Comparison of child and ATD belt fit and posture on belt-positioning boosters during self-selected, holding device, and nominal conditions

OBJECTIVE

Pediatric anthropomorphic test devices (ATDs) are important tools for the assessment of child occupant protection and should represent realistic child belt fit and posture on belt-positioning boosters. Previous comparisons have been made to children in either self-selected or nominal postural conditions. This study compares belt fit and postural measurements between pediatric ATDs and a single cohort of children assuming different postures on boosters: self-selected, holding a portable electronic device, and nominal.

METHODS

A cohort of children (n = 25) were evaluated in a stationary vehicle on five boosters and in three postural conditions: nominal, self-selected, and a representative holding electronic device position. The Hybrid III 6- and 10-year-old and Q-Series 6- and 10-year-old ATDs were evaluated in the same five boosters and in two postural conditions: nominal and a representative holding electronic device position. A 3D coordinate measurement device was used to quantify belt fit (shoulder belt score, lap belt score, maximum gap size, and gap length) and anatomic landmark positions (head, suprasternale, ASIS, and patella). Landmark positions and belt fit were compared between ATDs and children for each booster and postural condition, and Pearson correlations (r) were assessed across boosters.

RESULTS

ATDs generally represented Nominal child postures across boosters. In the Device condition, ATDs were seldom able to be positioned to represent both the torso and head position of children, due to limited ATD spinal flexibility. When the torso position was matched, the ATD head was more rear by 63 mm. Correlations between Nominal child and ATD belt fit and belt gap metrics were generally weak and not significant, with the exception of lap belt score (all ATDs p < 0.07, r = 0.8549-0.9857).

DISCUSSION

ATDs were generally able to represent realistic child postures and lap belt fit in Nominal and short duration Self-selected postures in a laboratory setting. However, these results display the potential difficulty of utilizing ATDs to represent more naturalistic child postures, especially the more forward head positions and flexed spinal posture associated with utilizing a portable electronic device.

Biofidelity assessment of the GHBMC M50-O in a rear-facing seat configuration during high-speed frontal impact

The objective of this study was to assess the biofidelity of the Global Human Body Models Consortium (GHBMC) 50th male (M50-O) v6.0 seated in an upright (25-degree recline) all-belts-to-seat (ABTS) in a 56 km/h rear-facing frontal impact. The experimental boundary conditions from the post-mortem human subjects (PMHS) tests were replicated in the computational finite element (FE) environment. The performance of the rigidized FE ABTS model obtained from the original equipment manufacturer was validated via simulations using a Hybrid III FE model and comparison with experiments. Biofidelity of the GHBMC M50-O was evaluated using the most updated NHTSA Biofidelity Ranking System (BRS) method, where a biofidelity score under 2 indicates that the GHBMC response varies from the mean PMHS response by less than two standard deviations, suggesting good biofidelity. The GHBMC M50-O received an occupant response score and a seat loading score of 1.71 and 1.44, respectively. Head (BRS = 0.93) and pelvis (BRS = 1.29) resultant accelerations, and T-spine (avg. BRS = 1.55) and pelvis (BRS = 1.66) y-angular velocities were similar to the PMHS. The T-spine resultant accelerations (avg. BRS = 1.93) and head (BRS = 2.82), T1 (BRS = 2.10) and pelvis (BRS = 2.10) Z-displacements were underestimated in the GHBMC. Peak chest deflection in the anterior-posterior deflection in the GHBMC matched with the PMHS mean, however, the relative upward motion of abdominal contents and subsequent chest expansion were not observed in the GHBMC. Updates to the GHBMC M50-O towards improved thorax kinematics and mobility of abdominal organs should be considered to replicate PMHS characteristics more closely.

Comparison of small female PMHS thoracic responses to scaled response corridors in a frontal hub impact

OBJECTIVE

The purpose of this study was to generate biomechanical response corridors of the small female thorax during a frontal hub impact and evaluate scaled corridors that have been used to assess biofidelity of small female anthropomorphic test devices (ATDs) and human body models (HBMs).

METHODS

Three small female postmortem human subjects (PMHS) were tested under identical conditions, in which the thorax was impacted using a 14.0 kg pneumatic impactor at an impact velocity of 4.3 m/s. Impact forces to PMHS thoraces were measured using a load cell installed behind a circular impactor face with a 15.2 cm diameter. Thoracic deflections were quantified using a chestband positioned at mid-sternum. Strain gages installed on the ribs and sternum identified fracture timing. Biomechanical response corridors (force-deflection) were generated and compared to scaled small female thoracic corridors using a traditional scaling method (TSM) and rib response-based scaling method (RRSM). A BioRank System Score (BRSS) was used to quantify differences between the small female PMHS data and both scaled corridors.

RESULTS

Coefficients of variation from the three small female PMHS responses were less than 2% for peak force and 7% for peak deflection. Overall, the scaled corridor means determined from the TSM and RRSM were less than two standard deviations away from the mean small female PMHS corridors (BRSS < 2.0). The RRSM resulted in smaller deviation (BRSS = 1.1) from the PMHS corridors than the TSM (BRSS = 1.7), suggesting the RRSM is an appropriate scaling method.

CONCLUSIONS

New small female PMHS force-deflection data are provided in this study. Scaled corridors from the TSM, which have been used to optimize current safety tools, were comparable to the small female PMHS corridors. The RRSM, which has the great benefit of using rib structural properties instead of requiring whole PMHS data, resulted in better agreement with the small female PMHS data than the TSM and deserves further investigation to identify scaling factors for other population demographics.

Biomechanical effects of a halo orthotic on a pediatric anthropomorphic test device in a simulated frontal motor vehicle collision

Objective: Cervical spine injuries in children under 10 frequently involve the craniocervical junction. In patients too small for conventional spinal instrumentation, treatment may involve placement of a halo orthotic, and these patients will frequently be discharged home in a halo orthotic. To date, little research has been done on the biomechanics of motor vehicle collisions involving young children in halo orthotics. To better understand possible safety concerns, we applied a halo orthotic to an appropriately sized anthropomorphic test device (ATD, or crash test dummy) on an acceleration sled to simulate a frontal motor vehicle collision.Methods: For the tests, a Hybrid III 3-year-old ATD was instrumented with head and chest accelerometers, head angular rate sensors, a six-axis upper neck load cell, and a chest linear potentiometer. Four tests were conducted on an acceleration sled, and kinematics were recorded with high speed video. Testing variables included 1) with or without a halo orthotic and 2) with a standard booster seat or a commercially available harness vest.Results: The halo orthotic reduced flexion and extension but was associated with increased rotation, especially in the condition of a halo orthotic with a standard booster seat. Increased cervical distraction was noted with the halo orthotic, and this was especially increased in the condition of a halo orthotic with the harness vest.Conclusions: The biomechanics of a child involved in a motor vehicular collision may be dramatically altered with a halo orthotic, as modeled by an acceleration sled test. While cervical spine flexion and extension are reduced with the halo orthotic, rotation appears to increase. Immobilization from a halo orthotic also appears to increase cervical distraction, especially when used in conjunction with a harness vest. Further testing is needed to determine the safest restraints for this small, but at-risk, population.

Development of a Strain-Based Model to Predict Eviscerated Thoracic Response From Dynamic Individual Rib Tests

The objective of this study was to develop an analytical model using strain-force relationships from individual rib and eviscerated thorax impacts to predict bony thoracic response. Experimental eviscerated thorax forces were assumed to have two distinct responses: an initial inertial response and subsequently, the main response. A second order mass-spring-damper model was used to characterize the initial inertial response of eviscerated thorax force using impactor kinematics. For the main response, equivalent strains in rib levels 4-7 were mapped at each time point and a strain-based summed force model was constructed using individual rib tests and the same ribs in the eviscerated thorax test. A piecewise approach was developed to join the two components of the curve and solve for mass, damping, stiffness parameters in the initial response, transition point, and scale factor of the strain-based summed force model. The final piecewise model was compared to the overall experimental eviscerated thorax forces for each PMHS (n=5) and resulted in R2 values of 0.87-0.96. A bootstrapping approach was utilized to validate the model. Final model predictions for the validation subjects were compared with the corridors constructed for the eviscerated thorax tests. BRSS values were approximately 0.71 indicating that this approach can predict eviscerated responses within one standard deviation from the mean response. This model can be expanded to other tissue states by quantifying soft tissue and visceral contributions, therefore successfully establishing a link between individual rib tests and whole thoracic response.

Evaluation of static belt fit and belt torso contact for children on belt-positioning booster seats

Objective: Previous studies have indicated that gap between the seatbelt and torso (reduced belt torso contact) for children on belt-positioning booster seats (BPBs) may lead to less torso engagement and increased likelihood of shoulder belt slip-off during evasive vehicle maneuvers, potentially increasing injury risk during crashes. However, current BPB belt fit measures do not quantify belt gap and may not be able to fully discriminate between designs which provide good vs. poor dynamic outcomes. The goal of this study was to evaluate both novel (belt gap characteristics) and conventional measures of seatbelt fit for BPB-seated children.Methods: Ten BPBs and three seatbelt anchor locations were investigated. Fifty volunteers (4-14 years) were recruited and each evaluated on six unique combinations of BPB and seatbelt anchor location on a vehicle rear seat in a laboratory setting. A 3 D coordinate measurement system quantified positions of anatomic, seatbelt, BPB, and vehicle reference points. Novel belt gap (gap size, length, location, and percent torso contact) and conventional belt fit (position of belt on shoulder and pelvis) metrics were calculated using anatomic and seatbelt landmarks. Variation in belt fit and belt gap outcomes due to BPB, seatbelt anchor location, and anthropometry were investigated.Results: BPBs produced significantly different outcomes, while seatbelt anchor location did not. BPBs with features that directly routed the lower portion of the shoulder belt more forward on the buckle side produced the largest (29.3 ± 12.6 mm) and longest (106.9 ± 68.2 mm) belt gap on average, while BPBs that pulled the belt less forward or did not directly route the belt produced the smallest (13.9 ± 6.7 mm) and shortest (16.9 ± 33.9 mm) gap on average. Belt gap outcomes were not strongly correlated with conventional belt fit metrics, indicating that evaluation of belt gap may provide additional insight when attempting to discriminate between BPBs which provide good vs. poor seatbelt engagement during vehicle maneuvers and crashes.Conclusions: This is the first study to evaluate belt gap characteristics for BPB-seated children. Results suggest that belt fit and belt gap are influenced by BPB design, particularly lower shoulder belt routings, and may have implications for belt engagement during dynamic events.

Evaluation of LATCH vs. non-LATCH installations for boosters in frontal impacts

OBJECTIVES

The objective was to understand how the use or nonuse of the Lower Anchors and Tethers for Children (LATCH) system affects the performance of booster seats during frontal impacts.

METHODS

Sixteen frontal impact sled tests were conducted at 24.8 ± 0.3 g and 50.1 ± 0.2 kph. A production vehicle seat buck was attached to the sled. Four high-back boosters or combination seats in high-back booster mode and two backless booster models were tested. Each booster model was installed two different ways: using the LATCH system ("LATCH" installation) and without using the LATCH system ("non-LATCH" installation). All installations used a 3-point seat belt with retractor in emergency locking mode (ELR) to restrain a Hybrid III 6-year-old anthropomorphic test device (ATD). The retractor, belt webbing, buckle, vehicle seat cushion, and booster were replaced after each test. Some conditions were tested twice to establish repeatability. ATD and booster responses were compared between LATCH and non-LATCH tests.

RESULTS

Using LATCH reduced the forward movement of the booster itself by 32.3% to 71.5% compared to non-LATCH installations. Differences in most other metrics were small and often within the range of normal test-to-test variation. Forward movements of the ATD head and heel were similar between LATCH and non-LATCH tests (typically less than 10% difference). HIC36 values trended slightly higher for LATCH installations compared to non-LATCH installations (0.8% to 17.2%). Chest resultant accelerations were typically 7.3% to 21.2% higher for LATCH installations, except for one booster for which it was lower with LATCH. Chest deflections trended higher for LATCH installations compared to non-LATCH installations for the backless boosters (6.9% to 14.1%). For high-back boosters, chest deflection was similar between installation conditions (less than 5% difference). Shoulder belt loads showed the greatest reductions when LATCH installations included a top tether (12.9% to 20.8%). Instances of the ATD submarining under the lap belt were not observed in these tests.

CONCLUSIONS

Overall, the differences in kinematics and injury metrics were small between boosters installed using LATCH vs. non-LATCH.

Biomechanical Responses and Injury Assessment of Post Mortem Human Subjects in Various Rear-facing Seating Configurations

The objective of this study was to generate biomechanical corridors from post-mortem human subjects (PMHS) in two different seatback recline angles in 56 km/h sled tests simulating a rear-facing occupant during a frontal vehicle impact. PMHS were placed in a production seat which included an integrated seat belt. To achieve a repeatable configuration, the seat was rigidized in the rearward direction using a reinforcing frame that allowed for adjustability in both seatback recline angle and head restraint position. The frame contained instrumentation to measure occupant loads applied to the head restraint and seatback. To measure PMHS kinematics, the head, spine, pelvis, and lower extremities were instrumented with accelerometers and angular rate sensors. Strain gages were attached to anterior and posterior aspects of the ribs, as well as the mid-shaft of the femora and tibiae, to determine fracture timing. A chestband was installed at the mid sternum to quantify chest deformation. Biomechanical corridors for each body and seat location were generated for each recline angle to provide data for quantitatively evaluating the biofidelity of ATDs and HBMs. Injuries included upper extremity injuries, rib fractures, pelvis fractures, and lower extremity injuries. More injuries were documented in the 45-degree recline case than in the 25-degree recline case. These injuries are likely due to the excessive ramping up and corresponding kinematics of the PMHS. Biomechanical corridors and injury information presented in this study could guide the design of HBMs and ATDs in rigid, reclined, rear-facing seating configurations during a high-speed frontal impact.

System providing automated feedback improves task learning outcomes during child restraint system (CRS) installations

OBJECTIVES

The objective was to build and test an automated, interactive educational system to teach adults how to install a child restraint system (CRS) into a vehicle seat.

METHODS

The automated feedback system (AFS) consisted of a mockup vehicle fixture, convertible CRS, and doll. Sensors were implemented into the equipment so that forward-facing (FF) CRS installation errors could be detected. An interactive display monitor guided users through the CRS installation process and alerted them when steps were done incorrectly. Sixty adult volunteers were recruited and randomized into either the treatment group or the control group. The treatment group used the AFS to guide them through a practice installation. The control group also completed a practice installation using the same equipment fixture without the feedback feature turned on; they only had standard printed instruction manuals to guide their tasks. Then, participants from both groups completed a second CRS installation in a real vehicle with standard instruction manuals only. The frequencies and types of errors in all the installations were evaluated by a Child Passenger Safety Technician (CPST). Error rates were compared between the treatment and control groups using lower-tailed t-tests and Pearson's chi-square tests. Error rates were evaluated considering minor and serious errors together and also considering serious errors alone.

RESULTS

Compared to the control group, participants who trained with the AFS exhibited fewer overall errors (minor and serious) in their fixture installations (p < 0.0001) as well as their follow-up vehicle installations (p < 0.0001). Specifically, participants in the treatment group had fewer errors in choosing an installation method, locking the seat belt (SB), tightening the SB or lower anchors (LA), and tightening the harness (p = 0.0002, p = 0.0003, p = 0.0084, and p = 0.0098, respectively, compared to control group during follow-up vehicle installations). The treatment group also performed significantly better than the control group when only serious errors were considered.

CONCLUSIONS

An automated feedback system is an effective way to teach basic CRS installation skills to users.

Efficacy of dance-based paradigms, wearable sensors, and auditory feedback for gait retraining in children: A feasibility study

BACKGROUND

Different feedback modes such as auditory, visual and haptic have been used in the past for gait retraining or learning movement patterns. The primary goal of this study was to investigate whether real time auditory feedback would be effective in children learning novel, dance-based movement patterns. For this purpose, a prototype wearable sensor was developed to provide auditory feedback whenever a child touches their heel to the ground.

METHODS

To test the effectiveness of the auditory feedback in learning new patterns, typically developing children were taught simple Indian dance protocols consisting of four counts of foot-work which involved alternating heel-toe movements. The effect of wearing the sensor was assessed by the maximum vertical force with which the subjects struck their foot on the plate.

RESULTS

Auditory feedback reduced the learning time and increased the number of correct movement patterns for trial duration of 2 min. The prototype device did not alter the maximum force with which the subject placed the foot on the ground.

CONCLUSIONS

Real time auditory feedback can be reliably used to learn novel movement patterns.

A Novel Approach to Scaling Age-, Sex-, and Body Size-Dependent Thoracic Responses using Structural Properties of Human Ribs

Thoracic injuries are frequently observed in motor vehicle crashes, and rib fractures are the most common of those injuries. Thoracic response targets have previously been developed from data obtained from post-mortem human subject (PMHS) tests in frontal loading conditions, most commonly of mid-size males. Traditional scaling methods are employed to identify differences in thoracic response for various demographic groups, but it is often unknown if these applications are appropriate, especially considering the limited number of tested PMHS from which those scaling factors originate. Therefore, the objective of this study was to establish a new scaling approach for generating age-, sex-, and body size- dependent thoracic responses utilizing structural properties of human ribs from direct testing of various demographics. One-hundred forty-seven human ribs (140 adult; 7 pediatric) from 132 individuals (76 male; 52 female; 4 pediatric) ranging in age from 6 to 99 years were included in this study. Ribs were tested at 2 m/s to failure in a frontal impact scenario. Force and displacement for individual ribs were used to develop new scaling factors, with a traditional mid-size biomechanical target as a baseline response. This novel use of a large, varied dataset of dynamic whole rib responses offers vast possibilities to utilize existing biomechanical data in creative ways to reduce thoracic injuries in diverse vehicle occupants.

Human Response and Injury Resulting from Head Impacts with Unmanned Aircraft Systems

Unmanned aircraft systems (UAS), commonly known as drones, are part of a new and budding industry in the United States. Economic and public benefits associated with UAS use across multiple commercial sectors are driving new regulations which alter the stringent laws currently restricting UAS flights over people. As new regulations are enacted and more UAS populate the national airspace, there is a need to both understand and quantify the risk associated with UAS impacts with the uninvolved public. The purpose of this study was to investigate the biomechanical response and injury outcomes of Post Mortem Human Surrogates (PMHS) subjected to UAS head impacts. For this work, PMHS were tested with differing UAS vehicles at multiple impact angles, locations and speeds. Using a custom designed launching device, UAS vehicles were accelerated into the frontal, parietal, or vertex portions of subjects' craniums at speeds up to 22 m/s. Of the 35 UAS impacts carried out, one AIS 2+ injury was observed: a 13 cm linear skull fracture resulting from a Phantom 3 impact. Additionally, injury risk curves used in automotive testing were found to over predict the risk of injury in UAS impact scenarios. Finally, localized skull deformation was observed during severe impacts; the effect that this deformation had on measured kinematics should be further evaluated. Overall, the study found that AIS 2+ head injuries may occur as a result of UAS impacts and that automotive injury metrics may not be able to accurately predict head injury risk in UAS impact scenarios.

Evaluation of interventions to make top tether hardware more visible during child restraint system (CRS) installations

Objectives: The objective of the study is to determine whether specific child restraint system (CRS) or vehicle conditions improve top tether attachment rates during volunteer installations. Methods: A factorial randomized controlled trial was designed to evaluate 4 different experimental categories: (1) Color of tether adjuster casing (black or red), (2) labeling on tether adjuster casing (labeled with "Tether: Use for forward-facing" or unlabeled), (3) storage location of tether (bundled in a rubber band on the back of CRS or Velcroed over the forward-facing belt path), and (4) labeling in vehicle (labeled under head restraint and below anchor or unlabeled). Ninety-six volunteers were randomly assigned to one combination of conditions. One installation per volunteer was completed. The primary outcome measure was acceptable attachment of the top tether to the tether anchor. The secondary outcome measure was overall secureness of the installation. Pearson's chi-square tests were used to identify significant predictors of acceptable outcomes and logistic regression was used to investigate interaction effects. Results: A total of 66/96 subjects (68.8%) attached the top tether in an acceptable manner, with either zero errors (n = 50) or minor errors (n = 16). A total of 30/96 subjects (31.2%) had unacceptable tether outcomes, with either major errors (n = 10) or nonuse the tether at all (n = 20). None of the 4 experimental categories significantly affected tether outcomes. Subjects who opted to install the CRS with the lower anchors (LAs) had higher rates of acceptable tether attachment compared to subjects who installed using the seat belt or those who used both LA and seat belt together (χ² = 6.792, P = .034). Tether outcomes were not correlated with previous CRS experience, use of instruction manual(s), age, or sex. Only 15.6% of subjects produced overall correct and tight installations. Of those who used the seat belt in some manner, 70.2% neglected to switch the retractor into locking mode. Conclusions: Conditions in this study including tether color, tether labeling, storage location, and vehicle labeling did not significantly affect tether attachment rates. High rates of tether misuse and nonuse warrant further exploration to find effective solutions to this usability problem.

A Military Case Review Method to Determine and Record the Mechanism of Injury (BioTab) from In-Theater Attacks

A recent study of all mounted vehicle underbody blast attacks found that 21% of Abbreviated Injury Scale Severity 2+ injuries in the Joint Trauma Analysis and Prevention of Injury in Combat network were injuries to the leg and ankle. To develop effective countermeasure systems for these attacks, the epidemiology and mechanisms of injury from this loading environment need to be quantified. The goal of this study was to develop a military correlate of an existing civilian case review framework, the Crash Injury Research and Engineering Network (CIREN), to consider the differences in military event types and the amount of available vehicle/attack information. Additional data fields were added to the CIREN process to cover military-specific data and "certainty" definitions in the proposed injury hypothesis were modified. To date, six group reviews have been conducted analyzing 253 injuries to the foot/ankle, tibia, femur, pelvis, and lumbar spine from 52 occupants. The familiar format and unclassified nature of the presentations allowed for the involvement of biomechanics experts from multiple disciplines.

Usability of non-standard lower anchor configurations for child restraint system (CRS) installation

OBJECTIVES

The objective of this study was to determine whether the amount of tension required for proper child restraint system (CRS) installation varies with lower anchor spacing and to determine whether nonexperts can produce adequate tension on wider-than-standard lower anchor configurations.

METHODS

CRSs were installed by certified child passenger safety technicians (CPSTs; n = 6 subjects, n = 72 installations) and nonexperts (n = 30 subjects, n = 120 installations) on a mock-up vehicle seat fixture with lower anchors set at 11 (standard), 15, 19, and 23 in. apart from one another. Each CPST installed a rear-facing (RF) infant base, RF convertible, and forward-facing (FF) convertible into each of the 4 spacing configurations in random order. The CPSTs were instructed to tighten the lower connector strap until the tension was exactly at the threshold between passing and failing the 1-in. test. Each nonexpert installed one CRS model into all 4 spacing conditions in random order. Nonexperts were instructed to install the CRS to the best of their ability. The tension produced on the lower connector strap was recorded via load cell in the lower anchor assembly of the vehicle seat. Resultant tension magnitudes were compared across spacing conditions using matched pair t-tests. The CPSTs' mean 1-in. test threshold values were compared to tensions produced by nonexperts. Installations were visually evaluated for errors and qualitative usability feedback was collected via survey.

RESULTS

CPSTs installed the infant base with higher tensions in the 15-, 19-, and 23-in. configurations compared to the standard 11-in. configuration (P = .034, .032, and .003, respectively). The nonexperts installed the infant base with higher tension in the 15- and 23-in. configurations compared to the 11-in. configuration (P = .004 and .026, respectively). The RF convertible and FF convertible installations showed no significant differences in tension among any of the spacing configurations for either group. Only 19% of the nonexperts' installations were tight enough to pass CPST thresholds, and the pass rate did not vary with respect to lower anchor spacing. In feedback surveys, the nonexpert group did not show a consistent preference for either standard or wider-than-standard lower anchor configurations.

CONCLUSIONS

The amount of tension required to pass the 1-in. rule did not vary with lower anchor spacing configurations for the RF and FF convertible CRS, but the infant base required more tension in wider anchor configurations. Nonexperts tended to produce less than ideal tension in all configurations, although their tension magnitudes increased for the infant base in wider configurations.

Quantification of Skeletal and Soft Tissue Contributions to Thoracic Response in a Dynamic Frontal Loading Scenario

Thoracic injuries continue to be a major health concern in motor vehicle crashes. Previous thoracic research has focused on 50^th percentile males and utilized scaling techniques to apply results to different demographics. Individual rib testing offers the advantage of capturing demographic differences; however, understanding of rib properties in the context of the intact thorax is lacking. Therefore, the objective of this study was to obtain the data necessary to develop a transfer function between individual rib and thoracic response. A series of non-injurious frontal impacts were conducted on six PMHS, creating a loading environment commensurate to previously published individual rib testing. Each PMHS was tested in four tissue states: intact, intact with upper limbs removed, denuded, and eviscerated. Following eviscerated thoracic testing, eight individual mid-level ribs from each PMHS were removed and loaded to failure. A simplified model in which ribs of each thorax are treated as parallel springs was utilized to evaluate the ability of individual rib response data to predict each subject's eviscerated thoracic response. On average across subjects, denuded thoraces retained 89% and eviscerated thoraces retained 46% of intact force. Similarly, denuded thoraces retained 70% and eviscerated thoraces retained 30% of intact stiffness. The rib model did not adequately predict eviscerated thoracic response but provided a better understanding of the influence of connective tissue on a rib's behavior with-in the thorax. Results of this study could be used in conjunction with the database of individual rib test results to improve thoracic response targets and help assess biofidelity of current anthropomorphic test devices.

Sources of Variability in Structural Bending Response of Pediatric and Adult Human Ribs in Dynamic Frontal Impacts

Despite safety advances, thoracic injuries in motor vehicle crashes remain a significant source of morbidity and mortality, and rib fractures are the most prevalent of thoracic injuries. The objective of this study was to explore sources of variation in rib structural properties in order to identify sources of differential risk of rib fracture between vehicle occupants. A hierarchical model was employed to quantify the effects of demographic differences and rib geometry on structural properties including stiffness, force, displacement, and energy at failure and yield. Three-hundred forty-seven mid-level ribs from 182 individual anatomical donors were dynamically (~2 m/s) tested to failure in a simplified bending scenario mimicking a frontal thoracic impact. Individuals ranged in age from 4 - 108 years (mean 53 ± 23 years) and included 59 females and 123 males of diverse body sizes. Age, sex, body size, aBMD, whole rib geometry and cross-sectional geometry were explored as predictors of rib structural properties. Measures of cross-sectional rib size (Tt.Ar), bone quantity (Ct.Ar), and bone distribution (Z) generally explained more variation than any other predictors, and were further improved when normalized by rib length (e.g., robustness and WBSI). Cortical thickness (Ct.Th) was not found to be a useful predictor. Rib level predictors performed better than individual level predictors. These findings moderately explain differential risk for rib fracture and with additional exploration of the rib's role in thoracic response, may be able contribute to ATD and HBM development and alterations in addition to improvements to thoracic injury criteria and scaling methods.

Compatibility of booster seats and vehicles in the U.S. market

OBJECTIVE

The objective of this study was to analyze booster and rear vehicle seat dimensions to identify the most frequent compatibility problems.

METHODS

Measurements were collected from 40 high-back and backless boosters and 95 left rear and center rear row seating positions in 50 modern vehicles. Dimensions were compared for 3,800 booster/vehicle seat combinations. For validation and estimation of tolerance and correction factors, 72 booster installations were physically completed and compared with measurement-based compatibility predictions. Dimensions were also compared to the International Organization for Standardization (ISO) volumetric envelopes of forward-facing child restraints and boosters.

RESULTS

Seat belt buckles in outboard positions accommodated the width of boosters better than center positions (success rates of 85.4 and 34.7%, respectively). Adequate head restraint clearance occurred in 71.9 to 77.2% of combinations, depending on the booster's head support setting. Booster recline angles aligned properly with vehicle seat cushion angles in 71.5% of combinations. In cases of poor angle alignment, booster angles were more obtuse than the vehicle seat angles 97.7% of the time. Head restraint interference exacerbated angle alignment issues. Data indicate success rates above 90% for boosters being fully supported by the length of the seat cushion and for adequate height clearance with the vehicle roofline. Comparison to ISO envelopes indicates that most boosters on the U.S. market are taller and angled more obtusely than ISO target envelopes.

CONCLUSIONS

This study quantifies some of the common interferences between boosters and vehicles that may complicate booster usage. Data are useful for design and to prioritize specific problem areas.

A heel-strike real-time auditory feedback device to promote motor learning in children who have cerebral palsy: a pilot study to test device accuracy and feasibility to use a music and dance-based learning paradigm

Background

Cerebral palsy (CP) is a developmental disorder of movement and posture that occurs due to damage to the developing nervous system. As part of therapy, wearable sensors that trigger interactive feedback may provide multi-sensory guidance and motivation. A prototype of a heel-strike real-time feedback system has been developed which records the number of heel strikes during gait and indicates successful heel contact through real-time auditory feedback. The first aim of this feasibility study was to test the prototype accuracy.Since the end user for this device is a child, the device should be esthetically appealing and sufficiently motivating for children to perform repetitive challenging therapeutic movements. The second aim of this study was to collect feedback from the subjects with regard to the device usability and understand if the bell sound used as feedback used was motivating enough for children to continue using the prototype. This would help us in developing the next generation of the device.

Methods

The prototype was tested with typically developing children and children who have CP. The accuracy in detecting heel strikes was calculated. As part of the study, the subjects were also asked questions to test the device compliance and acceptability of the musical beats with the pediatric population.

Results

The device accuracy in identifying heel strikes is 97.44% (95% CI 96.31, 98.88%). The subjects did not show any hesitation to put on the device and the sound feedback motivated them to move. Based on this pilot study, a minimum age limit of 5 years is appropriate and the intervention study should be conducted for no more than 30 min per week.

Conclusions

The pilot study showed that a main study can be conducted to test auditory feedback as an intervention to promote motor learning in children who have cerebral palsy. No adverse event or safety issues were reported in the feasibility study.

COMPARISON OF A HEAD MOUNTED IMPACT MEASUREMENT DEVICE TO THE HYBRID III ANTHROPOMORPHIC TESTING DEVICE IN A CONTROLLED LABORATORY SETTING

BACKGROUND

Reports estimate that 1.6 to 3.8 million cases of concussion occur in sports and recreation each year in the United States. Despite continued efforts to reduce the occurrence of concussion, the rate of diagnosis continues to increase. The mechanisms of concussion are thought to involve linear and rotational head accelerations and velocities. One method of quantifying the kinematics experienced during sport participation is to place measurement devices into the athlete's helmet or directly on the athlete's head.

PURPOSE

The purpose of this research to determine the accuracy of a head mounted device for measuring the head accelerations experienced by the wearer. This will be accomplished by identifying the error in Peak Linear Acceleration (PLA), Peak Rotational Acceleration (PRA) and Peak Rotational Velocity (PRV) of the device.

STUDY DESIGN

Laboratory study.

METHODS

A helmeted Hybrid III 50th percentile male headform was impacted via a pneumatic ram from the front, side, rear, front oblique and rear oblique at speeds from 1.5 to 5 m/s. The X2 Biosystems xPatch® (Seattle, WA) sensor was placed on the headform's right side at the approximate location of the mastoid process. Measures of PLA, PRA, PRV from the xPatch ® and Hybrid III were analyzed for Root Mean Square Error (RMSE), and Absolute and Relative Error (AE, RE).

RESULT

Seventy-six impacts were analyzed. All measures of correlation, fixed through the origin, were found to be strong: PLA R²=0.967 p<0.01, PRA R²=0.933 p<0.01, PRV R²=0.999 p<0.00. PLA RMSE was 34%, RE 31.0%±14.0, and AE 31.1%±13.7. PRA RMSE was 23.4%, RE -6.7 ± 22.4 and AE 18.9%±13.8. PRV RMSE was 2.2%, RE 0.1 ± 2.2, and AE 1.8 ± 1.3.

CONCLUSION

Without including corrections for effect of skin artifact, the xPatch® produces measurements highly correlated with the gold standard yet above the average error of testing devices in both PLA and PRA, but a low error in PRV. PLA measures from the xPatch® system demonstrated a high level of correlation with the PLA data from the Hybrid III mounted data collection system.

LEVEL OF EVIDENCE

3.

Repeatability testing of a new Hybrid III 6-year-old ATD lower extremity

OBJECTIVE

Vehicle safety is improving, thus decreasing the number of life-threatening injuries and increasing the need for research in other areas of the body. The current child anthropomorphic test device (ATD) does not have the capabilities or instrumentation to measure many of the potential interactions between the lower extremity and the vehicle interior. A prototype Hybrid III 6-year-old ATD lower extremity (ATD-LE) was developed and contains a tibia load cell and a more biofidelic ankle. The repeatability of the device has not yet been assessed; thus, the objective was to evaluate the repeatability of the ATD-LE. Additionally, a dynamic assessment was conducted to quantify injury threshold values.

METHODS

A pneumatic ram impactor was used at 2 velocities to evaluate repeatability. The ATD-LE was fixed to a table and impacted on the plantar aspect of the forefoot. Three repeated trials at 1.3 and 2.3 m/s without shoes and 2.3 m/s with shoes were conducted. The consistency of tibia force (N), bending moment (Nm), ankle range of motion (ROM, °), and stiffness (Nm/°) were quantified. A dynamic assessment using knee bolster airbag (KBA) tests was also conducted. The ATD-LE was positioned to mimic 3 worst-case scenarios: toes touching the mid-dashboard, touching the lower dashboard, and flat on the floor prior to airbag deployment. The impact responses in the femur and tibia were directly collected and compared with published injury threshold values.

RESULTS

Ram impact testing indicated primarily excellent repeatability for the variables tested. For all 3 conditions the coefficients of variance (CV) were as follows: tibia force, 1.9-2.7%; tibia moment, 1.0-2.2%; ROM, 1.3-1.4%; ankle stiffness, 4.8-15.6%. The shoe-on condition resulted in a 25% reduction in tibia force and a 56% reduction in tibia bending moment. The KBA tests indicate that the highest injury risk may be when the toes touch the lower dashboard, due to the high bending moments recorded in the tibia at 76.2 Nm, which was above the injury threshold.

CONCLUSIONS

The above work has demonstrated that the repeatability of the ATD-LE was excellent for tibia force, bending moment, and ankle ROM. The ATD-LE has the ability to provide new information to engineers and researchers due to its ability to directly evaluate the crash response of the ankle and leg. New information on injury mechanism and injury tolerance may lead to injury reduction and thus help advance the safety of children.

Rib Geometry Explains Variation in Dynamic Structural Response: Potential Implications for Frontal Impact Fracture Risk

The human thorax is commonly injured in motor vehicle crashes, and despite advancements in occupant safety rib fractures are highly prevalent. The objective of this study was to quantify the ability of gross and cross-sectional geometry, separately and in combination, to explain variation of human rib structural properties. One hundred and twenty-two whole mid-level ribs from 76 fresh post-mortem human subjects were tested in a dynamic frontal impact scenario. Structural properties (peak force and stiffness) were successfully predicted (p < 0.001) by rib cross-sectional geometry obtained via direct histological imaging (total area, cortical area, and section modulus) and were improved further when utilizing a combination of cross-sectional and gross geometry (robusticity, whole bone strength index). Additionally, preliminary application of a novel, adaptive thresholding technique, allowed for total area and robusticity to be measured on a subsample of standard clinical CT scans with varied success. These results can be used to understand variation in individual rib response to frontal loading as well as identify important geometric parameters, which could ultimately improve injury criteria as well as the biofidelity of anthropomorphic test devices (ATDs) and finite element (FE) models of the human thorax.

Biomechanical Responses of PMHS Subjected to Abdominal Seatbelt Loading

Past studies have found that a pressure based injury risk function was the best predictor of liver injuries due to blunt impacts. In an effort to expand upon these findings, this study investigated the biomechanical responses of the abdomen of post mortem human surrogates (PMHS) to high-speed seatbelt loading and developed external response targets in conjunction with proposing an abdominal injury criterion. A total of seven unembalmed PMHS, with an average mass and stature of 71 kg and 174 cm respectively were subjected to belt loading using a seatbelt pull mechanism, with the PMHS seated upright in a freeback configuration. A pneumatic piston pulled a seatbelt into the abdomen at the level of the umbilicus with a nominal peak penetration speed of 4.0 m/s. Pressure transducers were placed in the re-pressurized abdominal vasculature, including the inferior vena cava (IVC) and abdominal aorta, to measure internal pressure variation during the event. Jejunum tear, colon hemorrhage, omentum tear, splenic fracture and transverse processes fracture were identified during post-test anatomical dissection. Peak abdominal forces ranged from 2.8 to 4.7 kN. Peak abdominal penetrations ranged from 110 to 177 mm. A force-penetration corridor was developed from the PMHS tests in an effort to benchmark ATD biofidelity. Peak aortic pressures ranged from 30 to 104 kPa and peak IVC pressures ranged from 36 to 65 kPa. Updated pressure based abdominal injury risk functions were developed for vascular Ṗ_max and P_max*Ṗ_max.

Biofidelity Evaluation of a Prototype Hybrid III 6 Year-Old ATD Lower Extremity

Incomplete instrumentation and a lack of biofidelity in the extremities of the 6 year-old anthropomorphic test device (ATD) pose challenges when studying regions of the body known to interact with the vehicle interior. This study sought to compare a prototype Hybrid III 6 year-old ATD leg (ATD-LE), with a more biofidelic ankle and tibia load cell, to previously collected child volunteer data and to the current Hybrid III 6 year-old ATD (HIII). Anthropometry, range of motion (ROM), and stiffness measurements were taken, along with a dynamic evaluation of the ATD-LE using knee-bolster airbag (KBA) test scenarios. Anthropometry values were similar in eight of twelve measurements. Total ankle ROM was improved in the ATD-LE with no bumper compared to the HIII. The highest tibia moments and tibia index values were recorded in KBA scenarios when the toes were positioned in contact with the dashboard prior to airbag deployment, forcing the ankle into axial loading and dorsiflexion. While improvements in the biofidelity of the ATD-LE are still necessary, the results of this study are encouraging. Continued advancement of the 6 year-old ATD ankle is necessary to provide a tool to directly study the behavior of the leg during a motor vehicle crash.

Comparison of ATD to PMHS Response in the Under-Body Blast Environment

A blast buck (Accelerative Loading Fixture, or ALF) was developed for studying underbody blast events in a laboratory-like setting. It was designed to provide a high-magnitude, high-rate, vertical loading environment for cadaver and dummy testing. It consists of a platform with a reinforcing cage that supports adjustable-height rigid seats for two crew positions. The platform has a heavy frame with a deformable floor insert. Fourteen tests were conducted using fourteen PMHS (post mortem human surrogates) and the Hybrid III ATD (Anthropomorphic Test Device). Tests were conducted at two charge levels: enhanced and mild. The surrogates were tested with and without PPE (Personal Protective Equipment), and in two different postures: nominal (knee angle of 90°) and obtuse (knee angle of 120°). The ALF reproduces damage in the PMHS commensurate with injuries experienced in theater, with the most common damage being to the pelvis and ankle. Load is transmitted through the surrogates in a caudal-to-cranial sequential fashion. Damage to the PMHS lower extremities begins within 2 ms after the initiation of foot/floor motion. The Hybrid III cannot assume the posture of the PMHS in rigid seats and exhibits a stiffer overall response compared to the PMHS. The ATD does not mimic the kinematic response of the PMHS lower extremities. Further, the Hybrid III does not have the capability to predict the potential for injury in the high-rate, vertical loading environment. A new ATD dedicated to under-body blast is needed to assist in the effort to mitigate injuries sustained by the mounted soldier.

Investigation of Child Restraint System (CRS) Compatibility in the Vehicle Seat Environment

OBJECTIVE

Child restraint system (CRS) misuse is common and can have serious consequences to child safety. Physical incompatibilities between CRS and vehicles can complicate the installation process and may worsen CRS misuse rates. This study aims to identify the most common sources of incompatibility between representative groups of CRS and vehicles.

METHODS

Detailed dimensional data were collected from 59 currently marketed CRS and 61 late model vehicles. Key dimensions were compared across all 3,599 theoretical CRS/vehicle combinations and the most common predicted incompatibilities were determined. A subset of 34 physical installations was analyzed to validate the results.

RESULTS

Only 58.2% of rear-facing (RF) CRS/vehicle combinations were predicted to have proper agreement between the vehicle's seat pan angle and the CRS manufacturers' required base angle. The width of the base of the CRS was predicted to fit snugly between the vehicle's seat pan bolsters in 63.3% of RF CRS/vehicle combinations and 62.2% of forward-facing (FF) CRS/vehicle combinations. FF CRS were predicted to be free of interaction with the vehicle's head restraint in 66.4% of combinations. Roughly 90.0% of RF CRS/vehicle combinations were predicted to have enough horizontal clearance space to set the front seat in the middle its fore/aft slider track. Compatibility rates were above 98% regarding the length of the CRS base compared to the length of the vehicle seat pan and the ability of the top tether to reach the tether anchor. Validation studies revealed that the predictions of RF CRS base angle range vs. seat pan angle compatibility were accurate within 6%, and head restraint interference and front row clearance incompatibilities may be more common than the dimensional analysis approach has predicted.

CONCLUSIONS

The results of this study indicate that RF CRS base angles and front row clearance space, as well as FF CRS head restraint interference, are frequent compatibility concerns. These results enable manufacturers, researchers, and consumers to focus their attention on the most relevant CRS/vehicle incompatibility issues in today's market.

Simulation of occupant response in space capsule landing configurations with suit hardware

The purpose of this study was to compare the response of the total human model for safety (THUMS) human body finite element model (FEM) to experimental postmortem human subject (PMHS) test results and evaluate possible injuries caused by suit ring elements. Experimental testing evaluated the PMHS response in frontal, rear, side, falling, and spinal impacts. The THUMS was seated in a rigid seat that mirrored the sled buck used in the experimental testing. The model was then fitted with experimental combinations of neck, shoulder, humerus and thigh rings with a five-point restraint system. Experimental seat acceleration data was used as the input for the simulations. The simulation results were analyzed and compared to PMHS measurements to evaluate the response of the THUMS in these loading conditions. The metrics selected to compare the THUMS simulation to PMHS tests were the chest acceleration, seat acceleration and belt forces with additional metrics implemented in THUMS. The chest acceleration of the simulations and the experimental data was closely matched except in the Z-axis (superior/inferior) loading scenarios based on signal analysis. The belt force data of the model better correlated to the experimental results in loading scenarios where the THUMS interacted primarily with the restraint system compared to load cases where the primary interaction was between the seat and the occupant (rear, spinal and lateral impacts). The simulation output demonstrated low injury metric values for the occupant in these loading conditions. In the experimental testing, rib fractures were recorded for the frontal and left lateral impact scenarios. Fractures were not seen in the simulations, most likely due to variations between the simulation and the PMHS initial configuration. The placement of the rings on the THUMS was optimal with symmetric placement about the centerline of the model. The experimental placement of the rings had more experimental variation. Even with this discrepancy, the THUMS can still be considered a valuable predictive tool for occupant injury because it can compare results across many simulations. The THUMS also has the ability to assess a wider variety of other injury information, compared to anthropomorphic test devices (ATDs), that can be used to compare simulation results.

Validation of a helmet-based system to measure head impact biomechanics in ice hockey

PURPOSE

This study aimed to quantify differences between head acceleration measured by a helmet-based accelerometer system for ice hockey and an anthropometric test device (ATD) to validate the system's use in measuring on-ice head impacts.

METHODS

A Hybrid III 50th percentile male ATD head and neck was fit with a helmet instrumented with the Head Impact Telemetry (HIT) System for hockey and impacted at various speeds and directions with different interfaces between the head and helmet. Error between the helmet-based and reference peak accelerations was quantified, and the influence of impact direction and helmet-head interface was evaluated. Regression equations were used to reduce error. System-reported impact direction was validated.

RESULTS

Nineteen percent of impacts were removed from the data set by the HIT System processing algorithm and were not eligible for analysis. Errors in peak acceleration between the system and ATD varied from 18% to 31% and from 35% to 64% for linear and rotational acceleration, respectively, but were reduced via regression equations. The relationship between HIT System and reference acceleration varied by direction (P < 0.001) and head-helmet interface (P = 0.005). Errors in impact azimuth were approximately 4%, 10%, and 31% for side, back, and oblique back impacts, respectively.

CONCLUSIONS

This is the first comprehensive evaluation of peak head acceleration measured by the HIT System for hockey. The HIT System processing algorithm removed 19% of the impacts from the data set, the correlation between HIT System and reference peak resultant acceleration was strong and varied by head surface and impact direction, and the system error was larger than reported for the 6-degree-of-freedom HIT System for football but could be reduced via calibration factors. These findings must be considered when interpreting on-ice data.

Comparison of cervical vertebrae rotations for PMHS and BioRID II in rear impacts

OBJECTIVE

The objectives of this study are to propose a new instrumentation technique for measuring cervical spine kinematics, validate it, and apply the instrumentation technique to postmortem human subjects (PMHS) in rear impact sled tests so that cervical motions can be investigated.

METHODS

First, a new instrumentation and dissection technique is proposed in which instrumentation (3 accelerometers, 3 angular rate sensors) capable of measuring the detailed intervertebral kinematics are installed on the anterior aspects of each vertebral body with minimal muscular damage. The instrumentation was validated by conducting 10 km/h rear impact tests with 2 PMHS in a rigid rolling chair. After this validation, a total of 14 sled tests using 8 male PMHS (175 ± 6.9 cm stature and 78.4 ± 7.7 kg weight) were conducted in 2 moderate-speed rear impacts (8.5 g, 17 km/h; 10.5 g, 24 km/h). A current rear impact dummy, BioRID II, was also tested under the same condition with an angular rate sensor installed on each of the cervical vertebrae so that rotations of the cervical spine of the BioRID II could be compared to those measured from the PMHS. The National Highway Traffic Safety Administration (NHTSA) biofidelity ranking system was used for quantitative analysis of the BioRID II cervical spine biofidelity.

RESULTS

Results show that the BioRID II exhibited comparable rotations to the PMHS in the 17 km/h test, but the vertebrae in the lower cervical spine (C5-C7) of the BioRID II showed less rearward rotation than the PMHS. For the 24 km/h test, the vertebrae in the cervical spine of the BioRID II exhibited less rearward rotation than the PMHS at all levels (C2-C7). The average biofidelity score for C2 through C7 was 1.02 for the 17 km/h test, and 2.27 for the 24 km/h test.

CONCLUSIONS

These results reflect the fact that the fully articulated spine of the BioRID II was designed and tuned to model low speed rear impacts. The intervertebral rotations for both the PMHS and the BioRID II were primarily relative flexion rotations even though the cervical vertebrae rotated rearward with respect to the global coordinate system.

Biomechanical responses of PMHS in moderate-speed rear impacts and development of response targets for evaluating the internal and external biofidelity of ATDS

The objectives of this study were to obtain biomechanical responses of post mortem human subjects (PMHS) by subjecting them to two moderate-speed rear impact sled test conditions (8.5g, 17 km/h; 10.5g, 24 km/h) while positioned in an experimental seat system, and to create biomechanical targets for internal and external biofidelity evaluation of rear impact ATDs. The experimental seat was designed to measure external loads on the head restraint (4 load cells), seat back (6 load cells), and seat pan (4 load cells) such that subject dynamic interaction with the seat could be evaluated. This seat system was capable of simulating the dynamic characteristics of modern vehicle seat backs by considering the moment-rotation properties of a typical passenger vehicle, thus providing a more realistic test environment than using a rigid seat with a non-rotating seat back as done in previous studies. Instrumentation used to measure biomechanical responses of the PMHS included both accelerometers and angular rate sensors (ARS). A total of fourteen sled tests using eight PMHS (males 175.8 ± 6.2 cm of stature and 78.4 ± 7.2 kg of weight) provided data sets of seven PMHS for both test conditions. The biomechanical responses are described at both speeds, and cervical spine injuries are documented. Biomechanical targets are also created for internal and external biofidelity evaluation of rear impact anthropomorphic test devices (ATDs).

Evaluation of the internal and external biofidelity of current rear impact ATDs to response targets developed from moderate-speed rear impacts of PMHS

The goal of this study is to evaluate both the internal and external biofidelity of existing rear impact anthropomorphic test devices (BioRID II, RID3D, Hybrid III 50th) in two moderate-speed rear impact sled test conditions (8.5g, 17 km/h; 10.5g, 24 km/h) by quantitatively comparing the ATD responses to biomechanical response targets developed from PMHS testing in a corresponding study. The ATDs and PMHS were tested in an experimental seat system that is capable of simulating the dynamic seat back rotation response of production seats. The experimental seat contains a total of fourteen load cells installed such that external loads from the ATDs and PMHS can be measured to evaluate external biofidelity. The PMHS were instrumented to correspond to the instrumentation contained in the ATDs so that direct comparison between ATDs and PMHS could be made to evaluate internal biofidelity. The NHTSA Biofidelity Ranking system was used to quantitatively evaluate the biofidelity of the ATDs and an additional tool was introduced and utilized which allows for the biofidelity score to be partitioned into components of amplitude, phase, and shape. For internal biofidelity, the BioRID II and RID3D were more biofidelic than the Hybrid III in the 17 km/h test, and the BioRID II was most biofidelic in the 24 km/h test. For external biofidelity, the BioRID II was most biofidelic in the 17 km/h test, while both the BioRID II and the RID3D were more biofidelic than the Hybrid III in the 24 km/h test. Overall, the BioRID II demonstrated the best biofidelity in both the 17 km/h and 24 km/h tests.

Measurement of six degrees of freedom head kinematics in impact conditions employing six accelerometers and three angular rate sensors (6aω configuration)

The ability to measure six degrees of freedom (6 DOF) head kinematics in motor vehicle crash conditions is important for assessing head-neck loads as well as brain injuries. A method for obtaining accurate 6 DOF head kinematics in short duration impact conditions is proposed and validated in this study. The proposed methodology utilizes six accelerometers and three angular rate sensors (6aω configuration) such that an algebraic equation is used to determine angular acceleration with respect to the body-fixed coordinate system, and angular velocity is measured directly rather than numerically integrating the angular acceleration. Head impact tests to validate the method were conducted using the internal nine accelerometer head of the Hybrid III dummy and the proposed 6aω scheme in both low (2.3 m/s) and high (4.0 m/s) speed impact conditions. The 6aω method was compared with a nine accelerometer array sensor package (NAP) as well as a configuration of three accelerometers and three angular rate sensors (3aω), both of which have been commonly used to measure 6 DOF kinematics of the head for assessment of brain and neck injuries. The ability of each of the three methods (6aω, 3aω, and NAP) to accurately measure 6 DOF head kinematics was quantified by calculating the normalized root mean squared deviation (NRMSD), which provides an average percent error over time. Results from the head impact tests indicate that the proposed 6aω scheme is capable of producing angular accelerations and linear accelerations transformed to a remote location that are comparable to that determined from the NAP scheme in both low and high speed impact conditions. The 3aω scheme was found to be unable to provide accurate angular accelerations or linear accelerations transformed to a remote location in the high speed head impact condition due to the required numerical differentiation. Both the 6aω and 3aω schemes were capable of measuring accurate angular displacement while the NAP instrumentation was unable to produce accurate angular displacement due to double numerical integration. The proposed 6aω scheme appears to be capable of measuring accurate 6 DOF kinematics of the head in any severity of impact conditions.

Pressure-based abdominal injury criteria using isolated liver and full-body post-mortem human subject impact tests

Liver trauma research suggests that rapidly increasing internal pressure plays a role in liver injury. Previous work has shown a correlation between pressure and liver injury in pressurized ex vivo human livers when subjected to blunt impacts. The purpose of this study was to extend the investigation of this relationship between pressure and liver injury by testing full-body post-mortem human surrogates (PMHS). Pressure-related variables were compared with one another and also to previously proposed biomechanical predictors of abdominal injury. Ten PMHS were tested. The abdominal vessels were pressurized to physiological levels using saline, and a pneumatic ram impacted the right side of the specimen ribcage at a nominal velocity of 7.0 m/s. Specimens were subjected to either lateral (n = 5) or oblique (n = 5) impacts, and the impact- induced pressures were measured by transducers inserted into the hepatic veins and inferior vena cava. The liver injuries observed were similar to those documented in the Crash Injury Research Engineering Network (CIREN) trauma database. Using binary logistic regression to develop injury risk functions, it was determined the peak rate of pressure change (Ṗmax) was a statistically significant predictor of AIS ≥ 3 liver injury for both the PMHS and ex vivo testing. This suggests that Ṗmax is a good predictor of liver injury regardless of the impact boundary conditions.

Response of PMHS to high- and low-speed oblique and lateral pneumatic ram impacts

In ISO Technical Report 9790 (1999) normalized lateral and oblique thoracic force-time responses of PMHS subjected to blunt pendulum impacts at 4.3 m/s were deemed sufficiently similar to be grouped together in a single biomechanical response corridor. Shaw et al. (2006) presented results of paired oblique and lateral thoracic pneumatic ram impact tests to opposite sides of seven PMHS at sub-injurious speed (2.5 m/s). Normalized responses showed that oblique impacts resulted in more deflection and less force, whereas lateral impacts resulted in less deflection and more force. This study presents results of oblique and lateral thoracic impacts to PMHS at higher speeds (4.5 and 5.5 m/s) to assess whether lateral relative to oblique responses are different as observed by Shaw et al. or similar as observed by ISO. Twelve PMHS were impacted by a 23 kg pneumatic ram with a 152.4 mmx304.8 mm rectangular face plate at the level of the xyphoid process in either the pure lateral or 30° anterior-to-lateral oblique direction. Because these tests were potentially injurious, only one test per subject was conducted. Normalized responses demonstrate similar characteristics for both lateral and oblique impacts, indicating that it may be reasonable to combine lateral and oblique responses together at these higher speeds to define characteristic PMHS response as was done by ISO. The small number of tests conducted indicates that less chest compression may be required to obtain serious thoracic injury in oblique impacts as compared to lateral impacts at speeds of 4.5 or 5.5 m/s.

Using pressure to predict liver injury risk from blunt impact

Liver trauma research suggests that rapidly increasing internal pressure plays a role in causing blunt liver injury. Knowledge of the relationship between pressure and the likelihood of liver injury could be used to enhance the design of crash test dummies. The objectives of this study were (1) to characterize the relationship between impact-induced pressures and blunt liver injury in an experimental model to impacts of ex vivo organs; and (2) to compare human liver vascular pressure and tissue pressure in the parenchyma with other biomechanical variables as predictors of liver injury risk. Test specimens were 14 ex vivo human livers. Specimens were perfused with normal saline solution at physiological pressures, and a drop tower applied blunt impact at varying energies. Impact-induced pressures were measured by transducers inserted into the hepatic veins and the parenchyma (caudate lobe) of ex vivo specimens. Experimentally induced liver injuries were consistent with those documented in the Crash Injury Research and Engineering Network (CIREN) database. Binary logistic regression analysis demonstrated that injury predictors associated with tissue pressure measured in the parenchyma were the best indicators of serious liver injury risk. The best injury predictor overall was the product of the peak rate of tissue pressure increase and the peak tissue pressure, P T max * P T max (pseudo-R2 = .82, p = .001). A burst injury mechanism directly related to hydrostatic pressure is postulated for the ex vivo liver loaded dynamically in a drop test experiment.

Oblique and lateral impact response of the PMHS thorax

This study characterizes the PMHS thoracic response to blunt impact in oblique and lateral directions. A significant amount of data has been collected from lateral impacts conducted on human cadavers. Substantially less data has been collected from impacts that are anterior of lateral in an oblique direction. In the past, data collected from the handful of oblique impact studies were considered to be similar enough to the data from purely lateral impacts such that the oblique data were combined with data from lateral impacts. Defining the biomechanical response of the PMHS thorax to oblique impact is of great importance in side impact vehicle crashes where the loading is often anterior-oblique in direction. Data in this study was obtained from a chestband placed on the thorax at the level of impact to measure thoracic deflection. Two low energy impacts were conducted on each of seven subjects at 2.5 m/s, with one lateral impact and one oblique impact to opposite sides of each PMHS. Data was normalized using the Mertz-Viano method for a two mass system to allow for inter-subject comparisons. Force versus deflection response corridors were generated for the two impact types using an objective mathematical approach and compared to one another. Results were also compared to existing data for oblique and lateral thoracic impacts. The oblique thoracic response in low speed pendulum impacts was found to be different than the lateral thoracic response, in terms of force and deflection. Specifically, the lateral force was greater than the oblique force, and oblique deflection greater than lateral deflection for equal energy impacts.

Shoulder injury and response due to lateral glenohumeral joint impact: an analysis of combined data

To date, several lateral impact studies (Bolte et al., 2000, 2003, Marth, 2002 and Compigne et al., 2004) have been performed on the shoulder to determine the response characteristics and injury threshold of the shoulder complex. Our understanding of the biomechanical response and injury tolerance of the shoulder would be improved if the results of these tests were combined. From a larger data base shoulder injury tolerance criteria can be developed as well as corridors for side impact dummies. Data from the study by Marth (2002, 12 tests) was combined with data from the previous studies. Twenty-two low speed tests (4.5 +/- 0.7 m/s) and 9 high speed tests (6.7 +/- 0.7 m/s) were selected from the combined data for developing corridors. Shoulder force, deflection and T1y acceleration corridors were developed using a minimization of cumulative variance technique. The reduction in impact speed and the addition of padding reduced the magnitude and increased the time to peak of shoulder forces and T1y accelerations. Logistic analyses were performed on the combined data sets to determine the best predictors of MAIS-2 shoulder injuries. Maximum normalized shoulder deflection and Cmax had p values of 0.0000 and were the best predictors of shoulder injuries. For the 50(th)-percentile male, a shoulder deflection of 40 mm and a Cmax of 20% corresponded to a 50 % risk of MAIS-2 shoulder injury. In linear regression analysis, maximum normalized medial scapula X acceleration and maximum normalized sternum X acceleration were best related with the shoulder deflection and confirmed the forward movement of the sternum and rearward movement of the scapula.

Shoulder impact response and injury due to lateral and oblique loading

Little is known about the response of the shoulder complex due to lateral and oblique loading. Increasing this knowledge of shoulder response due to these types of loading could aid in improving the biofidelity of the shoulder mechanisms of anthropomorphic test devices (ATDs). The first objective of this study was to define force versus deflection corridors for the shoulder corresponding to both lateral and oblique loading. A second focus of the shoulder research was to study the differences in potential injury between oblique and lateral loading. These objectives were carried out by combining previously published lateral impact data from 24 tests along with 14 additional recently completed lateral and oblique tests. The newly completed tests utilized a pneumatic ram to impact the shoulder of approximately fiftieth percentile sized cadavers at the level of the glenohumeral joint with a constant speed of approximately 4.4 m/sec. Of the 14 tests, four of them were conducted lateral to the shoulder along the subject's y-axis, four of them were conducted 15 anterior to this axis, and six were conducted 30 anterior to the subject's y-axis. As in the previous testing, the first thoracic vertebrae and both shoulders of the subject were instrumented with tri-axial linear accelerometers on the sternum, clavicle, acromion process, and inferior angle of the scapula. The impacting mass was instrumented with an accelerometer and displacement transducer. In addition to this instrumentation, the tests were documented by high-speed digital imagery. Radiographs (x-rays), magnetic resonance images (MRIs), and autopsies were used to document injury to the subjects. The results from the tests revealed differences between the stiffness of the shoulder when loaded laterally to that when it is loaded obliquely. The shoulder was found to deflect twice as much medially when loaded obliquely then when it is loaded laterally. This can be attributed to the ability of the scapula to slide posteriorly around the thoracic cage. The ability of the shoulder to displace medially while simultaneously deflecting posteriorly in oblique impact is important to replicate in the ATDs because it results in the load being transmitted to the upper thoracic cage.

Development of a new biofidelity ranking system for anthropomorphic test devices

A new biofidelity assessment system is being developed and applied to three side impact dummies: the WorldSID-alpha, the ES-2 and the SID-HIII. This system quantifies (1) the ability of a dummy to load a vehicle as a cadaver does, "External Biofidelity," and (2) the ability of a dummy to replicate those cadaver responses that best predict injury potential, "Internal Biofidelity." The ranking system uses cadaver and dummy responses from head drop tests, thorax and shoulder pendulum tests, and whole body sled tests. Each test condition is assigned a weight factor based on the number of human subjects tested to form the biomechanical response corridor and how well the biofidelity tests represent FMVSS 214, side NCAP (SNCAP) and FMVSS 201 Pole crash environments. For each response requirement, the cumulative variance of the dummy response relative to the mean cadaver response (DCV) and the cumulative variance of the mean cadaver response relative to the mean plus one standard deviation (CCV) are calculated. The ratio of DCV/CCV expresses how well the dummy response duplicates the mean cadaver response: a smaller ratio indicating better biofidelity. For each test condition, the square root is taken of each Response Comparison Value (DCV/CCV), and then these values are averaged and multiplied by the appropriate Test Condition Weight. The weighted and averaged comparison values are then summed and divided by the sum of the Test Condition Weights to obtain a rank for each body region. Each dummy obtains an overall rank for External Biofidelity and an overall rank for Internal Biofidelity comprised of an average of the ranks from each body region. Of the three dummies studied, the selected comparison test data indicate that the WorldSID-alpha prototype dummy demonstrated the best overall External Biofidelity although improvement is needed in all of the dummies to better replicate human kinematics. All three dummies estimate potential injury assessment with similar levels of Internal Biofidelity.

Comparison of autopsy, X-ray, and M.R.I. findings following a low speed impact to the shoulder

The objectives of the study was to generate data useful to engineers improving crash test dummies and to physicians in anticipating low speed lateral impact injuries to the shoulder. Constant impact mass, distance and variable speeds were used to generate impact forces. Twelve unembalmed human cadavers were studied within 48 hours of death. Pre-test and Post-test physical, X-Ray, and Magnetic Resonance examinations were completed. X-Ray best identified bone injury, Magnetic Resonance intratendinous and intramuscular pathology and autopsy joint instability. Low speed (3.5-7.0 m/sec) impacts under these testing conditions frequently produce soft tissue and bone injuries. Sternoclavicular and acromioclavicular joint instabilities were found in 83% of the cadavers. The most frequent bone fractures were in the distal clavicle of 42% and labral or rotator cuff tears in 13% of the cadavers.

Shoulder response characteristics and injury due to lateral glenohumeral joint impacts

The objective of this study was to determine response characteristics and injury of the shoulder due to lateral impacts. The need for this data was heightened in the 1990s with increasing interest in harmonization of side impact standards, and questions regarding the measurement capabilities of dummies used in evaluating side impacts. A pneumatic impacting ram was employed in carrying out twentytwo lateral impacts to eleven unembalmed human cadavers at the level of the glenohumeral joint. Velocity of the ram at the time of impact was varied throughout the impacts from 3.5 to 7.0 m/sec, in an attempt to determine injury threshold. The cadavers were instrumented with tri-axial accelerometer blocks at ten locations in the shoulder region. Bony structures instrumented included the sternum, the first thoracic vertebra (T1), clavicles and scapulae. Output from the accelerometers was utilized to calculate impact forces and to exa mine the movement of the instrumented structures. Photographic target pins were inserted into the accelerometer blocks, thus permitting image analysis of the shoulder girdle displacement. Autopsies, radiographs, and magnetic resonance images (MRIs) were performed to document trauma that occurred as a result of the impact to the shoulder. Clavicles from the cadavers were subjected to bone density scans and threepoint bending tests. Results from these evaluations were used to assess and compare properties of bones of the upper extremities. Observations from autopsy, MRI, and radiography have shown looseness of the sternoclavicular joint and fracture of the distal clavicle to be the most common injuries. Significant findings include normalized shoulder forcedeflection curves and probability of injury distribution.