A Comparison of Sacroiliac and Pubic Rami Fracture Occurrences in Oblique Side Impact Tests on Nine Post Mortem Human Subjects.

UNLABELLED: The WorldSID dummy can be equipped with both a pubic and a sacroiliac joint (S-I joint) loadcell. Although a pubic force criterion and the associated injury risk curve are currently available and used in regulation (ECE95, FMVSS214), as of today injury mechanisms, injury criteria, and injury assessment reference values are not available for the sacroiliac joint itself. The aim of this study was to investigate the sacroiliac joint injury mechanism. Three configurations were identified from full-scale car crashes conducted with the WorldSID 50th percentile male where the force passing through the pubis in all three tests was approximately 1500 N while the sacroiliac Fy/Mx peak values were 4500 N/50 Nm, 2400 N/130 Nm, and 5300 N/150 Nm, respectively. These tests were reproduced using a 150 kg guided probe impacting Post Mortem Human Subjects (PMHS) at 8 m/s, 5.4 m/s and 7.5 m/s. The shape and the orientation of the impacting face of the probe were selected to match the WorldSID pubic Fy and sacroiliac Fy/Mx loads of the three vehicle test configurations. Three PMHS were tested in each of the three configurations (nine PMHS in total). RESULTS: In the first PMHS configuration, one specimen sustained an AIS 3 injury and one sustained an AIS 4 injury (an unstable pelvis with complete disruption of the posterior arch, a sacroiliac joint disruption associated with an iliac fracture, and a pubic symphysis separation). In the second configuration, all specimens sustained a fracture of the superior lateral iliac wing (AIS 2). In the third configuration, one specimen sustained a partial disruption of the anterior arch (AIS 2). Based on the data from strain gauges located on the pubic rami and near the sacroiliac joint, the pubic rami fractures were identified as occurring prior to the sacroiliac fractures. CONCLUSIONS: Out of nine impactor tests performed, the PMHS S-I joint injuries were observed to consistently be associated with pelvic anterior arch fractures. In addition, from the injury sequences derived from strain gauges located on the specimen pelvises and on the injury assessments obtained by necropsy, the S-I joint fractures were observed to occur after the anterior arch fractures.

Age-dependent factors affecting thoracic response: a finite element study focused on Japanese elderly occupants.

OBJECTIVES: The ultimate goal of this research is to reduce thoracic injuries due to traffic crashes, especially in the elderly. The specific objective is to develop and validate a full-body finite element model under 2 distinct settings that account for factors relevant for thoracic fragility of elderly: one setting representative of an average size male and one representative of an average size Japanese elderly male. METHODS: A new thorax finite element model was developed from medical images of a 71-year-old average Japanese male elderly size (161cm, 60 kg) postmortem human subject (PMHS). The model was validated at component and assembled levels against original series of published test data obtained from the same elderly specimen. The model was completed with extremities and head of a model previously developed. The rib cage and the thoracic flesh materials were assigned age-dependent properties and the model geometry was scaled up to simulate a 50th percentile male. Thereafter, the model was validated against existing biomechanical data for younger and elderly subjects, including hub-to-thorax impacts and frontal impact sled PMHS test data. Finally, a parametric study was conducted with the new models to understand the effect of size and aging factors on thoracic response and risk of rib fractures. RESULTS: The model behaved in agreement with tabletop test experiments in intact, denuded, and eviscerated tissue conditions. In frontal impact sled conditions, the model showed good 3-dimensional head and spine kinematics, as well as rib cage multipoint deflections. When properties representative of an aging person were simulated, both the rib cage deformation and the predicted number of rib fractures increased. The effects of age factors such as rib cortical thickness, mechanical properties, and failure thresholds on the model responses were consistent with the literature. Aged and thereby softened flesh reduced load transfer between ribs; the coupling of the rib cage was reduced. Aged costal cartilage increased the severity of the diagonal belt loading sustained by the lower loaded rib cage. CONCLUSIONS: When age-specific parameters were implemented in a finite element (FE) model of the thorax, the rib cage kinematics and thorax injury risk increased. When the effect of size was isolated, 2 factors, in addition to rib material properties, were found to be important: flesh and costal cartilage properties. These 2 were identified to affect rib cage deformation mechanisms and may potentially increase the risk of rib fractures.

Investigation of a relationship between external force to shoulder and chest injury of WorldSID and THUMS in 32 km/h oblique pole side impact.

OBJECTIVE: This article describes the chest injury risk reduction effect of shoulder restraints using finite element (FE) models of the worldwide harmonized side impact dummy (WorldSID) and Total Human Model for Safety (THUMS) in an FE model 32 km/h oblique pole side impact. METHODS: This research used an FE model of a mid-sized vehicle equipped with various combinations of curtain shield air bags, torso air bags, and shoulder restraint air bags. As occupant models, AM50 WorldSID and THUMS AM50 Version 4 were used for comparison. RESULTS: The research investigated the effect of shoulder restraint air bag on chest injury by comparing cases with and without a shoulder side air bag. The maximum external force to the chest was reduced by shoulder restraint air bag in both WorldSID and THUMS, reducing chest injury risk as measured by the amount of rib deflection, number of the rib fractures, and rib deflection ratio. However, it was also determined that the external force to shoulder should be limited to the chest injury threshold because the external shoulder force transmits to the chest via the arm in the case of WorldSID and via the scapula in the case of THUMS. Because these results show the shoulder restraint air bag effect on chest injury risk, the vent hole size of the shoulder restraint air bag was changed for varying reaction forces to investigate the relationship between the external force to the shoulder and the risk of chest injury. In the case of THUMS, an external shoulder force of 1.8 kN and more force from the shoulder restraint air bag was necessary to help prevent rib fracture. Increasing external force applied to shoulder up to 6.2 kN (the maximum force used in this study) did not induce any rib or clavicle fractures in the THUMS. When the shoulder restraint air bag generated external force to the shoulder from 1.8 to 6.2 kN in THUMS, which were applied to the WorldSID, the shoulder deflection ranged from 35 to 68 mm, and the shoulder force ranged from 1.8 to 2.3 kN. CONCLUSIONS: In the test configuration used, a shoulder restraint using the air bag helps reduce chest injury risk by lowering the maximum magnitude of external force to the shoulder and chest. To help reduce rib fracture risk in the THUMS, the shoulder restraint air bag was expected to generate a force of 3.7 kN with a minimum rib deflection ratio. This corresponds to a shoulder rib deflection of 60 mm and a shoulder load of 2.2 kN in WorldSID. Supplemental materials are available for this article. Go to the publisher's online edition of Traffic Injury Prevention to view the supplemental file.

Kinematics of the unrestrained vehicle occupants in side-impact crashes.

A test series involving direct right-side impact of a moving wall on unsupported, unrestrained cadavers with no arms was undertaken to better understand human kinematics and injury mechanisms during side impact at realistic speeds. The tests conducted provided a unique opportunity for a detailed analysis of the kinematics resulting from side impact. Specifically, this study evaluated the 3-dimensional (3D) kinematics of 3 unrestrained male cadavers subjected to lateral impact by a multi-element load wall carried by a pneumatically propelled rail-mounted sled reproducing a conceptual side crash impact. Three translations and 3 rotations characterize the movement of a solid body in the space, the 6 degrees of freedom (6DoF) kinematics of 15 bone segments were obtained from the 3D marker motions and computed tomography (CT)-defined relationships between the maker array mounts and the bones. The moving wall initially made contact with the lateral aspect of the pelvis, which initiated lateral motion of the spinal segments beginning with the pelvis and moving sequentially up through the lumbar spine to the thorax. Analyzing the 6DoF motions kinematics of the ribs and sternum followed right shoulder contact with the wall. Overall thoracic motion was assessed by combining the thoracic bone segments as a single rigid body. The kinematic data presented in this research provides quantified subject responses and boundary condition interactions that are currently unavailable for lateral impact.

Research of the relationship of pedestrian injury to collision speed, car-type, impact location and pedestrian sizes using human FE model (THUMS Version 4).

Injuries in car to pedestrian collisions are affected by various factors such as the vehicle body type, pedestrian body size and impact location as well as the collision speed. This study aimed to investigate the influence of such factors taking a Finite Element (FE) approach. A total of 72 collision cases were simulated using three different vehicle FE models (Sedan, SUV, Mini-Van), three different pedestrian FE models (AM50, AF05, AM95), assuming two different impact locations (center and the corner of the bumper) and at four different collision speeds (20, 30, 40 and 50 km/h). The impact kinematics and the responses of the pedestrian model were validated against those in the literature prior to the simulations. The relationship between the collision speed and the predicted occurrence of head and chest injuries was examined for each case, analyzing the impact kinematics of the pedestrian against the vehicle body and resultant loading to the head and the chest. Strain based indicators were used in the simulation model to estimate skeletal injury (bony fracture) and soft tissue (brain and internal organs) injury. The study results primarily showed that the injury risk became higher with the collision speed, but was also affected by the combination of the factors such as the pedestrian size and the impact location. The study also discussed the injury patterns and trends with respect to the factors examined. In all of the simulated conditions, the model did not predict any severe injury at a collision speed of 20 km/h.

Whole-body response to pure lateral impact.

The objective of the current study was to provide a comprehensive characterization of human biomechanical response to whole-body, lateral impact. Three approximately 50th-percentile adult male PMHS were subjected to right-side pure lateral impacts at 4.3 ± 0.1 m/s using a rigid wall mounted to a rail-mounted sled. Each subject was positioned on a rigid seat and held stationary by a system of tethers until immediately prior to being impacted by the moving wall with 100 mm pelvic offset. Displacement data were obtained using an optoelectronic stereophotogrammetric system that was used to track the 3D motions of the impacting wall sled; seat sled, and reflective targets secured to the head, spine, extremities, ribcage, and shoulder complex of each subject. Kinematic data were also recorded using 3-axis accelerometer cubes secured to the head, pelvis, and spine at the levels of T1, T6, T11, and L3. Chest deformation in the transverse plane was recorded using a single chestband. Following the impact the subject was captured in an energy-absorbing net that provided a controlled non-injurious deceleration. The wall maintained nearly constant velocity throughout the impact event. One of the tested subjects sustained 16 rib fractures as well as injury to the struck shoulder while the other two tested subjects sustained no injuries. The collected response data suggest that the shoulder injury may have contributed to the rib fractures in the injured subject. The results suggest that the shoulder presents a substantial load path and may play an important role in transmitting lateral forces to the spine, shielding and protecting the ribcage. This characterization of whole-body, lateral impact response provides quantified subject responses and boundary condition interactions that are currently unavailable for whole-body, lateral impacts at impact speeds less than 6.7 m/s.

Occupant kinematics and estimated effectiveness of side airbags in pole side impacts using a human FE model with internal organs.

When a car collides against a pole-like obstacle, the deformation pattern of the vehicle body-side tends to extend to its upper region. A possible consequence is an increase of loading to the occupant thorax. Many studies have been conducted to understand human thoracic responses to lateral loading, and injury criteria have been developed based on the results. However, injury mechanisms, especially those of internal organs, are not well understood. A human body FE model was used in this study to simulate occupant kinematics in a pole side impact. Internal organ parts were introduced into the torso model, including their geometric features, material properties and connections with other tissues. The mechanical responses of the model were validated against PMHS data in the literature. Although injury criterion for each organ has not been established, pressure level and its changes can be estimated from the organ models. Finite element simulations were conducted assuming a case where a passenger vehicle collides against a pole at 29km/h. Occupant kinematics, force-deformation responses and pressure levels were compared between cases with and without side airbag deployment. The results indicated that strain to the ribs and pressure to the organs was smaller with side airbag deployment. The side airbag widened the contact area at the torso, helping to distribute the force to the shoulder, arm and chest. Such distributed force helped generate relatively smaller deformation in the ribs. Furthermore, the side airbag deployment helped restrict the spine displacement. The smaller displacement contributed to lowering the magnitude of contact force between the torso and the door. The study also examined the correlations between the pressure levels in the internal organs, rib deflection, and V*C of chest. The study found that the V*C(t) peak appeared to be synchronized with the organ pressure peak, suggesting that the pressure level of the internal organs could be one possible indicator to estimate their injury risk.

Research study on neck injury lessening with active head restraint using human body FE model.

OBJECTIVES: The objective of this study is to examine the effectiveness of the active head restraint system in reducing neck injury risk of car occupants in low-speed rear impacts. METHODS: A human body FE model "THUMS" was used to simulate head and neck kinematics of the occupant and to evaluate loading to the neck. Joint capsule strain was calculated to predict neck injury risk as well as NIC. The validity of the model was confirmed comparing its mechanical responses to those in human subjects in the literatures. Seat FE models were also prepared representing one with a fixed head restraint and the other one with an active head restraint system. The active head restraint system was designed to move the head restraint forward and upward when the lower unit was lower unit was loaded by the pelvis. Rear impact simulations were performed assuming a triangular acceleration pulse at a delta-V of 25 km/h. RESULTS: The model reproduced similar head and neck motions to those measured in the human volunteer test, except for active muscular responses. The calculated joint capsule strain also showed a good match with those of PMHS tests in the literature. A rear-impact simulation was conducted using the model with the fixed head restraint. The result revealed that NIC was strongly correlated with the relative acceleration between the head and the torso and that its maximum peak appeared when the head contacted the head restraint. It was also found that joint capsule strain grew in later timing synchronizing with the relative displacement. Another simulation with the active head restraint system showed that both NIC and joint capsule strain were lowered owing to the forward and upward motion of the head restraint. A close investigation of the vertebral motion indicated that the active head restraint reduced the magnitude of shear deformation in the facet joint, which contributed to the strain growth in the fixed head restraint case. CONCLUSIONS: Rear-impact simulations were conducted using a human body FE model, THUMS, representing an average-size male occupant. The cervical system including the facet joint capsules was incorporated to the model. The validity of the model was examined comparing its mechanical responses to those in the literature such as the whole body motion of the volunteer subject and the vertebral motion in the PMHS tests. Rear-impact simulations were conducted using the validated THUMS model and two prototype seat models; one had a fixed head restraint and the other one was equipped with an active head restraint system. The active head restraint system works moving the head restraint forward and upward when the lower unit is loaded by the pelvis. The head and neck kinematics and responses were analyzed from the simulation results. The force and acceleration rose at the pelvis first, followed by T1 and the head. The early timing of force rise and its magnitude indicated that the pelvis force was a good trigger for the active head restraint system. The results showed that the head was supported earlier in a case with the active head restraint system, and both NIC and joint capsule strain were lowered. The study also analyzed the mechanism of strain growth in the joint capsules. Relatively greater strain was observed in the direction of the facet joint surface, which was around 45 degrees inclined to the spinal column. The forward and upward motion of the active head restraint were aligned with the direction of the joint deformation and contributed to lower strain in the joint capsules. The results indicated that the active head restraint could help reduce the neck injury risk not only by supporting the head at an early timing but also through its trajectory stopping the joint deformation.

Head-turned postures increase the risk of cervical facet capsule injury during whiplash.

STUDY DESIGN: In vitro experiments using cadaveric cervical spine motion segments to quantify facet capsular ligament strain during whiplash-like loading. OBJECTIVE: To quantify facet capsule strains during whiplash-like loading with an axial intervertebral prerotation simulating an initial head-turned posture and to then compare these strains to previously-published strains for partial failure and gross failure of the facet capsule for these specimens. SUMMARY OF BACKGROUND DATA: Clinical data have shown that a head-turned posture at impact increases the severity and duration of whiplash-related symptoms. METHODS: Thirteen motion segments were used from 7 women donors (50 +/- 10 years). Axial pretorques (+/-1.5 Nm), axial compressive preloads (45, 197, and 325 N), and quasi-static shear loads (posteriorly-directed horizontal forces from 0 to 135 N) were applied to the superior vertebral body to simulate whiplash kinematics with the head turned. Three-dimensional displacements of markers placed on the right facet capsular ligament were used to estimate the strain field in the ligament during loading. The effects of pretorque direction, compression, and posterior shear on motion segment motion and maximum principal strain in the capsule were examined using repeated-measures analyses of variance. RESULTS: Axial pretorque affected peak capsule strains more than axial compression or posterior shear. Peak strains reached 34% +/- 18% and were higher for pretorques toward rather than away from the facet capsule (i.e.-, head rotation to the right caused higher strain in the right facet capsule). CONCLUSION: Compared to previously-reported data for these specimens, peak capsule strains with a pretorque were double those without a pretorque (17% +/- 6%) and not significantly different from those at partial failure of the ligament (35% +/- 21%). Thus a head-turned posture increases facet capsular ligament strain compared to a neutral head posture-a finding consistent with the greater symptom severity and duration observed in whiplash patients who have their head turned at impact.

Correlation of strain and loads measured in the long bones with observed kinematics of the lower limb during vehicle-pedestrian impacts.

The purpose of this study is to determine the loads in the long bones of the lower extremities during vehicle-pedestrian impact tests, and to correlate load data with observed kinematics in an effort to understand how stature and vehicle shape influence pedestrian response. In tests with a large sedan and a small multi-purpose vehicle (MPV), four post mortem human surrogates (PMHS) in mid-stance gait were struck laterally at 40 km/h. Prior to the tests, each PMHSwas instrumented with four uniaxial strain gages around the mid-shaft cross section of the struck-side (right) tibia and the femora bilaterally. After the tests, the non-fractured bones were harvested and subjected to three-point bending experiments. The effective elastic moduli were determined by relating the applied bending loads with the measured strains using strain gage locations, detailed bone geometry, and elastic beam theory. Using the strains measured in the vehicle-pedestrian tests and the calculated effective elastic moduli, the axial load and bending moments in the instrumented bone cross-sections were calculated. Peak longitudinal strains in the mid-shaft cross-sections approached 1% in the right tibiae and exceeded 0.5% in the right femora with peak strain rates of 200%s(-1)-750%s(-1) in the right tibiae and 100%s(-1)-170%s(-1) in the femora. While peak axial forces were consistent for both vehicles and ranged from 1 kN to 3 kN, bending moments in the right lower extremity exceeded 300 Nm in the sedan impacts but were substantially lower in impacts with the MPV. The right tibia bent predominantly in the medial direction during the impact whereas bi-modal patterns were observed in the sagittal bending moment time histories of the femora. Stature differences caused variations in hip and knee impact locations relative to the hood edge and bumper of each vehicle that may have been a contributing factor resulting in more severe struck-side lower extremity injuries in the tall subject tested with the MPV, and more severe struck-side lower extremity injuries in the shorter subject tested with the sedan.

A study of cervical spine kinematics and joint capsule strain in rear impacts using a human FE model.

Many efforts have been made to understand the mechanism of whiplash injury. Recently, the cervical facet joint capsules have been focused on as a potential site of injury. An experimental approach has been taken to analyze the vertebral motion and to estimate joint capsule stretch that was thought to be a potential cause of pain. The purpose of this study is to analyze the kinematics of the cervical facet joint using a human FE model in order to better understand the injury mechanism. The Total Human Model for Safety (THUMS) was used to visually analyze the local and global kinematics of the spine. Soft tissues in the neck were newly modeled and introduced into THUMS for estimating the loading level in rear impacts. The model was first validated against human test data in the literature by comparing vertebrae motion as well as head and neck responses. Joint capsule strain was estimated from a maximum principal strain output from the elements representing the capsule tissues. A rear-end collision was then simulated using THUMS and a prototype seat model, assuming a delta-V of 25 km/h. The trajectory of the vertebrae was analyzed in a local coordinate system defined along the joint surface. Strain growth in the joint capsules was explained, as related to contact events between the occupant and the seat. A new seat concept was proposed to help lessen the loading level to the neck soft tissues. The foam material of the seat back was softened, the initial gap behind the head was reduced and the head restraint was stiffened for firm support. The lower seat back frame was also reinforced to withstand the impact severity at the given delta-V. Another rear impact simulation was conducted using the new seat concept model to examine the effectiveness of the new concept. The joint capsule strain was found to be relatively lower with the new seat concept. The study also discusses the influence of seat parameters to the vertebral motion and the resultant strain in the joint capsules. The meaning of the contact timing of the head to the head restraint was examined based on the results in terms of correlation with injury indicators such as NIC and the joint capsule strain.

A Study of Knee Joint Kinematics and Mechanics using a Human FE Model.

Posterior translation of the tibia with respect to the femur can stretch the posterior cruciate ligament (PCL). Fifteen millimeters of relative displacement between the femur and tibia is known as the Injury Assessment Reference Value (IARV) for the PCL injury. Since the anterior protuberance of the tibial plateau can be the first site of contact when the knee is flexed, the knee bolster is generally designed with an inclined surface so as not to directly load the projection in frontal crashes. It should be noted, however, that the initial flexion angle of the occupant knee can vary among individuals and the knee flexion angle can change due to the occupant motion. The behavior of the tibial protuberance related to the knee flexion angle has not been described yet. The instantaneous angle of the knee joint at the timing of restraining the knee should be known to manage the geometry and functions of knee restraint devices. The purposes of this study are first to understand the kinematics of the knee joint during flexion, and second to characterize the mechanics of the knee joint under anterior-posterior loading. A finite element model of the knee joint, extracted from the Total Human Model for Safety (THUMS), was used to analyze the mechanism. The model was validated against kinematics and mechanical responses of the human knee joint. By tracking the relative positions and angles between the patella and the tibia in a knee flexing simulation, the magnitude of the tibial anterior protuberance was described as a function of the knee joint angle. The model revealed that the mechanics of the knee joint was characterized as a combination of stiffness of the patella-femur structure and the PCL It was also found that the magnitude of the tibial anterior protuberance determined the amount of initial stretch of the PCL in anterior-posterior loading. Based on the knee joint kinematics and mechanics, an interference boundary was proposed for different knee flexion angles, so as not to directly load the anterior protuberance of the tibial plateau in restraining of the knee. A frontal crash simulation was performed using a partial vehicle model with the THUMS seated. The performance and effects of the knee airbag, as one of the candidates for knee restraint devices, were evaluated through the simulation.