Andrew M Damon

University of Virginia, Charlottesville, Virginia, United States

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Publications (7)10.2 Total impact

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    ABSTRACT: Military aviators are susceptible to spinal injuries during high-speed ejection scenarios. These injuries commonly arise as a result of strains induced by extreme flexion or compression of the spinal column. This study characterizes the vertebral motion of two postmortem human surrogates (PMHS) during a simulated catapult phase of ejection on a horizontal decelerator sled. During testing, the PMHS were restrained supinely to a mock ejection seat and subjected to a horizontal deceleration profile directed along the local z-axis. Two midsized males (175.3 cm, 77.1 kg; 185.4 cm, 72.6 kg) were tested. High-rate motion capture equipment was used to measure the three-dimensional displacement of the head, vertebrae, and pelvis during the ejection event. The two PMHS showed generally similar kinematic motion. Head injury criterion (HIC) results were well below injury threshold levels for both specimens. The specimens both showed compression of the spine, with a reduction in length of 23.9 mm and 45.7 mm. Post-test autopsies revealed fractures in the C5, T1, and L1 vertebrae. This paper provides an analysis of spinal motion during an aircraft ejection.The injuries observed in the test subjects were consistent with those seen in epidemiological studies. Future studies should examine the effects of gender, muscle tensing, out-of-position (of head from neutral position) occupants, and external forces (e.g., windblast) on spinal kinematics during aircraft ejection.
    Aviation Space and Environmental Medicine 05/2010; 81(5):453-9. DOI:10.3357/ASEM.2688.2010 · 0.78 Impact Factor
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    ABSTRACT: The neck injury index, NII, developed in ISO 13232 (2005) as a testing and evaluation procedure for assessing the risk of injury to the AO/C1/C2 region of the cervical spine in motorcycle riders is reevaluated using an existing postmortem human subjects (PMHS) data set and resulting in a reformulated NII criterion applicable to PMHS tests. A recent series of 36 PMHS head/neck component tests was used to examine the risk of neck injury in frontal impacts and to assess the predictive capability of NII for impacts of various orientations. Using force and moment load cell PMHS experimental data, injury risk was assessed using NII evaluated with the ISO 13232-5 algorithms. The injury risk predictions are compared with the injury outcomes from the head/neck PMHS. The NII criterion underestimated the injury incidence of the PMHS experimental group. The average predicted risk of injuries for the experimental injury tests based on NII across the MAIS levels was 0.7 percent, though there were 11 AIS 3+ injuries observed in the actual testing (30.6%). Using the experimental injury outcomes and the experimental force and moment time histories, the normalizing coefficients from NII are reevaluated to minimize the difference between NII risk assessment and the experimental injury outcome in the least squares (L(2)) basis. This reanalysis is compared with existing human and PMHS neck injury criteria. By reanalyzing the NII formulation using an existing PMHS injury data set with known forces and moments and known injury outcomes, a new NII(PMHS) is developed that uses PMHS loads to predict injury. This reformulation removes the dependency of the original NII formulation on the forces and moments from motorcyclist anthropomorphic test device (MATD) experiments and simulations yet retains the advantages of the multi-axial neck injury criterion.
    Traffic Injury Prevention 04/2010; 11(2):194-201. DOI:10.1080/15389580903501864 · 1.29 Impact Factor
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    ABSTRACT: Primary blast injuries, specifically lung injuries, resulting from blast overpressure exposures are a major source of mortality for victims of blast events. However, existing pulmonary injury criteria are inappropriate for common exposure environments. This study uses Drosophila melanogaster larvae to develop a simple phenomenological model for human pulmonary injury from primary blast exposure. Drosophila larvae were exposed to blast overpressures generated by a 5.1-cm internal diameter shock tube and their mortality was observed after the exposure. To establish mortality thresholds, a survival analysis was conducted using survival data and peak incident pressures. In addition, a histologic analysis was performed on the larvae to establish the mechanisms of blast injury. The results of the survival analysis suggest that blast overpressure for 50% Drosophila survival is greater than human threshold lung injury and is similar to human 50% survival levels, in the range of overpressure durations tested (1-5 ms). A "parallel" analysis of the Bass et al. 50% human survival curves indicates that 50% Drosophila survival is equivalent to a human injury resulting in a 69% chance of survival. Histologic analysis of the blast-exposed larvae failed to demonstrate damage to the dorsal trunk of the tracheal system; however, the presence of flocculent material in the larvae body cavities and tracheas suggests tissue damage. This study shows that D. melanogaster survival can be correlated with large animal injury models to approximate a human blast lung injury tolerance. Within the range of durations tested, Drosophila larvae may be used as a simple model for blast injury.
    The Journal of trauma 02/2010; 69(1):179-84. DOI:10.1097/TA.0b013e3181c42649 · 2.96 Impact Factor
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    ABSTRACT: Quantifying the kinematics of the human spine during a frontal impact is a challenge due to the multi-degree-of-freedom structure of the vertebral column. This papers reports on a series of six frontal impacts sled tests performed on three Post Mortem Human Surrogates (PMHS). Each subject was exposed first to a low-speed, non-injurious frontal impact (9 km/h) and then to a high-speed one (40 km/h). Five additional tests were performed using the Hybrid III 50(th) percentile male ATD for comparison with the PMHS. A 3D motion capture system was used to record the 6-degree-of-freedom motion of body segments (head, T1, T8, L2, L4 and pelvis). The 3D trajectories of individual bony structures in the PMHS were determined using bone-mounted marker arrays, thus avoiding skin-attached markers and their potential measurements artifacts. The PMHS spines showed different behavior between low and high speed. While at low speed the head and upper spinal segments lagged the lower portion of the spine and pelvis in reaching their maximum forward displacement (time for maximum forward head excursion was 254.3±31.9 ms and 140.3±9 ms for the pelvis), these differences were minimal at high speed (127±2.6 ms for the head vs. 116.7±3.5 ms for the pelvis). The ATD did not exhibit this speed-dependant behavior. Furthermore, the ATD's forward displacements were consistently less than those exhibited by the PMHS, regardless of the speed. Neck loads at the atlanto-occipital joint were estimated for the PMHS using inverse dynamics techniques and compared to those measured in the ATD. It was found that the axial and shear forces and the flexion moment at the upper neck of the PMHS were higher than those measured in the ATD.
    Annals of advances in automotive medicine 01/2010; 54:61-78.
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    ABSTRACT: An accurate understanding of the relationship between pulmonary pressure and volume is required for modeling pulmonary mechanics in a variety of clinical applications. In this study the experimental techniques and mathematical formulations used to characterize viscoelastic materials are applied to characterize transient pulmonary compliance in juvenile swine. Fixed volumes of air were insufflated into 5 swine and held constant for 45 s while the transient decay in tracheal pressure was measured. An analytical model was developed using an optimization scheme that maximized the model fit to the experimental data over the entire time convolution. The initial injected volume was varied to assess the spatial and temporal linearity of the behavior. Model performance was assessed by comparing measured and predicted pressure during insufflations of erratic volume waveforms. It is concluded that the pulmonary impedance of healthy juveniles can be adequately described over a wide volume and frequency range using a relatively simple 5-parameter model that is linear both spatially and temporally.
    Journal of Biomechanics 07/2009; 42(11):1656-63. DOI:10.1016/j.jbiomech.2009.04.027 · 2.50 Impact Factor
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    ABSTRACT: Lateral loading of the pelvis occurs for both vehicle occupants struck during side impacts as well as pedestrians. This research investigated the load distribution through the anterior (i.e. pubic symphysis) and posterior (i.e. sacrum) aspects of the pelvis for both acetabular and iliac loading. Sixteen male post-mortem human surrogate pelves were tested in quasi-static (n = 4) anddynamic (n = 12) conditions. On the basis of finite element model simulations of a pedestrian being struck at 40 km/hr, a velocity profile for the dynamic tests was prescribed that began at rest (v = 0 m/s) and then achieved apeak velocity of the struck pelvis moving relative to the midline at 4.5 m/s. The average anterior load at fracture from a high − rate acetabulumimp act was 1911 ± 929 N compared to the posterior load averaging 1022 ± 630 N. The average anterior load at fracture from a high − rate iliumimpact was 418 ± 388 N compared to the posterior load averaging 3107 ± 1473 N.
    International Journal of Crashworthiness 02/2009; 14(1):99-110. DOI:10.1080/13588260802517378 · 0.81 Impact Factor
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    ABSTRACT: Thoracolumbar injuries resulting from motor vehicle accidents, falls, and assaults have a high risk of morbidity and mortality. However, there are no biomechanically based standards that address this problem. This study used four cadaveric porcine specimens as a model for direct spinal impact injuries to humans to determine an appropriate injury tolerance value. The anthropometric parameters of these specimens are compared with values found in a large human cadaveric dataset. Each specimen was subjected to five impacts on the dorsal surface of the lower thorax and abdomen. The injuries ranged from mild spinous process fractures to endplate fractures with anterior longitudinal ligament (ALL) transactions with a maximum AIS=3. The average peak reaction force for the thoracic failure tests was 4720+/-1340 N, and the average peak reaction force for the lumbar failure tests was 4650+/-1590 N. When scaled to human values using anthropometric parameters determined in this study, the force at which there is a 50% risk of injury is 10,200+/-3900 N. This value favorably compares to that found in the existing literature on isolated vertebral segments. After demonstrating that the porcine model can be used as a spinal impact model for the human, the resulting injury risk value can be used in determining new standards for human injury risk or in guiding the design of safety equipment for the back.
    Accident Analysis & Prevention 04/2008; 40(2):487-95. DOI:10.1016/j.aap.2007.08.006 · 1.87 Impact Factor