Anatomically-based skeletal coordinate systems for use with impact biomechanics data intended for anthropomorphic test device development

Objective: Physical biomechanical surrogates are critical for testing the efficacy of injury-mitigating safety strategies. The interpretation of measured Hybrid III neck loads in test scenarios resulting in compressive loading modes would be aided by a further understanding of the correlation between the mechanical responses in the Hybrid III neck and the probability of injury in the human cervical spine. The anthropomorphic test device (ATD) peak upper and lower neck responses were measured during dynamic compressive loading conditions comparable to those of postmortem human subject (PMHS) experiments. The peak ATD response could then be compared to the PMHS injury outcomes.Methods: A Hybrid III 50th percentile ATD head and neck assembly was tested under conditions matching those of male PMHS tests conducted on an inverted drop track. This includes variation in impact plate orientation (4 sagittal plane and 2 frontal plane orientations), impact plate surface friction, and ATD initial head/neck orientation. This unique matched data with known injury outcomes were used to evaluate existing ATD neck injury criteria.Results: The Hybrid III ATD head and neck assembly was found to be robust and repeatable under severe loading conditions. The initial axial force response of the ATD head and neck is very comparable to PMHS experiments up to the point of PMHS cervical column buckle or material failure. An ATD lower neck peak compressive force as low as 6,290 N was associated with an unstable orthopedic cervical injury in a PMHS under equivalent impact conditions. ATD upper neck peak compressive force associated with a 5% probability of unstable cervical orthopedic injury ranged from as low as 3,708 to 3,877 N depending on the initial ATD neck angle.Conclusions: The correlation between peak ATD compressive neck response and PMHS test outcome in the current study resulted in a relationship between axial load and injury probability consistent with the current Hybrid III injury assessment reference values. The results add to the current understanding of cervical injury probability based on ATD neck compressive loading in that it is the only known study, in addition to Mertz et al. (1978), formulated directly from ATD compressive loading scenarios with known human injury outcomes.

Research was conducted involving a series of lateral impact tests on a horizontal sled facility by scientists at the Air Force Research Laboratory (AFRL). The purpose of the research was to conduct an assessment of the biodynamic response of an anthropomorphic test device (ATD) to support the development of AFRL neck injury criteria. Impacts were completed using a 50th male Hybrid III aerospace ATD due to this ATD being used by the USAF to qualify and evaluate ejection systems. A test matrix was developed to assess ATD response as a function of various seat configurations which were an approximation of the seat configurations used by the Medical College of Wisconsin (MCW) for previously conducted lateral impact tests of PMHS subjects (post-mortem human subjects). The specially fabricated seat configurations were a rigid seat fixture with a 5-point harness and a padded rigid seat with a 3-point harness. The input acceleration pulses were trapezoidal in shape and varied in peak magnitude from 8.5 to 17 G. The rigid and padded seat configurations both generated fairly linear ATD responses across the input acceleration range. The ATD’s response with the padded seat and the 3-point restraint was greater than the ATD’s response with the rigid seat and the 5-point restraint with the upper neck. The My torque showed the greatest increase from the rigid seat configuration to the padded seat configuration. This highlights the importance of a proper restraint and the importance of controlling the motion of the torso since it could reduce the loads and torques of the unrestrained head and neck, resulting in a lower probability of injury. The lateral impact program with the ATD provided critical impact data to fill data gaps that support the development of the ATD-to-human transfer functions for AFRL’s Multi-Axial Neck Injury Criteria (MANIC) for lateral impact or MANICy calculation. The program also highlighted gaps in human and PMHS head response data in identical lateral impact configurations that would not only improve the current MANICy transfer function but would allow the investigation of the efficacy of using the 6F-MANICy to replace the current MANICy.

The EuroSID-2re (ES-2re) Anthropomorphic Test Device (ATD) commonly known as the crash test dummy is also used in the military domain to assess the risk of injury of armored vehicles occupants from lateral impact. The loading conditions range from low velocity - long duration impacts (4 m/s - 50 ms) similar to the automotive domain, to high velocity - short duration impacts (28 m/s - 3 ms) corresponding to cases where the panel deforms under an explosion. The human shoulder response to lateral impact was investigated at bounds of the loading condition spectrum previously mentioned, and also at intermediate conditions (14 m/s - 9 ms) in previous studies. The aim of the current study is to provide additional insight at the intermediate loading conditions which are not found in the literature. Eight pure lateral shoulder impact tests were performed on Post Mortem Human Subjects (PMHS) using an 8.1 kg rigid impactor at velocities ranging from 3.3 m/s to 8.8 m/s with the duration ranging from 25 ms to 35 ms. The PMHS were instrumented with accelerometers attached to the sternum, and the upper thoracic spine (T1 vertebra). Strain gages were glued onto the right and left clavicles and ribs 2 to 6. The shoulder force was measured at the interface with the impactor and the impact was filmed by high speed cameras (5000 fps) to track the YZ displacements of the impactor, T1 vertebra, and sternum in the laboratory frame. Three shoulders out of the eight sustained AIS 2 injuries which included a clavicle fracture. The impactor forces ranged from 1200 to 4600 N. The PMHS accelerations ranged from 44 to 163 g at the sternum, and from 17 to 60 g at the T1 vertebra. The analysis of the strain gage signals revealed that the clavicle fractures occurred at the beginning of the impact and coincided with a peak force. An estimate of the acromion-to-shoulder compression (Cmax) was computed. It ranged from 0% to 15% for the non-injured shoulders, and from 19% to 28% for the injured shoulders. This new PMHS test series will be used in a future work to develop a shoulder injury criterion for the ES-2re ATD that is relevant for the whole loading conditions spectrum of the military domain.

<div class="section abstract"><div class="htmlview paragraph">Posterior cruciate ligament (PCL) injuries, although rarely life threatening, affect the quality of life of the person who sustains the injury. The PCL is the primary restraint to posterior tibial translation and can be injured when the tibia moves posteriorly relative to the femur. This type of injury is common in frontal crashes where the tibia may impact the dashboard or steering column. To quantify what happens during dynamic loading of the tibial plateau, isolated cadaveric lower limbs (n = 14) were impacted at dynamic rates with a linear pneumatic ram. During the testing, a static load was applied to the quadriceps tendon to simulate active musculature. Forces as well as the stretch of the PCL were measured. The most common injuries were tibia fractures and PCL tears. The stiffness for the tests at impact velocities of 1.4 and 2.9 m/s were on average 120 N/mm and 141N/mm, respectively. A trend towards increasing femur force with increasing velocity was found. The study presents biofidelity targets for the response of the cadaveric limbs, which can be used in the development of anthropometric test devices or computational models.</div></div>

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. Supplemental materials are available for this article. Go to the publisher's online edition of Traffic Injury Prevention to view the supplemental file.

Development of thoracic injury risk functions for the THOR ATD

Motor vehicle crashes are the leading cause of death and injury for children in the United States. Pediatric anthropomorphic test devices (ATD) and computational models are important tools for the evaluation and optimization of automotive restraint systems for child occupants. The thorax interacts with the restraints within the vehicle, and any thoracic model must mimic this interaction in a biofidelic manner to ensure that restraint designs protect humans as intended. To define thoracic biofidelity for adults, Kroell et al. (1974) conducted blunt impacts to the thoraces of adult postmortem human subjects (PMHS), which have formed the basis for biofidelity standards for modern adult ATD thoraces (Mertz et al. 1989). The paucity of pediatric PMHS for impact research led to the development of pediatric model biofidelity requirements through scaling. Geometric scale factors and elastic moduli of skull and long bone have been used to scale the adult thoracic biofidelity responses to the 3-, 6-, and 10-year-old child (Irwin and Mertz 1997; Mertz et al. 2001; van Ratingen et al. 1997). There is currently a need for data that apply to the child without scaling, both for validation of scaling methods used in the past and to confirm the validity of the specifications currently used to develop models of the child.

Honda has been studying ways of improving vehicle design to reduce the severity of pedestrian injury. Full-scale tests using a pedestrian dummy are an important way to assess the aggressiveness of a vehicle to pedestrians. However, from test results, it is concluded that current pedestrian dummies have stiffer characteristics than post mortem human subjects (PMHS). Also, the dummy kinematics during a collision are different from that of a human body. Because of the limitations of current dummies, it was decided to develop a new pedestrian dummy. At the first stage of the project, a computer simulation model that represented the PMHS tests was developed. Joint characteristics obtained from the simulation model were used in building a new pedestrian dummy named Polar I. The advanced frontal crash test dummy, known as Thor, was selected as the base dummy. Modifications were made for the thorax, spine, knee, and other joints. Component tests were conducted to obtain and check the characteristics of each part. An initial series of full-scale tests was conducted, and the kinematics of the dummy were compared with PMHS test results.

Surgical simulation models have been developed using post-mortem human subjects (PMHS). These models involve the pressurization and ventilation of the PMHS to create a more realistic environment for training and the practice of surgical procedures. The overall objective of this study was to determine the feasibility of a previously developed surgical simulation model to detect soft tissue injuries during a ballistic impact to the torso. One of the main limitations of using PMHS for the assessment of soft tissue injuries in the field of injury biomechanics is the lack of physiological blood flow. To overcome this limitation, the assessment of the surgical simulation model for use in injury biomechanics applications was conducted based on data collected from behind armor blunt trauma (BABT) case studies. Documented injuries in real-world cases included anterior lung contusion, posterior lung contusion, and liver contusion. These real-world injuries were compared to those seen post-impact in the PMHS using pathological and histological techniques. Discussion of limitations and future work is presented.

Hybrid III anthropomorphic test device (ATD) response to head impacts and potential implications for athletic headgear testing

A series of tip-over and off-the-dock impact tests were performed with stand-up forklifts to investigate the potential for injury to the operator of a forklift in these types of accidents, when the forklift is equipped with an operator’s compartment door. One Crown Equipment Company 35RRTT Model and one 35RCTT Model stand-up forklifts were used in the impact tests. The only modification to the forklifts for the tests was the placement of a door on the entrance to the operator’s compartment. A Hybrid III anthropomorphic test device (ATD) was placed in the operator’s compartment as a human surrogate. During each test, head accelerations, chest accelerations, neck loads, and lumbar loads were measured on the ATD. The motion of the forklift and the ATD were filmed with real-time video and high-speed cameras. Results from the impact tests indicate that there is a high risk of head injury in a right-side tip-over accident and a high risk of head injury and neck injury in a left-side tip-over accident. There is a high risk of a head injury, neck injury, and thoracic injury in off-the-dock forks-trailing accidents. In an off-the-dock forks-leading accident, there is a high risk of arm/shoulder injury, head injury, and neck injury. In both tip-over and off-the-dock forks-trailing accidents, there is a high probability of an entrapment injury under the overhead guard on the forklift.

Although blast mitigation seats are historically designed to protect the 50th percentile male occupant based on mass, the scope of the occupant centric platform (OCP) Technology Enabled Capability Demonstration (TEC-D) within the U.S. Army Tank Automotive Research Development Engineering Center (TARDEC) Ground System Survivability has been expanded to encompass lighter and heavier occupants which represents the central 90th percentile of the military population. A series of drop tower tests were conducted on twelve models of blast energy-attenuating (EA) seats to determine the effects of vertical accelerative loading on ground vehicle occupants. Two previous technical publications evaluated specific aspects of the results of these drop tower tests on EA seats containing the three sizes of anthropomorphic test devices (ATDs) including the Hybrid III 5th percentile female, the Hybrid III 50th percentile male, and the Hybrid III 95th percentile male. The first publication addressed the overall trends of the forces, moments, and accelerations recorded by the ATDs when compared to Injury Assessment Reference Values (IARVs), as well as validating the methodology used in the drop tower evaluations1. Review of ATD data determined that the lumbar spine compression in the vertical direction could be used as the “go/no-go” indicator of seat performance. The second publication assessed the quantitative effects of Personal Protective Equipment (PPE) on the small occupant, as the addition of a helmet and Improved Outer Tactical Vest (IOTV) with additional gear increased the weight of the 5th percentile female ATD more than 50%2. Comparison of the loading data with and without PPE determined that the additional weight of PPE increased the overall risk of compressive injury to the lumbar and upper neck of the small occupant during an underbody blast event. Using the same data set, this technical paper aimed to evaluate overall accelerative loading trends of the 5th percentile female ATD when compared to those of the 50th percentile male ATD in the same seat and PPE configuration. This data trend comparison was conducted to gain an understanding of how seat loading may differ with a smaller occupant. The focus of the data analysis centered around the lumbar spine compression, as this channel was the most likely to exceed the IARV limit for the 5th percentile female ATD. Based on the previous analysis of this data set, the lightest occupant trends showed difficulty in protecting against lumbar compression injuries with respect to the 5th percentile female’s IARV, whereas the larger occupants experienced fewer issues in complying with their respective IARVs for lumbar compression. A review of pelvis acceleration was also conducted for additional kinetic insight into the motion of the ATDs as the seat strokes. This analysis included a review of how the weight and size of the occupant may affect the transmission of forces through a stroking seat during the vertical accelerative loading impulse.

Objective This study presents a comparison of the Test Device for Human Occupant Restraint (THOR) 50M and Hybrid III (HIII) 50M anthropomorphic test device (ATD) geometries and rear impact head and neck biofidelity to each other and to postmortem human surrogate (PMHS) data to evaluate the usefulness of the THOR in rear impact testing. Methods Both ATDs were scanned in a seated position on a rigid bench seat. A series of rear impact sled tests with the rigid bench seat with no head restraint support were conducted with a HIII-50M at 16 and 24 kph. Tests at each speed were performed twice with the THOR-50M to allow an assessment of the repeatability of the THOR-50M. A comparison of the test results from THOR-50M testing were made to the results of a previous study that included PMHS. Rear impact sled tests with both ATDs in a modern seat were then conducted at 40 kph. Results The THOR-50M head was 48.4 mm rearward and 60.1 mm higher than the HIII-50M head when seated in the rigid bench seat. In the repeated rigid bench testing at 16 and 24 kph, the THOR-50M head longitudinal and vertical accelerations, upper neck moment, and overall kinematics showed good test-to-test repeatability. In the rigid bench tests, the THOR-50M neck experienced flexion prior to extension in the 16 kph tests, where the neck of the HIII only experienced extension. At 24 kph both ATDs only experienced extension. The THOR-50M head displaced more rearward at both test velocities. The rigid bench tests show that the THOR-50M neck allows for more extension motion or articulation than the HIII-50M neck. The rigid bench test also shows that the head longitudinal and vertical accelerations, angular head kinematics, and upper neck moments were reasonably comparable between the ATDs. The THOR-50M results were closer to the average of the PMHS results than the HIII-50-M results, with the exception of the upper neck. In the 40 kph tests, with a modern seat design, the THOR-50M resulted in more deformation of the seatback with greater head restraint loading than the HIII-50M. The THOR-50M head backset distance was less. Conclusion This study provides insight into the differences and similarities between the THOR and the HIII-50M ATD geometries, instrumentation responses, and kinematics, as well as the repeatability of the THOR-50M in rear impacts testing. The overall geometries of the THOR-50M and the HIII-50M are similar. The seated head position of the THOR-50M is slightly further rearward and higher than the HIII-50M. The results indicate that the THOR-50M matches the PMHS results more closely than the HIII-50M and may have improved neck biofidelity in rear impact testing. The results indicate that the studied THOR-50M responses are repeatable within expected test-to-test variations in rear impacts. Early data suggest that the THOR-50M can be used in rear impact testing, though a more complete understanding of the THOR-50M differences to the HIII ATDs will allow for better correlation to the existing body of HIII rear impact testing.

Wearable devices are developed to measure head impact kinematics but are intrinsically noisy because of the imperfect interface with human bodies. This study aimed to improve the head impact kinematics measurements obtained from instrumented mouthguards using deep learning to enhance traumatic brain injury (TBI) risk monitoring. We developed one-dimensional convolutional neural network (1D-CNN) models to denoise mouthguard kinematics measurements for tri-axial linear acceleration and tri-axial angular velocity from 163 laboratory dummy head impacts. The performance of the denoising models was evaluated on three levels: kinematics, brain injury criteria, and tissue-level strain and strain rate. Additionally, we performed a blind test on an on-field dataset of 118 college football impacts and a test on 413 post-mortem human subject (PMHS) impacts. On the dummy head impacts, the denoised kinematics showed better correlation with reference kinematics, with relative reductions of 36% for pointwise root mean squared error and 56% for peak absolute error. Absolute errors in six brain injury criteria were reduced by a mean of 82%. For maximum principal strain and maximum principal strain rate, the mean error reduction was 35% and 69%, respectively. On the PMHS impacts, similar denoising effects were observed and the peak kinematics after denoising were more accurate (relative error reduction for 10% noisiest impacts was 75.6%). The 1D-CNN denoising models effectively reduced errors in mouthguard-derived kinematics measurements on dummy and PMHS impacts. This study provides a novel approach for denoising head kinematics measurements in dummy and PMHS impacts, which can be further validated on more real-human kinematics data before real-world applications.

Cervical spine injury in rollover crashes: Anthropometry, excursion, roof deformation, and ATD prediction