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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: Gait & posture | Year: 2010

Bathtubs and showers are a common source of unintentional slips and falls. The goal of this study was to quantify the friction used by barefoot subjects entering and exiting a typical bathtub/shower enclosure under dry and wet conditions. Sixty subjects (30F, 30M) from three age groups (20-30 years, 40-50 years, 60-70 years) entered and exited a slip-resistant bathtub using six movement patterns (three entering and three exiting the tub) simulating actual use. Force plates installed in the tub floor and the slip-resistant deck outside the tub measured ground reaction forces, from which utilized friction and double support times were calculated. Overall, utilized friction varied from 0.102 to 0.442 (0.235+/-0.057) and was 0.058+/-0.040 lower in wet than dry conditions across all movement patterns (p<0.0001). During tub exiting movements, older subjects used less friction than young subjects (p<0.006). Utilized friction did not vary between genders (p>0.14). Double support times were longer in older subjects than in both young and middle-aged subjects for all movement patterns (p<0.0009) and longer under wet than dry conditions for all entry movements (p<0.0001). These data suggest that subjects regard the wet condition as more hazardous than the dry condition and adapt their utilized friction accordingly. These data also show that older subjects are more cautious than young subjects when confronted with the dual tasks of stepping over the tubs apron and transitioning to a surface perceived to be more slippery.


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
Type: Journal Article | Journal: Spine | Year: 2011

Literature-based review.To review the published data on occupant kinematic and neuromuscular responses during low-speed impacts and analyze how these data inform our understanding of whiplash injury.A stereotypical kinematic and neuromuscular response has been observed in human subjects exposed to rear-end impacts. Combined with various models of injury, these response data have been used to develop anti-whiplash seats that prevent whiplash injury in many, but not all, individuals exposed to a rear-end crash.Synthesis of the literature.Understanding of the occupant kinematics and neuromuscular responses, combined with data from various seat-related interventions, have shown that differential motion between the superior and inferior ends of the cervical spine is responsible for many whiplash injuries. The number of whiplash injuries not prevented by current anti-whiplash seats suggests than further work remains, possibly related to designing seats that respond dynamically to the occupant and collision properties. Neck muscles alter the head and neck kinematics during the interval in which injury likely occurs, even in initially relaxed occupants. It remains unclear whether muscle activation mitigates or exacerbates whiplash injury. If muscle activation mitigates injury, then advance warning could be used to help occupant tense their muscles before impact. Alternatively, if muscle activation exacerbates whiplash injury, then a loud preimpact sound that uncouples the startle and postural components of the muscle response could reduce peak muscle activation during a whiplash exposure.Our improved understanding of whiplash injury has led to anti-whiplash seats that have prevented many whiplash injuries. Further work remains to optimize these and possibly other systems to further reduce the number of whiplash injuries.


PubMed | MEA Forensic Engineers & Scientists
Type: Comparative Study | Journal: Accident; analysis and prevention | Year: 2010

Helmets reduce the frequency and severity of head and brain injuries over a range of impact severities broader than those covered by the impact attenuation standards. Our goal was to document the impact attenuation performance of common helmet types over a wide range of impact speeds. Sixty-five drop tests were performed against the side of 10 different helmets onto a flat anvil at impact speeds of 0.9-10.1 m/s (energy=2-260J; equivalent drop heights of 0.04-5.2 m). Three non-approved beanie helmets performed poorly, with the worst helmet reaching a peak headform acceleration of 852g at 29J. Three full-face and one open-face helmet responded similarly from about 100g at 30J to between 292g and 344g at 256-260J. Three shorty style helmets responded like the full-face helmets up to 150J, above which varying degrees of foam densification appeared to occur. Impact restitution values varied from 0.19 to 0.46. A three-parameter model successfully captured the plateau and densification responses exhibited by the various helmets (R(2)=0.95-0.99). Helmet responses varied with foam thickness, foam material and possibly shell material, with the largest response differences consistent with either the presence/absence of a foam liner or the densification of the foam liner.


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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