Kinetics of the cervical spine in pediatric and adult volunteers during low speed frontal impacts

Previous research has quantified differences in head and spinal kinematics between children and adults restrained in an automotive-like configuration subjected to low speed dynamic loading. The forces and moments that the cervical spine imposes on the head contribute directly to these age-based kinematic variations. To provide further explanation of the kinematic results, this study compared the upper neck kinetics - including the relative contribution of shear and tension as well as flexion moment - between children (n=20, 6-14 yr) and adults (n=10, 18-30 yr) during low-speed (<4 g, 2.5 m/s) frontal sled tests. The subjects were restrained by a lap and shoulder belt and photo-reflective targets were attached to skeletal landmarks on the head, spine, shoulders, sternum, and legs. A 3D infrared tracking system quantified the position of the targets. Shear force (F(x)), axial force (F(z)), bending moment (M(y)), and head angular acceleration (θ(head)) were computed using inverse dynamics. The method was validated against ATD measured loads. Peak F(z) and θ(head) significantly decreased with increasing age while M(y) significantly increased with increasing age. F(x) significantly increased with age when age was considered as a univariate variable; however when variations in head-to-neck girth ratio and change in velocity were accounted for, this difference as a function of age was not significant. These results provide insight into the relationship between age-based differences in head kinematics and the kinetics of the cervical spine. Such information is valuable for pediatric cervical spine models and when scaling adult-based upper cervical spine tolerance and injury metrics to children.     

Mid-sagittal dimensions of cervical vertebral bodies.

A series of lateral radiographs of the cervical spinal column was evaluated in order to determine vertebral body dimensions. The sample included males (N=30) and females (N=31) 18 to 24 years old, comprising three stature percentile ranges (1-20; 40-60; 80-99) of the U.S. adult population. A two-dimensional analysis of vertebral body height (average distance between superior-inferior surgaces), depth (average distance between anteriorposterior surfaces), and area (average height X average depth) revealed minimal effects due to stature. In all subjects, average depth exceeded average height for vertebral bodies C3 through C7. Upon combining stature groups, both sexes revealed maximum average values for these dimensions at the seventh cervical vertebral body. Minimum average height occurred at C5 whereas minimum average depth was found at C3. Significant correlation (alpha greater than 0.05) was found for males between ponderal index and height and depth of the C7 vertebra. Male head weight correlated significantly with C3, C4, C5 and C6 vertebral body height and with C3, C5 and C6 vertebral body depth. For females, C7 height and C6 depth correlated significantly with ponderal index and head weight respectively. Probable biomechanical relationships of specific cervical vertebral bodies are noted     

GlideScope视频喉镜和Macintosh直接喉镜在颈椎损伤患者气管插管中的应用比较

目的:比较GlideScope视频喉镜(加拿大Saturn生物技术有限公司)和普通直接喉镜在颈椎损伤患者气管插管中的难易,及两种工具插管对血液动力学的影响。方法:拟在经口气管插管全身麻醉下行择期手术的患者40例,ASAI级,年龄18～60岁,随机分为G组和M组(n=20)。常规麻醉诱导后,手法制动头颈部,G组采用GlideScope视频喉镜,M组用Macintosh直接喉镜行气管插管。分析比较两组声门暴露情况(Cormark-Lehane分级)以及暴露时间,试插次数,失败例数,有无助手辅助,插管前后心率与收缩压乘积(RPP)变化。结果:与M组比较,G组声门暴露情况较好,但暴露时间显著延长(P<0.05)。M组需要助手辅助及插管失败的比例均高于G组。两组RPP的变化在各个时点无显著差别。结论:在为颈椎损伤患者气管插管中,GlideScope视频喉镜能够更好的显露声门,降低插管难度,提高插管的成功率。     

The effect of static neck flexion on mechanical and neuromuscular behaviors of the cervical spine

Occupations that involve sustained or repetitive neck flexion are associated with a higher incidence of neck pain. Little in vivo information is available on the impact of static neck flexion on cervical spinal tissue. The aim of this study was to assess changes in mechanical and neuromuscular behaviors to sustained neck flexion in healthy adults. Sixty healthy subjects aged 20–35 years participated in this study. The participants were exposed to static neck flexion at a fixed angle of full flexion for 10 min. Mechanical and neuromuscular responses of the cervical spine to sudden perturbations were measured pre- and post-exposure. Magnitude of load-relaxation during flexion exposure, stiffness, peak head angular velocity, and reflexive activities of cervical muscles were recorded. Effective neck stiffness decreased significantly, especially in female participants (P = 0.0001). The reflexive response of the cervical erector spinae muscles to head perturbation delayed significantly (P = 0.0001). Peak head angular velocity was significantly increased after exposure to neck flexion for 10 min, especially in female participants (P = 0.001). In the present study, static flexion resulted in changes in mechanical and neuromuscular behavior of the cervical spine, potentially leading to decreased stiffness of the cervical spine. The results confirm the importance of maintaining a correct head and neck position during work and improving the work environment to reduce the cervical spinal load and work-related neck pain.     

Cervical flexion–relaxation response to neck muscle fatigue in males and females

In this study the effect of muscle fatigue on the cervical spine flexion–relaxation response was studied. Twenty healthy participants (10 males and 10 females) were recruited for data collection. The Sorenson protocol was utilized to induce neck muscle fatigue. Surface electromyography and optical motion capture systems were used to measure neck muscle activation and head–neck posture, respectively. A post-fatigue reduction in the Flexion–Relaxation Ratio (FRR) and higher FRR for females compared to males were observed. A post-fatigue decrease was also observed in the onset and offset angles resulting in an expansion of the myoelectric silence period. Gender had no effect on the onset and offset angles of the silence period. Post-fatigue shift in the onset and offset angles and the expansion of the silence period indicate an increased contribution by the passive viscoelastic tissues in stabilizing the cervical spine under fatigued condition.     

Comparative strengths and structural properties of the upper and lower cervical spine in flexion and extension

The purpose of this study is to test the hypothesis that the upper cervical spine is weaker than the lower cervical spine in pure flexion and extension bending, which may explain the propensity for upper cervical spine injuries in airbag deployments. An additional objective is to evaluate the relative strength and flexibility of the upper and lower cervical spine in an effort to better understand injury mechanisms, and to provide quantitative data on bending responses and failure modes. Pure moment flexibility and failure testing was conducted on 52 female spinal segments in a pure-moment test frame. The average moment at failure for the O-C2 segments was 23.7+/-3.4Nm for flexion and 43.3+/-9.3Nm for extension. The ligamentous upper cervical spine was significantly stronger in extension than in flexion (p=0.001). The upper cervical spine was significantly stronger than the lower cervical spine in extension. The relatively high strength of the upper cervical spine in tension and in extension is paradoxical given the large number of upper cervical spine injuries in out-of-position airbag deployments. This discrepancy is most likely due to load sharing by the active musculature.     

A female head–neck model for rear impact simulations

Several mathematical cervical models of the 50th percentile male have been developed and used for impact biomechanics research. However, for the 50th percentile female no similar modelling efforts have been made, despite females being subject to a higher risk of soft tissue neck injuries. This is a limitation for the development of automotive protective systems addressing Whiplash Associated Disorders (WADs), most commonly caused in rear impacts, as the risk for females sustaining WAD symptoms is double that of males.In this study, a finite element head and neck model of a 50th percentile female was validated in rear impacts. A previously validated ligamentous cervical spine model was complemented with a rigid body head, soft tissues and muscles. In both physiological flexion-extension motions and simulated rear impacts, the kinematic response at segment level was comparable to that of human subjects. Evaluation of ligament stress levels in simulations with varied initial cervical curvature revealed that if an individual assumes a more lordotic posture than the neutral, a higher risk of WAD might occur in rear impact.The female head and neck model, together with a kinematical whole body model which is under development, addresses a need for tools for assessment of automotive protection systems for the group which is at the highest risk to sustain WAD.     

Analysis of control strategies for VIVA OpenHBM with active reflexive neck muscles

Modeling muscle activity in the neck muscles of a finite element (FE) human body model can be based on two biological reflex systems. One approach is to approximate the Vestibulocollic reflex (VCR) function, which maintains the head orientation relative to a fixed reference in space. The second system tries to maintain the head posture relative to the torso, similar to the Cervicocolic reflex (CCR). Strategies to combine these two neck muscle controller approaches in a single head-neck FE model were tested, optimized, and compared to rear-impact volunteer data. The first approach, Combined-Control, assumed that both controllers simultaneously controlled all neck muscle activations. In the second approach, Distributed-Control, one controller was used to regulate activation of the superficial muscles while a different controller acted on deep neck muscles. The results showed that any muscle controller that combined the two approaches was less effective than only using one of VCR- or CCR-based systems on its own. A passive model had the best objective rating for cervical spine kinematics, but the addition of a single active controller provided the best response for both head and cervical spine kinematics. The present study demonstrates the difficulty in completely capturing representative head and cervical spine responses to rear-impact loading and identified a controller capturing the VCR reflex as the best candidate to investigate whiplash injury mechanisms through FE modeling.

     

Spinal constraint modulates head instantaneous center of rotation and dictates head angular motion

The head is kinematically constrained to the torso through the spine and thus, the spine dictates the amount of output head angular motion expected from an input impact. Here, we investigate the spinal kinematic constraint by analyzing the head instantaneous center of rotation (HICOR) with respect to the torso in head/neck sagittal extension and coronal lateral flexion during mild loads applied to 10 subjects. We found the mean HICOR location was near the C5-C6 intervertebral joint in sagittal extension, and T2-T3 intervertebral joint in coronal lateral flexion. Using the impulse-momentum relationship normalized by subject mass and neck length, we developed a non-dimensional analytical ratio between output angular velocity and input linear impulse as a function of HICOR location. The ratio was 0.65 and 0.50 in sagittal extension and coronal lateral flexion respectively, implying 30% greater angular velocities in sagittal extension given an equivalent impulse. Scaling to subject physiology also predicts larger required impulses given greater subject mass and neck length to achieve equivalent angular velocities, which was observed experimentally. Furthermore, the HICOR has greater motion in sagittal extension than coronal lateral flexion, suggesting the head and spine can be represented with a single inverted pendulum in coronal lateral flexion, but requires a more complex representation in sagittal extension. The upper cervical spine has substantial compliance in sagittal extension, and may be responsible for the complex motion and greater extension angular velocities. In analyzing the HICOR, we can gain intuition regarding the neck’s role in dictating head motion during external loading.     

Craniocervical morphology and posture in Australian aboriginals

The length of the spinal column as a percentage of stature is smaller in the Australian aboriginal than in most other ethnic groups (Abbie, 1957). It is conceivable that relative lengths of the cervical column might influence population differences in craniocervical posture and craniofacial morphology. The present study aimed to elucidate this relationship by comparing head posture and craniofacial morphology in Australian aboriginals to the same features in a previously studied sample of 120 Danish students (Solow and Tallgren, 1976). The aboriginal sample consisted of 42 young male adults from the Yuendumu settlement, Northern Territory, Australia. Cephalometric films of the natural head position were taken during a field trip to the settlement. The comparison comprised 18 postural and 61 morphological variables. In the aboriginals, the cervical column was shorter and had a less pronounced lordosis. The head was held about 3° lower, and the upper cervical column was 81/2° more forward inclined. As a consequence, the craniocervical angle was about 6° larger. Comparison of the craniofacial morphology in the two groups showed in the aboriginals a shorter upper facial height, a larger anterior lower facial height, and a larger vertical jaw relationship (NL/ML). The length of the posterior cranial base, s-ba, was 4 mm shorter (P <0.001) in the aboriginals, possibly developmentally related to the generally shorter spinal column in Australian aboriginals.     

An apparatus for tensile and bending tests of perinatal, neonatal, pediatric and adult cadaver osteoligamentous cervical spines

Investigations of biomechanical properties of pediatric cadaver cervical spines subjected to tensile or bending modes of loading are generally limited by a lack of available tissue and limiting sample sizes, both per age and across age ranges. It is therefore important to develop fixation techniques capable of testing individual cadavers in multiple modes of loading to obtain more biomechanical data per subject. In this study, an experimental apparatus and fixation methodology was developed to accommodate cadaver osteoligamentous head-neck complexes from around birth (perinatal) to full maturation (adult) [cervical length: 2.5-12.5 cm; head breadth: 6-15 cm; head length: 6-19 cm] and sequentially test the whole cervical spine in tension, the upper cervical spine in bending and the upper cervical spine in tension. The experimental apparatus and the fixation methodology provided a rigid casting of the head during testing and did not compromise the skull. Further testing of the intact skull and sub-cranial material was made available due to the design of the apparatus and fixation techniques utilized during spinal testing. The stiffness of the experimental apparatus and fixation technique are reported to better characterize the cervical spine stiffness data obtained from the apparatus. The apparatus and fixation technique stiffness was 1986 N/mm. This experimental system provides a stiff and consistent platform for biomechanical testing across a broad age range and under multiple modes of loading.     

蜡皮蜥的两性异形和繁殖输出

为研究蜡皮蜥(Leiolepis reevesii)两性异形和繁殖输出,于2002、2003年4月下旬从海南乐东一种群捕获423头蜡皮蜥。经检测得到繁殖雌体的最小体长为89．0mm,据此判定≥89．0mm的个体为性成熟。研究结果表明：①蜡皮蜥具有两性异形,雄性大于雌性且具有较大的头部。成体雄性头长和头宽随体长的增长速率大于雌性,幼体头长和头宽随体长的增长速率无显著的两性差异。以性别和年龄(成、幼体)为因子的双因子ANOVA比较两性头长和头宽与体长的回归剩余值发现,雄性头部大于雌性,幼体头部相对大于成体。②饲养于实验室的母体中有42头于2002、2003年5月22日～7月16日产出正常卵,这些繁殖雌体具有年产多窝卵的潜力。窝卵数和卵重的变异系数分别为0．18和0．13,前者变异度大于后者。窝卵数、窝卵重和卵重均与母体体长无关。卵重与相对生育力之间无显著的负相关性,表明蜡皮蜥缺乏卵数量与卵大小之间的权衡。相对窝卵重与母体体长呈显著的负相关,表明较小的母体具有相对较大的繁殖输出。因雌体繁殖会滞缓其生长,小母体具有相对较大的繁殖输出,至少部分地解释了雌性蜡皮蜥的成体为什么个体较小。     

Finite element analysis of moment-rotation relationships for human cervical spine

A comprehensive, geometrically accurate, nonlinear C0-C7 FE model of head and cervical spine based on the actual geometry of a human cadaver specimen was developed. The motions of each cervical vertebral level under pure moment loading of 1.0 Nm applied incrementally on the skull to simulate the movements of the head and cervical spine under flexion, tension, axial rotation and lateral bending with the inferior surface of the C7 vertebral body fully constrained were analysed. The predicted range of motion (ROM) for each motion segment were computed and compared with published experimental data. The model predicted the nonlinear moment-rotation relationship of human cervical spine. Under the same loading magnitude, the model predicted the largest rotation in extension, followed by flexion and axial rotation, and least ROM in lateral bending. The upper cervical spines are more flexible than the lower cervical levels. The motions of the two uppermost motion segments account for half (or even higher) of the whole cervical spine motion under rotational loadings. The differences in the ROMs among the lower cervical spines (C3-C7) were relatively small. The FE predicted segmental motions effectively reflect the behavior of human cervical spine and were in agreement with the experimental data. The C0-C7 FE model offers potentials for biomedical and injury studies.     

Impairment of proprioception after whiplash injury

Whiplash injury usually occurs in traffic accidents. Persons experienced this injury might have an impairment of proprioception clinically expressed as inability to determine the exact position of their heads. The aim of this study was to examine the loss of proprioception in people who had a whiplash injury. The study included 60 subjects with cervical spine injury, aged 20 to 50 years and 60 healthy volunteers matched by sex and age. The instrument used for cervical spine mobility assessment was the Cervical Measurement System (CMS), which determines the ability of subjects to return their head in the exact position as it was before they turned it 30 degrees left or right. Patients with cervical spine injury showed significant impairment of proprioception in comparison with healthy subjects (P < 0.001). The results support the hypothesis that subject with recent cervical spine injury have incorrect perception of their head position. Therefore, their rehabilitation should include the correction of proprioception and head coordination.     

A comparison of lumbar spine and muscle loading between male and female workers during box transfers

There is a clear relationship between lumbar spine loading and back musculoskeletal disorders in manual materials handling. The incidence of back disorders is greater in women than men, and for similar work demands females are functioning closer to their physiological limit. It is crucial to study loading on the spine musculoskeletal system with actual handlers, including females, to better understand the risk of back disorders. Extrapolation from biomechanical studies conducted on unexperienced subjects (mainly males) might not be applicable to actual female workers. For male workers, expertise changes the lumbar spine flexion, passive spine resistance, and active/passive muscle forces. However, experienced females select similar postures to those of novices when spine loading is critical. This study proposes that the techniques adopted by male experts, male novices, and females (with considerable experience but not categorized as experts) impact their lumbar spine musculoskeletal systems differently. Spinal loads, muscle forces, and passive resistance (muscle and ligamentous spine) were predicted by a multi-joint EMG-assisted optimization musculoskeletal model of the lumbar spine. Expert males flexed their lumbar spine less (avg. 21.9° vs 30.3–31.7°) and showed decreased passive internal moments (muscle avg. 8.9% vs 15.9–16.0%; spine avg. 4.7% vs 7.1–7.8%) and increased active internal moments (avg. 72.9% vs 62.0–63.9%), thus producing a different impact on their lumbar spine musculoskeletal systems. Experienced females sustained the highest relative spine loads (compression avg. 7.3 N/BW vs 6.2–6.4 N/BW; shear avg. 2.3 N/BW vs 1.7–1.8 N/BW) in addition to passive muscle and ligamentous spine resistance similar to novices. Combined with smaller body size, less strength, and the sequential lifting technique used by females, this could potentially mean greater risk of back injury. Workers should be trained early to limit excessive and repetitive stretching of their lumbar spine passive tissues.     

Extreme cyclomorphosis in Daphnia lumholtzi

1. Daphnia lumholtzi, not previously reported in North America, was found in a small reservoir in East Texas in January, 1991, This species possesses extremely long spines and large fornices; an allometric study was performed to detect any temporal differences in specific growth rates of the spines relative to the body. 2. In nature, mature females attained 1.8mm body length, excluding spines, but when the head and tail spines are included, the total length reached a maximum of 5.6mm. 3. Differences in the growth patterns of the head spine and the tail spine relative to the body existed for D. lumholtzi from January to March 1991. Both the head and the tail spines grew at a faster rate than the body during all 3 months although the rates varied between them. The results contradict the invertebrate predation hypothesis (Dodson, 1974) in that D. lumholtzi's head and tail spines continue to grow during adulthood instead of stopping after the juvenile instars. 4. The head spines grew at a constant allometric rate over time while the tail spine grew faster as the temperature increased. Both varied significantly in length over the 3 months, with animals having the shortest spines in February and the longest in March.     

The dynamic behaviour of the head and cervical spine during ‘whiplash’

Using the method of Orne and Liu (1971) a discrete-parameter model of the head, neck and torso has been developed to allow investigation of the ‘whiplash’ problem. Following a 5g acceleration pulse applied to the seat base it was found that some degree of initial flexion of the head relative to the torso occurred prior to rapid hyperextension. The degree of initial flexion was found to increase with decreasing seatback stiffness. Head, horizontal and rotational acceleration profiles revealed that the peak values reached displayed a similar relationship to seatback stiffness. An examination of the loading distribution in the cervical spine showed that maximums were reached during the hyperextension phase and were of greatest magnitude in the low cervical region. These forces were larger and consequently more damaging for seatbacks of decreasing stiffness characteristics.     

Mechanically simulated muscle forces strongly stabilize intact and injured upper cervical spine specimens

Although muscles are assumed to be capable of stabilizing the spinal column in vivo, they have only rarely been simulated in vitro. Their effect might be of particular importance in unstable segments. The present study therefore tests the hypothesis that mechanically simulated muscle forces stabilize intact and injured cervical spine specimens. In the first step, six human occipito-cervical spine specimens were loaded intact in a spine tester with pure moments in lateral bending (+/- 1.5 N m), flexion-extension (+/- 1.5 N m) and axial rotation (+/- 0.5 N m). In the second step, identical flexibility tests were carried out during constant traction of three mechanically simulated muscle pairs: splenius capitits (5 N), semispinalis capitis (5 N) and longus colli (15 N). Both steps were repeated after unilateral and bilateral transection of the alar ligaments. The muscle forces strongly stabilized C0-C2 in all loading and injury states. This was most obvious in axial rotation, where a reduction of range of motion (ROM) and neutral zone to <50% (without muscles=100%) was observed. With increasing injury the normalized ROM (intact condition=100%) increased with and without muscles approximately to the same extend. With bilateral injury this increase was 125-132% in lateral bending, 112%-119% in flexion-extension and 103-116% in axial rotation. Mechanically simulated cervical spine muscles strongly stabilized intact and injured cervical spine specimens. Nevertheless, it could be shown that in vitro flexibility tests without muscle force simulation do not necessarily lead to an overestimation of spinal instability if the results are normalized to the intact state.     

Gender dependent cervical spine segmental kinematics during whiplash

Clinical and epidemiological studies have frequently reported that female occupants sustain whiplash injuries more often than males. The current study was based on the hypothesis that segmental level-by-level cervical intervertebral motions in females are greater than in males during rear impact. The hypothesis was tested by subjecting 10 intact human cadaver head-neck complexes (five males, five females) to rear impact loading. Intervertebral kinematics were analyzed as a function of spinal level at the time of maximum cervical S-curve, which occurred during the loading phase. Segmental angles were significantly greater (p<0.05) in female specimens at C2-C3, C4-C5, C5-C6, and C6-C7 levels. Because greater angulations are associated with stretch in the innervated components of the cervical spinal column, these findings may offer a biomechanical explanation for the higher incidence of whiplash-related complaints in female patients secondary to rear impact acceleration.     

In vivo three-dimensional intervertebral kinematics of the subaxial cervical spine during seated axial rotation and lateral bending via a fluoroscopy-to-CT registration approach

Accurate measurement of the coupled intervertebral motions is helpful for understanding the etiology and diagnosis of relevant diseases, and for assessing the subsequent treatment. No study has reported the in vivo, dynamic and three-dimensional (3D) intervertebral motion of the cervical spine during active axial rotation (AR) and lateral bending (LB) in the sitting position. The current study fills the gap by measuring the coupled intervertebral motions of the subaxial cervical spine in ten asymptomatic young adults in an upright sitting position during active head LB and AR using a volumetric model-based 2D-to-3D registration method via biplane fluoroscopy. Subject-specific models of the individual vertebrae were derived from each subject’s CT data and were registered to the fluoroscopic images for determining the 3D poses of the subaxial vertebrae that were used to obtain the intervertebral kinematics. The averaged ranges of motion to one side (ROM) during AR at C3/C4, C4/C5, C5/C6, and C6/C7 were 4.2°, 4.6°, 3.0° and 1.3°, respectively. The corresponding values were 6.4°, 5.2°, 6.1° and 6.1° during LB. Intervertebral LB (ILB) played an important role in both AR and LB tasks of the cervical spine, experiencing greater ROM than intervertebral AR (IAR) (ratio of coupled motion (IAR/ILB): 0.23–0.75 in LB, 0.34–0.95 in AR). Compared to the AR task, the ranges of ILB during the LB task were significantly greater at C5/6 (p=0.008) and C6/7 (p=0.001) but the range of IAR was significantly smaller at C4/5 (p=0.02), leading to significantly smaller ratios of coupled motions at C4/5 (p=0.0013), C5/6 (p<0.001) and C6/7 (p=0.0037). The observed coupling characteristics of the intervertebral kinematics were different from those in previous studies under discrete static conditions in a supine position without weight-bearing, suggesting that the testing conditions likely affect the kinematics of the subaxial cervical spine. While C1 and C2 were not included owing to technical limitations, the current results nonetheless provide baseline data of the intervertebral motion of the subaxial cervical spine in asymptomatic young subjects under physiological conditions, which may be helpful for further investigations into spine biomechanics.