Publications by authors named "Sarah Manoogian"

29 Publications

  • Page 1 of 1

The Effect of Insertion Technique on Temperatures for Standard and Self-Drilling External Fixation Pins.

J Orthop Trauma 2017 Aug;31(8):e247-e251

*Mechanical Engineering, Bucknell University, Lewisburg, PA; and †Orthopaedics, Geisinger Health System, Danville, PA.

Objectives: No studies have assessed the effects of parameters associated with insertion temperature in modern self-drilling external fixation pins. The current study assessed how varying the presence of irrigation, insertion speed, and force impacted the insertion temperatures of 2 types of standard and self-drilling external fixation half pins.

Methods: Seventy tests were conducted with 10 trials for 4 conditions on self-drilling pins, and 3 conditions for standard pins. Each test used a thermocouple inside the pin to measure temperature rise during insertion.

Results: Adding irrigation to the standard pin insertion significantly lowered the maximum temperature (P <0.001). Lowering the applied force for the standard pin did not have a significant change in temperature rise. Applying irrigation during the self-drilling pin tests dropped average rise in temperature from 151.3 ± 21.6°C to 124.1 ± 15.3°C (P = 0.005). When the self-drilling pin insertion was decreased considerably from 360 to 60 rpm, the temperature decreased significantly from 151.3 ± 21.6°C to 109.6 ± 14.0°C (P <0.001). When the force applied increased significantly, the corresponding self-drilling pin temperature increase was not significant.

Conclusions: The standard pin had lower peak temperatures than the self-drilling pin for all conditions. Moreover, slowing down the insertion speed and adding irrigation helped mitigate the temperature increase of both pin types during insertion.
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http://dx.doi.org/10.1097/BOT.0000000000000859DOI Listing
August 2017

Measuring temperature rise during orthopaedic surgical procedures.

Med Eng Phys 2016 09 28;38(9):1016-20. Epub 2016 May 28.

Geisinger Health System, 100 N Academy Ave, Danville, PA 17822, USA.

A reliable means for measuring temperatures generated during surgical procedures is needed to recommend best practices for inserting fixation devices and minimizing the risk of osteonecrosis. Twenty four screw tests for three surgical procedures were conducted using the four thermocouples in the bone and one thermocouple in the screw. The maximum temperature rise recorded from the thermocouple in the screw (92.7±8.9°C, 158.7±20.9°C, 204.4±35.2°C) was consistently higher than the average temperature rise recorded in the bone (31.8±9.3°C, 44.9±12.4°C, 77.3±12.7°C). The same overall trend between the temperatures that resulted from three screw insertion procedures was recorded with significant statistical analyses using either the thermocouple in the screw or the average of several in-bone thermocouples. Placing a single thermocouple in the bone was determined to have limitations in accurately comparing temperatures from different external fixation screw insertion procedures. Using the preferred measurement techniques, a standard screw with a predrilled hole was found to have the lowest maximum temperatures for the shortest duration compared to the other two insertion procedures. Future studies evaluating bone temperature increase need to use reliable temperature measurements for recommending best practices to surgeons.
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http://dx.doi.org/10.1016/j.medengphy.2016.05.003DOI Listing
September 2016

Comparison of pregnant and non-pregnant occupant crash and injury characteristics based on national crash data.

Authors:
Sarah Manoogian

Accid Anal Prev 2015 Jan 28;74:69-76. Epub 2014 Oct 28.

Bucknell University, One Dent Drive, Lewisburg, PA 17837, USA. Electronic address:

The objective of this study was to provide specific characteristics of injuries and crash characteristics for pregnant occupants from the National Automotive Sampling System/Crashworthiness Data System (NASS/CDS) database for pregnant women as a group, broken down by trimester, and compared to non-pregnant women. Using all NASS/CDS cases collected between the years 2000 and 2012 with at least one pregnant occupant, the entire pregnant data set included 321,820 vehicles, 324,535 occupants, and 640,804 injuries. The pregnant occupant data were compared to the characteristics of NASS/CDS cases for 14,719,533 non-pregnant females 13-44 years old in vehicle crashes from 2000 to 2012. Sixty five percent of pregnant women were located in the front left seat position and roughly the same percentage of pregnant women was wearing a lap and shoulder belt. The average change in velocity was 11.6 mph for pregnant women and over 50% of crashes for pregnant women were frontal collisions. From these collisions, less than seven percent of pregnant women sustained MAIS 2+ injuries. Minor differences between the pregnant and non-pregnant occupants were identified in the body region and source of injuries sustained. However, the data indicated no large differences in injury or crash characteristics based on trimester of pregnancy. Moreover, the risk of an MAIS 2+ level injury for pregnant occupants is similar to the risk of injury for non-pregnant occupants based on the total vehicle change in velocity. Overall this study provides useful data for researchers to focus future efforts in pregnant occupant research. Additionally, this study reinforces that more detailed and complete data on pregnant crashes needs to be collected to understand the risk for pregnant occupants.
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http://dx.doi.org/10.1016/j.aap.2014.10.017DOI Listing
January 2015

Dynamic material properties of the pregnant human uterus.

J Biomech 2012 Jun 25;45(9):1724-7. Epub 2012 Apr 25.

Virginia Tech-Wake Forest University, School of Biomedical Engineering and Sciences, 313 ICTAS Building, Stanger Street MC 0298, Blacksburg, VA 24061, USA.

Given that automobile crashes are the largest single cause of death for pregnant females, scientists are developing advanced computer models of pregnant occupants. The purpose of this study is to quantify the dynamic material properties of the human uterus in order to increase the biofidelity of these models. A total of 19 dynamic tension tests were performed on pregnant human uterus tissues taken from six separate donors. The tissues were collected during full term Cesarean style deliveries and tested within 36 h of surgery. The tissues were processed into uniform coupon sections and tested at 1.5 strains/s using linear motors. Local stress and strain were determined from load data and optical markers using high speed video. The experiments resulted in a non-linear stress versus strain curves with an overall average peak failure true strain of 0.32±0.112 and a corresponding peak failure true stress of 656.3±483.9 kPa. These are the first data available for the dynamic response of pregnant human uterus tissues, and it is anticipated they will increase the accuracy of future pregnant female computational models.
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http://dx.doi.org/10.1016/j.jbiomech.2012.04.001DOI Listing
June 2012

Comparison of risk factors for cervical spine, head, serious, and fatal injury in rollover crashes.

Accid Anal Prev 2012 Mar 26;45:67-74. Epub 2011 Dec 26.

Biodynamic Research Corporation, 5711 University Heights Blvd., Suite 100, San Antonio, TX 78249, USA.

Previous epidemiological studies of rollover crashes have focused primarily on serious and fatal injuries in general, while rollover crash testing has focused almost exclusively on cervical spine injury. The purpose of this study was to examine and compare the risk factors for cervical spine, head, serious, and fatal injury in real world rollover crashes. Rollover crashes from 1995-2008 in the National Automotive Sampling System-Crashworthiness Data System (NASS-CDS) were investigated. A large data set of 6015 raw cases (2.5 million weighted) was generated. Nonparametric univariate analyses, univariate logistic regression, and multivariate logistic regression were conducted. Complete or partial ejection, a lack of seatbelt use, a greater number of roof inversions, and older occupant age significantly increased the risk of all types of injuries studied (p<0.05). Far side seating position increased the risk of fatal, head, and cervical spine injury (p<0.05), but not serious injury in general. Higher BMI was associated with an increased risk of fatal, serious, and cervical spine injury (p<0.05), but not head injury. Greater roof crush was associated with a higher rate of fatal and cervical spine injury (p<0.05). Vehicle type, occupant height, and occupant gender had inconsistent and generally non-significant effects on injury. This study demonstrates both common and unique risk factors for different types of injuries in rollover crashes.
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http://dx.doi.org/10.1016/j.aap.2011.11.009DOI Listing
March 2012

The tolerance of the maxilla to blunt impact.

J Biomech Eng 2011 Jun;133(6):064501

Biodynamic Research Corporation, San Antonio, TX 78249, USA.

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.
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http://dx.doi.org/10.1115/1.4004248DOI Listing
June 2011

The tolerance of the frontal bone to blunt impact.

J Biomech Eng 2011 Feb;133(2):021004

Biodynamic Research Corporation, San Antonio, TX 78249, USA.

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.
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http://dx.doi.org/10.1115/1.4003312DOI Listing
February 2011

The tolerance of the nasal bone to blunt impact.

Ann Adv Automot Med 2010 ;54:3-14

Biodynamic Research Corporation Virginia Tech - Wake Forest Center for Injury Biomechanics The Ohio State University Transportation Research Center.

The nasal bone is among the most frequently broken facial bone due to all types of trauma and is the most frequently fractured facial bone due to motor vehicle collisions. This study reports the results of anterior-posterior impacts performed on male cadavers using a free-falling impactor with a flat impacting surface. The force at fracture onset was determined using an acoustic emission sensor. These non-censored data were utilized in parametric and non-parametric techniques to determine a relationship between applied force and fracture risk. Based on these analyses a 50% risk of fracture corresponded to an applied force of approximately 450 to 850 N. There was no correlation between fracture force and anthropometric measures of the nasal bone. Interestingly, age had a statistically significant relationship with the risk of nasal bone fracture. This study demonstrates the need for a non-censored measure of fracture occurrence when evaluating structures that can continue to support load after fracture onset.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3242551PMC
April 2016

Head and neck loading in everyday and vigorous activities.

Ann Biomed Eng 2011 Feb 20;39(2):766-76. Epub 2010 Oct 20.

Biodynamic Research Corporation, 5711 University Heights Blvd., San Antonio, TX 78249, USA.

The purpose of this study was to document head and neck loading in a group of ordinary people engaged in non-injurious everyday and more vigorous physical activities. Twenty (20) volunteers that were representative of the general population were subjected to seven test scenarios: a soccer ball impact to the forehead, a self-imposed hand strike to the forehead, vigorous head shaking, plopping down in a chair, jumping off a step, a seated drop onto the buttocks, and a vertical drop while seated supine in a chair. Some scenarios involved prescribed and well-controlled stimuli, while others allowed the volunteers to perform common activities at a self-selected level of intensity. Head accelerations up to 31 g and 2888 rad/s(2) and neck loads up to 268 N in posterior shear, 526 N in compression, and 36 Nm in extension were recorded. Most head and neck injury criteria predicted a low risk of injury in all activities. However, rotational head accelerations and Neck Injury Criterion (NIC) values were much higher than some proposed tolerance limits in a large number of tests, all of which were non-injurious. The data from this study help us to establish an envelope of head and neck loading that is commonly encountered and presents a minimal risk of injury.
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http://dx.doi.org/10.1007/s10439-010-0183-3DOI Listing
February 2011

Finite element modeling of human placental tissue.

Ann Adv Automot Med 2009 Oct;53:257-70

Wake Forest University School of Medicine, USA.

Motor vehicle crashes account for a large portion of placental abruption and fetal losses. To better understand the material properties of the human placenta, a Finite Element (FE) model of human placenta tissue was created and verified using data from uniaxial tension tests. Sixty-four tensile tests at three different strain rates of 7% strain/s, 70% strain/s, and 700% strain/s from six whole human placentas were used for model development. Nominal stresses were calculated by dividing forces at the grips by the original cross-sectional area. Nominal strains were calculated by dividing cross-head displacement by the original gauge length. A detailed methodology for interpreting experimental data for application to material model development is presented. A model of the tension coupon was created in LS-DYNA and stretched in the same manner as the uniaxial tension tests. The behavior of the material was optimized to the uniaxial tension test using a multi-island genetic algorithm. The results demonstrate good correlation between experiments and the model, with an average difference of 2% between the optimized FE and experimental first principal stress at the termination state. The material parameters found in this study can be utilized in FE models of placental tissues for behavior under dynamic loading.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3256807PMC
October 2009

Effect of strain rate on the tensile material properties of human placenta.

J Biomech Eng 2009 Sep;131(9):091008

Center for Injury Biomechanics, Virginia Tech-Wake Forest, Blacksburg, VA 24061, USA.

Automobile crashes are the largest cause of injury death for pregnant females and the leading cause of traumatic fetal injury mortality in the United States. Computational models, useful tools to evaluate the risk of fetal loss in motor vehicle crashes, are based on a limited number of quasistatic material tests of the placenta. This study presents a total of 64 uniaxial tensile tests on coupon specimens from six human placentas at three strain rates. Material properties of the placental tissue were evaluated at strain rates of 0.07/s, 0.70/s, and 7.00/s. The test data have average failure strains of 0.34, 0.36, and 0.37, respectively. Failure stresses of 10.8 kPa, 11.4 kPa, and 18.6 kPa correspond to an increase in strain rate from 0.07/s to 7.0/s. The results indicate rate dependence only when comparing the highest strain rate of 7.0/s to either of the lower rates. There is no significant rate dependence between 0.07/s and 0.70/s. When compared with previous testing of placental tissue, the current study addresses the material response to more strain rates as well as provides a much larger set of available data. In summary, tensile material properties for the placenta have been determined for use in computational modeling of pregnant occupant kinematics in events ranging from low impact activities to severe impacts such as in motor vehicle crashes.
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http://dx.doi.org/10.1115/1.3194694DOI Listing
September 2009

Dynamic material properties of the human sclera.

J Biomech 2009 Jul 9;42(10):1493-1497. Epub 2009 May 9.

Virginia Tech, Blacksburg, VA.

As a result of trauma, approximately 30,000 people become blind in one eye every year in the United States. A common injury prediction tool is computational modeling, which requires accurate material properties to produce reliable results. Therefore, the purpose of this study was to determine the dynamic material properties of the human sclera. A high-rate pressurization system was used to create dynamic pressure to the point of rupture in 12 human eyes. Measurements were obtained for the internal pressure, the diameter of the globe, the thickness of the sclera, and the changing coordinates of the optical markers using high-rate video. A relationship between true stress and true strain was determined for the sclera tissue in two directions. It was found that the average maximum true stress was 13.89+/-4.81 MPa for both the equatorial and meridional directions, the average maximum true strain along the equator was 0.041+/-0.014, and the average maximum true strain along the meridian was 0.058+/-0.018. Results show a significant difference in the maximum strain in the equatorial and meridional directions (p=0.02). In comparing these data with previous studies, it is concluded that the human sclera is both anisotropic and viscoelastic. The dynamic material properties presented in this study can be used for advanced models of the human eye to help prevent eye injuries in the future.
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http://dx.doi.org/10.1016/j.jbiomech.2009.03.043DOI Listing
July 2009

Tensile material properties of human tibia cortical bone effects of orientation and loading rate.

Biomed Sci Instrum 2008 ;44:419-27

Virginia Tech - Wake Forest, Center for Injury Biomechanics, Blacksburg, Virginia, USA.

The purpose of this study was to quantify effects of both specimen orientation and loading rate on the tensile material properties for human tibia cortical bone in a controlled study. This study presents 25 human tibia cortical bone coupon tests obtained from the mid-diaphysis of two fresh frozen male human cadavers: 11 axial and 14 lateral. The primary component for the tension coupon testing was a high rate servo-hydraulic Material Testing System (MTS) with a custom slack adaptor. The specimen were loaded at a constant strain rate of approximately 0.05 strains/s, 0.5 strains/s, or 5.0 strains/s. Axial specimens were found to have a significantly larger ultimate stress and ultimate strain compared to lateral specimens for all loading rates, and a significantly larger modulus for low and high loading rates. This finding illustrates the anisentropic behavior of bone over a range of strain rates, which is attributed to the microstructure of the bone and the osteon orientation along the long axis of the bone. With respect to loading rate, both axial and lateral specimens showed significant increases in the modulus and significant decreases in ultimate strain with increased loading rate. Although not significant, axial specimens showed another traditional viscoelastic trend, with ultimate stress increasing with increased loading rate.
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February 2016

Pregnant occupant injury risk in severe frontal crashes using computer simulations.

Biomed Sci Instrum 2008 ;44:249-55

Center for Injury Biomechanics, Virginia Tech - Wake Forest, USA.

Automobile crashes are the largest cause of death for pregnant females and the leading cause of traumatic fetal injury mortality in the United States. A previously validated MADYMO computer model of a 30-week pregnant occupant was used in this study to investigate the pregnant occupant response in a severe frontal motor vehicle crash. This study presents simulations of 26 different severe car crash tests, encompassing nine vehicle models that represent the compact, medium, and sport utility vehicle classes during the years 1996 to 2006. With the pregnant occupant in the passenger seat, these tests involve a vehicle with an initial velocity of 35 mph into a fixed barrier with the full width of the front of the vehicle. Uterine strain from the computational model indicates the risk of adverse fetal outcome for a pregnant occupant in each vehicle. The average risk of fetal loss associated with these frontal crashes is 85 +/- 13% with a minimum risk of 55% and a maximum risk of 100%. This high risk of fetal loss is consistent with published pregnant occupant case studies that have an equivalent change in velocity. When compared to testing for the average male, this study suggests that current safety standards do not accurately address the risk to a pregnant occupant in a severe frontal crash.
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February 2016

Evaluation of pregnant female injury risk during everyday activities.

Biomed Sci Instrum 2008 ;44:183-8

Virginia Tech - Wake Forest, Center for Injury Biomechanics, USA.

Exercise is encouraged for the pregnant female, but there are no data available indicating the risk of fetal loss associated with the level of exercise. The purpose of this study was to assess the risk of fetal loss by simulating exercises using the pregnant computational model. A previously validated MADYMO computer model of a 30-week pregnant female has proven a useful tool in calculating the risk of adverse fetal outcome. Four small female nonpregnant volunteers performed six activities including sitting in a chair normally, walking at 1.3 m/s, running at 2.7 m/s, performing jumping jacks, achieving maximum vertical leap in place, and jumping off of a step 20 cm high. The results for this study are 12 simulations with an average risk of fetal loss equal to 10.0 +/- 4.1%. The minimum risk from the simulations is 3.1% for walking and the maximum risk is 18.8% for running. The low impact exercises have effectively no risk when taken in context with the validation of the computational model from motor vehicle crash data. However, the pregnant female can have an appreciable risk of adverse fetal outcome for the higher impact activities. In conclusion, this study confirms a low risk of adverse fetal outcome for a healthy pregnant female during low impact exercise events.
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February 2016

The use of acoustic emission in facial fracture detection.

Biomed Sci Instrum 2008 ;44:147-52

Virginia Tech - Wake Forest Center for Injury Biomechanics, Blacksburg VA, USA.

This study describes a method for utilizing Acoustic Emission (AE) in facial fracture detection and demonstrates the association between fracture and acoustic emission magnitude. AE sensors were mounted to the frontal bone and mandible of cadaver skulls (n=14) exposed to impacts to the frontal bone, nasal bone, maxilla and mandible. The presence of AE during fracture and non-fracture tests necessitated the development of a threshold to distinguish AE associated with fracture. Based on the obtained data, a threshold of 9 volts was established. The association between above-threshold AE and fracture was demonstrated by performing low-severity impacts on pre-fractured frontal bones. These tests demonstrated that above threshold AE is produced as a result of high-severity impacts, resulting in fracture as well as low-severity impacts on prefracture bone. The results of these tests indicate that above threshold AE was associated with the fracture process and not a function of the force applied to the facial bones.
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February 2016

The influence of arm position on thoracic response in side impacts.

Stapp Car Crash J 2008 Nov;52:379-420

Virginia Tech - Wake Forest Center for Injury Biomechanics.

The purpose of this study was to investigate the influence of arm position on thoracic response and injury severity in side impacts. A total of sixteen non-destructive side impact tests and four destructive side impact tests were preformed using four human male cadavers. Single-axis strain gages were placed on the lateral and posterior regions of ribs three through eight on the impacted side, and the lateral region of ribs three through eight on the non-impacted side. Thoracic rods attached to ribs five, seven, and nine were used to measure lateral rib deflection. For the non-destructive tests, four test conditions with different arm positions were evaluated for each cadaver by performing displacement-controlled, low-energy, lateral impacts, 16 kg at 3 m/s, with a pneumatic impactor. The results of these tests showed that the highest average peak forces, peak rib deflections, and peak rib strains were observed when only the ribs were impacted and lowest when the shoulder was impacted. In addition, higher average peak forces, peak rib deflections, and rib strains were observed when the arm was placed parallel with the thorax versus 45 degrees. For the destructive tests, two test conditions were evaluated by performing high-energy lateral impacts, 23.4 kg at 12 m/s, with a pneumatic impactor. Only one destructive test was performed per cadaver with the arm placed at either 45 degrees or parallel with the thorax. Using rib fractures as the parameter for AIS, both tests conducted with the arm at 45 degrees resulted in an AIS = 4 due to the large number of ribs with multiple fractures which resulted in a flail chest. Conversely, both tests conducted with the arm parallel with the thorax resulted in an AIS=3. The analysis of thoracic strain gage time histories showed that, in general, the rib fracture timing varied with respect to thoracic region. Using scaled rib 5 deflection, lateral fractures on the impacted side occurred between 4.2 mm and 34.9 mm, posterior fractures on the impacted side occurred between 19.0 mm and 37.8 mm, and lateral fractures on the non-impacted side occurred between 60.2 mm and 74.3 mm of deflection. It was found that AIS = 1 injuries occurred at scaled rib deflections of 4.2 mm to 8.6 mm (2% to 3% compression), AIS = 2 at 9.6 to 17.4 mm (4% to 7% compression), and AIS = 3 at 13.1 mm to 20.1 mm (5% to 9% compression) measured at rib five. In conclusion, the results of the current study show that in low-energy side impacts both the arm and shoulder reduce impactor force, rib deflection, and rib strain. In high-energy side impacts, the position of the arm has a considerable effect on both the total number and distribution of rib fractures.
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November 2008

Dynamic biaxial tissue properties of pregnant porcine uterine tissue.

Stapp Car Crash J 2008 Nov;52:167-85

Virginia Tech-Wake Forest Center for Injury Biomechanics, VA, USA.

Automobile crashes are the largest single cause of death for pregnant females and the leading cause of traumatic fetal injury mortality in the United States. Current research for pregnant occupant safety utilizing computational models is limited by available pregnant tissue data. The purpose of this study is to collect experimental data from biaxial tissue tests on pregnant uterine tissue at a dynamic rate. Experimental tests were completed on pregnant porcine uterus which was chosen as a surrogate for the human pregnant uterus given its similarity and availability. Biaxial dynamic tensile tests were performed using a custom designed system of linear motors to pull a cruciform shaped specimen in tension simultaneously with four tissue clamps. The test series included 23 tests with corresponding peak stress and strain measurements of the central region of the specimen where optical markers tracked local displacements. The specimen was loaded at a rate of 0.7 strains per second to match the uterine strain rate in a motor vehicle crash. Experimental results include peak stresses and peak strains for the pregnant uterine tissue in tension. When loaded biaxially, the circumferential peak stress is 500 +/- 219 kPa with a corresponding peak true strain 0.30 +/- 0.09 and the longitudinal peak stress is 320 +/- 176 kPa with a corresponding peak true strain 0.30 +/- 0.09. This material information can be implemented in pregnant occupant models to evaluate the uterine tissue response to impact loading scenarios.
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November 2008

Dynamic tensile properties of human placenta.

J Biomech 2008 Dec 8;41(16):3436-40. Epub 2008 Nov 8.

Virginia Tech-Wake Forest, Center for Injury Biomechanics, Randolph 100F, MC 0238, Blacksburg, VA 24061, USA.

Automobile crashes are the largest cause of injury death for pregnant females and the leading cause of traumatic fetal injury mortality in the United States. Computational models, useful tools to evaluate the risk of fetal loss in motor vehicle crashes, are based on a limited number of quasi-static material tests of the placenta. This study presents a total of 20 dynamic uniaxial tensile tests on the maternal side of the placenta and 10 dynamic uniaxial tensile tests on the chorion layer of the placenta. These tests were completed from 6 human placentas to determine material properties at a strain rate of 7.0 strains/s. The results show that the average peak strain at failure for both the maternal portion and the chorion layer of the placenta are similar with a value of 0.56 and 0.61, respectively. However, the average failure stress for the chorion layer, 167.8 kPa, is much higher than the average failure stress for the placenta with the chorionic plate removed, 18.6 kPa. This is due to differences in the structure and function of these layers in the placenta. In summary, dynamic loading data for the placenta have been determined for use in computational modeling of pregnant occupant kinematics in motor vehicle crashes. Moreover the computational model should utilize the material properties for the placenta without the chorion layer.
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http://dx.doi.org/10.1016/j.jbiomech.2008.09.020DOI Listing
December 2008

Utilizing cryogenic grips for dynamic tension testing of human placenta tissue.

Biomed Sci Instrum 2007 ;43:354-9

Virginia Tech-Wake Forest Center for Injury Biomechanics, Blacksburg, VA, USA.

Computational models are used to investigate placental abruption in motor vehicle crashes, which is the leading cause of traumatic fetal injury mortality in the United States. Material parameters for computational modeling of pregnant occupant kinematics come from early research on placenta tissue at quasi-static loading rates. The purpose of this research is to develop a methodology for using cryogenic grips to test placenta specimens in uniaxial tension at a rate normally seen in a motor vehicle crash. For dynamic testing of placental tissue, implementing and adapting a cryogenic grip mechanism provides the ability to grip the tissue throughout the thickness and eliminates potential slipping of the tissue in the grip during the dynamic test. The validation for using the cryogenic grips is presented with video images of a typical test event showing the tissue failing in the active area. Additionally, local and global strain measures are compared to confirm the tissue strain is similar throughout the specimen. The cryogenic grips provide a low-cost and effective method of gripping and pulling a thick soft tissue in uniaxial tension. As a result, these methods can be used to acquire the material properties of placenta tissue loaded at a dynamic rate to apply in a computational pregnant model.
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June 2007

Methodology for dynamic biaxial tension testing of pregnant uterine tissue.

Biomed Sci Instrum 2007 ;43:230-5

Virginia Tech-Wake Forest Center for Injury Biomechanics, Blacksburg, VA, USA.

Placental abruption accounts for 50% to 70% of fetal losses in motor vehicle crashes. Since automobile crashes are the leading cause of traumatic fetal injury mortality in the United States, research of this injury mechanism is important. Before research can adequately evaluate current and future restraint designs, a detailed model of the pregnant uterine tissues is necessary. The purpose of this study is to develop a methodology for testing the pregnant uterus in biaxial tension at a rate normally seen in a motor vehicle crash. Since the majority of previous biaxial work has established methods for quasi-static testing, this paper combines previous research and new methods to develop a custom designed system to strain the tissue at a dynamic rate. Load cells and optical markers are used for calculating stress strain curves of the perpendicular loading axes. Results for this methodology show images of a tissue specimen loaded and a finite verification of the optical strain measurement. The biaxial test system dynamically pulls the tissue to failure with synchronous motion of four tissue grips that are rigidly coupled to the tissue specimen. The test device models in situ loading conditions of the pregnant uterus and overcomes previous limitations of biaxial testing. A non-contact method of measuring strains combined with data reduction to resolve the stresses in two directions provides the information necessary to develop a three dimensional constitutive model of the material. Moreover, future research can apply this method to other soft tissues with similar in situ loading conditions.
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June 2007

Material properties of human rib cortical bone from dynamic tension coupon testing.

Stapp Car Crash J 2005 Nov;49:199-230

Virginia Tech - Wake Forest, Center for Injury Biomechanics, Blacksburg, VA, 24061, USA.

The purpose of this study was to develop material properties of human rib cortical bone using dynamic tension coupon testing. This study presents 117 human rib cortical bone coupon tests from six cadavers, three male and three female, ranging in age from 18 to 67 years old. The rib sections were taken from the anterior, lateral, and posterior regions on ribs 1 through 12 of each cadaver's rib cage. The cortical bone was isolated from each rib section with a low speed diamond saw, and milled into dog bone shaped tension coupons using a small computer numerical control machine. A high-rate servo-hydraulic Material Testing System equipped with a custom slack adaptor, to provide constant strain rates, was used to apply tension loads to failure at an average rate of 0.5 strains/sec. The elastic modulus, yield stress, yield strain, ultimate stress, ultimate strain, and strain energy density were determined from the resulting stress versus strain curves. The overall average of all cadaver data gives an elastic modulus of 13.9 GPa, a yield stress of 93.9 MPa, a yield strain of 0.88 %, an ultimate stress of 124.2 MPa, an ultimate strain of 2.7 %, and a strain energy density of 250.1 MPa-microstrain. For all cadavers, the plastic region of the stress versus strain curves was substantial and contributed approximately 60 % to the strain energy and over 80 % in the tests with the 18 year old cadaver. The rib cortical bone becomes more brittle with increasing age, shown by an increase in the modulus (p < 0.01) and a decrease in peak strain (p < 0.01). In contrast to previous three-bending tests on whole rib and rib cortical bone coupons, there were no significant differences in material properties with respect to rib region or rib level. When these results are considered in conjunction with the previous three-point bending tests, there is regional variation in the structural response of the human rib cage, but this variation appears to be primarily a result of changes in the local geometry of each rib while the material properties remain nearly constant within an individual.
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November 2005

Analysis of pregnant occupant crash exposure and the potential effectiveness of four-point seatbelts in far side crashes.

Annu Proc Assoc Adv Automot Med 2006 ;50:187-98

Virginia Tech - Wake Forest, Center for Injury Biomechanics, Blacksburg, VA, USA.

The purpose of this paper is to present the crash exposure patterns of pregnant occupants and to evaluate the effectiveness of restraint systems, including four-point seatbelts, in far side crashes. The NASS CDS database revealed that 53.0 % of pregnant occupants are exposed to frontal crashes while 13.5 % are exposed to far side impacts. Given that far side crashes were the second leading crash mode after frontal impacts, a previously validated MADYMO computer model of a 30 week pregnant occupant was utilized to investigate pregnant occupant biomechanics in far side crashes. Three impact speeds (5, 15, and 25 mph) were simulated with four restraint conditions: unbelted, lap-belt only, three-point belt, and a four-point belt. Direct abdominal contact from the shoulder strap of the three-point or four-point belt caused uterine-placental strain in contrast to the inertial loading induced strain in the lap-belt and unbelted cases. Overall, the three-point and four-point belt systems provide superior restraint effectiveness for the pregnant occupant compared to the lap-belt and no restraint cases. The four-point resulted in slightly better performance than the three-point belt by reducing the fetal injury risk and occupant excursion.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3217485PMC
August 2008

Head acceleration is less than 10 percent of helmet acceleration in football impacts.

Biomed Sci Instrum 2006 ;42:383-8

Virginia Tech - Wake Forest, Center for Injury Biomechanics, Blacksburg, VA, USA.

Sports-related concussions constitute 20 percent of brain injuries each year in the United States. Concussion research has included a variety of instrumentation and techniques to measure head accelerations. Most recently, the Head Impact Telemetry (HIT) System (Simbex, Lebanon, NH), a wireless system that provides real-time data from impacts, is used to measure in-situ head accelerations in collegiate football. The purpose of this study is to compare helmet shell acceleration to head center of gravity acceleration using two measures of linear head acceleration. A study of 50 helmet to helmet impact tests using a pendulum provided a range of head accelerations from 5 g to 50 g. The primary measure of head acceleration is accelerometers mounted at the center of gravity of the Hybrid III head. A secondary measure is the in-helmet HIT System. The series of 50 pendulum impacts included three impact velocities of 2.0 m/s, 3.5 m/s and 5.0 m/s at four different impact locations. The impact locations were on the side, back, top and just above the facemask on the front. By comparing these two measured head accelerations and the helmet acceleration during a pendulum impact, it is shown that the response of the head and the helmet vary greatly and the in-helmet system matches the head and not helmet acceleration. Specifically, head acceleration is less than 10 percent of helmet acceleration in football impacts; moreover, the HIT System is able to accurately measure the head acceleration.
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July 2006

The effects of extraocular muscles on static displacements of the human eye.

Biomed Sci Instrum 2006 ;42:372-7

Virginia Tech-Wake Forest, Center for Injury Biomechanics, USA.

More than 30,000 people lose sight in at least one eye every year in the United States. Globe rupture is one of the most severe injuries and can often result in the loss of an eye. Previous studies to determine the injury tolerance of the human eye to globe rupture have not investigated the effects of extraocular muscles on the response of the eye. The purpose of the current study is to quantify the effects of the extraocular muscles using quasistatic displacement tests of the human eye in situ. A total of three post-mortem human heads were used for the matched pair tests designed to elucidate any differences in the force-deflection response of the human eye with the extraocular muscles intact and transected. Computed tomography imaging was utilized to observe the deformation of the eye within the orbit for each displacement, from 0 mm to 30 mm. Slight differences in the force-deflection response are observed; however, it is not clear how these differences will influence impact response at a dynamic rate. It was also observed that under quasistatic displacements that the eye is able to translate out of the way of the impactor assembly, even under large deflections, and without globe rupture. Additional dynamic tests are recommended to determine the effects of the extraocular muscles on eye impact response.
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July 2006

Prevention of facial fractures from night vision goggle impact.

Biomed Sci Instrum 2006 ;42:13-8

Virginia Tech- Wake Forest Center for Injury Biomechanics, Blacksburg, VA, USA.

Facial bone fractures in the military can result from direct loading of night vision goggles on the orbital region. Facial fracture research has shown that increasing the area over which the load is applied increases the load tolerance. The purpose of this study is to apply this concept to reducing the risk of facial bone fracture from night vision goggle impacts. The effectiveness of countermeasures in prevention of orbital fracture was evaluated using a vertical drop tower with two impact velocities of 2.6 m/s and 3.6 m/s. The countermeasure used was a rigid plastic custom face shield made from a plaster impression of each head. In addition to two human cadaver subjects, one male and one female, tests were completed on a Hybrid III 50th percentile dummy head. Three impacts to the dummy headform included no countermeasure, safety glasses, and a custom face shield. These tests yielded peak loads of 8700 N, 7500 N, and 5640 N respectively. Using the female subject, impacts were preformed successively until injury occurred. These two impacts to the subject wearing a custom face shield resulted in peak loads of 4025 N and 5158 N. The highest load corresponds to an impact velocity of 3.6 m/s and a nasal bone fracture. Two impacts to the male subject with a custom face shield resulted in peak loads of 4554 N and 5101 N with no injury. The final impact to the male subject had a peak load of 2010 N with complete orbital fracture due to the absence of a countermeasure. From these tests it is shown that facial fracture risk from night vision goggle impact can be reduced using a contoured rigid face shield.
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July 2006

Predicting neck injuries due to head-supported mass.

Aviat Space Environ Med 2006 May;77(5):509-14

Center for Injury Biomechanics, Virginia Tech, 114 Randolph Hall (MC 0238), Mechanical Engineering, Blacksburg, VA 24061, USA.

Background: Technological advances in military equipment have resulted in more devices being mounted on the helmet to enhance the capability of the soldier. The soldier's neck must bear this head-supported mass (HSM) and the resulting dynamic characteristics of the head and neck system are changed. The purpose of this study was to vary the conditions of impact as well as the design criteria to quantify the effect of HSM on neck injury risk through computational modeling.

Methods: The TNO MADYMO detailed neck model was used for a matrix of 196 simulations designed to vary the impact conditions and HSM properties added to the model. These parameters included seven impact directions, three impact magnitudes, nine mass locations, and three mass magnitudes. The data collected from these simulations were evaluated for injury risk using the lower neck beam criterion equation.

Results: The results from these simulations provide detailed information regarding the risk of injury based on a particular HSM configuration and the acceleration of the body. The predominant factor in increasing risk in the lower neck is the increase in pulse magnitude. The effect of pulse magnitude is more dominant in the directions that create a flexion or lateral bending moment.

Conclusion: HSM increases the level of injury, but the impact level that the subject is exposed to is a more dominating factor in determining injury risk.
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May 2006

Analysis of linear head accelerations from collegiate football impacts.

Curr Sports Med Rep 2006 Feb;5(1):23-8

Division of Sports Medicine, Edward Via Virginia College of Osteopathic Medicine, Virginia Tech Department of Athletics, Blacksburg, VA 24061, USA.

Sports-related concussions result in 300,000 brain injuries in the United States each year. We conducted a study utilizing an in-helmet system that measures and records linear head accelerations to analyze head impacts in collegiate football. The Head Impact Telemetry (HIT) System is an in-helmet system with six spring-mounted accelerometers and an antenna that transmits data via radio frequency to a sideline receiver and laptop computer system. A total of 11,604 head impacts were recorded from the Virginia Tech football team throughout the 2003 and 2004 football seasons during 22 games and 62 practices from a total of 52 players. Although the incidence of injury data are limited, this study presents an extremely large data set from human head impacts that provides valuable insight into the lower limits of head acceleration that cause mild traumatic brain injuries.
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http://dx.doi.org/10.1097/01.csmr.0000306515.87053.faDOI Listing
February 2006

Analysis of real-time head accelerations in collegiate football players.

Clin J Sport Med 2005 Jan;15(1):3-8

Virginia Tech-Wake Forest Center for Injury Biomechanics, Blacksburg, VA 24061, USA.

Objective: To measure and analyze head accelerations during American collegiate football practices and games.

Methods: A newly developed in-helmet 6-accelerometer system that transmits data via radio frequency to a sideline receiver and laptop computer system was implemented. From the data transfer of these accelerometer traces, the sideline staff has real-time data including the head acceleration, the head injury criteria value, the severity index value, and the impact location. Data are presented for instrumented players for the entire 2003 football season, including practices and games.

Setting: American collegiate football.

Subjects: Thirty-eight players from Virginia Tech's varsity football team.

Main Outcome Measurements: Accelerations and pathomechanics of head impacts.

Results: : A total of 3312 impacts were recorded over 35 practices and 10 games for 38 players. The average peak head acceleration, Gadd Severity Index, and Head Injury Criteria were 32 g +/- 25 g, 36 g +/- 91 g, and 26 g +/- 64 g, respectively. One concussive event was observed with a peak acceleration of 81 g, a 267 Gadd Severity Index, and 200 Head Injury Criteria. Because the concussion was not reported until the day after of the event, a retrospective diagnosis based on his history and clinical evaluation suggested a mild concussion.

Conclusions: The primary finding of this study is that the helmet-mounted accelerometer system proved effective at collecting thousands of head impact events and providing contemporaneous head impact parameters that can be integrated with existing clinical evaluation techniques.
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http://dx.doi.org/10.1097/00042752-200501000-00002DOI Listing
January 2005
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