Orthopaedic Surgery Training in North Carolina: The Impact of The Flexner Report and The Sherman Antitrust Act.

The current medical schools and orthopaedic residency programs in the state of North Carolina have evolved based upon geopolitical, economic events, historical reports and regulations. The American Medical Association Committee on Medical Education, the Flexner Report and the Sherman Antitrust Act and their recommendations were codified by state regulatory agencies and state law. These important pressures created the programs as they are known today. The result was the forced closure of most early medical institutions in the state of North Carolina in the early 1900s. Industrial resource consolidation by monopolies was the motivation for the Sherman antitrust act. Enforced by Theodore Roosevelt, this legislation disbanded major monopolies and encouraged philanthropy. This manuscript details the evolution of modern medical education and highlights the impact of historical social, economic and political events on the development of Duke, Wake Forest, University of North Carolina and Charlotte/ Atrium Health orthopedic programs in North Carolina. (Journal of Surgical Orthopaedic Advances 31(3):139-143, 2022).

An Innovative Seven-year Physician Scientist Residency Training Program That Addresses the Shortage of Academic Surgeons.

Due to the declining number of scientifically trained physicians and increasing demand for high-quality literature, our institution pioneered a seven-year Physician Scientist Training Program (PSTP) to provide research-oriented residents the knowledge and skills for a successful academic career. The present study sought to identify orthopaedic surgeons with MD/PhD degrees, residency programs with dedicated research tracks, and to assess the effectiveness of the novel seven-year program in training prospective academic orthopaedic surgeons. Surgeons with MD/PhD degrees account for 2.3% of all 3,408 orthopaedic faculty positions in U.S. residency programs. During the last 23 years, our PSTP residents produced 752 peer-reviewed publications and received $349,354 from 23 resident-authored extramural grants. Eleven of our seven-year alumni practice orthopaedic surgery in an academic setting. The seven-year PSTP successfully develops clinically trained surgeon scientists with refined skills in basic science and clinical experimental design, grant proposals, scientific presentations, and manuscript preparation. (Journal of Surgical Orthopaedic Advances 31(3):144-149, 2022).

Distal Radius Fractures and Bone Health: A Survey of Hand Surgeons.

Following low-energy distal radius fractures (DRF) patients rarely receive a bone health evaluation. The purpose of this survey was to investigate the attitudes and practices of American Society for Surgery of the Hand (ASSH) members regarding osteoporosis and low-energy DRF. An electronic survey was sent to 4,125 members of the ASSH. Physicians were asked about referral patterns, comfort level with labs and imaging related to bone health, and barriers. There were 475 responses (response rate 11.5%). Most respondents always (33.1%) or often (32.8%) talk about osteoporosis risk after low-energy DRF. Most respondents (87.6%) do not routinely order metabolic labs. Less than half knew of an available Fracture Liaison Service. Barriers to discussion included not enough time (32.6%), not comfortable with the topic (12.6%), and not within practice scope (33.3%). Respondents reported variable comfort levels discussing and implementing osteoporosis care in the setting of low-energy DRF. (Journal of Surgical Orthopaedic Advances 31(3):155-160, 2022).

Methodology for Evaluation of WIAMan Injury Assessment Reference Curves Using Whole Body Match-Paired Data.

Development of the Warrior Injury Assessment Manikin (WIAMan) capability has included the creation of injury assessment reference curves (IARCs) specific to under-body blast (UBB) loading mechanisms and injuries. The WIAMan IARCs were created from high-rate vertical loading tests of component post-mortem human surrogates (PMHS) and analogous components of the WIAMan anthropomorphic test device (ATD). Validation of the WIAMan IARCs is required prior to the WIAMan ATD being utilized for injury assessment in live-fire vehicle test events. A portion of the validation process involves evaluating the ability of the IARCs to predict injury at the system level (whole body). This study evaluates a methodology to assess the performance of the WIAMan IARCs using match-paired tests of whole body PMHS and the WIAMan ATD. The methodology includes a qualitative analysis designed to identify false-positive and false-negative ATD predictions, as well as a quantitative analysis that utilizes area under the receiver-operating characteristic curve (AROC) and Brier score indices to grade IARC performance. Three WIAMan IARCs were used to exemplify the proposed methodology and results are provided. Attributes of the false-prediction, AROC, and Brier score portions of the methodology are presented, with results indicating the new methodology is thorough and robust in evaluation of IARCs.

Newer generation of proximal tibia locking plates demonstrate large variability in their ability to capture the posteromedial fragment in bicondylar tibial plateau fractures.

INTRODUCTION: The early generations of proximal tibial locking plates demonstrated inferior results when compared to dual plating in bicondylar tibial plateau fractures with posteromedial fragments (PMF). Modern plates have multiple rows of locking screws and variable angle technology -which tote the ability to capture the PMF. The purpose of this study was to determine if the modern plates could capture the PMF in a large series of bicondylar tibial plateau fractures. MATERIALS & METHODS: Axial computer topography (CT) scans of 114 bicondylar tibial plateau fractures with PMF were analyzed. Five proximal tibia locking plates-in seven total configurations-were applied to radiopaque tibiae models. All possible screws were placed. Templates of screw trajectories were created based on the model CT scans. These were superimposed onto patient CT scan images to assess for screw penetration into the PMF. Number of screws fully within the PMF were recorded. Capture of the PMF was defined as having at least two screws within the fragment. RESULTS: On average, all plates were able to capture 81.6% of PMF with an average of 3.77 [95% Confidence Interval (CI): 3.47-4.07] screws. However, their ability to capture all fragments varied greatly, from 55.7%-95.2% in fixed angle constructs. Overall, variable angle constructs had a significantly higher capture rate (98.5% vs. 74.9%; p<0.0001) and more screws in the PMF (5.88 [95% CI: 5.58-6.17] vs 2.93 [95% CI: 2.62-3.24]; p<0.0001) when compared to fixed angle constructs. CONCLUSION: Newer generation locking plates vary greatly in their ability to capture the PMF. Variable angle technology dramatically increases the ability to capture the majority of PMFs. Prior biomechanical and clinical studies may yield substantially different results if repeated with these newer implants. Use of newer generation locked plates should not replace thorough preoperative planning.

The Effect of the Strengthen Opioid Misuse Prevention Act on Opiate Prescription Practices Within the Orthopaedic Surgery Department of an Academic Medical Center.

In 2017, the Department of Health and Human Service declared a public health emergency known as the opioid crisis. In North Carolina, the "Strengthen Opioid Misuse Prevention Act of 2017" (STOP Act) went into effect on January 1, 2018, seeking to strengthen oversight over opioid prescriptions. Among other mandates, this legislation limited the duration of the initial prescription to 5 or 7 days. The purpose of this study was to compare narcotic prescription practices within the Department of Orthopaedic Surgery at an academic medical center before and after the enactment of the STOP Act. We hypothesized that there would be a statistically significant decrease in the amount of postoperative opioids prescribed after the STOP Act and that this decrease would be consistent across all types of providers in the Orthopaedic Surgery Department. Methods: Opiate prescriptions data from all orthopaedic surgery providers at our academic institution were collected from January to the end of September in 2017 and from January to the end of September in 2018. After filtering the providers by our study's inclusion and exclusion criteria, we included data from 49 providers in our analysis. We used a paired t-test to compare the prescription data between the two periods. Results: There was a 35% decrease in morphine milligram equivalents prescribed at our institution between 2017 and 2018 (P = 0.0003). This reduction was statistically significant and equaled 27,374 less morphine milligram equivalents prescribed per provider (95% confidence interval 13,226 to 41,523). The average number of opiate prescriptions per provider decreased from 171.5 in 2017 to 161 in 2018 (P = 0.48), although this was not statistically significant. Conclusion: The STOP Act effectively decreased the amount of opiates prescribed within our Orthopaedic Surgery Department. Similar legislation may be effective in other states and at the federal level to decrease narcotic prescriptions and subsequent abuse.

Optimizing the Double-Row Construct: An Untied Medial Row Demonstrates Equivalent Mean Contact Pressures in a Rotator Cuff Model.

BACKGROUND: The merits of a double-row rotator cuff repair (RCR) construct are well-established for restoration of the footprint and lateral-row security. The theoretical benefit of leaving the medial row untied is to prevent damage to the rotator cuff by tissue strangulation, and the benefit of suture tape is a more even distribution of force across the repair site. These benefits, to our knowledge, have not been evaluated in the laboratory. HYPOTHESIS: Leaving the medial row untied and using a suture bridge technique with suture tape will offer more even pressure distribution across the repair site without compromising total contact force. STUDY DESIGN: Controlled laboratory study. METHODS: A laboratory model of RCR was created using biomechanical research-grade composite humeri and human dermal allografts. The pressure distribution in a double-row suture bridge repair construct was analyzed using the following testing matrix: double-loaded suture anchors with the medial row tied (n = 15) versus untied (n = 15) compared with double-loaded suture tape and anchors with the medial row tied (n = 15) versus untied (n = 15). A digital pressure sensor was used to measure pressure over time after tensioning of the repair site. A multivariate analysis of variance was used for statistical analysis with post hoc testing. RESULTS: The total contact force did not significantly differ between constructs. The contact force between double-loaded suture anchors and double-loaded suture tape and anchors was similar when tied (P = .15) and untied (P = .44). An untied medial row resulted in similar contact forces in both the double-loaded suture anchor (P = .16) and double-loaded suture tape and anchor (P = .25) constructs. Qualitative increases in focal contact pressure were seen when the medial row was tied. CONCLUSION: An untied medial row did not significantly affect the total contact force with double-loaded suture anchors and with double-loaded suture tape and anchors. Tying the medial row qualitatively increased crimping at the construct's periphery, which may contribute to tissue strangulation and hinder clinical healing. Qualitative improvements in force distribution were seen with double-loaded suture tape and anchors. CLINICAL RELEVANCE: Both tied and untied medial rows demonstrated similar pressures across the repair construct.

Investigating the Osteoinductive Potential of a Decellularized Xenograft Bone Substitute.

Bone grafting is the second most common tissue transplantation procedure worldwide. One of the alternative methods for bone repair under investigation is a tissue-engineered bone substitute. An ideal property of tissue-engineered bone substitutes is osteoinductivity, defined as the ability to stimulate primitive cells to differentiate into a bone-forming lineage. In the current study, we use a decellularization and oxidation protocol to produce a porcine bone scaffold and examine whether it possesses osteoinductive potential and can be used to create a tissue-engineered bone microenvironment. The decellularization protocol was patented by our lab and consists of chemical decellularization and oxidation steps using combinations of deionized water, trypsin, antimicrobials, peracetic acid, and triton-X100. To test if the bone scaffold was a viable host, preosteoblasts were seeded and analyzed for markers of osteogenic differentiation. The osteoinductive potential was observed in vitro with similar osteogenic markers being expressed in preosteoblasts seeded on the scaffolds and demineralized bone matrix. To assess these properties in vivo, scaffolds with and without preosteoblasts preseeded were subcutaneously implanted in mice for 4 weeks. MicroCT scanning revealed 1.6-fold increased bone volume to total volume ratio and 1.4-fold increase in trabecular thickness in scaffolds after implantation. The histological analysis demonstrates new bone formation and blood vessel formation with pentachrome staining demonstrating osteogenesis and angiogenesis, respectively, within the scaffold. Furthermore, CD31+ staining confirmed the endothelial lining of the blood vessels. These results demonstrate that porcine bone maintains its osteoinductive properties after the application of a patented decellularization and oxidation protocol developed in our laboratory. Future work must be performed to definitively prove osteogenesis of human mesenchymal stem cells, biocompatibility in large animal models, and osteoinduction/osseointegration in a relevant clinical model in vivo. The ability to create a functional bone microenvironment using decellularized xenografts will impact regenerative medicine, orthopedic reconstruction, and could be used in the research of multiple diseases.

A Military Case Review Method to Determine and Record the Mechanism of Injury (BioTab) from In-Theater Attacks.

A recent study of all mounted vehicle underbody blast attacks found that 21% of Abbreviated Injury Scale Severity 2+ injuries in the Joint Trauma Analysis and Prevention of Injury in Combat network were injuries to the leg and ankle. To develop effective countermeasure systems for these attacks, the epidemiology and mechanisms of injury from this loading environment need to be quantified. The goal of this study was to develop a military correlate of an existing civilian case review framework, the Crash Injury Research and Engineering Network (CIREN), to consider the differences in military event types and the amount of available vehicle/attack information. Additional data fields were added to the CIREN process to cover military-specific data and "certainty" definitions in the proposed injury hypothesis were modified. To date, six group reviews have been conducted analyzing 253 injuries to the foot/ankle, tibia, femur, pelvis, and lumbar spine from 52 occupants. The familiar format and unclassified nature of the presentations allowed for the involvement of biomechanics experts from multiple disciplines.

Quantifying the force transmission through the pelvic joints during total hip arthroplasty: A pilot cadaveric study.

BACKGROUND: Total hip arthroplasty is one of the most successful and cost effective procedures in orthopedics. The purpose of this study is to investigate force transmission through the sacroiliac joint as a possible source of post-operative pain after total hip arthroplasty through the following three questions: Does the ipsilateral sacroiliac joint, contralateral sacroiliac joint, or pubic symphysis experience more force during placement? Does the larger mallet used to seat the implant generate a higher force? Does the specimen's bone density or BMI alter force transmission? METHODS: A solid design acetabular component was impacted into five human cadaver pelves with intact soft tissues. The pressure at both sacroiliac joints and the pubic symphysis was measured during cup placement. This same procedure was replicated using an existing pelvis finite element model to use for comparison. FINDINGS: The location of the peak force for each hammer strike was found to be specimen specific. The finite model results indicated the ipsilateral sacroiliac joint had the highest pressure and strain followed by the pubic symphysis over the course of the full simulation. The heft of the mallet and bone mineral density did not predict force values or locations. The largest median force was generated in extremely obese specimens. INTERPRETATION: Contrary to previous ideas, it is highly unlikely that forces experienced at the pelvic joints are large enough to contribute post-operative pain during impaction of an acetabular component. These results indicate more force is conveyed to the pubic symphysis compared to the sacroiliac joints.

The effect of strain and age on the mechanical properties of rat Achilles tendons.

BACKGROUND: Achilles tendon (AT) ruptures are common in the middle age population; however, the pathophysiology and influence of age on AT ruptures is not fully understood. This study evaluates the effect and interactions between, strain and age on the in vitro biomechanical properties of ATs. METHODS: Bilateral ATs were harvested from 17 young (8 months) and 14 middle-aged (24 months) rats and underwent stress-relaxation using Fung's quasilinear viscoelastic (QLV) modeling and load-to-failure testing. RESULTS: The initial viscoelastic response (parameter B) in middle-age animals was dependent on the amount of strain applied to the tendon and was significantly increased in middle-aged animals at higher strain. Higher strain in older animals led to a prolonged relaxation time (parameter tau 2). There was a trend toward an increased magnitude of the relaxation response (parameter C) at higher strain in the middle-aged animals. Middle-aged animals had a significantly lower mean stress at ultimate failure (p=0.01), while Young's modulus was similar in both groups (p=0.46). CONCLUSIONS: The passive biomechanical properties of the rat AT change with age and the influence stress-relaxation response of the AT, thereby possibly predisposing the AT of older animals to fail at lower loads compared to younger animals. LEVEL OF EVIDENCE: Not applicable, this is a basic science study.

The Role of Fluid Dynamics in Distributing Ankle Stresses in Anatomic and Injured States.

BACKGROUND: In 1976, Ramsey and Hamilton published a landmark cadaveric study demonstrating a dramatic 42% decrease in tibiotalar contact area with only 1 mm of lateral talar shift. An increase in maximum principal stress of at least 72% is predicted based on these findings though the delayed development of arthritis in minimally misaligned ankles does not appear to be commensurate with the results found in dry cadaveric models. We hypothesized that synovial fluid could be a previously unrecognized factor that contributes significantly to stress distribution in the tibiotalar joint in anatomic and injured states. METHODS: As it is not possible to directly measure contact stresses with and without fluid in a cadaveric model, finite element analysis (FEA) was employed for this study. FEA is a modeling technique used to calculate stresses in complex geometric structures by dividing them into small, simple components called elements. Four test configurations were investigated using a finite element model (FEM): baseline ankle alignment, 1 mm laterally translated talus and fibula, and the previous 2 bone orientations with fluid added. The FEM selected for this study was the Global Human Body Models Consortium-owned GHBMC model, M50 version 4.2, a model of an average-sized male (distributed by Elemance, LLC, Winston-Salem, NC). The ankle was loaded at the proximal tibia with a distributed load equal to the GHBMC body weight, and the maximum principal stress was computed. RESULTS: All numerical simulations were stable and completed with no errors. In the baseline anatomic configuration, the addition of fluid between the tibia, fibula, and talus reduced the maximum principal stress computed in the distal tibia at maximum load from 31.3 N/mm2 to 11.5 N/mm2. Following 1 mm lateral translation of the talus and fibula, there was a modest 30% increase in the maximum stress in fluid cases. Qualitatively, translation created less high stress locations on the tibial plafond when fluid was incorporated into the model. CONCLUSIONS: The findings in this study demonstrate a meaningful role for synovial fluid in distributing stresses within the ankle that has not been considered in historical dry cadaveric studies. The increase in maximum stress predicted by simulation of an ankle with fluid was less than half that projected by cadaveric data, indicating a protective effect of fluid in the injured state. The trends demonstrated by these simulations suggest that bony alignment and fluid in the ankle joint change loading patterns on the tibia and should be accounted for in future experiments. CLINICAL RELEVANCE: Synovial fluid may play a protective role in ankle injuries, thus delaying the onset of arthritis. Reactive joint effusions may also function to additionally redistribute stresses with higher volumes of viscous fluid.

Robust human body model injury prediction in simulated side impact crashes.

This study developed a parametric methodology to robustly predict occupant injuries sustained in real-world crashes using a finite element (FE) human body model (HBM). One hundred and twenty near-side impact motor vehicle crashes were simulated over a range of parameters using a Toyota RAV4 (bullet vehicle), Ford Taurus (struck vehicle) FE models and a validated human body model (HBM) Total HUman Model for Safety (THUMS). Three bullet vehicle crash parameters (speed, location and angle) and two occupant parameters (seat position and age) were varied using a Latin hypercube design of Experiments. Four injury metrics (head injury criterion, half deflection, thoracic trauma index and pelvic force) were used to calculate injury risk. Rib fracture prediction and lung strain metrics were also analysed. As hypothesized, bullet speed had the greatest effect on each injury measure. Injury risk was reduced when bullet location was further from the B-pillar or when the bullet angle was more oblique. Age had strong correlation to rib fractures frequency and lung strain severity. The injuries from a real-world crash were predicted using two different methods by (1) subsampling the injury predictors from the 12 best crush profile matching simulations and (2) using regression models. Both injury prediction methods successfully predicted the case occupant's low risk for pelvic injury, high risk for thoracic injury, rib fractures and high lung strains with tight confidence intervals. This parametric methodology was successfully used to explore crash parameter interactions and to robustly predict real-world injuries.

Comparison of ATD to PMHS Response in the Under-Body Blast Environment.

A blast buck (Accelerative Loading Fixture, or ALF) was developed for studying underbody blast events in a laboratory-like setting. It was designed to provide a high-magnitude, high-rate, vertical loading environment for cadaver and dummy testing. It consists of a platform with a reinforcing cage that supports adjustable-height rigid seats for two crew positions. The platform has a heavy frame with a deformable floor insert. Fourteen tests were conducted using fourteen PMHS (post mortem human surrogates) and the Hybrid III ATD (Anthropomorphic Test Device). Tests were conducted at two charge levels: enhanced and mild. The surrogates were tested with and without PPE (Personal Protective Equipment), and in two different postures: nominal (knee angle of 90°) and obtuse (knee angle of 120°). The ALF reproduces damage in the PMHS commensurate with injuries experienced in theater, with the most common damage being to the pelvis and ankle. Load is transmitted through the surrogates in a caudal-to-cranial sequential fashion. Damage to the PMHS lower extremities begins within 2 ms after the initiation of foot/floor motion. The Hybrid III cannot assume the posture of the PMHS in rigid seats and exhibits a stiffer overall response compared to the PMHS. The ATD does not mimic the kinematic response of the PMHS lower extremities. Further, the Hybrid III does not have the capability to predict the potential for injury in the high-rate, vertical loading environment. A new ATD dedicated to under-body blast is needed to assist in the effort to mitigate injuries sustained by the mounted soldier.

Finite element comparison of human and Hybrid III responses in a frontal impact.

The improvement of finite element (FE) Human Body Models (HBMs) has made them valuable tools for investigating restraint interactions compared to anthropomorphic test devices (ATDs). The objective of this study was to evaluate the effect of various combinations of safety restraint systems on the sensitivity of thoracic injury criteria using matched ATD and Human Body Model (HBM) simulations at two crash severities. A total of seven (7) variables were investigated: 3-point belt with two (2) load limits, frontal airbag, knee bolster airbag, a buckle pretensioner, and two (2) delta-v's - 40kph and 50kph. Twenty four (24) simulations were conducted for the Hybrid III ATD FE model and repeated with a validated HBM for 48 total simulations. Metrics tested in these conditions included sternum deflection, chest acceleration, chest excursion, Viscous Criteria (V*C) criteria, pelvis acceleration, pelvis excursion, and femur forces. Additionally, chest band deflection and rib strain distribution were measured in the HBM for additional restraint condition discrimination. The addition of a frontal airbag had the largest effect on the occupant chest metrics with an increase in chest compression and acceleration but a decrease in excursion. While the THUMS and Hybrid III occupants demonstrated the same trend in the chest compression measurements, there were conflicting results in the V*C, acceleration, and displacement metrics. Similarly, the knee bolster airbag had the largest effect on the pelvis with a decrease in acceleration and excursion. With a knee bolster airbag the simulated occupants gave conflicting results, the THUMS had a decrease in femur force and the ATD had an increase. Preferential use of dummies or HBM's is not debated; however, this study highlights the ability of HBM metrics to capture additional chest response metrics.

Estimation of Pleural Fluid Volumes on Chest Radiography Using Computed Tomography Volumetric Analysis: An Update of the Visual Prediction Rule.

PURPOSE: The purpose of the study was to determine the volumes of pleural fluid (PF) required to produce visible menisci in the lateral and posterior costophrenic angles (CPA) and obscure the hemidiaphragms (HD) on upright frontal and lateral chest radiographs (CXRs), using volumetric analysis of chest computed tomography (CT). MATERIALS AND METHODS: A total of 98 patients with small pleural effusions on chest CT, in whom CXRs were obtained within a 24-hour interval, were selected for retrospective analysis. PF within each hemithorax was quantified using a semiautomatic method of image segmentation. A cardiothoracic radiologist scored each hemithorax on each CXR from 0 to 3 (0-normal CPA, 1--fluid meniscus below the HD, 2--fluid meniscus at the level of the HD, 3--fluid opacity obscures the HD). Each CXR category was correlated with CT-determined PF volumes. RESULTS: A mean of 20 mL of PF was present on CT without a visible correlate on CXR. A meniscus below the HD on CXR correlated with roughly 100 mL; a meniscus occurring at the HD correlated with roughly 250 mL; a meniscus obscuring the HD correlated with a mean of approximately 650 mL. There were large standard deviations for all PF volumes. CONCLUSIONS: We provide guidelines for estimating PF volumes on upright frontal and lateral CXRs. We also confirm that the lateral radiograph is more sensitive for detection of small pleural effusions, with blunting of the posterior CPA only correlating with a mean of 26 mL of PF.

Finite element model prediction of pulmonary contusion in vehicle-to-vehicle simulations of real-world crashes.

OBJECTIVE: Pulmonary contusion (PC) is a common chest injury following motor vehicle crash (MVC). Because this injury has an inflammatory component, studying PC in living subjects is essential. Medical and vehicle data from the Crash Injury Research and Engineering Network (CIREN) database were utilized to examine pulmonary contusion in case occupants with known crash parameters. METHOD: The selected CIREN cases were simulated with vehicle finite element models (FEMs) with the Total HUman Model for Safety (THUMS) version 4 as the occupant. To match the CIREN crash parameters, vehicle simulations were iteratively improved to optimize maximum crush location and depth. Fifteen cases were successfully modeled with the simulated maximum crush matching the CIREN crush to within 10%. Following the simulations, stress and strain metrics for the elements within the lungs were calculated. These injury metrics were compared to patient imaging data to determine the best finite element predictor of pulmonary contusion. RESULTS: When the thresholds were evaluated using volumetric criteria, first principal strain was the metric with the least variation in the FEM prediction of PC. CONCLUSIONS: A preliminary threshold for maximum crush was calculated to predict a clinically significant volume of pulmonary contusion.

Simulation of occupant response in space capsule landing configurations with suit hardware.

The purpose of this study was to compare the response of the total human model for safety (THUMS) human body finite element model (FEM) to experimental postmortem human subject (PMHS) test results and evaluate possible injuries caused by suit ring elements. Experimental testing evaluated the PMHS response in frontal, rear, side, falling, and spinal impacts. The THUMS was seated in a rigid seat that mirrored the sled buck used in the experimental testing. The model was then fitted with experimental combinations of neck, shoulder, humerus and thigh rings with a five-point restraint system. Experimental seat acceleration data was used as the input for the simulations. The simulation results were analyzed and compared to PMHS measurements to evaluate the response of the THUMS in these loading conditions. The metrics selected to compare the THUMS simulation to PMHS tests were the chest acceleration, seat acceleration and belt forces with additional metrics implemented in THUMS. The chest acceleration of the simulations and the experimental data was closely matched except in the Z-axis (superior/inferior) loading scenarios based on signal analysis. The belt force data of the model better correlated to the experimental results in loading scenarios where the THUMS interacted primarily with the restraint system compared to load cases where the primary interaction was between the seat and the occupant (rear, spinal and lateral impacts). The simulation output demonstrated low injury metric values for the occupant in these loading conditions. In the experimental testing, rib fractures were recorded for the frontal and left lateral impact scenarios. Fractures were not seen in the simulations, most likely due to variations between the simulation and the PMHS initial configuration. The placement of the rings on the THUMS was optimal with symmetric placement about the centerline of the model. The experimental placement of the rings had more experimental variation. Even with this discrepancy, the THUMS can still be considered a valuable predictive tool for occupant injury because it can compare results across many simulations. The THUMS also has the ability to assess a wider variety of other injury information, compared to anthropomorphic test devices (ATDs), that can be used to compare simulation results.

Implementation and validation of thoracic side impact injury prediction metrics in a human body model.

This study's purpose was to implement injury metrics into the Total Human Model for Safety (THUMS) mirroring the spinal accelerometers, rib accelerometers and chest band instrumentation from two lateral post-mortem human subject sled test configurations. In both sled configurations, THUMS contacted a flat rigid surface (either a wall or beam) at 6.7 m/s. Sled A maximum simulated wall forces for the thorax, abdomen and pelvis were 7.1, 5.0 and 10.0 kN versus 5.7 ± 0.8, 3.4 ± 1.2 and 6.2 ± 2.7 kN experimentally. Sled B maximum simulated beam forces for the torso and pelvis were 8.0 and 7.6 kN versus 8.5 ± 0.2 and 7.9 ± 2.5 kN experimentally. Quantitatively, force magnitude contributed more to variation between simulated and experimental forces than phase shift. Acceleration-based injury metrics were within one standard deviation of experimental means except for the lower spine in the rigid wall sled test. These validated metrics will be useful for quantifying occupant loading conditions and calculating injury risks in various loading configurations.

Optimization of a simplified automobile finite element model using time varying injury metrics.

In 2011, frontal crashes resulted in 55% of passenger car injuries with 10,277 fatalities and 866,000 injuries in the United States. To better understand frontal crash injury mechanisms, human body finite element models (FEMs) can be used to reconstruct Crash Injury Research and Engineering Network (CIREN) cases. A limitation of this method is the paucity of vehicle FEMs; therefore, we developed a functionally equivalent simplified vehicle model. The New Car Assessment Program (NCAP) data for our selected vehicle was from a frontal collision with Hybrid III (H3) Anthropomorphic Test Device (ATD) occupant. From NCAP test reports, the vehicle geometry was created and the H3 ATD was positioned. The material and component properties optimized using a variation study process were: steering column shear bolt fracture force and stroke resistance, seatbelt pretensioner force, frontal and knee bolster airbag stiffness, and belt friction through the D-ring. These parameters were varied using three successive Latin Hypercube Designs of Experiments with 130-200 simulations each. The H3 injury response was compared to the reported NCAP frontal test results for the head, chest and pelvis accelerations, and seat belt and femur forces. The phase, magnitude, and comprehensive error factors, from a Sprague and Geers analysis were calculated for each injury metric and then combined to determine the simulations with the best match to the crash test. The Sprague and Geers analyses typically yield error factors ranging from 0 to 1 with lower scores being more optimized. The total body injury response error factor for the most optimized simulation from each round of the variation study decreased from 0.466 to 0.395 to 0.360. This procedure to optimize vehicle FEMs is a valuable tool to conduct future CIREN case reconstructions in a variety of vehicles.