MEA Forensic Engineers & Scientists

Richmond, Canada

MEA Forensic Engineers & Scientists

Richmond, Canada
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Finan J.D.,NorthShore University Health System | Sundaresh S.N.,Columbia University | Elkin B.S.,MEA Forensic Engineers & Scientists | McKhann G.M.,Columbia University Medical Center | Morrison B.,Columbia University
Acta Biomaterialia | Year: 2017

To determine viscoelastic shear moduli, stress relaxation indentation tests were performed on samples of human brain tissue resected in the course of epilepsy surgery. Through the use of a 500 µm diameter indenter, regional mechanical properties were measured in cortical grey and white matter and subregions of the hippocampus. All regions were highly viscoelastic. Cortical grey matter was significantly more compliant than the white matter or hippocampus which were similar in modulus. Although shear modulus was not correlated with the age of the donor, cortex from male donors was significantly stiffer than from female donors. The presented material properties will help to populate finite element models of the brain as they become more anatomically detailed. Statement of Significance We present the first mechanical characterization of fresh, post-operative human brain tissue using an indentation loading mode. Indentation generates highly localized data, allowing structure-specific mechanical properties to be determined from small tissue samples resected during surgery. It also avoids pitfalls of cadaveric tissue and allows data to be collected before degenerative processes alter mechanical properties. To correctly predict traumatic brain injury, finite element models must calculate intracranial deformation during head impact. The functional consequences of injury depend on the anatomical structures injured. Therefore, morbidity depends on the distribution of deformation across structures. Accurate prediction of structure-specific deformation requires structure-specific mechanical properties. This data will facilitate deeper understanding of the physical mechanisms that lead to traumatic brain injury. © 2017 Acta Materialia Inc.


Bonin S.J.,University of Miami | Gardiner J.C.,MEA Forensic Engineers & Scientists | Onar-Thomas A.,St Jude Childrens Hospital | Asfour S.S.,University of Miami | And 2 more authors.
Accident Analysis and Prevention | Year: 2017

Proper helmet fit is important for optimizing head protection during an impact, yet many motorcyclists wear helmets that do not properly fit their heads. The goals of this study are i) to quantify how a mismatch in headform size and motorcycle helmet size affects headform peak acceleration and head injury criteria (HIC), and ii) to determine if peak acceleration, HIC, and impact speed can be estimated from the foam liner's maximum residual crush depth or residual crush volume. Shorty-style helmets (4 sizes of a single model) were tested on instrumented headforms (4 sizes) during linear impacts between 2.0 and 10.5 m/s to the forehead region. Helmets were CT scanned to quantify residual crush depth and volume. Separate linear regression models were used to quantify how the response variables (peak acceleration (g), HIC, and impact speed (m/s)) were related to the predictor variables (maximum crush depth (mm), crush volume (cm3), and the difference in circumference between the helmet and headform (cm)). Overall, we found that increasingly oversized helmets reduced peak headform acceleration and HIC for a given impact speed for maximum residual crush depths less than 7.9 mm and residual crush volume less than 40 cm3. Below these levels of residual crush, we found that peak headform acceleration, HIC, and impact speed can be estimated from a helmet's residual crush. Above these crush thresholds, large variations in headform kinematics are present, possibly related to densification of the foam liner during the impact. © 2017 Elsevier Ltd


DeMarco A.L.,MEA Forensic Engineers & Scientists | Good C.A.,Collision Analysis | Good C.A.,University of Calgary | Chimich D.D.,MEA Forensic Engineers & Scientists | And 3 more authors.
Annals of Biomedical Engineering | Year: 2017

Helmet manufacturers recommend replacing a bicycle helmet after an impact or after anywhere from 2 to 10 years of use. The goal of this study was to quantify the effect of helmet age on peak headform acceleration during impact attenuation testing of field-used bicycle helmets. Helmets were acquired by donation from consumers and retail stores, and were included in the study if they were free of impact-related damage, had a legible manufacture date label, and were certified to at least one helmet standard. Helmets (n = 770) spanning 0–26 years old were drop tested to measure peak linear headform acceleration during impacts to the right and left front regions of the helmets at two impact speeds (3.0 and 6.2 m/s). General linear mixed models were used to assess the effect of age and three covariates (helmet style, size and certification impact speed) on peak acceleration. Overall, age was related to either no difference or a statistically significant but small increase (≤0.76 g/year of helmet age) in peak headform acceleration. Extrapolated across 20 years, age-related differences were less than both style- (traditional vs. BMX) and size-related differences. The age-related differences were also less than the variability observed between different helmets after accounting for style, size and certification effects. These findings mean that bicycle helmets (up to 26-year-old traditional helmets and 13-year-old BMX helmets) do not lose their ability to attenuate impacts with age; however, other helmet features that may change with age were not evaluated in this study. © 2017 Biomedical Engineering Society


PubMed | MEA Forensic Engineers & Scientists, Clemson University, University of Florida, Eastern Maine Medical Center and Leslie Orthopaedics & Sports Medicine
Type: | Journal: Advances in orthopedics | Year: 2014

Evidence for selecting the same total knee arthroplasty prosthesis whether the posterior cruciate ligament (PCL) is retained or resected is rarely documented. This study reports prospective midterm clinical, radiographic, and functional outcomes of a fixed-bearing design implanted using two different surgical techniques. The PCL was completely retained in 116 knees and completely resected in 43 knees. For the entire cohort, clinical knee (96 7) and function (92 13) scores and radiographic outcomes were good to excellent for 84% of patients after 5-10 years in vivo. Range of motion averaged 124 9, with 126 knees exhibiting 120 flexion. Small differences in average knee flexion and function scores were noted, with the PCL-resected group exhibiting an average of 5 more flexion but an average function score that was 7 points lower compared to the PCL-retained group. Fluoroscopic analysis of 33 knees revealed stable tibiofemoral translations. This study demonstrates that a TKA articular design with progressive congruency in the lateral compartment can provide for femoral condyle rollback in maximal flexion activities and achieve good clinical and functional performance in patients with PCL-retained and PCL-resected TKA. This TKA design proved suitable for use with either surgical technique, providing surgeons with the choice of maintaining or sacrificing the PCL.


Siegmund G.P.,MEA Forensic Engineers & Scientists | Siegmund G.P.,University of British Columbia | Guskiewicz K.M.,University of North Carolina at Chapel Hill | Marshall S.W.,University of North Carolina at Chapel Hill | And 2 more authors.
Annals of Biomedical Engineering | Year: 2015

Wearable sensors can measure head impact frequency and magnitude in football players. Our goal was to quantify the impact detection rate and validity of the direction and peak kinematics of two wearable sensors: a helmet system (HITS) and a mouthguard system (X2). Using a linear impactor, modified Hybrid-III headform and one helmet model, we conducted 16 impacts for each system at 12 helmet sites and 5 speeds (3.6–11.2 m/s) (N = 896 tests). Peak linear and angular accelerations (PLA, PAA), head injury criteria (HIC) and impact directions from each device were compared to reference sensors in the headform. Both sensors detected ~96% of impacts. Median angular errors for impact directions were 34° for HITS and 16° for X2. PLA, PAA and HIC were simultaneously valid at 2 sites for HITS (side, oblique) and one site for X2 (side). At least one kinematic parameter was valid at 2 and 7 other sites for HITS and X2 respectively. Median relative errors for PLA were 7% for HITS and -7% for X2. Although sensor validity may differ for other helmets and headforms, our analyses show that data generated by these two sensors need careful interpretation. © 2015 Biomedical Engineering Society


Bonin S.J.,University of Miami | Luck J.F.,Duke University | Bass C.R.,Duke University | Gardiner J.C.,MEA Forensic Engineers & Scientists | And 4 more authors.
Annals of Biomedical Engineering | Year: 2016

Biomechanical headforms are used for helmet certification testing and reconstructing helmeted head impacts; however, their biofidelity and direct applicability to human head and helmet responses remain unclear. Dynamic responses of cadaver heads and three headforms and residual foam liner deformations were compared during motorcycle helmet impacts. Instrumented, helmeted heads/headforms were dropped onto the forehead region against an instrumented flat anvil at 75, 150, and 195 J. Helmets were CT scanned to quantify maximum liner crush depth and crush volume. General linear models were used to quantify the effect of head type and impact energy on linear acceleration, head injury criterion (HIC), force, maximum liner crush depth, and liner crush volume and regression models were used to quantify the relationship between acceleration and both maximum crush depth and crush volume. The cadaver heads generated larger peak accelerations than all three headforms, larger HICs than the International Organization for Standardization (ISO), larger forces than the Hybrid III and ISO, larger maximum crush depth than the ISO, and larger crush volumes than the DOT. These significant differences between the cadaver heads and headforms need to be accounted for when attempting to estimate an impact exposure using a helmet’s residual crush depth or volume. © 2016 Biomedical Engineering Society


PubMed | MEA Forensic Engineers & Scientists, Duke University, University of Miami and St Jude Childrens Research Hospital
Type: | Journal: Annals of biomedical engineering | Year: 2016

Biomechanical headforms are used for helmet certification testing and reconstructing helmeted head impacts; however, their biofidelity and direct applicability to human head and helmet responses remain unclear. Dynamic responses of cadaver heads and three headforms and residual foam liner deformations were compared during motorcycle helmet impacts. Instrumented, helmeted heads/headforms were dropped onto the forehead region against an instrumented flat anvil at 75, 150, and 195J. Helmets were CT scanned to quantify maximum liner crush depth and crush volume. General linear models were used to quantify the effect of head type and impact energy on linear acceleration, head injury criterion (HIC), force, maximum liner crush depth, and liner crush volume and regression models were used to quantify the relationship between acceleration and both maximum crush depth and crush volume. The cadaver heads generated larger peak accelerations than all three headforms, larger HICs than the International Organization for Standardization (ISO), larger forces than the Hybrid III and ISO, larger maximum crush depth than the ISO, and larger crush volumes than the DOT. These significant differences between the cadaver heads and headforms need to be accounted for when attempting to estimate an impact exposure using a helmets residual crush depth or volume.


PubMed | MEA Forensic Engineers & Scientists
Type: Journal Article | Journal: Annals of biomedical engineering | Year: 2014

A headform is needed to validate and compare helmet- and mouthguard-based sensors that measure the severity and direction of football head impacts. Our goal was to quantify the dynamic response of a mandibular load-sensing headform (MLSH) and to compare its performance and repeatability to an unmodified Hybrid III headform. Linear impactors in two independent laboratories were used to strike each headform at six locations at 5.5 m/s and at two locations at 3.6 and 7.4 m/s. Impact severity was quantified using peak linear acceleration (PLA) and peak angular acceleration (PAA), and direction was quantified using the azimuth and elevation of the PLA. Repeatability was quantified using coefficients of variation (COV) and standard deviations (SD). Across all impacts, PLA was 1.61.8 g higher in the MLSH than in the Hybrid III (p=0.002), but there were no differences in PAA (p=0.25), azimuth (p=0.43) and elevation (p=0.11). Both headforms exhibited excellent or acceptable repeatability for PLA (HIII:COV=2.10.8%, MLSH:COV=2.01.2%, p=0.98), but site-specific repeatability ranging from excellent to poor for PAA (HIII:COV=7.24.0%, MLSH:COV=8.35.8%, p=0.58). Direction SD were generally <1 and did not vary between headforms. Overall, both headforms are similarly suitable for validating PLA in sensors that measure head impact severity in football players, however their utility for validating sensor PAA values varies with impact location.


PubMed | MEA Forensic Engineers & Scientists and University of North Carolina at Chapel Hill
Type: Journal Article | Journal: Annals of biomedical engineering | Year: 2016

Wearable sensors can measure head impact frequency and magnitude in football players. Our goal was to quantify the impact detection rate and validity of the direction and peak kinematics of two wearable sensors: a helmet system (HITS) and a mouthguard system (X2). Using a linear impactor, modified Hybrid-III headform and one helmet model, we conducted 16 impacts for each system at 12 helmet sites and 5 speeds (3.6-11.2 m/s) (N = 896 tests). Peak linear and angular accelerations (PLA, PAA), head injury criteria (HIC) and impact directions from each device were compared to reference sensors in the headform. Both sensors detected ~96% of impacts. Median angular errors for impact directions were 34 for HITS and 16 for X2. PLA, PAA and HIC were simultaneously valid at 2 sites for HITS (side, oblique) and one site for X2 (side). At least one kinematic parameter was valid at 2 and 7 other sites for HITS and X2 respectively. Median relative errors for PLA were 7% for HITS and -7% for X2. Although sensor validity may differ for other helmets and headforms, our analyses show that data generated by these two sensors need careful interpretation.


PubMed | MEA Forensic Engineers & Scientists and University of British Columbia
Type: | Journal: Accident; analysis and prevention | Year: 2016

Bicycle helmets reduce the frequency and severity of severe to fatal head and brain injuries in bicycle crashes. Our goal here was to measure the impact attenuation performance of common bicycle helmets over a range of impact speeds. We performed 127 drop tests using 13 different bicycle helmet models (6 traditional style helmets and 7 BMX-style helmets) at impact speeds ranging from 1 to 10m/s onto a flat anvil. Helmets were struck on their left front and/or right front areas, a common impact location that was at or just below the test line of most bicycle helmet standards. All but one of the 10 certified helmet models remained below the 300g level at an impact speed of 6m/s, whereas none of the 3 uncertified helmets met this criterion. We found that the helmets with expanded polystyrene liners performed similarly and universally well. The single certified helmet with a polyurethane liner performed below the level expected by the Consumer Product Safety Commission (CPSC) standard at our impact location and the helmet structure failed during one of two supplemental tests of this helmet above the test line. Overall, we found that increased liner thickness generally reduced peak headform acceleration, particularly at higher impact speeds.

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