Session: 05-02-02: Injury and Damage Biomechanics II

Paper Number: 73664

Start Time: Wednesday, 01:50 PM

73664 - Effects of Personal Protective Equipment on Spinal Column Loads From Underbody Blast Loading 

Introduction: Combat-related injuries from improvised explosive devices are attributed to vertical loading transmitted from the seat to the pelvis to the torso and head-neck regions.  Field data show spine injuries in Service Members. The presence of the body armor (personal protective equipment, PPE) adds to the weight of the torso and influences the load transmission within the vertebral column. This study aimed to investigate the effect of PPE on spine kinematics, forces, and moments along the vertebral column.

Methods: The detailed mid-size male model from the Global Human Body Models Consortium was used. The simulation environment consisted of positioning the model on a rigid seat and restraining with a five-point seatbelt, typical of a military harness. The model was settled on the rigid seat under gravity (G_z, vertical axis) and G_x (along the posterior to anterior axis). The final posture was extracted from the initial settling simulations such that the model represented an upright seated solider in a military vehicle. The model was updated with the PPE: 1.4 kg military helmet and 11 kg body armor vest. Cross-sectional planes were defined at the midlevel of the intervertebral discs to obtain the loads along the vertebral column. Acceleration profiles at T1, T5, T8, T12, and pelvis were also obtained. Different scenarios were used to determine the role of the PPE: model without PPE and with PPE, and two high acceleration G_z pulses (peak magnitudes of 160 g and 110 g) simulating underbody blast scenarios. The models without PPE were simulated for 50 ms, and the models with PPE were first settled for 50 ms to account for the effect of PPE and then simulated for 50 ms under the same underbody loading scenarios.

Results: The kinematics, forces, moments, and accelerations for cervical, thoracic, and lumbar spines were compared for with and without PPE cases. In both cases, i.e., with and without PPE, the cervical spine underwent extension, thoracic spine underwent flexion, upper lumbar spine underwent extension and lower lumbar spine underwent flexion. Compressive forces decreased from caudal to cephalad ends (5 kN to 1 kN). The presence of PPE increased forces in the thoracic and cervical spines (~10%) while its effect was minimal (<3%) in the lumbar spine. Without PPE, peak extension moments occurred in the cervical and lumbar spines occurred at C3-C4 and L1-L2 (3.7 Nm and 17.9 Nm), and peak flexion moments occurred in the thoracic and lumbar spines at T6-T7 and L5-S1 (17.6 Nm and 18.5 Nm) levels. With PPE the locations of peak moment were same, with higher magnitude. The presence of PPE increased cervical spine moments by 38%, thoracic spine moments by 9%, and decreased lumbar spine extension moments by 5%, whereas the lumbar spine flexion moment remained same. Spinal accelerations peaked earlier with PPE; however, their peak and morphologies were unchanged. Results at each level will be reported in the full-length paper.

Discussion/Conclusion: Increases in the compressive forces and flexion moments in the thoracic spine suggest compression-flexion mechanism of injury, such as anterior or burst fractures of the thoracic vertebrae with or without distraction of posterior elements/ligaments. While limited, human cadaver tests conducted by the military have revealed these types of injuries. Both thoracic and lower lumbar spines underwent flexion while the upper lumbar spine went into extension, and this may be due to the lordosis of the column. Lower lumbar spine fractures may occur under compression-flexion mechanism. Earlier attainment of spine accelerations with the PPE may be attributed to the added mass from the body armor that acts as a constraint to the torso. This modeling study delineates the kinetics (motions and loads) of the cervical, thoracic, and lumbar spines from underbody blast loading and the role of PPE on potential injuries and injury mechanisms.

Presenting Author: Sagar Umale Medical College of Wisconsin

Authors:

Sagar Umale Medical College of Wisconsin
John R. Humm Medical College of Wisconsin
Narayan Yoganandan Medical College of Wisconsin