The human cervical spine in tension: Effects of frame and fixation compliance on structural responses
Duke University, Department of Biomedical Engineering and Division of Orthopaedic Surgery, Durham, North Carolina 27708-0281, USA.Traffic Injury Prevention (Impact Factor: 1.41). 07/2004; 5(2):151-5. DOI: 10.1080/15389580490435213
There is little data available on the responses of the human cervical spine to tensile loading. Such tests are mechanistically and technically challenging due to the variety of end conditions that need to be imposed and the difficulty of strong specimen fixation. As a result, spine specimens need to be tested using fairly complex, and potentially compliant, apparati in order to fully characterize the mechanical responses of each specimen. This, combined with the relatively high stiffness of human spine specimens, can result in errors in stiffness calculations. In this study, 18 specimen preparations were tested in tension. Tests were performed on whole cervical spines and on spine segments. On average, the linear stiffness of the segment preparations was 257 N/mm, and the stiffness of the whole cervical spine was 48 N/mm. The test frame was found to have a stiffness of 933 N/mm. Assembling a whole spine from a series combination of eight segments with a stiffness of 257 N/mm results in an estimated whole spine stiffness of 32.1 N/mm (32% error). The segment stiffnesses were corrected by assuming that the segment preparation stiffness is a series combination of the stiffnesses of the segment and the frame. This resulted in an average corrected segment stiffness of 356 N/mm. Taking the frame compliance into account, the whole spine stiffness is 51 N/mm. A series combination of eight segments using the corrected stiffnesses results in an estimated whole spine stiffness of 45.0 N/mm (12% error). We report both linear and nonlinear stiffness models for male spines and conclude that the compliance of the frame and the fixation must be quantified in all tension studies of spinal segments. Further, reported stiffness should be adjusted to account for frame and fixation compliance.
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ABSTRACT: In this paper, the advantages and disadvantages of the pnp separation of reverse conducting gate commutated thyristor (RC-GCT) are analyzed. Based on the results, a new separation method with p<sup>+</sup> diffusion ring is presented, and the forward blocking characteristic of the RC-GCT is analyzed by using MEDICI simulator. The results show that the new separation method used in RC-GCT devices can improve the forward blocking characteristic of RC-GCT, and has no influence on the gate reverse characteristics and the commutation current, and increase hardly the complexity of process simultaneity. Only reduce the effective cathode areas of RC-GCT. Lastly, the width of p<sup>+</sup> diffusion ring and the space between the p+ diffusion ring and p base region are optimized.Industrial Technology, 2005. ICIT 2005. IEEE International Conference on; 01/2006
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ABSTRACT: Epidemiological data and clinical indicia reveal devastating consequences associated with pediatric neck injuries. Unfortunately, neither injury prevention nor clinical management strategies will be able to effectively reduce these injuries or their effects on children, without an understanding of the cervical spine developmental biomechanics. Thus, we investigated the relationship between spinal development and the functional (stiffness) and failure biomechanical characteristics of the cervical spine in a baboon model. A correlation study design was used to define the relationships between spinal tissue maturation and spinal biomechanics in both tension and compression. Eighteen baboon cervical spine specimens distributed across the developmental spectrum (1-26 human equivalent years) were dissected into osteoligamentous functional spinal units. Using a servo-hydraulic MTS, these specimens (Oc-C2, C3-C4, C5-C6, C7-T1) were non-destructively tested in tension and compression and then displaced to failure in tension while measuring the six-axes of loads and displacements. The functions describing the developmental biomechanical response of the cervical spine for stiffness and normalized stiffness exhibited a significant direct relationship in both tension and compression loading. Similarly, the tensile failure load and normalized failure load demonstrated significant maturational increases. Further, differences in biomechanical response were observed between the spinal levels examined and all levels exhibited clinically relevant failure patterns. These data support our understanding of the child cervical spine from a developmental biomechanics perspective and facilitate the development of injury prevention or management schema for the mitigation of child spine injuries and their deleterious effects.Journal of Biomechanics 02/2006; 39(16):3045-54. DOI:10.1016/j.jbiomech.2005.10.014 · 2.75 Impact Factor
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ABSTRACT: New vehicle safety standards are designed to limit the amount of neck tension and extension seen by out-of-position motor vehicle occupants during airbag deployments. The criteria used to assess airbag injury risk are currently based on volunteer data and animal studies due to a lack of bending tolerance data for the adult cervical spine. This study provides quantitative data on the flexion-extension bending properties and strength on the male cervical spine, and tests the hypothesis that the male is stronger than the female in pure bending. An additional objective is to determine if there are significant differences in stiffness and strength between the male upper and lower cervical spine. Pure-moment flexibility and failure testing was conducted on 41 male spinal segments (O-C2, C4-C5, C6-C7) in a pure-moment test frame and the results were compared with a previous study of females. Failures were conducted at approximately 90 N-m/s. In extension, the male upper cervical spine (O-C2) fails at a moment of 49.5 (s.d. 17.6)N-m and at an angle of 42.4 degrees (s.d. 8.0 degrees). In flexion, the mean moment at failure is 39.0 (s.d. 6.3 degrees) N-m and an angle of 58.7 degrees (s.d. 5.1 degrees). The difference in strength between flexion and extension is not statistically significant. The difference in the angles is statistically significant. The upper cervical spine was significantly stronger than the lower cervical spine in both flexion and extension. The male upper cervical spine was significantly stiffer than the female and significantly stronger than the female in flexion. Odontoid fractures were the most common injury produced in extension, suggesting a tensile mechanism due to tensile loads in the odontoid ligamentous complex.Journal of Biomechanics 02/2007; 40(3):535-42. DOI:10.1016/j.jbiomech.2006.02.015 · 2.75 Impact Factor
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