Introduction Underbody blast loading can result in injuries to the pelvis and the lumbosacral spine. The purpose of this study was to determine human tolerance in this region based on survival analysis.
Methods Twenty-six unembalmed postmortem human surrogate lumbopelvic complexes were procured and pretest medical images were obtained. They were fixed in polymethylmethacrylate at the cranial end and a six-axis load cell was attached. The specimens were aligned in a seated soldier posture. Impacts were applied to the pelvis using a custom vertical accelerator. The experimental design consisted of non-injury and injury tests. Pretest and post-test X-rays and palpation were done following non-injury test, and after injury test medical imaging and gross dissections were done. Injuries were scored using the Abbreviated Injury Scale (AIS). Axial and resultant forces were used to develop human injury probability curves (HIPCs) at AIS 3+ and AIS 4 severities using survival analysis. Then ±95% CI was computed using the delta method, normalised CI size was obtained, and the quality of the injury risk curves was assigned adjectival ratings.
Results At the 50% probability level, the resultant and axial forces at the AIS 3+ level were 6.6 kN and 5.9 kN, and at the AIS 4 level these were 8.4 kN and 7.5 kN, respectively. Individual injury risk curves along with ±95% CIs are presented in the paper. Increased injury severity increased the HIPC metrics. Curve qualities were in the good and fair ranges for axial and shear forces at all probability levels and for both injury severities.
Conclusions This is the first study to develop axial and resultant force-based HIPCs defining human tolerance to injuries to the pelvis from vertical impacts using parametric survival analysis. Data can be used to advance military safety under vertical loading to the seated pelvis.
- orthopaedic & trauma surgery
- adult orthopaedics
Data availability statement
All data relevant to the study are included in the article or uploaded as supplementary information.
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Contributors NY contributed to the entire manuscript preparation, experimental design, interpretation of data and development of risk curves. JM conducted the experiments and data processing and analysis. AB was responsible for the statistical aspects. KLL reviewed and edited the manuscript to obtain approval from the US government and DRB assisted in these aspects along with data analysis in concert with JRH and JM. NY and FAP were responsible for the supervision and acquisition of the financial support for the project and were involved in the project administration along with KLL and DRB, who participated in the discussions on a regular basis with the team of experimentalists. JLB assisted in the clinical aspects of the study. NY and KL are responsible for the overall content as the guarantors from academia and the United States Department Of Defence.
Funding The study was funded by the US Department of Defense (W81XWH-16-1-0010 and W911NF-21-2-0011).
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.