Load-Based Lower Neck Injury Criteria for Females from Rear Impact from Cadaver Experiments

Kinematic analysis of an unrestrained passenger in an autonomous vehicle during emergency braking

Analyzing human body movement is a critical aspect of biomechanical studies in road safety. While most studies have traditionally focused on assessing the head-neck system due to the restraint provided by seat belts, it is essential to examine the entire pelvis-thorax-head kinematic chain when these body regions are free to move. The absence of restraint systems is prevalent in public transport and is also being considered for future integration into autonomous vehicles operating at low speeds. This article presents an experimental study examining the movement of the pelvis, thorax and head of 18 passengers seated without seat belts during emergency braking in an autonomous bus. The movement was recorded using a video analysis system capturing 100 frames per second. Reflective markers were placed on the knee, pelvis, lumbar region, thorax, neck and head, enabling precise measurement of the movement of each body segment and the joints of the lumbar and cervical spine. Various kinematic variables, including angles, displacements, angular velocities and accelerations, were measured. The results delineate distinct phases of body movement during braking and elucidate the coordination and sequentiality of pelvis, thorax and head rotation. Additionally, the study reveals correlations between pelvic rotation, lumbar flexion, and vertical trunk movement, shedding light on their potential impact on neck compression. Notably, it is observed that the elevation of the C7 vertebra is more closely linked to pelvic tilt than lumbar flexion. Furthermore, the study identifies that the maximum angular acceleration of the head and the maximum tangential force occur during the trunk's rebound against the seatback once the vehicle comes to a complete stop. However, these forces are found to be insufficient to cause neck injury. While this study serves as a preliminary investigation, its findings underscore the need to incorporate complete trunk kinematics, particularly of the pelvis, into braking and impact studies, rather than solely focusing on the head-neck system, as is common in most research endeavors.

Subaxial Cervical Spine Motion With Different Sizes of Head-supported Mass Under Accelerative Forces

INTRODUCTION

The evolution of military helmet devices has increased the amount of head-supported mass (HSM) worn by warfighters. HSM has important implications for spine biomechanics, and yet, there is a paucity of studies that investigated the effects of differing HSM and accelerative profiles on spine biomechanics. The aim of this study is to investigate the segmental motions in the subaxial cervical spine with different sizes of HSM under Gx accelerative loading.

METHODS

A three-dimensional finite element model of the male head-neck spinal column was used. Three different size military helmets were modeled and incorporated into head-neck model. The models were exercised under Gx accelerative loading by inputting low and high pulses to the cervical vertebra used in the experimental studies. Segmental motions were obtained and normalized with respect to the non-HSM case to quantify the effect of HSM.

RESULTS

Segmental motions increased with an increase in velocity at all segments of the spine. Increasing helmet size resulted in larger motion increases. Angulations ranged from 0.9° to 9.3° at 1.8 m/s and from 1.3° to 10.3° at 2.6 m/s without a helmet. Helmet increased motion between 5% to 74% at 1.8 m/s. At 2.6 m/s, the helmet increased segmental motion anywhere from 10% to 105% in the subaxial cervical spine. The greatest motion was seen at the C5-C6 level, followed by the C6-C7 level.

CONCLUSIONS

The subaxial cervical spine experiences motion increases at all levels at both velocity profiles with increasing HSM. Larger helmet and greater impact velocity increased motion at all levels, with C5-C6 demonstrating the largest range of motion. HSM should be minimized to reduce the risk of cervical spine injury to the warfighter.

Human pelvis injury risk curves from underbody blast impact

INTRODUCTION

Underbody blast loading can result in injuries to the pelvis and the lumbosacral spine. The purpose of this study was to determine human tolerance in this region based on survival analysis.

METHODS

Twenty-six unembalmed postmortem human surrogate lumbopelvic complexes were procured and pretest medical images were obtained. They were fixed in polymethylmethacrylate at the cranial end and a six-axis load cell was attached. The specimens were aligned in a seated soldier posture. Impacts were applied to the pelvis using a custom vertical accelerator. The experimental design consisted of non-injury and injury tests. Pretest and post-test X-rays and palpation were done following non-injury test, and after injury test medical imaging and gross dissections were done. Injuries were scored using the Abbreviated Injury Scale (AIS). Axial and resultant forces were used to develop human injury probability curves (HIPCs) at AIS 3+ and AIS 4 severities using survival analysis. Then ±95% CI was computed using the delta method, normalised CI size was obtained, and the quality of the injury risk curves was assigned adjectival ratings.

RESULTS

At the 50% probability level, the resultant and axial forces at the AIS 3+ level were 6.6 kN and 5.9 kN, and at the AIS 4 level these were 8.4 kN and 7.5 kN, respectively. Individual injury risk curves along with ±95% CIs are presented in the paper. Increased injury severity increased the HIPC metrics. Curve qualities were in the good and fair ranges for axial and shear forces at all probability levels and for both injury severities.

CONCLUSIONS

This is the first study to develop axial and resultant force-based HIPCs defining human tolerance to injuries to the pelvis from vertical impacts using parametric survival analysis. Data can be used to advance military safety under vertical loading to the seated pelvis.

Characterizing In-Situ Metatarsal Fracture Risk During Simulated Workplace Impact Loading

Metatarsal fractures represent the most common traumatic foot injury; however, metatarsal fracture thresholds remain poorly characterized, which affects performance targets for protective footwear. This experimental study investigated impact energies, forces, and deformations to characterize metatarsal fracture risk for simulated in situ workplace impact loading. A drop tower setup conforming to ASTM specifications for testing impact resistance of metatarsal protective footwear applied a target impact load (22-55 J) to 10 cadaveric feet. Prior to impact, each foot was axially loaded through the tibia with a specimen-specific bodyweight load to replicate a natural weight-bearing stance. Successive iterations of impact tests were performed until a fracture was observed with X-ray imaging. Descriptive statistics were computed for force, deformation, and impact energy. Correlational analysis was conducted on donor age, BMI, deformation, force, and impact energy. A survival analysis was used to generate injury risk curves (IRC) using impact energy and force. All 10 specimens fractured with the second metatarsal being the most common fracture location. The mean peak energy, force, and deformation during fracture were 46.6 J, 4640 N, 28.9 mm, respectively. Survival analyses revealed a 50% fracture probability was associated with 35.8 J and 3562 N of impact. Foot deformation was not significantly correlated (p = 0.47) with impact force, thus deformation is not recommended to predict metatarsal fracture risk. The results from this study can be used to improve test standards for metatarsal protection, provide performance targets for protective footwear developers, and demonstrate a methodological framework for future metatarsal fracture research.

Design and simulation of a PK testbed for head impact evaluation

This paper presents the design and simulation of a Parallel Kinematic (PK) testbed for head impacts. The proposed design is presented as a novel head impact testbed using a parallel platform as main motion simulation mechanism. The testbed is used to give a motion to a head mannequin to impact against a steel plate. In addition, the platform in the testbed allows to modify the orientation of the head mannequin model to evaluate different types of impacts. The testbed has been modeled with software MS ADAMS® to evaluate its performance with a dynamic simulation and to characterize the testbed design during top and lateral impact events. Results show that PK testbed gives a significant force and acceleration to the head mannequin at the moment of the impact.

Lower Neck Injury Assessment Risk Curves Based on Matched-Pair Human Data for Anthropomorphic Test Devices

INTRODUCTION

Under G +x accelerative loading, the Hybrid III anthropomorphic test device (ATD) is used to advance human safety. Although injury assessment risk curves (IARCs) are available at the level of the occipital condyles (commonly termed as upper neck), they do not exist for the cervical-thoracic junction (lower neck). The objectives of this study are to develop IARCs under G +x impact accelerations for the Hybrid III ATD and test device for human occupant restraint (THOR) ATD at the cervical thoracic junction.

METHODS

A series of Hybrid III ATD tests were conducted using input conditions that matched previously published cadaver tests. A separate series of THOR-ATD tests were conducted using the same input conditions that matched the same previously published cadaver tests. This type of experimental design where the cadaver input condition is the same as the ATD tests are termed matched-pair tests (Cadaver-Hybrid III and Cadaver-THOR-ATD). Injury outcomes from human cadaver tests were used with loads at the cervical thoracic junction, measured in the ATD tests. Data were censored based on injury outcomes and the number of tests conducted on each specimen. Parametric survival analysis was used to derive IARCs for cervical thoracic junction force-, moment-, and interaction-based lower neck injury criterion (LNic).

RESULTS

Injuries were scored according to the Abbreviated Injury Scale scheme. Abbreviated Injury Scale 1 or 2 was scored as injured. The 50% risk levels for the Hybrid III ATD were 315 N, 70 Nm, and 1.12 for the cervical thoracic A/P shear force-, sagittal plane extension moment-, and LNic-based injury criterion, respectively. Results for the THOR ATD were 261 N, 69 Nm, and 1.51.

CONCLUSIONS

This is the first study to develop cervical thoracic junction IARCs for the ATDs based on force, moment, and LNic for posterior to anterior loading.

Study of the Emergency Braking Test with an Autonomous Bus and the sEMG Neck Response by Means of a Low-Cost System

Nowadays, due to the advances and the increasing implementation of the autonomous braking systems in vehicles, the non-collision accident is expected to become more common than a crash when a sudden stop happens. The most common injury in this kind of accident is whiplash or cervical injury since the neck has high sensitivity to sharp deceleration. To date, biomechanical research has usually been developed inside laboratories and does not entirely represent real conditions (e.g., restraint systems or surroundings of the experiment). With the aim of knowing the possible neck effects and consequences of an automatic emergency braking inside an autonomous bus, a surface electromyography (sEMG) system built by low-cost elements and developed by us, in tandem with other devices, such as accelerometers or cameras, were used. Moreover, thanks to the collaboration of 18 participants, it was possible to study the non-collision effects in two different scenarios (braking test in which the passenger is seated and looking ahead while talking with somebody in front of him (BT1) and, a second braking test where the passenger used a smartphone (BT2) and nobody is seated in front of him talking to him). The aim was to assess the sEMG neck response in the most common situations when somebody uses some kind of transport in order to conclude which environments are riskier regarding a possible cervical injury.

Lower neck injury criteria for THOR and Hybrid III dummies in rear impact

OBJECTIVE

The objectives of the study are to derive lower-neck-injury probability curves under rear impact loading from matched pair Hybrid III and THOR dummy tests.

METHODS

Twelve whole-body and 15 isolated head-neck rear-impact sled tests were conducted using the 2 dummies. They were positioned on a rigid seat that was attached to an acceleration sled. The dummies were positioned with the head parallel to the ground, torso against the seat back, and legs stretched such that there was no axial rotation. The acceleration pulse matched the previous in-house human cadaver tests. The 6-axis lower-neck load cell was used in both dummies. For the isolated rear-impact tests, the head-neck was excised from the dummies, and the lower-neck load cell was mounted to the top of the sled with the head parallel to the ground and such that the acceleration vector was in the rear impact mode. Lower-neck loads and lower-neck-injury criteria (LN_ij) were obtained using the load cell data and survival analysis was used to develop injury-assessment-risk values and curves for both dummies. The LN_ij criteria were determined for both dummies using the intercept value corresponding to the 90% probability level for the forces and moments.

RESULTS

The lognormal and Weibull distributions were the optimal distributions for the Hybrid III and THOR devices. At the 50% risk level, the mean LN_ij was 1.1 and NCIS was 0.77 for the Hybrid III, and 1.5 and 0.30 for the THOR device. The quality indices were in the fair range and good range for the 2 dummies, respectively, at this risk level.

CONCLUSIONS

The lower neck based LN_ij injury assessment risk curves and reference values, IARCs and IARVs, serve as the first dataset for injury assessments, and the THOR may be a better test device for assessing injures in rear impact environments.

Uncertainty Evaluations for Risk Assessment in Impact Injuries and Implications for Clinical Practice

Injury risk curves (IRCs) represent the quantification of risk of adverse outcomes, such as a bone fracture, quantified by a biomechanical metric such as force or deflection. From a biomechanical perspective, they are crucial in crashworthiness studies to advance human safety. In clinical settings, they can be used as an assistive tool to aid in the decision-making process for surgical or conservative treatment. The estimation of risk corresponding to a level of biomechanical metric is done using a regression technique, such as a parametric survival regression model. As with any statistical procedure, error measures are computed for the IRC, representing the quality of the estimated risk. For example, confidence intervals (CIs) are recommended by the International Standards Organization, and the normalized confidence interval width (NCIW) is computed based on the width of the CI. This is a surrogate for the quality of the risk curve. A 95% CI means that if the same experiment were hypothetically repeated 100 times, at least 95 of the computed CIs should contain the true risk curve. Such an interpretation is problematic in most biomechanical contexts as rarely the same experiment is repeated. The notion that a wider confidence interval implies a poorer quality risk curve can be misleading. This article considers the evaluation of CIs and its implications in biomechanical settings for safety engineering and clinical practice. Alternatives are suggested for future studies.

Lumbar Spine Response of Computational Finite Element Models in Multidirectional Spaceflight Landing Conditions

The goals of this study are to compare the lumbar spine response variance between the hybrid III, test device for human occupant restraint (THOR), and global human body models consortium simplified 50th percentile (GHBMC M50-OS) finite element models and evaluate the sensitivity of lumbar spine injury metrics to multidirectional acceleration pulses for spaceflight landing conditions. The hybrid III, THOR, and GHBMC models were positioned in a baseline posture within a generic seat with side guards and a five-point restraint system. Thirteen boundary conditions, which were categorized as loading condition variables and environmental variables, were included in the parametric study using a Latin hypercube design of experiments. Each of the three models underwent 455 simulations for a total of 1365 simulations. The hybrid III and THOR models exhibited similar lumbar compression forces. The average lumbar compression force was 45% higher for hybrid III (2.2 ± 1.5 kN) and 51% higher for THOR (2.0 ± 1.6 kN) compared to GHBMC (1.3 ± 0.9 kN). Compared to hybrid III, THOR sustained an average 64% higher lumbar flexion moment and an average 436% higher lumbar extension moment. The GHBMC model sustained much lower bending moments compared to hybrid III and THOR. Regressions revealed that lumbar spine responses were more sensitive to loading condition variables than environmental variables across all models. This study quantified the intermodel lumbar spine response variations and sensitivity between hybrid III, THOR, and GHBMC. Results improve the understanding of lumbar spine response in spaceflight landings.

Application of resampling techniques to improve the quality of survival analysis risk curves for human frontal bone fracture

BACKGROUND

In automotive events, head injuries (skull fractures and/or brain injuries) are associated with head contact loading. While the widely-used head injury criterion is based on frontal bone fracture and linear accelerations, injury risk curves were not developed from original datasets.

OBJECTIVES

Develop skull fracture-based risk curves for using previously published data and apply resampling techniques to assess their qualities.

METHODS

Force, deflection, energy, and stiffness data from thirteen human cadaver head impact tests were used to develop risk curves using parametric survival analysis. Injuries occurred to all specimens. Data points were treated as uncensored. Variables were ranked, and the variable best explaining the underlying fracture response was determined using the Brier Score Metric (BSM). The qualities of the risk curves were determined using normalized confidence interval sizes. Statistical resampling methods were used to assess the quality of the risk curves and the impact of the sample size by conducting 2000 simulations. Sample sizes ranged from 13 to 26.

FINDINGS

The Weibull distribution was optimal for all the response variables, except deflection (log-logistic). The quality of the risk curves was the highest for deflection. This variable best explained the underlying head injury response, based on BSM. Improvements in the quality of the risk curves were achieved with additional samples of force and deflection (<13), while energy and stiffness variables required more size. Individual risk curves are given.

INTERPRETATION

These probability curves from head contact loading add to the understanding skull fractures and can be used to improve safety in injury producing environments.

Computational modeling and analysis of thoracolumbar spine fractures in frontal crash reconstruction

OBJECTIVE

This study aimed to reconstruct 11 motor vehicle crashes (6 with thoracolumbar fractures and 5 without thoracolumbar fractures) and analyze the fracture mechanism, fracture predictors, and associated parameters affecting thoracolumbar spine response.

METHODS

Eleven frontal crashes were reconstructed with a finite element simplified vehicle model (SVM). The SVM was tuned to each case vehicle and the Total HUman Model for Safety (THUMS) Ver. 4.01 was scaled and positioned in a baseline configuration to mimic the documented precrash driver posture. The event data recorder crash pulse was applied as a boundary condition. For the 6 thoracolumbar fracture cases, 120 simulations to quantify uncertainty and response variation were performed using a Latin hypercube design of experiments (DOE) to vary seat track position, seatback angle, steering column angle, steering column position, and D-ring height. Vertebral loads and bending moments were analyzed, and lumbar spine indices (unadjusted and age-adjusted) were developed to quantify the combined loading effect. Maximum principal strain and stress data were collected in the vertebral cortical and trabecular bone. DOE data were fit to regression models to examine occupant positioning and thoracolumbar response correlations.

RESULTS

Of the 11 cases, both the vertebral compression force and bending moment progressively increased from superior to inferior vertebrae. Two thoracic spine fracture cases had higher average compression force and bending moment across all thoracic vertebral levels, compared to 9 cases without thoracic spine fractures (force: 1,200.6 vs. 640.8 N; moment: 13.7 vs. 9.2 Nm). Though there was no apparent difference in bending moment at the L1-L2 vertebrae, lumbar fracture cases exhibited higher vertebral bending moments in L3-L4 (fracture/nonfracture: 45.7 vs. 33.8 Nm). The unadjusted lumbar spine index correctly predicted thoracolumbar fracture occurrence for 9 of the 11 cases (sensitivity = 1.0; specificity = 0.6). The age-adjusted lumbar spine index correctly predicted thoracolumbar fracture occurrence for 10 of the 11 cases (sensitivity = 1.0; specificity = 0.8). The age-adjusted principal stress in the trabecular bone was an excellent indicator of fracture occurrence (sensitivity = 1.0; specificity = 1.0). A rearward seat track position and reclined seatback increased the thoracic spine bending moment by 111-329%. A more reclined seatback increased the lumbar force and bending moment by 16-165% and 67-172%, respectively.

CONCLUSIONS

This study provided a computational framework for assessing thoracolumbar fractures and also quantified the effect of precrash driver posture on thoracolumbar response. Results aid in the evaluation of motor vehicle crash-induced vertebral fractures and the understanding of factors contributing to fracture risk.