Characterizing thoracic morphology variation to develop representative 3D models for applications in chest trauma.

BACKGROUND: Rib fracture(s) occurs in 85% of blunt chest trauma cases. Increasing evidence supports that surgical intervention, particularly for multiple fractures, may improve outcomes. Thoracic morphology diversity across ages and sexes is important to consider in the design and use of surgical intervention devices in chest trauma. However, research on non-average thoracic morphology is lacking. METHODS: The rib cage was segmented from patient computed tomography (CT) scans to create 3D point clouds. These point clouds were uniformly oriented and chest height, width, and depth were measured. Size categorization was determined by grouping each dimension into small, medium, and large tertiles. From small and large size combinations, subgroups were extracted to develop thoracic 3D models of the rib cage and surrounding soft tissue. RESULTS: The study population included 141 subjects (48% male) ranging from age 10-80 with ∼20 subjects/age decade. Mean chest volume increased with age by 26% from the age groups 10-20 to 60-70, with 11% of this increase occurring between the youngest groups of 10-20 and 20-30. Across all ages, chest dimensions were ∼10% smaller in females and chest volume was highly variable (SD: ±3936.5 cm3). Representative thoracic models of four males (ages 16, 24, 44, 48) and three females (ages 19, 50, 53) were developed to characterize morphology associated with combinations of small and large chest dimensions. CONCLUSIONS: The seven models developed cover a broad range of non-average thoracic morphologies and can serve as a basis for informing device design, surgical planning, and injury risk assessments.

Effect of Active Muscles on Astronaut Kinematics and Injury Risk for Piloted Lunar Landing and Launch While Standing.

While astronauts may pilot future lunar landers in a standing posture, the response of the human body under lunar launch and landing-related dynamic loading conditions is not well understood. It is important to consider the effects of active muscles under these loading conditions as muscles stabilize posture while standing. In the present study, astronaut response for a piloted lunar mission in a standing posture was simulated using an active human body model (HBM) with a closed-loop joint-angle based proportional integral derivative controller muscle activation strategy and compared with a passive HBM to understand the effects of active muscles on astronaut body kinematics and injury risk. While head, neck, and lumbar spine injury risk were relatively unaffected by active muscles, the lower extremity injury risk and the head and arm kinematics were significantly changed. Active muscle prevented knee-buckling and spinal slouching and lowered tibia injury risk in the active vs. passive model (revised tibia index: 0.02-0.40 vs. 0.01-0.58; acceptable tolerance: 0.43). Head displacement was higher in the active vs. passive model (11.6 vs. 9.0 cm forward, 6.3 vs. 7.0 cm backward, 7.9 vs. 7.3 cm downward, 3.7 vs. 2.4 cm lateral). Lower arm movement was seen with the active vs. passive model (23 vs. 35 cm backward, 12 vs. 20 cm downward). Overall simulations suggest that the passive model may overpredict injury risk in astronauts for spaceflight loading conditions, which can be improved using the model with active musculature.

Development and Validation of an Active Muscle Simplified Finite Element Human Body Model in a Standing Posture.

Active muscles play an important role in postural stabilization, and muscle-induced joint stiffening can alter the kinematic response of the human body, particularly that of the lower extremities, under dynamic loading conditions. There are few full-body human body finite element models with active muscles in a standing posture. Thus, the objective of this study was to develop and validate the M50-PS+Active model, an average-male simplified human body model in a standing posture with active musculature. The M50-PS+Active model was developed by incorporating 116 skeletal muscles, as one-dimensional beam elements with a Hill-type material model and closed-loop Proportional Integral Derivative (PID) controller muscle activation strategy, into the Global Human Body Models Consortium (GHBMC) simplified pedestrian model M50-PS. The M50-PS+Active model was first validated in a gravity standing test, showing the effectiveness of the active muscles in maintaining a standing posture under gravitational loading. The knee kinematics of the model were compared against volunteer kinematics in unsuited and suited step-down tests from NASA's active response gravity offload system (ARGOS) laboratory. The M50-PS+Active model showed good biofidelity with volunteer kinematics with an overall CORA score of 0.80, as compared to 0.64 (fair) in the passive M50-PS model. The M50-PS+Active model will serve as a useful tool to study the biomechanics of the human body in vehicle-pedestrian accidents, public transportation braking, and space missions piloted in a standing posture.

Sensitivity Analysis for Multidirectional Spaceflight Loading and Muscle Deconditioning on Astronaut Response.

A sensitivity analysis for loading conditions and muscle deconditioning on astronaut response for spaceflight transient accelerations was carried out using a mid-size male human body model with active musculature. The model was validated in spaceflight-relevant 2.5-15 g loading magnitudes in seven volunteer tests, showing good biofidelity (CORA: 0.69). Sensitivity analysis was carried out in simulations varying pulse magnitude (5, 10, and 15 g), rise time (32.5 and 120 ms), and direction (10 directions: frontal, rear, vertical, lateral, and their combination) along with muscle size change (± 15% change) and responsiveness (pre-braced, relaxed, vs. delayed response) changes across 600 simulations. Injury metrics were most sensitive to the loading direction (50%, partial-R2) and least sensitive to muscle size changes (0.2%). The pulse magnitude also had significant effect on the injury metrics (16%), whereas muscle responsiveness (3%) and pulse rise time (2%) had only slight effects. Frontal and upward loading directions were the worst for neck, spine, and lower extremity injury metrics, whereas rear and downward directions were the worst for head injury metrics. Higher magnitude pulses and pre-bracing also increased the injury risk.

Effects of Standing, Upright Seated, vs. Reclined Seated Postures on Astronaut Injury Biomechanics for Lunar Landings.

Astronauts may pilot a future lunar lander in a standing or upright/reclined seated posture. This study compared kinematics and injury risk for the upright/reclined (30°; 60°) seated vs. standing postures for lunar launch/landing using human body modeling across 30 simulations. While head metrics for standing and upright seated postures were comparable to 30 cm height jumps, those of reclined postures were closer to 60 cm height jumps. Head linear acceleration for 60° reclined posture in the 5 g/10 ms pulse exceeded NASA's tolerance (10.1 g; tolerance: 10 g). Lower extremity metrics exceeding NASA's tolerance in the standing posture (revised tibia index: 0.36-0.53; tolerance: 0.43) were lowered in seated postures (0.00-0.04). Head displacement was higher in standing vs. seated (9.0 cm vs. 2.4 cm forward, 7.0 cm vs. 1.3 cm backward, 2.1 cm vs. 1.2 cm upward, 7.3 cm vs. 0.8 cm downward, 2.4 cm vs. 3.2 cm lateral). Higher arm movement was seen with seated vs. standing (40 cm vs. 25 cm forward, 60 cm vs. 15 cm upward, 30 cm vs. 20 cm downward). Pulse-nature contributed more than 40% to the injury metrics for seated postures compared to 80% in the standing posture. Seat recline angle contributed about 22% to the injury metrics in the seated posture. This study established a computational methodology to simulate the different postures of an astronaut for lunar landings and generated baseline injury risk and body kinematics data.

Simulated Astronaut Kinematics and Injury Risk for Piloted Lunar Landings and Launches While Standing.

During future lunar missions, astronauts may be required to pilot vehicles while standing, and the associated kinematic and injury response is not well understood. In this study, we used human body modeling to predict unsuited astronaut kinematics and injury risk for piloted lunar launches and landings in the standing posture. Three pulses (2-5 g; 10-150 ms rise times) were applied in 10 directions (vertical; ± 10-degree offsets) for a total of 30 simulations. Across all simulations, motion envelopes were computed to quantify displacement of the astronaut's head (max 9.0 cm forward, 7.0 cm backward, 2.1 cm upward, 7.3 cm downward, 2.4 cm lateral) and arms (max 25 cm forward, 35 cm backward, 15 cm upward, 20 cm downward, 20 cm lateral). All head, neck, lumbar, and lower extremity injury metrics were within NASA's tolerance limits, except tibia compression forces (0-1543 N upper tibia; 0-1482 N lower tibia; tolerance-1350 N) and revised tibia index (0.04-0.58 upper tibia; 0.03-0.48 lower tibia; tolerance-0.43) for the 2.7 g/150 ms pulse. Pulse magnitude and duration contributed over 80% to the injury metric values, whereas loading direction contributed less than 3%. Overall, these simulations suggest piloting a lunar lander vehicle in the standing posture presents a tibia injury risk which is potentially outside NASA's acceptance limits and warrants further investigation.