Kathleen D. Klinich

Fetal outcome in motor-vehicle crashes: effects of crash characteristics and maternal restraint

OBJECTIVE This project was undertaken to improve understanding of factors associated with adverse fetal outcomes of pregnant occupants involved in motor-vehicle crashes. STUDY DESIGN In-depth investigations of crashes involving 57 pregnant occupants were performed. Maternal and fetal injuries, restraint information, measures of external and internal vehicle damage, and details about the crash circumstances were collected. Crash severity was calculated using vehicle crush measurements. Chi-square analysis and logistic regression models were used to determine factors with a significant association with fetal outcome. RESULTS Fetal outcome is most strongly associated with crash severity (P < .001) and maternal injury (P = .002). Proper maternal belt-restraint use (with or without airbag deployment) is associated with acceptable fetal outcome (odds ratio = 4.5, P = .033). Approximately half of fetal losses in motor-vehicle crashes could be prevented if all pregnant women properly wore seat belts. CONCLUSION Higher crash severity, more severe maternal injury, and lack of proper seat belt use are associated with a higher risk of adverse fetal outcome. These results strongly support recommendations that pregnant women use properly positioned seatbelts.

Evaluation of the static belt fit provided by belt-positioning booster seats

Belt-positioning booster seats are recommended for children who use vehicle seat belts as primary restraints but who are too small to obtain good belt fit. Previous research has shown that belt-positioning boosters reduce injury risk, but the belt fit produced by the wide range of boosters in the US market has not previously been assessed. The present study describes the development of a method for quantifying static belt fit with a Hybrid-III 6-year-old test dummy. The measurement method was applied in a laboratory seat mockup to 31 boosters (10 in both backless and highback modes) across a range of belt geometries obtained from in-vehicle measurements. Belt fit varied widely across boosters. Backless boosters generally produced better lap belt fit than highback boosters, largely because adding the back component moved the dummy forward with respect to the lap belt routing guides. However, highback boosters produced more consistent shoulder belt fit because of the presence of belt routing guides near the shoulder. Some boosters performed well on both lap belt and shoulder belt fit. Lap belt fit in dedicated boosters was generally better than in combination restraints that also can be used with an integrated harness. Results demonstrate that certain booster design features produce better belt fit across a wide range of belt geometries. Lap belt guides that hold the belt down, rather than up, and shoulder belt guides integrated into the booster backrest provided better belt fit.

Quantifying dynamic mechanical properties of human placenta tissue using optimization techniques with specimen-specific finite-element models

Motor-vehicle crashes are the leading cause of fetal deaths resulting from maternal trauma in the United States, and placental abruption is the most common cause of these deaths. To minimize this injury, new assessment tools, such as crash-test dummies and computational models of pregnant women, are needed to evaluate vehicle restraint systems with respect to reducing the risk of placental abruption. Developing these models requires accurate material properties for tissues in the pregnant abdomen under dynamic loading conditions that can occur in crashes. A method has been developed for determining dynamic material properties of human soft tissues that combines results from uniaxial tensile tests, specimen-specific finite-element models based on laser scans that accurately capture non-uniform tissue-specimen geometry, and optimization techniques. The current study applies this method to characterizing material properties of placental tissue. For 21 placenta specimens tested at a strain rate of 12/s, the mean failure strain is 0.472+/-0.097 and the mean failure stress is 34.80+/-12.62 kPa. A first-order Ogden material model with ground-state shear modulus (mu) of 23.97+/-5.52 kPa and exponent (alpha(1)) of 3.66+/-1.90 best fits the test results. The new method provides a nearly 40% error reduction (p<0.001) compared to traditional curve-fitting methods by considering detailed specimen geometry, loading conditions, and dynamic effects from high-speed loading. The proposed method can be applied to determine mechanical properties of other soft biological tissues.

Anthropometric specification of child crash dummy pelves through statistical analysis of skeletal geometry

The pelves of the child dummies of the widely used Hybrid-III family are based on minimal data from children. Because an accurate pelvis design is critical for realistic assessments of belt restraint interactions, an analysis of medical imaging data was conducted to develop guidance for improved pelvis design. Three-dimensional polygonal meshes of the bony pelvis were generated from computed tomography (CT) data from 81 children from ages 5 to 11. After aligning to a uniform anatomical coordinate system, the meshes were resampled to create a quadrilateral mesh with 12,960 vertices for each pelvis. A principal components analysis was conducted with the mesh vertex coordinates and the locations of 31 landmarks. Over 99% of the variance in size and shape was accounted for by the first 40 components. A three-dimensional model representing the target for a new dummy pelvis was developed using bispinous breadth as the predictor variable. To obtain the appropriate geometry for the six-year-old (6YO) and 10YO Hybrid-III dummies, a regression analysis was conducted using a large sample of child anthropometry data from a previous study to obtain a target dimension for bispinous breadth, using the design stature for each dummy as input. A separate regression analysis was conducted to predict principal component scores from bispinous breadth. Reconstructing a pelvis model from the principal components scores predicted for the target bispinous breadth values yielded a three-dimensional design target for the each dummy. The new pelvis target is similar in overall size to the current pelvis components, but the location of the anterior-superior iliac spine is markedly lower, which has important implications for belt interaction.

A New Database of Child Anthropometry and Seated Posture for Automotive Safety Applications

This paper presents a laboratory study of body dimensions, seated posture, and seatbelt fit for children weighing from 40 to 100 lb (18 to 45 kg). Sixty-two boys and girls were measured in three vehicle seats with and without each of three belt-positioning boosters. In addition to standard anthropometric -measurements, three-dimensional body landmark locations were recorded with a coordinate digitizer in sitter-selected and standardized postures. This new database quantifies the vehicle-seated postures of children and provides quantitative evidence of the effects of belt-positioning boosters on belt fit. The data will provide guidance for child restraint design, crash dummy development, and crash dummy positioning procedures.

Survey of Older Children in Automotive Restraints

The survey discussed in this paper investigates how well current vehicle restraints and belt-positioning booster seats meet the needs of children aged 7 to 12 years. The restraint fit study recorded how seat belts fit 155 older children seated in three different vehicles when they were used with and without belt-positioning booster seats. One specific goal was to determine the largest size child who benefited from booster seats, and the smallest child that could effectively use three-point belts alone. A simple anthropometric survey of the child volunteers was also conducted as part of the restraint fit study.

A Stochastic Visco-hyperelastic Model of Human Placenta Tissue for Finite Element Crash Simulations

Placental abruption is the most common cause of fetal deaths in motor-vehicle crashes, but studies on the mechanical properties of human placenta are rare. This study presents a new method of developing a stochastic visco-hyperelastic material model of human placenta tissue using a combination of uniaxial tensile testing, specimen-specific finite element (FE) modeling, and stochastic optimization techniques. In our previous study, uniaxial tensile tests of 21 placenta specimens have been performed using a strain rate of 12/s. In this study, additional uniaxial tensile tests were performed using strain rates of 1/s and 0.1/s on 25 placenta specimens. Response corridors for the three loading rates were developed based on the normalized data achieved by test reconstructions of each specimen using specimen-specific FE models. Material parameters of a visco-hyperelastic model and their associated standard deviations were tuned to match both the means and standard deviations of all three response corridors using a stochastic optimization method. The results show a very good agreement between the tested and simulated response corridors, indicating that stochastic analysis can improve estimation of variability in material model parameters. The proposed method can be applied to develop stochastic material models of other biological soft tissues.

Vehicle LATCH system features associated with correct child restraint installations

Objective: Lower anchors and tethers for children (LATCH) was intended to standardize the attachment between child restraints and vehicle seats. However, LATCH implementations vary, resulting in differences in ease of attachment of child restraint connectors. Identifying vehicle characteristics associated with correct child restraint installations can provide guidance for designing vehicle LATCH systems that increase correct child restraint installations. Methods: The LATCH system and other relevant vehicle characteristics were documented in 98 top-selling 2010–2011 vehicles. These features, together with proposed LATCH usability recommendations from the International Organization for Standardization and Society of Automotive Engineers, were used to select 12 vehicles for volunteer testing with a range of LATCH system characteristics. Thirty-six volunteers were assigned to 4 groups; each group tested 3 vehicles, 4 child restraints (infant, rear-facing convertible, forward-facing convertible, and combination seat), and 2 installation methods (lower anchors and seat belt) in a split-plot experimental design. Mixed-effects logistic regression models were used to identify predictors of tight installation and correct lower anchor use. Results: Vehicle survey results indicated that most vehicle manufacturers provide the minimum number of LATCH hardware locations required by regulation. Among 21 vehicles with a third row, 4 had no tether anchors and 11 had no lower anchors in the third row. Study volunteers correctly used the lower anchors in 60 percent of LATCH installations and used the top tether in 48 percent of forward-facing installations. When the tether was used, use was correct in 46 percent of trials (22% of all forward-facing installations). Only 13 percent of all trials had completely correct child restraint installation (correct use of lower anchors or seat belt, correct tether anchor use, tight seat installation, and correct installation angle). Tight installation was 3.3 times as likely with correct lower anchor use compared to trials with incorrect use. Three lower anchor characteristics were associated with rates of correct lower anchor use above 50 percent: clearance angle around the lower anchors greater than 54°, attachment forces less than 178 N, and anchor depth within the seat bight of less than 2 cm. Vehicles meeting all 3 criteria were 19 times as likely to have lower anchors used correctly compared to vehicles meeting none of the criteria. No vehicle features predicted either use of tethers or correct use of tethers. Conclusions: Vehicle LATCH systems that improve lower anchor accessibility could increase the rate of correct lower anchor use, but more research is needed to understand factors associated with tether use and correct use.

Rear Seat Restraint System Optimization for Older Children in Frontal Crashes

Objective: Analyses of crash injury data have shown that injury risk increases when children transition from belt-positioning boosters to the vehicle seat belt alone. The objective of this study is to investigate how to improve the restraint environment for these children. Methods: A parametric analysis was conducted to investigate the effects of body size, seat belt anchorage locations, and rear seat design parameters on the injury risks in frontal crashes of children aged 6 to 12 years old using a newly developed parametric child anthropomorphic test dummy (ATD) model. Restraint design optimizations were also conducted to obtain ranges of optimal restraint system configurations that provide best protections for 6-, 9-, and 12-year-old children. Results: Simulation results showed that child body size was the dominant factor affecting outcome measures. In general, lower and more rearward D-rings (upper belt anchorages), higher and more forward lap belt anchorages, and shorter, stiffer, and thinner seat cushions were associated with improved restraint performance. In these simulations, children with smaller body sizes require more-forward D-rings, inboard anchors, and outboard anchor locations to avoid submarining. However, these anchorage locations increase head excursions relative to more-rearward anchorages. Conclusions: The balance of reducing head and knee excursions and preventing submarining indicates that an optimization approach is necessary to improve protection for 6- to 12-year-old child occupants. The findings of this study provided design guidelines for future rear seat restraint system. Supplemental materials are available for this article. Go to the publishers online edition of Traffic Injury Prevention to view the supplemental file.

Effects of vehicle seat and belt geometry on belt fit for children with and without belt positioning booster seats

A laboratory study was conducted to quantify the effects of belt-positioning boosters on lap and shoulder belt fit. Postures and belt fit were measured for forty-four boys and girls ages 5-12 in four highback boosters, one backless booster, and on a vehicle seat without a booster. Belt anchorage locations were varied over a wide range. Seat cushion angle, seat back angle, and seat cushion length were varied in the no-booster conditions. All boosters produced better mean lap belt fit than was observed in the no-booster condition, but the differences among boosters were relatively large. With one midrange belt configuration, the lap belt was not fully below the anterior-superior iliac spine (ASIS) landmark on the front of the pelvis for 89% of children in one booster, and 75% of children failed to achieve that level of belt fit in another. In contrast, the lap belt was fully below the ASIS for all but two children in the best-performing booster. Child body size had a statistically significant but relatively small effect on lap belt fit. The largest children sitting without a booster had approximately the same lap belt fit as the smallest children experienced in the worst-performing booster. Increasing lap belt angle relative to horizontal produced significantly better lap belt fit in the no-booster condition, but the boosters isolated the children from the effects of lap belt angles. Reducing seat cushion length in the no-booster condition improved lap belt fit but changing cushion angle did not. Belt upper anchorage (D-ring) location had a strong effect on shoulder belt fit in conditions without shoulder belt routing from the booster. Unexpectedly, the worst average shoulder belt fit was observed in one highback booster with a poorly positioned shoulder belt routing clip. The shoulder belt was routed more outboard, on average, with a backless booster than without a booster, but raising the child also amplified the effect of D-ring location, such that children were more likely to experience poor shoulder belt fit due to outboard and forward D-ring locations when sitting on the booster. Taller children experienced more-outboard shoulder belt fit in conditions without shoulder belt routing by the booster and in the one booster with poor shoulder belt routing. Adjustable shoulder belt routing on three of the highback boosters effectively eliminated stature effects, providing approximately the same shoulder belt fit for all children. Seat back angle did not have a significant effect on shoulder belt fit. The results of this study have broad applicability toward the improvement of occupant restraints for children The data show substantial effects of booster design on belt fit, particularly the effects of alternative lap and torso belt routing approaches. The data quantify the critical importance of belt anchorage location for child belt fit, providing an important foundation for efforts to optimize belt geometry for children.