Human lumbar spinal column injury criteria from vertical loading at the base: Applications to military environments
Introduction
Injuries to the human lumbar spine have been reported in civilian and military environments. In the civilian automotive field, compression-related injuries are reported to restrained occupants in frontal crashes (Kaufman et al., 2013). In the military field, recent combat events have resulted in mounted soldiers (sitting in military vehicles) sustaining injuries from underbody blast loading, and this is a unique scenario as the seated posture, vector, and loading rate are different from the civilian automotive field (Vasquez et al., 2018; Danelson et al., 2015). Cited studies are not all inclusive. Vertical loading to the lumbar spinal column is the main mechanical stimulus in underbody blast loading events. Lumbar spinal column studies specific to this load vector are limited. The fundamental requirement to define human tolerance and advance safety in impact loading events is the development of injury criteria in the form of risk curves. They are obtained by subjecting human cadaver specimens, intact or subsystems, to appropriate load vectors. Automotive crashworthiness standards for the civilian environment lack injury criteria for the lumbar spinal column. While the dynamic response index is used as a criterion for aircraft ejection seat designs, its applicability for the underbody blast environment has not been validated (Payne and Stech, 1969). Consequently, to directly address tolerance and human safety in this environment, injury risk curves (IRCs) are needed.
Section snippets
Objectives
The objectives of the present study are to develop IRCs for the human lumbar spine using force and covariate variables under vertical loading and identify the optimal metric for two types of injury outcomes that describe the underlying response using novel statistical techniques.
PMHS procurement
Unembalmed human cadaver specimens were procured for the study. The experimental protocol was approved by the local Institutional Review Board of the institution and by the United States Department of Defense. Before specimen procurement, medical records and x-rays were evaluated, and screened for human immunodeficiency virus, and Hepatitis B and C, to rule out pre-existing trauma to the spine. The specimens selected had no radiological evidence of osteophytes and joint degeneration, considered
General results
The mean age, stature, total body mass, and body mass index (BMI) of the 43 male specimens were: 65 ± 10 years, 1.78 ± 0.06 m, 83 ± 13 kg, and 26 ± 4 kg/m2, respectively. The mean column height, disc and body areas, and BMD were: 17.8 ± 0.9 cm, 18.9 ± 2.8 cm2, 12.4. ± 1.6 cm2, and 140 ± 37 mg/cc, respectively (Table 1). Testing was stopped in three specimens after the first impact because injury was detected or suspected. All injuries sustained in this testing series involved vertebral
Discussion
As stated in the introductory paragraphs, the aim of the study was to describe tolerances of the human lumbar spinal column under vertical impacts. Data are applicable to the military environments as specimens were oriented in the seated soldier posture (Reed, 2013). In addition, impact loading was applied along the inferior-to-superior direction from the base of the preparation, reflecting the modality seen in recent conflicts and the need to understand the biomechanics for injury prevention
Conclusions
Force-based lumbar spine IRCs were developed by subjecting human cadaver thoracolumbar spinal columns to impacts along the inferior to superior direction. The optimal metric describing the underlying response to injury was associated with the distal resultant force for group A and proximal axial force for group B outcomes. For group A, resultant force with trabecular BMD was the optimum, while for the other group, body area was associated with the axial force. The IRCs developed for all
CRediT authorship contribution statement
Narayan Yoganandan: Project administration, Funding acquisition, Supervision, Data curation, Writing - original draft, Writing - review & editing. Jason Moore: Methodology, Resources, Data curation, Writing - review & editing. Nicholas DeVogel: Data curation. Frank Pintar: Project administration, Funding acquisition, Supervision, Resources, Writing - review & editing. Anjishnu Banerjee: Data curation. Jamie Baisden: Formal analysis, Data curation. Jiang Yue Zhang: Project administration.
Declaration of competing interest
None of the authors of this study have any financial or personal relationships with other people or organizations that could inappropriately influence (bias) the presented work, i.e., no conflict of interest for this paper.
Acknowledgments
This research was supported in part by Cooperative Agreement W81XWH-16-01-0010, Department of Veterans Affairs, United States Medical Research, and the Department of Neurosurgery at the Medical College of Wisconsin, United States. This material is the result of work supported with resources and use of facilities at the Zablocki VA Medical Center, Milwaukee, Wisconsin and Medical College of Wisconsin. The first three authors are part time employees of the Zablocki VA Medical Center. The views
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