Lumbar Spine Response of Computational Finite Element Models in Multidirectional Spaceflight Landing Conditions.

The goals of this study are to compare the lumbar spine response variance between the hybrid III, test device for human occupant restraint (THOR), and global human body models consortium simplified 50th percentile (GHBMC M50-OS) finite element models and evaluate the sensitivity of lumbar spine injury metrics to multidirectional acceleration pulses for spaceflight landing conditions. The hybrid III, THOR, and GHBMC models were positioned in a baseline posture within a generic seat with side guards and a five-point restraint system. Thirteen boundary conditions, which were categorized as loading condition variables and environmental variables, were included in the parametric study using a Latin hypercube design of experiments. Each of the three models underwent 455 simulations for a total of 1365 simulations. The hybrid III and THOR models exhibited similar lumbar compression forces. The average lumbar compression force was 45% higher for hybrid III (2.2 ± 1.5 kN) and 51% higher for THOR (2.0 ± 1.6 kN) compared to GHBMC (1.3 ± 0.9 kN). Compared to hybrid III, THOR sustained an average 64% higher lumbar flexion moment and an average 436% higher lumbar extension moment. The GHBMC model sustained much lower bending moments compared to hybrid III and THOR. Regressions revealed that lumbar spine responses were more sensitive to loading condition variables than environmental variables across all models. This study quantified the intermodel lumbar spine response variations and sensitivity between hybrid III, THOR, and GHBMC. Results improve the understanding of lumbar spine response in spaceflight landings.

Neck Muscle Changes Following Long-Duration Spaceflight.

The effects of long-duration spaceflight on crewmember neck musculature have not been adequately studied. The purpose of this study was to evaluate the changes in the neck musculature on pre-flight and post-flight magnetic resonance imaging (MRI) examinations of six crewmembers on 4- to 6-month missions equipped with the advanced resistive exercise device (aRED). The MRI images were resliced to remove variations in spinal curvature, the cross-sectional area (CSA), and muscle fat infiltration (MFI) of neck musculature at the C1-C2, C4-C5, C7-T1, and T1-T2 intervertebral disc levels were measured bilaterally. Percent changes in the neck muscle CSA and fatty infiltration following spaceflight were calculated, and mixed models were used to assess significance of these changes. Crewmembers on missions equipped with the aRED experienced an average 25.1% increase in CSA for the trapezius muscle at C6-C7, an average 11.5% increase in CSA for the semispinalis capitis muscle at C4-C5, an average 9.0% increase in CSA for the sternocleidomastoid muscle at C4-C5, and an average 23.1% increase in CSA for the rhomboid minor at T1-T2. There were no significant changes in the CSA of the levator scapulae, splenius capitis, rectus capitis posterior major, scalenus anterior, scalenus posterior, scalenus medius, longissimus capitis, or obliquus capitis inferior muscles at the locations measured. None of the muscles analyzed experienced statistically significant changes in fatty infiltration with spaceflight. Our study indicates that long-duration spaceflight conditions are associated with preservation of CSA in most neck muscles and significant increases in the CSAs of the trapezius, semispinalis capitis, sternocleidomastoid, and rhomboid minor muscles. This may indicate that cervical muscles are not subjected to the same degradative effects microgravity imparts on the majority of muscles.

Lumbopelvic Muscle Changes Following Long-Duration Spaceflight.

Long-duration spaceflight has been shown to negatively affect the lumbopelvic muscles of crewmembers. Through analysis of computed tomography scans of crewmembers on 4- to 6-month missions equipped with the interim resistive exercise device, the structural deterioration of the psoas, quadratus lumborum, and paraspinal muscles was assessed. Computed tomography scans of 16 crewmembers were collected before and after long-duration spaceflight. The volume and attenuation of lumbar musculature at the L2 vertebral level were measured. Percent changes in the lumbopelvic muscle volume and attenuation (indicative of myosteatosis, or intermuscular fat infiltration) following spaceflight were calculated. Due to historical studies demonstrating only decreases in the muscles assessed, a one-sample t test was performed to determine if these decreases persist in more recent flight conditions. Crewmembers on interim resistive exercise device-equipped missions experienced an average 9.5% (2.0% SE) decrease in volume and 6.0% (1.5% SE) decrease in attenuation in the quadratus lumborum muscles and an average 5.3% (1.0% SE) decrease in volume and 5.3% (1.6% SE) decrease in attenuation in the paraspinal muscles. Crewmembers experienced no significant changes in psoas muscle volume or attenuation. No significant changes in intermuscular adipose tissue volume or attenuation were found in any muscles. Long-duration spaceflight was associated with preservation of psoas muscle volume and attenuation and significant decreases in quadratus lumborum and paraspinal muscle volume and attenuation.

Modeling Human Volunteers in Multidirectional, Uni-axial Sled Tests Using a Finite Element Human Body Model.

A goal of the Human Research Program at National Aeronautics and Space Administration (NASA) is to analyze and mitigate the risk of occupant injury due to dynamic loads. Experimental tests of human subjects and biofidelic anthropomorphic test devices provide valuable kinematic and kinetic data related to injury risk exposure. However, these experiments are expensive and time consuming compared to computational simulations of similar impact events. This study aimed to simulate human volunteer biodynamic response to unidirectional accelerative loading. Data from seven experimental studies involving 212 volunteer tests performed at the Air Force Research Laboratory were used to reconstruct 13 unique loading conditions across four different loading directions using finite element human body model (HBM) simulations. Acceleration pulses and boundary conditions from the experimental tests were applied to the Global Human Body Models Consortium (GHBMC) simplified 50th percentile male occupant (M50-OS) using the LS-Dyna finite element solver. Head acceleration, chest acceleration, and seat belt force traces were compared between the experimental and matched simulation signals using correlation and analysis (CORA) software and averaged into a comprehensive response score ranging from 0 to 1 with 1 representing a perfect match. The mean comprehensive response scores were 0.689 ± 0.018 (mean ± 1 standard deviation) in two frontal simulations, 0.683 ± 0.060 in four rear simulations, 0.676 ± 0.043 in five lateral simulations, and 0.774 ± 0.013 in two vertical simulations. The CORA scores for head and chest accelerations in these simulations exceeded mean scores reported in the original development and validation of the GHBMC M50-OS model. Collectively, the CORA scores indicated that the HBM in these boundary conditions closely replicated the kinematics of the human volunteers across all loading directions.

Validation of a Finite Element 50th Percentile THOR Anthropomorphic Test Device in Multiple Sled Test Configurations.

Computational models of anthropomorphic test devices (ATDs) can be used in crash simulations to quantify the injury risks to occupants in both a cost-effective and time-sensitive manner. The purpose of this study was to validate the performance of a 50th percentile THOR finite element (FE) model against a physical THOR ATD in 11 unique loading scenarios. Physical tests used for validation were performed on a Horizontal Impact Accelerator (HIA) where the peak sled acceleration ranged from 8-20 G and the time to peak acceleration ranged from 40-110 ms. The directions of sled acceleration relative to the THOR model consisted of -GX (frontal impact), +GY (left-sided lateral impact), and +GZ (downward vertical impact) orientations. Simulation responses were compared to physical tests using the CORrelation and Analysis (CORA) method. Using a weighted method, the average response and standard error by direction was +GY (0.83±0.03), -GX (0.80±0.01), and +GZ (0.76±0.03). Qualitative and quantitative results demonstrated the FE model's kinetics and kinematics were sufficiently validated against its counterpart physical model in the tested loading directions.

Biomechanical Comparison of Intrapelvic and Extrapelvic Fixation for Acetabular Fractures Involving the Quadrilateral Plate.

OBJECTIVES: Elderly patients represent the fastest growing and most difficult to treat population sustaining acetabular fractures. When treated surgically, isolated extrapelvic or combined intrapelvic-extrapelvic constructs may be used. No biomechanical or clinical study has compared the merits of these 2 techniques in cadaveric models. This research aims to biomechanically quantify the additional benefit of intrapelvic fixation to a standard extrapelvic fixation construct. METHODS: Ten cadaveric pelves underwent standardized anterior column and quadrilateral plate fracture creation. One hemipelvis from each subject received isolated extrapelvic fixation, whereas the other received adjunctive intrapelvic fixation. Specimens were then subjected to a 50% of body weight (BW) nondestructive stiffness test followed by loading to failure. For the 50% BW test, displacement at 50% BW and stiffness were calculated. For the load to failure test, stiffness, elastic energy, and plastic energy were calculated. Yield point, force at clinical failure (defined at 2 mm of displacement), and maximum force were also identified. A Wilcoxon matched-pairs t test was used to compare fixation groups. RESULTS: The addition of an intrapelvic plate improved construct performance for all test parameters. A statistically significant difference (P < 0.05) was reached for yield force, maximum force, and plastic energy. CONCLUSIONS: These findings demonstrate that the addition of intrapelvic plating may offer distinct advantages in prevention of catastrophic construct failure in situations in which significant lateral to medial force is applied to the greater trochanter such as patient falling.