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Introduction: The evolution of military helmet devices has increased the amount of head-supported mass (HSM) worn by warfighters. HSM has important implications for spine biomechanics, and yet, there is a paucity of studies that investigated the effects of differing HSM and accelerative profiles on spine biomechanics. The aim of this study is to investigate the segmental motions in the subaxial cervical spine with different sizes of HSM under Gx accelerative loading., Methods: A three-dimensional finite element model of the male head-neck spinal column was used. Three different size military helmets were modeled and incorporated into head-neck model. The models were exercised under Gx accelerative loading by inputting low and high pulses to the cervical vertebra used in the experimental studies. Segmental motions were obtained and normalized with respect to the non-HSM case to quantify the effect of HSM., Results: Segmental motions increased with an increase in velocity at all segments of the spine. Increasing helmet size resulted in larger motion increases. Angulations ranged from 0.9° to 9.3° at 1.8 m/s and from 1.3° to 10.3° at 2.6 m/s without a helmet. Helmet increased motion between 5% to 74% at 1.8 m/s. At 2.6 m/s, the helmet increased segmental motion anywhere from 10% to 105% in the subaxial cervical spine. The greatest motion was seen at the C5-C6 level, followed by the C6-C7 level., Conclusions: The subaxial cervical spine experiences motion increases at all levels at both velocity profiles with increasing HSM. Larger helmet and greater impact velocity increased motion at all levels, with C5-C6 demonstrating the largest range of motion. HSM should be minimized to reduce the risk of cervical spine injury to the warfighter., (© The Association of Military Surgeons of the United States 2023. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The objective of this study was to determine force-based lumbar spine injury criteria due to vertical impact using Post Mortem Human Surrogate (PMHS) experiments. Mounted personnel in military vehicles sustain loads from the pelvis in combat events such as underbody blast loadings. Forty-three post mortem human subject thoracolumbar spinal columns were obtained, screened for pre-existing trauma, bone mineral densities (BMDs) were determined, pre-test radiological images were taken, fixed at the ends in polymethylmethacrylate, load cells were attached to the ends of the fixation, positioned on custom vertical accelerator device based on a military-seating posture, and impacted at the base. Posttest images were obtained, and gross dissection was done to confirm injuries, classified into single and multilevel groups, groups A and B. Axial and resultant forces at the thoracolumbar (proximal) and lumbosacral (distal) joints were used as response variables to develop lumbar spine injury risk curves using parametric survival analysis. The Brier score metric was used to rank the variables. Age, BMD, column length, and vertebral body and intervertebral disc areas were used as covariates. The optimal metric describing the underlying response to injury was the distal resultant force for group A and proximal axial force for group B specimens. Force-BMD for group A and force-body area for group B were the best combinations. The IRCs with ±95% confidence intervals and quality of risk curves are given in the paper, and they serve as lumbar spine injury criteria. The present human cadaver Injury Risk Curves (IRCs) can be used to conduct matched pair tests to obtain dummy-based injury assessment risk curves/values to predict injury. The present IRCs can be used in human body finite element models. The relationship between covariates and primary forces presented in this study contribute to a better understanding of the role of demographic, geometric, and material factors to impact acceleration loading., Competing Interests: 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., (Published by Elsevier Ltd.)

This study was conducted to quantify the human tolerance from inferior to superior impacts to whole lumbar spinal columns excised from 43 post mortem human subjects. The specimens were fixed at the ends, aligned in a consistent seated posture, load cells were attached to the proximal and distal ends of the fixation, and the impact was applied using a custom accelerator device. Pretest X-rays and computed tomography (CT) scans, prepositioned X-rays, and posttest X-rays, CT scans and dissection data were used to identify injuries. Right, left, and interval censoring processes were used for the survival analysis, 16 were right censored, 24 were interval censored, and three were left censored observations. Force-based injury risk curves were developed, and the optimal metric describing the underlying response to injury was identified using the Brier score metric. Material, geometry (disc and body areas), and demographic covariates were included in the analysis. The distal force was found to be optimal metric. The bone mineral density was a significant covariate for distal and proximal forces. Both material and geometrical factors affected the transmitted force in this mode of loading. These quantified data serve as the first set of human lumbar spinal column injury risk curves.

Objective: To determine role of lordosis in cervical spine injuries using a novel competing risk analysis model., Methods: The first subgroup of published experiments (n = 20) subjected upright human cadaver head-neck specimens to impact loading. The natural lordosis was removed. The second (n = 21) and third (n = 10) subgroups of published tests subjected inverted specimens to head impact loading. Lordosis was preserved in these 2 subgroups. Using axial force and age as variables, competing risks analysis techniques were used to determine the role of lordosis in the risk of bone-only, ligament-only, and bone and ligament injuries., Results: Bony injuries were focused more at 1 level to a straightened spine, and ligament injuries were spread around multiple levels. Age was not a significant (P < 0.05) covariate. A straightened spine had 3.23 times higher risk of bony injuries than a lordotic spine. The spine with maintained lordosis had 1.14 times higher risk of ligament injuries, and 2.67 times higher risk of bone and ligament injuries than a spine without lordosis (i.e., preflexed column)., Conclusions: Increased risk of bony injuries in a preflexed spine and ligament injuries in a lordotic spine may have implications for military personnel, as continuous use of helmets in the line of duty affects the natural curvature; astronauts, as curvatures are less lordotic after missions; and civilian patients with spondylotic myelopathy who use head protective devices, as curvatures may change over time in addition to the natural aging process., (Published by Elsevier Inc.)

Cervical spine injuries can occur in military scenarios from events such as underbody blast events. Such scenarios impart inferior-to-superior loads to the spine. The objective of this study is to develop human injury risk curves (IRCs) under this loading mode using Post Mortem Human Surrogates (PMHS). Twenty-five PMHS head-neck complexes were obtained, screened for pre-existing trauma, bone densities were determined, pre-tests radiological images were taken, fixed in polymethylmethacrylate at the T2-T3 level, a load cell was attached to the distal end of the preparation, positioned end on custom vertical accelerator device based on the military-seating posture, donned with a combat helmet, and impacted at the base. Posttest images were obtained, and gross dissection was done to confirm injuries to all specimens. Axial and resultant forces at the cervico-thoracic joint was used to develop the IRCs using survival analysis. Data were censored into left, interval, and uncensored observations. The Brier score metric was used to rank the variables. The optimal metric describing the underlying response to injury was associated with the axial force, ranking slightly greater than the resultant force, both with BMD covariates. The results from the survival analysis indicated all IRCs are in the "fair" to "good" category, at all risk levels. The BMD was found to be a significant covariate that best describes the response of the helmeted head-neck specimens to injury. The present experimental protocol and IRCs can be used to conduct additional tests, matched-pair tests with the WIAMan and/or other devices to obtain injury assessment risk curves (IARCs) and injury assessment risk values (IARVs) to predict injury in crash environments, and these data can also be used for validating component-based head-neck and human body computational models.

The human cervical spine sustains compressive loading in automotive events and military operational activities, and the contact and noncontact loading are the two primary impact modes. Biomechanical and anatomical studies have shown differences between male and female cervical spines. Studies have been conducted to determine the human tolerance in terms of forces from postmortem human subject (PMHS) specimens from male and female spines; however, parametric risk curves specific to female spines are not available from contact loading to the head-neck complex under the axial mode. This study was conducted to develop female-spine based risk curves from PMHS tests. Data from experiments conducted by the authors using PMHS upright head-spines were combined with data from published studies using inverted head-spines. The ensemble consisted of 20 samples with ages ranging from 29 to 95 years. Except one, all specimens sustained neck injuries, consisting of fractures to cervical vertebrae, and disruptions to the intervertebral disc and facet joints, and ligaments. Parametric survival analysis was used to derive injury probability curves using the compressive force, uncensored for injury and right censored for noninjury data points. The specimen age was used as the covariate. Injury probability curves were derived using the best fit distribution, and the ± 95% confidence interval limits were obtained. Results indicated that age is a significant covariate for injury for the entire ensemble. Peak forces were extracted for 35, 45, and 63 (mean) years of age, the former two representing the young (military) and the latter, the automobile occupant populations. The forces of 1.2 kN and 2.9 kN were associated with 5% and 50% probability of injury at 35 years. These values at 45 years were 1.0 kN and 2.4 kN, and at 63 years, they were 0.7 kN and 1.7 kN. The normalized widths of the confidence intervals at these probability levels for the mean age were 0.74 and 0.48. The preliminary injury risk curves presented should be used with appropriate caution. This is the first study to develop risk curves for females of different ages using parametric survival analysis, and can be used to advance human safety, and design and develop manikins for military and other environments., (Published by Elsevier Ltd.)

Objective: The objective of this study was to determine the influence of age and injury mechanism on cervical spine tolerance to injury from head contact loading using survival analysis., Methods: This study analyzed data from previously conducted experiments using post mortem human subjects (PMHS). Group A tests used the upright intact head-cervical column experimental model. The inferior end of the specimen was fixed, the head was balanced by a mechanical system, and natural lordosis was removed. Specimens were placed on a testing device via a load cell. The piston applied loading at the vertex region. Spinal injuries were identified using medical images. Group B tests used the inverted head-cervical column experimental model. In one study, head-T1 specimens were fixed distally, and C7-T1 joints were oriented anteriorly, preserving lordosis. Torso mass of 16 kg was added to the specimen. In another inverted head-cervical column study, occiput-T2 columns were obtained, an artificial head was attached, T1-T2 was fixed, C4-C5 disc was maintained horizontal in the lordosis posture, and C7-T1 was unconstrained. The specimens were attached to the drop test carriage carrying a torso mass of 15 kg. A load cell at the inferior end measured neck loads in both studies. Axial neck force and age were used as the primary response variable and covariate to derive injury probability curves using survival analysis., Results: Group A tests showed that age is a significant (P < .05) and negative covariate; that is, increasing age resulted in decreasing force for the same risk. Injuries were mainly vertebral body fractures and concentrated at one level, mid-to-lower cervical spine, and were attributed to compression-related mechanisms. However, age was not a significant covariate for the combined data from group B tests. Both group B tests produced many soft tissue injuries, at all levels, from C1 to T1. The injury mechanism was attributed to mainly extension. Multiple and noncontiguous injuries occurred. Injury probability curves, ±95% confidence intervals, and normalized confidence interval sizes representing the quality of the mean curve are given for different data sets., Conclusions: For compression-related injuries, specimen age should be used as a covariate or individual specimen data may be prescaled to derive risk curves. For distraction- or extension-related injuries, however, specimen age need not be used as a covariate in the statistical analysis. The findings from these tests and survival analysis indicate that the age factor modulates human cervical spine tolerance to impact injury.

Background: The Abbreviated Injury Scale (AIS) is an anatomical-based coding system created by the Association for the Advancement of Automotive Medicine, utilized to classify and code injuries resulting from trauma, in order of severity. According to the latest version, all Thoraco-Lumbar Compression Fractures (TLCF), even without injury to other spine components and with >20% loss of height, were branded AIS 3 injuries, reflecting a serious threat to life or permanent disability. Advances in spine imaging, recent biomechanical studies, and long-term outcomes research offer the opportunity to consider these injuries differently.Objective: To re-evaluate the percent compression threshold of TLCF of the spine from motor vehicle crashes (MVC) for serious risk to life identified as surgical treatment, delineating a reliable cut-off for fracture severity and morbidity. Little national data considers degree of compression and provides adequate followup imaging to determine degree of compression, justifying this effort.Methods: Charts and radiographs of patients admitted to our institution due to vehicle crashes with isolated (vertebral body only) TLCF between 2008 and 2015 were reviewed. Data were collected on degree of compression, treatment, and long-term outcomes to determine the threshold of permanent injury. Vertebral bodies at the level of fracture were measured both anteriorly and posteriorly, and compared to adjacent segments; percentage compression was calculated.Results: 1470 patient records with diagnoses of spine trauma were reviewed; 695 isolated compression fractures were identified, of which 194 were in vehicle crashes and had adequate imaging and follow-up. Ages ranged from 19 to 82, with a male: female ratio of 60:40. No patient with vertebral body compression of less than 30% underwent surgery unless presenting with a neurological deficit. All 22 surgical patients demonstrated significant retropulsion of bone into the spinal canal. Five surgical patients suffered eight complications; there were no adverse outcomes in the nonsurgical group.Conclusions: These results are consistent with evolving clinical thinking, resulting in decreasing surgical incidence and orthosis use. Our data strongly suggests that isolated compression fractures in the absence of neurologic deficit or severe cord compression due to retropulsed bone are self-limiting. Therefore, the AIS scores for these common injuries could be reconsidered and reflect their relatively benign outlook. [ABSTRACT FROM AUTHOR]