John H. Bolte

The tolerance of the frontal bone to blunt impact

The current understanding of the tolerance of the frontal bone to blunt impact is limited. Previous studies have utilized vastly different methods, which limits the use of statistical analyses to determine the tolerance of the frontal bone. The purpose of this study is to determine the tolerance of the frontal bone to blunt impact. Acoustic emission sensors were used to provide a noncensored measure of the frontal bone tolerance and were essential due to the increase in impactor force after fracture onset. In this study, risk functions for fracture were developed using parametric and nonparametric techniques. The results of the statistical analyses suggest that a 50% risk of frontal bone fracture occurs at a force between 1885 N and 2405 N. Subjects that were found to have a frontal sinus present within the impacted region had a significantly higher risk of sustaining a fracture. There was no association between subject age and fracture force. The results of the current study suggest that utilizing peak force as an estimate of fracture tolerance will overestimate the force necessary to create a frontal bone fracture.

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 systems 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.

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.

The tolerance of the maxilla to blunt impact

This study reports the results of 38 infraorbital maxilla impacts performed on male cadavers. Impacts were performed using an unpadded, cylindrical impactor (3.2 kg) at velocities between 1 and 5 m/s. The peak force and acoustic emission data were used to develop a statistical relationship of fracture risk as a function of impact force. Acoustic emission sensors were used to provide a noncensored measure of the maxilla tolerance and were essential due to the increase in impactor force after fracture onset. Parametric and nonparametric techniques were used to estimate the risk of fracture tolerance. The nonparametric technique produced an estimated 50% risk of fracture between 970 and 1223 N. The results obtained from the parametric and nonparametric techniques were in good agreement. Peak force values achieved in this study were similar to those of previous work and were unaffected by impactor velocity. The results of this study suggest that an impact to the infraorbital maxilla is a load-limited event due to compromise of structural integrity.

Measurement of Hybrid III Head Impact Kinematics Using an Accelerometer and Gyroscope System in Ice Hockey Helmets

Helmet-based instrumentation is used to study the biomechanics of concussion. The most extensively used systems estimate rotational acceleration from linear acceleration, but new instrumentation measures rotational velocity using gyroscopes, potentially reducing error. This study compared kinematics from an accelerometer and gyroscope-containing system to reference measures. A Hybrid III (HIII) adult male anthropometric test device head and neck was fit with two helmet brands, each instrumented with gForce Tracker (GFT) sensor systems in four locations. Helmets were impacted at various speeds and directions. Regression relationships between GFT-measured and reference peak kinematics were quantified, and influence of impact direction, sensor location, and helmet brand was evaluated. The relationship between the sensor output and the reference acceleration/velocity experienced by the head was strong. Coefficients of determination for data stratified by individual impact directions ranged from 0.77 to 0.99 for peak linear acceleration and from 0.78 to 1.0 for peak rotational velocity. For the data from all impact directions combined, coefficients of determination ranged from 0.60 to 0.80 for peak resultant linear acceleration and 0.83 to 0.91 for peak resultant rotational velocity. As expected, raw peak resultant linear acceleration measures exhibited large percent differences from reference measures. Adjustment using regressions resulted in average absolute errors of 10–15% if regression adjustments were done by impact direction or 25–40% if regressions incorporating data from all impact directions were used. Average absolute percent differences in raw peak resultant rotational velocity were much lower, around 10–15%. It is important to define system accuracy for a particular helmet brand, sensor location, and impact direction in order to interpret real-world data.

Assessing astronaut injury potential from suit connectors using a human body finite element model

BACKGROUND The new Orion space capsule requires additional consideration of possible injury during landing due to the dynamic nature of the impact. The purpose of this parametric study was to determine changes in the injury response of a human body finite element model with a suit connector (SC). METHODS The possibility of thoracic bony injury, thoracic soft tissue injury, and femur injury were assessed in 24 different model configurations. These simulations had two SC placements and two SC types, a 2.27-kg rectangular and a 3.17-kg circular SC. A baseline model was tested with the same acceleration pulses and no SC for comparison. Further simulations were conducted to determine the protective effect of SC location changes and adding small and large rigid chest plates. The possibilities of rib, chest soft tissue, and femur injury were evaluated using sternal deflection, chest deflection, viscous criterion, and strain values. RESULTS The results indicated a higher likelihood of chest injury than femur injury. The mean first principal strain in the femur was 0.136 +/- 0.007%, which is well below the failure limit for cortical bone. The placement of chest plates had a protective effect and reduced the sternal deflection, chest deflection, and viscous criterion values. CONCLUSION If possible, the SC should be placed on the thigh to minimize injury risk metrics. Chest plates appear to offer some protective value; therefore, a large rigid chest plate or similar countermeasure should be considered for chest SC placement.

AGE AND SEX ALONE ARE INSUFFICIENT TO PREDICT HUMAN RIB STRUCTURAL RESPONSE TO DYNAMIC A-P LOADING

Thoracic injuries from motor vehicle crashes (MVCs) are common in children and the elderly and are associated with a high rate of mortality for both groups. Rib fractures, in particular, are linked to high mortality rates which increase with the number of fractures sustained. Anthropomorphic test devices (ATDs) and computational models have been developed to improve vehicle safety, however these tools are constructed based on limited physical datasets. To-date, no study has explored variation of rib structural properties across the entire age spectrum with data obtained using the same experimental methodology to allow for comparison. One-hundred eighty-four ribs from 93 post mortem human subjects (PMHS) (70 male, 23 female; ages 4-99) were subjected to dynamic bending tests simulating a frontal impact to the thorax. Structural mechanical properties were calculated and a multi-level statistical model quantified the sample variance as explained by age and sex. Displacement (δX), peak force (Fpeak), linear structural stiffness (K), energy absorption to fracture (Utot), and plastic properties including post-yield energy absorption (UPl), plastic displacement (δPl), and the ratio of elastic to secant stiffness (K-ratio) all showed negative relationships with age, while only Fpeak, K, and Utot were dependent on sex. Despite these relationships being statistically significant, only 7-39% of variance is explained by age and only 3-17% of variance is explained by sex. This demonstrates that variability in bone properties is more complex than simply chronological age- and sex-dependence and should be explored in the context of biological mechanisms instead.

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

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 vehicles 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 vehicles 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 vehicles 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 todays market.

Comparison of Q3s ATD biomechanical responses to pediatric volunteers

Objective: The biofidelity of pediatric anthropomorphic test devices (ATDs) continues to be evaluated with scaled-down adult data, a methodology that requires inaccurate assumptions about the likeness of biomechanical properties of children and adults. Recently, evaluation of pediatric ATDs by comparison of pediatric volunteer (PV) data has emerged as a valuable and practical alternative to the use of scaled adult data. This study utilized existing PV data to evaluate a 3-year-old side impact ATD, the Q3s. Though ATDs have been compared to volunteer responses in frontal impacts, this study is the first to extend ATD-PV comparison methods to the Q3s ATD and among the first to extend these methods to side impacts. Methods: Previously conducted experiments were replicated in order to make a direct comparison between the Q3s and PVs. PV data were used from 4- to 7-year-olds (shoulder tests, n = 14) and 6- to 8-year-olds (sled tests, n = 7). Force–deflection data were captured during quasistatic shoulder tests through manual displacement of the shoulder joint. Resulting shoulder stiffness was compared between the Q3s and PVs. Low-speed far-side sled tests were conducted with the Q3s at lateral (90°) and oblique (60°) impacts. Primary outcomes of interest included (1) lateral displacement of the torso, (2) torso rollout angle, and (3) kinematic trajectories of the head and neck. Results: The Q3s exhibited shoulder stiffness values at least 32 N/mm greater than the PVs for all conditions (PV muscle tensed and relaxed, deflection calculated for full- and half-thoracic). In lateral sled tests, the Q3s demonstrated increased coronal torso rollout (Q3s: 49.2°; PVs: 35.7° ± 12.4°) and lateral (ΔY) movement of the top of the head (Q3s: −389 mm; PVs: −320 ± 23 mm) compared to PVs. In oblique trials, the Q3s achieved significantly decreased lateral torso displacement (Q3s: 153.3 mm; PVs: 193.6 ± 25.6 mm) and top of the head forward (ΔX) motion (Q3s: 68 mm; PVs: 133 ± 20 mm) compared to PVs. In all tests, greater downward (ΔZ) excursions of C4 and T1 were observed in the Q3s relative to PVs. Conclusions: Increased Q3s shoulder stiffness could affect head–neck kinematics as well as thorax responses because unrealistic force can be transmitted to the spine from the shoulder. Q3s and PV trajectories were of similar shape, although Q3s head kinematics displayed rigid body motion followed by independent lateral bending of the head, suggesting cervical and thoracic spine rigidity compared to PVs.