A parametric model of child body shape in seated postures

<p><b>Objective</b>: The shape of the current physical and computational surrogates of children used for restraint system assessments is based largely on standard anthropometric dimensions. These scalar dimensions provide valuable information on the overall size of the individual but do not provide good guidance on shape or posture. This study introduced the development of a parametric model that statistically predicts individual child body shapes in seated postures with a few given parameters.</p> <p><b>Methods</b>: Surface geometry data from a laser scanner of children ages 3 to 11 (<i>n</i> = 135) were standardized by a 2-level fitting method using intermediate templates. The standardized data were analyzed by principal component analysis (PCA) to efficiently describe the body shape variance. Parameters such as stature, body mass index, erect sitting height, and 2 posture variables related to torso recline and lumbar spine flexion were associated with the PCA model using regression.</p> <p><b>Results</b>: When the original scan data were compared with the predictions of the model using the given subject dimensions, the average root mean square error for the torso was 9.5 mm, and the 95th percentile error was 17.35 mm.</p> <p><b>Conclusions</b>: For the first time, a statistical model of child body shapes in seated postures is available. This parametric model allows the generation of an infinite number of virtual children spanning a wide range of body sizes and postures. The results have broad applicability in product design and safety analysis. Future work is needed to improve the representation of hands and feet and to extend the age range of the model. The model presented in this article is publicly available online through HumanShape.org.</p

Comparison of three-point belt fit between humans and ATDs in rear seats

<p><b>Objective</b>: The anthropomorphic test devices (ATDs) in the Hybrid III family are widely used as human surrogates to test the crash performance of vehicles. A previous study demonstrated that passenger belt fit in rear seats was affected by high body mass index (BMI) and to a lesser extent by increased age. Specifically, the lap belt was worn higher and more forward as BMI and age increased. The objective of this study was to compare passenger belt fit to the belt fit achieved when installing the small female and midsize male Hybrid III adult ATDs using standard procedures.</p> <p><b>Methods</b>: The ATDs were installed using standardized procedures in the same conditions previously used with volunteers. Belt fit was measured using methods analogous to those used for the volunteers. Comparative human belt fit values were obtained by using regression analysis with the volunteer data to calculate the mean expected belt fit for people the same size as the ATDs.</p> <p><b>Results</b>: For the small female ATD, the upper edge of the lap belt was on average 59 mm forward and 11 mm above the anterior–superior iliac spine (ASIS) landmark on the ATD pelvis bone. In contrast, the belt position for similar size passengers was 17 mm forward and 22 mm above the ASIS. For the midsize male ATD, the belt was 34 mm forward and 10 mm above the ASIS. For similar size passengers, the position was 38 mm forward and 44 mm above the ASIS. For context, the belt width in this study was 38 mm.</p> <p><b>Discussion</b>: The results suggest that the lap belt fit obtained by ATDs is more idealized but more repeatable compared to that achieved by similar size passengers. Future standardization efforts should consider investigating whether new belt-positioning procedures with ATDs may improve the biofidelity of ATD response.</p

Evaluation of ISO CRS Envelopes Relative to U.S. Vehicles and Child Restraint Systems

<div><p><b>Objectives</b>: The objectives of this study are to use computer simulation to evaluate the International Organization for Standardization (ISO) 13216-3:2006(E) child restraint system (CRS) envelopes relative to rear seat compartments from vehicles and CRSs in the U.S. market, investigate the potential compatibility issues of U.S. vehicles and CRSs, and demonstrate whether necessary modifications can be made to introduce such a system into compatibility evaluations between U.S. vehicles and CRSs.</p><p><b>Methods</b>: Three-dimensional geometry models for 26 vehicles and 16 convertible CRS designs developed previously were used. Geometry models of 3 forward-facing and 3 rear-facing CRS envelopes provided by the ISO were built in the current study. The virtual fit process closely followed the physical procedures described in the ISO standards.</p><p><b>Results</b>: The results showed that the current ISO rear-facing envelopes can provide reasonable classifications for CRSs and vehicles, but the forward-facing envelopes do not represent products currently in the U.S. market. In particular, all of the selected vehicles could accommodate the largest forward-facing CRS envelope at the second-row seat location behind the driver seat. In contrast, half of the selected CRSs could not fit within any of the forward-facing ISO CRS envelopes, mainly due to protrusion at the rear-top corner of the envelope. The results also indicate that the rear seat compartment in U.S. vehicles often cannot accommodate a large portion of convertible CRSs in the rear-facing position. The increased demand for vehicle fuel economy and the recommendation to keep children rear-facing longer may lead to smaller cars and larger CRSs, which may increase the potential for fit problems.</p><p><b>Conclusions</b>: The virtual classifications indicated that contact between the forward-facing CRSs and the head restraints in the rear seats as well as that between the rear-facing CRSs and the back of the front seats is a main concern regarding the compatibility between the vehicles and the CRSs. Therefore, modification of the current ISO forward-facing CRS envelopes will likely to be necessary to ensure that they are useful for the U.S. market.</p></div

Kinematics of Pediatric Crash Dummies Seated on Vehicle Seats with Realistic Belt Geometry

<div><p><b>Objective:</b> A series of sled tests was performed using vehicle seats and Hybrid-III 6-year-old (6YO) and 10YO anthropomorphic test devices (ATDs) to explore possibilities for improving occupant protection for children who are not using belt-positioning booster seats.</p><p><b>Methods:</b> Cushion length was varied from production length of 450 mm to a shorter length of 350 mm. Lap belt geometry was set to rear, mid, and forward anchorage locations that span the range of lap belt angles found in vehicles. Six tests each were performed with the 6YO and 10YO Hybrid III ATDs. One additional test was performed using a booster seat with the 6YO. The ATDs were positioned using an updated version of the University of Michigan Transportation Research Institute (UMTRI) seating procedure that positions the ATD hips further forward with longer seat cushions to reflect the effect of cushion length on posture that has been measured with child volunteers. ATD kinematics were evaluated using peak head excursion, peak knee excursion, the difference between peak head and peak knee excursion, and the maximum torso angle.</p><p><b>Results:</b> Shortening the seat cushion improved kinematic outcomes, particularly for the 10YO. Lap belt geometry had a greater effect on kinematics with the longer cushion length, with mid or forward belt geometries producing better kinematics than the rearward belt geometry. The worst kinematics for both ATDs occurred with the long cushion length and rearward lap belt geometry. The improvements in kinematics from shorter cushion length or more forward belt geometry are smaller than those provided by a booster seat.</p><p><b>Conclusions:</b> The results show potential benefits in occupant protection from shortening cushion length and increasing lap belt angles, particularly for children the size of the 10YO ATD.</p></div

A Simulation Study on the Efficacy of Advanced Belt Restraints to Mitigate the Effects of Obesity for Rear-Seat Occupant Protection in Frontal Crashes

<div><p><b>Objective:</b> Recent field data analyses have shown that the safety advantages of rear seats relative to the front seats have decreased in newer vehicles. Separately, the risks of certain injuries have been found to be higher for obese occupants. The objective of this study is to investigate the effects of advanced belt features on the protection of rear-seat occupants with a range of body mass index (BMI) in frontal crashes.</p><p><b>Methods:</b> Whole-body finite element human models with 4 BMI levels (25, 30, 35, and 40 kg/m²) developed previously were used in this study. A total of 52 frontal crash simulations were conducted, including 4 simulations with a standard rear-seat, 3-point belt and 48 simulations with advanced belt features. The parameters varied in the simulations included BMI, load limit, anchor pretensioner, and lap belt routing relative to the pelvis. The injury measurements analyzed in this study included head and hip excursions, normalized chest deflection, and torso angle (defined as the angle between the hip–shoulder line and the vertical direction). Analyses of covariance were used to test the significance (<i>P</i> <.05) of the results.</p><p><b>Results:</b> Higher BMI was associated with greater head and hip excursions and larger normalized chest deflection. Higher belt routing increased the hip excursion and torso angle, which indicates a higher submarining risk, whereas the anchor pretensioner reduced hip excursion and torso angle. Lower load limits decreased the normalized chest deflection but increased the head excursion. Normalized chest deflection had a positive correlation with maximum torso angle. Occupants with higher BMI have to use higher load limits to reach head excursions similar to those in lower BMI occupants.</p><p><b>Discussion and Conclusion:</b> The simulation results suggest that optimizing load limiter and adding pretensioner(s) can reduce injury risks associated with obesity, but conflicting effects on head and chest injuries were observed. This study demonstrated the feasibility and importance of using human models to investigate protection for occupants with various BMI levels. A seat belt system capable of adapting to occupant size and body shape will improve protection for obese occupants in rear seats.</p></div

Landmark information for 56 pediatric skulls from CT scans

This zip file includes 4 folders: subject info, landmark location, suture width, and thickness. Landmark information is provided for each subject in the last three folders, and the landmark numbers are corresponding to those listed in the paper

A Statistical Skull Geometry Model for Children 0-3 Years Old

<div><p>Head injury is the leading cause of fatality and long-term disability for children. Pediatric heads change rapidly in both size and shape during growth, especially for children under 3 years old (YO). To accurately assess the head injury risks for children, it is necessary to understand the geometry of the pediatric head and how morphologic features influence injury causation within the 0–3 YO population. In this study, head CT scans from fifty-six 0–3 YO children were used to develop a statistical model of pediatric skull geometry. Geometric features important for injury prediction, including skull size and shape, skull thickness and suture width, along with their variations among the sample population, were quantified through a series of image and statistical analyses. The size and shape of the pediatric skull change significantly with age and head circumference. The skull thickness and suture width vary with age, head circumference and location, which will have important effects on skull stiffness and injury prediction. The statistical geometry model developed in this study can provide a geometrical basis for future development of child anthropomorphic test devices and pediatric head finite element models.</p></div

Landmarks on the skull surfaces and suture-bone boundaries.

<p>Note: B01 to B24 represent landmarks located at the skull (bone) surface, S01 to S32 represent landmarks located at the suture center lines, and C01 to C04 represent landmarks located at the intersections of the sutures. Landmarks on the skull surface are generally evenly distributed on the reference curves. For example, landmark No. B12 on the skull surface is midway between landmarks No. S27 and S14; and landmark No. B14 is in the middle of landmarks No. B12 and S14.</p

Skull thickness distribution by age.

<p>The models shown here were generated by morphing a template mesh into the model-predicted skull geometry using a Radial Basis Function. The color contours were generated based on the skull thickness values associated with each node on the morphed mesh. The quantitative skull thickness data corresponding to each landmark location can be found in Table D in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0127322#pone.0127322.s001" target="_blank">S1 Appendix</a>.</p

Pediatric head circumference and CirOffset relative to the CDC median head circumference curve.

<p>Pediatric head circumference and CirOffset relative to the CDC median head circumference curve.</p