Prediction of lumbar vertebral body compressive strength of overweight and obese older adults using morphed subject-specific finite-element models to evaluate the effects of weight loss

BACKGROUND

Diet and exercise can promote weight loss in older adults; however, there is potential to increase fracture risk due to loss of bone mineral density (BMD) known to accompany weight loss. Weight loss effects on measures of bone quality and strength are currently unknown.

AIMS

The purpose of this study is to develop subject-specific finite-element (FE) models of the lumbar spine and study the effect of intentional weight loss on bone strength in a pilot data set.

METHODS

Computed tomography (CT) scans of the lumbar spine of 30 overweight and obese (mean BMI = 29.7 ± 3.9 kg/m²), older adults (mean age = 65.9 ± 4.6 years) undergoing an 18-month intentional weight loss intervention were obtained at baseline and post-intervention. Measures of volumetric BMD (vBMD) and variable cortical thickness were derived from each subject CT scan. Development of the subject-specific FE models of the lumbar spine involved model morphing techniques to accelerate the development of the models. vBMD-derived material properties and cortical thickness measures were directly mapped to baseline and post-intervention models. Bone strength was estimated through simulation of a quasi-static uniaxial compression test.

RESULTS

From baseline to 18-month post-weight loss intervention, there were statistically significant decreases in estimated bone strength (6.5% decrease; p < 0.05). Adjusting for baseline bone measures and gender revealed no statistically significant correlations between weight change and change in vBMD, cortical thickness, or bone strength.

CONCLUSION

Integration of CT-based measures and FE models with conventional areal BMD can improve the understanding of the effects of intentional weight loss on bone health.

Development of Subject-Specific Proximal Femur Finite Element Models Of Older Adults with Obesity to Evaluate the Effects of Weight Loss on Bone Strength

Study background

Recommendation of intentional weight loss in older adults remains controversial, due in part to the loss of bone mineral density (BMD) known to accompany weight loss. While finite element (FE) models have been used to assess bone strength, these methods have not been used to study the effects of weight loss. The purpose of this study is to develop subject-specific FE models of the proximal femur and study the effect of intentional weight loss on bone strength.

Methods

Computed tomography (CT) scans of the proximal femur of 25 overweight and obese (mean BMI=29.7 ± 4.0 kg/m²), older adults (mean age=65.6 ± 4.1 years) undergoing an 18-month intentional weight loss intervention were obtained at baseline and post-intervention. Measures of volumetric BMD (vBMD) and variable cortical thickness were derived from each subject CT scan and directly mapped to baseline and post-intervention models. Subject-specific FE models were developed using morphing techniques. Bone strength was estimated through simulation of a single-limb stance and sideways fall configuration.

Results

After weight loss intervention, there were significant decreases from baseline to 18 months in vBMD (total hip: -0.024 ± 0.013 g/cm³; femoral neck: -0.012 ± 0.014 g/cm³), cortical thickness (total hip: -0.044 ± 0.032 mm; femoral neck: -0.026 ± 0.039 mm), and estimated strength (stance: -0.15 ± 0.12 kN; fall: -0.04 ± 0.06 kN). Adjusting for baseline bone measures, body mass, and gender, correlations were found between weight change and change in total hip and femoral neck cortical thickness (all p<0.05). For every 1 kilogram of body mass lost cortical thickness in the total hip and femoral neck decreased by 0.003 mm and 0.004 mm, respectively. No significant correlations were present for the vBMD or strength data.

Conclusion

The developed subject-specific FE models could be used to better understand the effects of intentional weight loss on bone health.

Functional outcomes of motor vehicle crash thoracic injuries in pediatric and adult occupants

OBJECTIVE

Characterization of the severity of injury should account for both mortality and disability. The objective of this study was to develop a disability metric for thoracic injuries in motor vehicle crashes (MVCs) and compare the functional outcomes between the pediatric and adult populations.

METHODS

Disability risk (DR) was quantified using Functional Independence Measure (FIM) scores within the National Trauma Data Bank for the most frequently occurring Abbreviated Injury Scale (AIS) 2-5 thoracic injuries. Occupants with thoracic injury were classified as disabled or not disabled based on the FIM scale, and comparisons were made between the following age groups: pediatric, adult, middle-aged, and older occupants (ages 7-18, 19-45, 46-65, and 66+, respectively). For each age group, DR was calculated by dividing the number of patients who were disabled and sustained a given injury by the number of patients who sustained a given injury. To account for the effect of higher severity co-injuries, a maximum AIS adjusted DR (DR_MAIS) was also calculated for each injury. DR and DR_MAIS could range from 0 to 100% disability risk.

RESULTS

The mean DR_MAIS for MVC thoracic injuries was 20% for pediatric occupants, 22% for adults, 29% for middle-aged adults, and 43% for older adults. Older adults possessed higher DR_MAIS values for diaphragm laceration/rupture, heart laceration, hemo/pneumothorax, lung contusion/laceration, and rib and sternum fracture compared to the other age groups. The pediatric population possessed a higher DR_MAIS value for flail chest compared to the other age groups.

CONCLUSION

Older adults had significantly greater overall disability than each of the other age groups for thoracic injuries. The developed disability metrics are important in quantifying the significant burden of injuries and loss of quality life years. Such metrics can be used to better characterize severity of injury and further the understanding of age-related differences in injury outcomes, which can influence future age-specific modifications to AIS.

Characterization of the occult nature of frequently occurring pediatric motor vehicle crash injuries

BACKGROUND

Occult injuries are those likely to be missed on initial assessment by first responders and, though initially asymptomatic, they may present suddenly and lead to rapid patient decompensation. No scoring systems to quantify the occultness of pediatric injuries have been established. Such a scoring system will be useful in the creation of an Advanced Automotive Crash Notification (AACN) system that assists first responders in making triage decisions following a motor vehicle crash (MVC).

STUDY DESIGN

The most frequent MVC injuries were determined for 0-4, 5-9, 10-14 and 15-18 year olds. For each age-specific injury, experts with pediatric trauma expertise were asked to rate the likelihood that the injury may be missed by first responders. An occult score (ranging from 0-1) was calculated by averaging and normalizing the responses of the experts polled.

RESULTS

Evaluation of all injuries across all age groups demonstrated greater occult scores for the younger age groups compared to older age groups (mean occult score 0-4yo: 0.61 ± 0.23, 5-9yo: 0.53 ± 0.25, 10-14yo: 0.48 ± 0.23, and 15-18yo: 0.42 ± 0.22, p < 0.01). Body-region specific occult scores revealed that experts judged abdominal, spine and thoracic injuries to be more occult than injuries to other body regions.

CONCLUSIONS

The occult scores suggested that injuries are more difficult to detect in younger age groups, likely given their inability to express symptoms. An AACN algorithm that can predict the presence of clinically undetectable injuries at the scene can improve triage of children with these injuries to higher levels of care.

Functional outcomes of thoracic injuries in pediatric and adult occupants

OBJECTIVE

To develop a disability metric for motor vehicle crash (MVC) thoracic injuries and compare functional outcomes between pediatric and adult populations.

METHODS

Disability risk (DR) was quantified using Functional Independence Measure (FIM) scores within the National Trauma Data Bank (NTDB) for the top 95% most frequently occurring AIS 2, 3, 4, and 5 thoracic injuries in NASS-CDS 2000-2011. The NTDB contains a truncated form of the FIM score, including three items (self-feed, locomotion, and verbal expression), each graded from full functional dependence to full functional independence. Pediatric (ages 7-18 years), adult (19-45), middle-aged adult (46-65), and older adult (66+) MVC occupants were classified as disabled or not disabled based on the FIM scale. The DR was calculated for each injury within each age group by dividing the number of patients who were disabled that sustained the specific injury by the number of patients who sustained the specific injury. To account for the impact of more severe co-injuries, a maximum Abbreviated Injury Scale (MAIS) adjusted DR (DR_MAIS) was also calculated. DR and DR_MAIS could range from 0 (0% disability risk) to 1 (100% disability risk).

RESULTS

The mean DR_MAIS for MVC thoracic injuries was 20% for pediatric occupants, 22% for adults, 29% for middle-aged adults, and 43% for older adults. Older adults possessed higher DR_MAIS values for diaphragm laceration/rupture, heart laceration, hemo/pneumothorax, lung contusion/laceration, rib fracture, and sternum fracture compared to the other age groups. The pediatric population possessed a higher DR_MAIS value for flail chest compared to the other age groups.

CONCLUSIONS

Older adults had significantly greater overall disability than each of the other age groups for thoracic injuries. The developed disability metrics are important in quantifying the significant burden of injuries and loss of quality life years. Such metrics can be used to better characterize severity of injury and further the understanding of age-related differences in injury outcomes, which can impact future age-specific modifications to AIS.

Predicting Pediatric Patients Who Require Care at a Trauma Center: Analysis of Injuries and Other Factors

BACKGROUND

Triage decision correctness for children in motor vehicle crashes can be affected by occult injuries. There is a need to develop a transfer score (TS) metric for children that can help quantify the likelihood that an injury is present that would require transfer to a trauma center (TC) from a non-TC, and improve triage decision making. Ultimately, the TS metric might be useful in an advanced automatic crash notification algorithm, which uses vehicle telemetry data to predict the risk of serious injury after a motor vehicle crash using an approach that includes metrics to describe injury severity, time sensitivity, and predictability.

STUDY DESIGN

Transfer score metrics were calculated in 4 pediatric age groups (0 to 4, 5 to 9, 10 to 14, 15 to 18 years) for the most frequent motor vehicle crash injuries using the proportions of children transferred to a TC or managed at a non-TC using the National Inpatient Sample years 1998 to 2007. To account for the maximum Abbreviated Injury Scale (MAIS) injury, a co-injury adjusted transfer score (TS_MAIS) was calculated. The TS and TS_MAIS range from 0 to 1, with 1 indicating highly transferred injuries.

RESULTS

Injuries in younger patients were more likely to be transferred (median TS 0.48, 0.35, 0.25, and 0.23 for 0 to 4, 5 to 9, 10 to 14, and 15 to 18 years, respectively). Injuries more likely to be transferred in younger children occurred in the thorax and abdomen. Regardless of age, spine (median TS_MAIS 0.59), head (median TS_MAIS 0.48), and thorax (median TS_MAIS 0.46) injuries had the highest frequency for transfer.

CONCLUSIONS

The TS metrics quantitatively describe age-specific transfer practices for children with particular injuries. This information can be useful in advanced automatic crash notification systems to alert first responders to the possibility of occult injuries and reduce undertriage of commonly missed injuries.

Expert Perspectives on Time Sensitivity and a Related Metric for Children Involved in Motor Vehicle Crashes

OBJECTIVE

Advanced Automatic Crash Notification (AACN) uses vehicle telemetry data to predict risk of serious injury among motor vehicle crash occupants and can thus improve the accuracy with which injured children are triaged by first responders. To better define serious injury for AACN systems (which typically use Abbreviated Injury Scale [AIS] metrics), an age-specific approach evaluating severity, time sensitivity (TS), and predictability of injury has been developed. This study outlines the development of the TS score.

METHODS

The 95% most frequent AIS 2+ injuries in a national motor vehicle crash data set spanning 2000 to 2011 were determined for the following age groups: 0 to 4, 5 to 9, 10 to 14, and 15 to 18 years. For each age-specific injury, clinicians with pediatric trauma expertise were asked if treatment at a trauma center was required and were asked about the urgency of treatment. A TS score (range 0-1) was calculated by combining the mean trauma center decision and urgency scores.

RESULTS

A total of 30 to 32 responses were obtained for each age-specific injury. The most frequent motor vehicle crash-induced injuries in the younger groups received significantly higher scores than those in the older groups (median TS score 0 to 4 years: 0.89, 5-9 years: 0.87, 10-14 years: 0.82, 15-18 years: 0.72, P < .001). Large variations in TS existed within each AIS severity level; for example, scores among AIS 2 injuries in 0- to 4-year-olds ranged from 0.12 to 0.98.

CONCLUSIONS

The TS of common pediatric injuries varies on the basis of age and may not be accurately reflected by AIS metrics. AIS may not capture all aspects of injury that should be considered by AACN systems.

Characterization of the occult nature of injury for frequently occurring motor vehicle crash injuries

BACKGROUND

Occult injuries are not easily detected and can be potentially life-threatening. The purpose of this study was to quantify the perceived occultness of the most frequent motor vehicle crash injuries according to emergency medical services (EMS) professionals.

STUDY DESIGN

An electronic survey was distributed to 1,125 EMS professionals who were asked to quantify the likelihood that first responders would miss symptoms related to a particular injury on a 5-point Likert scale. The Occult Score for each injury was computed from the average of all the survey responses and normalized to be a continuous metric ranging from 0 to 1 where 0 is a non-occult (highly apparent on initial presentation) injury and 1 is an occult (unapparent on initial presentation) injury.

RESULTS

Overall, 110,671 survey responses were collected. The Occult Score ranged from 0 to 1 with a mean, median, and standard deviation of 0.443, 0.450, and 0.233, respectively. When comparing the Occult Score of an injury to its corresponding AIS severity, there was no relationship between the metrics. When stratifying by body region, injury type, and AIS severity, it was evident that AIS 2-4 abdominal injuries with lacerations, hemorrhage, or contusions were perceived as the most occult injuries.

CONCLUSIONS

Timely triage is key to reduce the morbidity and mortality associated with occult injuries. The Occult Score developed in this study to describe the predictability of an injury in a motor vehicle crash will be used as part of a larger effort, including incorporation into an advanced automatic crash notification (AACN) algorithm to detect crash conditions associated with a patient's need for prompt treatment at a trauma center.

Functional outcomes of motor vehicle crash head injuries in pediatric and adult occupants

OBJECTIVE

The objective of the study was to develop a disability-based metric for motor vehicle crash (MVC) injuries, with a focus on head injuries, and compare the functional outcomes between the pediatric and adult populations.

METHODS

Disability risk (DR) was quantified using Functional Independence Measure (FIM) scores within the National Trauma Data Bank-Research Data System (NTDB-RDS) for the top 95% most frequently occurring Abbreviated Injury Scale (AIS) 3, 4, and 5 head injuries in NASS-CDS 2000-2011. Pediatric (ages 7-18), adult (19-45), middle-aged (46-65), and older adult (66+) patients with an FIM score available who were alive at discharge and had an AIS 3, 4, or 5 injury were included in the study. The NTDB-RDS contains a truncated form of the FIM instrument, including 3 items (self-feed, locomotion, and verbal expression), each graded on a scale of 1 (full functional dependence) to 4 (full functional independence). Patients within each age group were classified as disabled or not disabled based on the FIM scale. The DR was calculated for each age group by dividing the number of patients who sustained a specific injury and were disabled by the number of patients who sustained the specific injury. To account for the impact of more severe associated coinjuries, a maximum AIS (MAIS) adjusted DR (DRMAIS) was also calculated for each injury. DR and DRMAIS ranged from 0 (0% disability risk) to 1 (100% disability risk).

RESULTS

An analysis of the most frequent FIM components associated with disabling MVC head injuries revealed that disability across all 3 items (self-feed, locomotion, and expression) was the most frequent for pediatric and adult patients. Only locomotion was the most frequent for middle-aged and older adults. The mean DRMAIS for MVC head injuries was 35% for pediatric patients, 36% for adults, 38% for middle-aged adults, and 44% for older adults. Further analysis was conducted by grouping the head injuries into 8 groups based on the structure of injury and injury type. The pediatric population possessed higher DRMAIS values for brain stem injuries as well as loss of consciousness injuries. Older adults possessed higher DRMAIS values for contusion/hemorrhage injuries, epidural hemorrhage, intracerebral hemorrhage, skull fracture, and subdural/subarachnoid hemorrhage.

CONCLUSION

At-risk populations such as pediatric and older adult patients possessed higher DRMAIS values for different head injuries. Disability in pediatric patients is critical due to loss of quality life years. Disability risk can supplement severity metrics to improve the ability of such metrics to discriminate the severity of different injuries that do not lead to death. Understanding of age-related differences in injury outcomes when compared to adults could inform future age-specific modifications to the AIS.

An Injury Severity-, Time Sensitivity-, and Predictability-Based Advanced Automatic Crash Notification Algorithm Improves Motor Vehicle Crash Occupant Triage

BACKGROUND

Advanced Automatic Crash Notification algorithms use vehicle telemetry measurements to predict risk of serious motor vehicle crash injury. The objective of the study was to develop an Advanced Automatic Crash Notification algorithm to reduce response time, increase triage efficiency, and improve patient outcomes by minimizing undertriage (<5%) and overtriage (<50%), as recommended by the American College of Surgeons.

STUDY DESIGN

A list of injuries associated with a patient's need for Level I/II trauma center treatment known as the Target Injury List was determined using an approach based on 3 facets of injury: severity, time sensitivity, and predictability. Multivariable logistic regression was used to predict an occupant's risk of sustaining an injury on the Target Injury List based on crash severity and restraint factors for occupants in the National Automotive Sampling System - Crashworthiness Data System 2000-2011. The Advanced Automatic Crash Notification algorithm was optimized and evaluated to minimize triage rates, per American College of Surgeons recommendations.

RESULTS

The following rates were achieved: <50% overtriage and <5% undertriage in side impacts and 6% to 16% undertriage in other crash modes. Nationwide implementation of our algorithm is estimated to improve triage decisions for 44% of undertriaged and 38% of overtriaged occupants. Annually, this translates to more appropriate care for >2,700 seriously injured occupants and reduces unnecessary use of trauma center resources for >162,000 minimally injured occupants.

CONCLUSIONS

The algorithm could be incorporated into vehicles to inform emergency personnel of recommended motor vehicle crash triage decisions. Lower under- and overtriage was achieved, and nationwide implementation of the algorithm would yield improved triage decision making for an estimated 165,000 occupants annually.

Development and Validation of an Older Occupant Finite Element Model of a Mid-Sized Male for Investigation of Age-related Injury Risk

The aging population is a growing concern as the increased fragility and frailty of the elderly results in an elevated incidence of injury as well as an increased risk of mortality and morbidity. To assess elderly injury risk, age-specific computational models can be developed to directly calculate biomechanical metrics for injury. The first objective was to develop an older occupant Global Human Body Models Consortium (GHBMC) average male model (M50) representative of a 65 year old (YO) and to perform regional validation tests to investigate predicted fractures and injury severity with age. Development of the GHBMC M50 65 YO model involved implementing geometric, cortical thickness, and material property changes with age. Regional validation tests included a chest impact, a lateral impact, a shoulder impact, a thoracoabdominal impact, an abdominal bar impact, a pelvic impact, and a lateral sled test. The second objective was to investigate age-related injury risks by performing a frontal US NCAP simulation test with the GHBMC M50 65 YO and the GHBMC M50 v4.2 models. Simulation results were compared to the GHBMC M50 v4.2 to evaluate the effect of age on occupant response and risk for head injury, neck injury, thoracic injury, and lower extremity injury. Overall, the GHBMC M50 65 YO model predicted higher probabilities of AIS 3+ injury for the head and thorax.

Image segmentation and registration algorithm to collect thoracic skeleton semilandmarks for characterization of age and sex-based thoracic morphology variation

Thoracic anthropometry variations with age and sex have been reported and likely relate to thoracic injury risk and outcome. The objective of this study was to collect a large volume of homologous semilandmark data from the thoracic skeleton for the purpose of quantifying thoracic morphology variations for males and females of ages 0-100 years. A semi-automated image segmentation and registration algorithm was applied to collect homologous thoracic skeleton semilandmarks from 343 normal computed tomography (CT) scans. Rigid, affine, and symmetric diffeomorphic transformations were used to register semilandmarks from an atlas to homologous locations in the subject-specific coordinate system. Homologous semilandmarks were successfully collected from 92% (7077) of the ribs and 100% (187) of the sternums included in the study. Between 2700 and 11,000 semilandmarks were collected from each rib and sternum and over 55 million total semilandmarks were collected from all subjects. The extensive landmark data collected more fully characterizes thoracic skeleton morphology across ages and sexes. Characterization of thoracic morphology with age and sex may help explain variations in thoracic injury risk and has important implications for vulnerable populations such as pediatrics and the elderly.

Predicting patients that require care at a trauma center: analysis of injuries and other factors

INTRODUCTION

The detection of occult or unpredictable injuries in motor vehicle crashes (MVCs) is crucial in correctly triaging patients and thus reducing fatalities. The purpose of the study was to develop a metric that indicates the likelihood that an injury sustained in a MVC would require management at a Level I/II trauma centre (TC) versus a non-trauma centre (non-TC).

METHODS

Transfer Scores (TSs) were computed for 240 injuries that comprise the top 95% most frequently occurring injuries in the National Automotive Sampling System-Crashworthiness Data System (NASS-CDS) with an Abbreviated Injury Scale (AIS) severity of 2 or greater. A TS for each injury was computed using the proportions of patients involved in a MVC from the National Inpatient Sample (NIS) that were transferred to a TC or managed at a non-TC. Similarly, a TSMAIS that excludes patients with higher severity co-injuries was calculated using the proportion of patients with a maximum AIS (MAIS) equal to the AIS severity of a given injury.

RESULTS

The results indicated for injuries of a given AIS severity, body region, and injury type, there were large variations in the TSMAIS. Overall results demonstrated higher TSMAIS values when injuries were internal, haemorrhagic, intracranial or of moderate severity (AIS 3-5). Specifically, injuries to the head possessed a TSMAIS that ranged from 0.000 to 0.889, with head injuries of AIS 3-5 severities being the most likely to be transferred.

DISCUSSION AND CONCLUSIONS

The analysis indicated that the TSMAIS is not solely correlated with AIS severity and therefore it captures other important aspects of injury such as predictability and trauma system capabilities. The TS and TSMAIS can be useful in advanced automatic crash notification (AACN) research for the detection of highly unpredictable injuries in MVCs that require direct transport to a TC.

Mortality Risk in Pediatric Motor Vehicle Crash Occupants: Accounting for Developmental Stage and Challenging Abbreviated Injury Scale Metrics

OBJECTIVE

Survival risk ratios (SRRs) and their probabilistic counterpart, mortality risk ratios (MRRs), have been shown to be at odds with Abbreviated Injury Scale (AIS) severity scores for particular injuries in adults. SRRs have been validated for pediatrics but have not been studied within the context of pediatric age stratifications. We hypothesized that children with similar motor vehicle crash (MVC) injuries may have different mortality risks (MR) based upon developmental stage and that these MRs may not correlate with AIS severity.

METHODS

The NASS-CDS 2000-2011 was used to define the top 95% most common AIS 2+ injuries among MVC occupants in 4 age groups: 0-4, 5-9, 10-14, and 15-18 years. Next, the National Trauma Databank 2002-2011 was used to calculate the MR (proportion of those dying with an injury to those sustaining the injury) and the co-injury-adjusted MR (MRMAIS) for each injury within 6 age groups: 0-4, 5-9, 10-14, 15-18, 0-18, and 19+ years. MR differences were evaluated between age groups aggregately, between age groups based upon anatomic injury patterns and between age groups on an individual injury level using nonparametric Wilcoxon tests and chi-square or Fisher's exact tests as appropriate. Correlation between AIS and MR within each age group was also evaluated.

RESULTS

MR and MRMAIS distributions of the most common AIS 2+ injuries were right skewed. Aggregate MR of these most common injuries varied between the age groups, with 5- to 9-year-old and 10- to 14-year-old children having the lowest MRs and 0- to 4-year-old and 15- to 18-year-old children and adults having the highest MRs (all P <.05). Head and thoracic injuries imparted the greatest mortality risk in all age groups with median MRMAIS ranging from 0 to 6% and 0 to 4.5%, respectively. Injuries to particular body regions also varied with respect to MR based upon age. For example, thoracic injuries in adults had significantly higher MRMAIS than such injuries among 5- to 9-year-olds and 10- to 14-year-olds (P =.04; P <.01). Furthermore, though AIS was positively correlated with MR within each age group, less correlation was seen for children than for adults. Large MR variations were seen within each AIS grade, with some lower AIS severity injuries demonstrating greater MRs than higher AIS severity injuries. As an example, MRMAIS in 0- to 18-year-olds was 0.4% for an AIS 3 radius fracture versus 1.4% for an AIS 2 vault fracture.

CONCLUSIONS

Trauma severity metrics are important for outcome prediction models and can be used in pediatric triage algorithms and other injury research. Trauma severity may vary for similar injuries based upon developmental stage, and this difference should be reflected in severity metrics. The MR-based data-driven determination of injury severity in pediatric occupants of different age cohorts provides a supplement or an alternative to AIS severity classification for pediatric occupants in MVCs.

Age- and sex-specific thorax finite element model development and simulation

OBJECTIVE

The shape, size, bone density, and cortical thickness of the thoracic skeleton vary significantly with age and sex, which can affect the injury tolerance, especially in at-risk populations such as the elderly. Computational modeling has emerged as a powerful and versatile tool to assess injury risk. However, current computational models only represent certain ages and sexes in the population. The purpose of this study was to morph an existing finite element (FE) model of the thorax to depict thorax morphology for males and females of ages 30 and 70 years old (YO) and to investigate the effect on injury risk.

METHODS

Age- and sex-specific FE models were developed using thin-plate spline interpolation. In order to execute the thin-plate spline interpolation, homologous landmarks on the reference, target, and FE model are required. An image segmentation and registration algorithm was used to collect homologous rib and sternum landmark data from males and females aged 0-100 years. The Generalized Procrustes Analysis was applied to the homologous landmark data to quantify age- and sex-specific isolated shape changes in the thorax. The Global Human Body Models Consortium (GHBMC) 50th percentile male occupant model was morphed to create age- and sex-specific thoracic shape change models (scaled to a 50th percentile male size). To evaluate the thoracic response, 2 loading cases (frontal hub impact and lateral impact) were simulated to assess the importance of geometric and material property changes with age and sex.

RESULTS

Due to the geometric and material property changes with age and sex, there were observed differences in the response of the thorax in both the frontal and lateral impacts. Material property changes alone had little to no effect on the maximum thoracic force or the maximum percent compression. With age, the thorax becomes stiffer due to superior rotation of the ribs, which can result in increased bone strain that can increase the risk of fracture. For the 70-YO models, the simulations predicted a higher number of rib fractures in comparison to the 30-YO models. The male models experienced more superior rotation of the ribs in comparison to the female models, which resulted in a higher number of rib fractures for the males.

CONCLUSION

In this study, age- and sex-specific thoracic models were developed and the biomechanical response was studied using frontal and lateral impact simulations. The development of these age- and sex-specific FE models of the thorax will lead to an improved understanding of the complex relationship between thoracic geometry, age, sex, and injury risk.

Estimated injury risk for specific injuries and body regions in frontal motor vehicle crashes

OBJECTIVE

Injury risk curves estimate motor vehicle crash (MVC) occupant injury risk from vehicle, crash, and/or occupant factors. Many vehicles are equipped with event data recorders (EDRs) that collect data including the crash speed and restraint status during a MVC. This study's goal was to use regulation-required data elements for EDRs to compute occupant injury risk for (1) specific injuries and (2) specific body regions in frontal MVCs from weighted NASS-CDS data.

METHODS

Logistic regression analysis of NASS-CDS single-impact frontal MVCs involving front seat occupants with frontal airbag deployment was used to produce 23 risk curves for specific injuries and 17 risk curves for Abbreviated Injury Scale (AIS) 2+ to 5+ body region injuries. Risk curves were produced for the following body regions: head and thorax (AIS 2+, 3+, 4+, 5+), face (AIS 2+), abdomen, spine, upper extremity, and lower extremity (AIS 2+, 3+). Injury risk with 95% confidence intervals was estimated for 15-105 km/h longitudinal delta-Vs and belt status was adjusted for as a covariate.

RESULTS

Overall, belted occupants had lower estimated risks compared to unbelted occupants and the risk of injury increased as longitudinal delta-V increased. Belt status was a significant predictor for 13 specific injuries and all body region injuries with the exception of AIS 2+ and 3+ spine injuries. Specific injuries and body region injuries that occurred more frequently in NASS-CDS also tended to carry higher risks when evaluated at a 56 km/h longitudinal delta-V. In the belted population, injury risks that ranked in the top 33% included 4 upper extremity fractures (ulna, radius, clavicle, carpus/metacarpus), 2 lower extremity fractures (fibula, metatarsal/tarsal), and a knee sprain (2.4-4.6% risk). Unbelted injury risks ranked in the top 33% included 4 lower extremity fractures (femur, fibula, metatarsal/tarsal, patella), 2 head injuries with less than one hour or unspecified prior unconsciousness, and a lung contusion (4.6-9.9% risk). The 6 body region curves with the highest risks were for AIS 2+ lower extremity, upper extremity, thorax, and head injury and AIS 3+ lower extremity and thorax injury (15.9-43.8% risk).

CONCLUSIONS

These injury risk curves can be implemented into advanced automatic crash notification (AACN) algorithms that utilize vehicle EDR measurements to predict occupant injury immediately following a MVC. Through integration with AACN, these injury risk curves can provide emergency medical services (EMS) and other patient care providers with information on suspected occupant injuries to improve injury detection and patient triage.

Application of Radial Basis Function Methods in the Development of a 95th Percentile Male Seated FEA Model

Human body finite element models (FEMs) are a valuable tool in the study of injury biomechanics. However, the traditional model development process can be time-consuming. Scaling and morphing an existing FEM is an attractive alternative for generating morphologically distinct models for further study. The objective of this work is to use a radial basis function to morph the Global Human Body Models Consortium (GHBMC) average male model (M50) to the body habitus of a 95th percentile male (M95) and to perform validation tests on the resulting model. The GHBMC M50 model (v. 4.3) was created using anthropometric and imaging data from a living subject representing a 50th percentile male. A similar dataset was collected from a 95th percentile male (22,067 total images) and was used in the morphing process. Homologous landmarks on the reference (M50) and target (M95) geometries, with the existing FE node locations (M50 model), were inputs to the morphing algorithm. The radial basis function was applied to morph the FE model. The model represented a mass of 103.3 kg and contained 2.2 million elements with 1.3 million nodes. Simulations of the M95 in seven loading scenarios were presented ranging from a chest pendulum impact to a lateral sled test. The morphed model matched anthropometric data to within a rootmean square difference of 4.4% while maintaining element quality commensurate to the M50 model and matching other anatomical ranges and targets. The simulation validation data matched experimental data well in most cases.

Morphometric analysis of variation in the ribs with age and sex

Rib cage morphology changes with age and sex are expected to affect thoracic injury mechanisms and tolerance, particularly for vulnerable populations such as pediatrics and the elderly. The size and shape variation of the external geometry of the ribs was characterized for males and females aged 0-100 years. Computed tomography (CT) scans from 339 subjects were analyzed to collect between 2700 and 10 400 homologous landmarks from each rib. Rib landmarks were analyzed using the geometric morphometric technique known as Procrustes superimposition. Age- and sex-specific functions of 3D rib morphology were produced representing the combined size and shape variation and the isolated shape variation. Statistically significant changes in the size and shape variation (P < 0.0001) and shape variation (P < 0.0053) of all 24 ribs were found to occur with age in males and females. Rib geometry, location, and orientation varied according to the rib level. From birth through adolescence, the rib cage experienced an increase in size, a decrease in thoracic kyphosis, and inferior rotation of the ribs relative to the spine within the sagittal plane. From young adulthood into elderly age, the rib cage experienced increased thoracic kyphosis and superior rotation of the ribs relative to the spine within the sagittal plane. The increased roundedness of the rib cage and horizontal angling of the ribs relative to the spine with age influences the biomechanical response of the thorax. With the plane of the rib oriented more horizontally, loading applied in the anterior-posterior direction will result in increased deformation within the plane of the rib and an increased risk for rib fractures. Thus, morphological changes may be a contributing factor to the increased incidence of rib fractures in the elderly. The morphological functions derived in this study capture substantially more information on thoracic skeleton morphology variation with age and sex than is currently available in the literature. The developed models of rib cage anatomy can be used to study age and sex variations in thoracic injury patterns due to motor vehicle crashes or falls, and clinically relevant changes due to chronic obstructive pulmonary disease or other diseases evidenced by structural and anatomic changes to the chest.

Development of an occult metric for common motor vehicle crash injuries - biomed 2013

Detection of occult injuries, which are not easily recognized and are life-threatening, in motor vehicle crashes (MVCs) is crucial in order to reduce fatalities. An Occult Injury Database (OID) was previously developed by the Center for Transportation Injury Research (CenTIR) using the National Automotive Sampling System Crashworthiness Data System (NASS-CDS) 1997-2001 which identified occult and non-occult head, thorax, and abdomen injuries. The objective of the current work was to develop an occult injury model based on underlying injury characteristics to derive an Occult Score for common MVC-induced injuries. A multiple logistic regression model was developed utilizing six injury parameters to generate a probability formula which assigned an Occult Score for each injury. The model was applied to a list of 240 injuries comprising the top 95 percent of injuries occurring in NASS-CDS 2000-2011. The parameters in the model included a continuous Cause MRR/year variable indicating the annual proportion of occupants sustaining a given injury whose cause of death was attributed to that injury. The categorical variables in the model were AIS 2-3 vs. 4-6, laceration, hemorrhage/hematoma, contusion, and intracranial. Results indicated that injuries with a low Cause MRR/year and AIS severity of 4-6 had an increased likelihood of being occult. In addition, the presence of a laceration, hemorrhage/hematoma, contusion, or intracranial injury also increased the likelihood of an injury being occult. The Occult Score ranges from zero to one with a threshold of 0.5 as the discriminator of an occult injury. Of the considered injuries, it was determined that 54% of head, 26% of thorax, and 23% of abdominal injuries were occult injuries. No occult injuries were identified in the face, spine, upper extremity, or lower extremity body regions. The Occult Score generated can be useful in advanced automatic crash notification research and for the detection of serious occult injuries in MVCs requiring prompt treatment at a trauma center.