Hybrid III lumbar spinal column injury risk curves from vertical impact.

内容摘要

Musculoskeletal injuries from underbody blasts due to the detonation of improvised explosive devices (IED) impart dynamic loading to the human vertebral column via the pelvis region, and the primary insult from the IED is absorbed first by the lumbar spine before it traverses to the thoracic and cervical spines. Injuries from these scenarios have been documented in many clinical and retrospective studies. Although the dynamic response index continues to be used to predict lumbar spine injuries, it is based on the accelerations of the seat pan. A need exists to develop lumbar spine injury criteria for human surrogates. The objective of this study was to develop lumbar spine injury criteria, in the form of injury assessment risk curves, specific to the Hybrid III anthropomorphic test device under the underbody blast vertical impact load vector. The Hybrid III human surrogate was prepared with load cells at the superior and inferior ends of the lumbar spinal column. The dynamic impact loading was applied to the inferior end of the spinal column spine using a custom vertical accelerator device. The peak axial, shear, and resultant forces at the ends of the column were obtained. The compressive force-based injury mechanism was confirmed with results from previous human cadaver lumbar spine results conducted under the same experimental protocol. The parametric survival analysis using the Weibull distribution was used to develop lumbar spine injury assessment risk curves, and using the ±95% confidence interval bounds, the quality of the risk curves at discrete injury probability levels were calculated for all metrics. At the superior end, at the mid-risk level, the estimated axial force was 14.7 kN, shear force was 2.1 kN, and resultant force was 14.8 kN, and at the 10% risk level, the estimated axial force was 6.7 kN, shear force was 0.9 kN, and resultant force was 6.7 kN. At the inferior end and at the mid-risk level, the estimated axial force was 16.7 kN, shear force was 2.8 kN, and resultant force was 16.8 kN. At the 10% risk level, the estimated axial force was 7.2 kN, shear force was 0.8 kN, and resultant force was 7.3 kN. The confidence intervals and quality of risk curves are reported in the paper. Axial forces were consistently greater than shear forces at both ends, mimicking the injury mechanisms based on fractures reported in clinical and cadaver studies from underbody blast loading scenarios. Injury risk curves at the superior end of the spine were shifted to the left for the axial, shear, and resultant forces compared to the inferior end, confirming the energy absorption and transmittal of the axial force along the spinal column. Resultant forces can be used as injury criteria because shear forces were low. The present survival analysis-based injury assessment risk curves can be used as a preliminary Hybrid III lumbar spinal column injury criteria for improving the Warfighter safety and evaluating current and future military vehicles under vertical impacts.