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This paper presents a survey of side impact trauma-related biomedical investigations with specific reference to certain aspects of epidemiology relating to the growing elderly population, improvements in technology such as side airbags geared toward occupant safety, and development of injury criteria. The first part is devoted to the involvement of the elderly by identifying variables contributing to injury including impact severity, human factors, and national and international field data. This is followed by a survey of various experimental models used in the development of injury criteria and tolerance limits. The effects of fragility of the elderly coupled with physiological changes (e.g., visual, musculoskeletal) that may lead to an abnormal seating position (termed out-of-position) especially for the driving population are discussed. Fundamental biomechanical parameters such as thoracic, abdominal and pelvic forces; upper and lower spinal and sacrum accelerations; and upper, middle and lower chest deflections under various initial impacting conditions are evaluated. Secondary variables such as the thoracic trauma index and pelvic acceleration (currently adopted in the United States Federal Motor Vehicle Safety Standards), peak chest deflection, and viscous criteria are also included in the survey. The importance of performing research studies with specific focus on out-of-position scenarios of the elderly and using the most commonly available torso side airbag as the initial contacting condition in lateral impacts for occupant injury assessment is emphasized.
STUDY DESIGN: This study determined bone mineral density (BMD) of cervical, thoracic, and lumbar vertebrae in healthy asymptomatic human subjects. OBJECTIVES: To test the hypothesis that BMD of neck vertebrae (C2-C7) is equivalent to BMD of lumbar vertebrae (L2-L4). SUMMARY OF BACKGROUND DATA: BMD of lumbar vertebrae is correlated to their strength. Although numerous studies exist quantifying BMD of the human lumbar spine, such information for the cervical spine is extremely limited. In addition, BMD correlations are not established between the two regions of the spinal column. METHODS: Adult healthy human female volunteers with ages ranging from 18 to 40 years underwent quantitative computed tomography (CT) scanning of the neck and back. All BMD data were statistically analyzed using paired nonrepeating measures ANOVA techniques. Significance was assigned at a P < 0.05. Linear regression analyses were used to compare BMD as a function of level and region; +/-95% confidence intervals were determined. RESULTS: When data were grouped by cervical (C2-C7), thoracic (T1), and lumbar (L2-L4) spines, mean BMD was 260.8 +/- 42.5, 206.9 +/- 33.5, and 179.7 +/- 23.4 mg/mL. Average BMD of cervical vertebrae was higher than (P < 0.0001) thoracic and lumbar spines. Correlations between BMD and level indicated the lowest r value for T1 (0.42); in general, the association was the strongest in the lumbar spine (r = 0.89-0.95). The cervical spine also responded with good correlations among cervical vertebrae (r ranging from 0.66 to 0.87). CONCLUSIONS: The present study failed to support the hypothesis that BMD of lumbar spine vertebrae is equivalent to its cranial counterparts. The lack of differences in BMD among the three lumbar vertebral bodies confirms the appropriateness of using L2, L3, or L4 in clinical or biomechanical situations. However, significant differences were found among different regions of the vertebral column, with the cervical spine demonstrating higher trabecular densities than the thoracic and lumbar spines. In addition, the present study found statistically significant variations in densities even among neck vertebrae.
BACKGROUND: While cervical spine injury biomechanics reviews in motor vehicle and sports environments are available, there is a paucity of studies in military loadings. This article presents an analysis on the biomechanics and applications of cervical spine injury research with an emphasis on human tolerance for underbody blast loadings in the military. METHODS: Following a brief review of published military studies on the occurrence and identification of field trauma, postmortem human subject investigations are described using whole body, intact head-neck complex, osteo-ligamentous cervical spine with head, subaxial cervical column, and isolated segments subjected to differing types of dynamic loadings (electrohydraulic and pendulum impact devices, free-fall drops). FINDINGS: Spine injuries have shown an increasing trend over the years, explosive devices are one of the primary causal agents and trauma is attributed to vertical loads. Injuries, mechanisms and tolerances are discussed under these loads. Probability-based injury risk curves are included based on loading rate, direction and age. INTERPRETATION: A unique advantage of human cadaver tests is the ability to obtain fundamental data to delineate injury biomechanics and establish human tolerance and injury criteria. Definitions of tolerances of the spine under vertical loads based on injuries have implications in clinical and biomechanical applications. Primary outputs such as forces and moments can be used to derive secondary variables such as the neck injury criterion. Implications are discussed for designing anthropomorphic test devices that may be used to predict injuries in underbody blast environments and improve the safety of military personnel.
BACKGROUND: Aging, trauma, or degeneration can affect intervertebral kinematics. While in vivo studies can determine motions, moments are not easily quantified. Previous in vitro studies on the cervical spine have largely used specimens from older individuals with varying levels of degeneration and have shown that moment-rotation responses under lateral bending do not vary significantly by spinal level. The objective of the present in vitro biomechanical study was, therefore, to determine the coronal and axial moment-rotation responses of degeneration-free, normal, intact human cadaveric cervicothoracic spinal columns under the lateral bending mode. METHODS: Nine human cadaveric cervical columns from C2 to T1 were fixed at both ends. The donors had ranged from twenty-three to forty-four years old (mean, thirty-four years) at the time of death. Retroreflective targets were inserted into each vertebra to obtain rotational kinematics in the coronal and axial planes. The specimens were subjected to pure lateral bending moment with use of established techniques. The range-of-motion and neutral zone metrics for the coronal and axial rotation components were determined at each level of the spinal column and were evaluated statistically. RESULTS: Statistical analysis indicated that the two metrics were level-dependent (p 0.95). CONCLUSIONS: Range-of-motion metrics compared favorably with those of in vivo investigations. Coronal and axial motions of degeneration-free cervical spinal columns under lateral bending showed substantially different level-dependent responses. The presentation of moment-rotation corridors for both metrics forms a normative dataset for the degeneration-free cervical spines.
The objective of this study was to determine the bone mineral density (BMD) of cervical vertebrae and correlate with the lumbar spine. Fifty-seven young adult healthy male volunteers, ranging from 18 to 41 years of age, underwent quantitative computed tomography (QCT) scanning of C2-T1 and L2-L4 vertebrae. To account for correlations, repeated measures techniques were used to compare data as a function of spinal level and region. Linear regression methods were used (+/-95% CI) to compare data as a function of spinal level and region. The mean age and body height were 25.0 +/- 5.8 years and 181.0 +/- 7.6 cm. BMD decreased from the rostral to caudal direction along the spinal column. Grouped data indicated that the neck is the densest followed by the first thoracic vertebra and low back with mean BMD of 256.0 +/- 48.1, 194.3 +/- 44.2, and 172.2 +/- 28.4 mg/cm(3), respectively; differences were statistically significant. While BMD did not vary significantly between the three lumbar bodies, neck vertebrae demonstrated significant trends. The matrix of correlation coefficients between BMD and spinal level indicated that the relationship is strong in the lumbar (r = 0.92-0.96) and cervical (r = 0.73-0.92) spines. Data from the present study show that the trabecular bony architecture of the neck is significantly different from the low back. These quantitative BMD data from a controlled young adult healthy human male volunteer population may be valuable in establishing normative data specifically for the neck. From a trabecular bone density perspective, these results indicate that lumbar vertebrae cannot act as the best surrogates for neck vertebrae. Significant variations in densities among neck vertebrae, unlike the low back counterpart, may underscore the need to treat these bones as different structures.