mm for the current study (n=6) and 16.2+/-3.9 mm for Viano et al. (1978) (n=4). This value is higher than the Injury Assessment Reference Value of 15 mm proposed by Mertz (1984) and used in various regulations. Both studies suggest that the existence of the soft tissues other than the PCL affect the injury outcome and that the intact knee would suffer predominantly tibial metaphyseal fractures possibly due to bending. Consequently, it is concluded that the current experimental setup can produce isolated PCL injuries but the data available are inadequate to characterize PCL tolerance. A Hybrid III knee equipped with a ball bearing knee slider was also tested using a pendulum setup. Apart from the initial higher stiffness, the overall response of this knee lies within the force-deflection corridors defined using the response of the cadaver knees with PCL mid-substance failure.