Moment arms of the human neck muscles in flexion, bending and rotation

There is a paucity of data available for the moment arms of the muscles of the human neck. The objective of the present study was to measure the moment arms of the major cervical spine muscles in vitro. Experiments were performed on five fresh-frozen human head-neck specimens using a custom-designed robotic spine testing apparatus. The testing apparatus replicated flexion-extension, lateral bending and axial rotation of each individual intervertebral joint in the cervical spine while all other joints were kept immobile. The tendon excursion method was used to measure the moment arms of 30 muscle sub-regions involving 13 major muscles of the neck about all three axes of rotation of each joint for the neutral position of the cervical spine. Significant differences in the moment arm were observed across sub-regions of individual muscles and across the intervertebral joints spanned by each muscle (p<0.05). Overall, muscle moment arms were larger in flexion-extension and lateral bending than in axial rotation, and most muscles had prominent moment arms in at least 2 out of the 3 joint motions investigated. This study emphasizes the importance of detailed representation of a muscle's architecture in prediction of its torque capacity about the individual joints of the cervical spine. The dataset produced may be useful in developing and validating computational models of the human neck.     

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.     

Artificial Cervical Vertebra and Intervertebral Complex Replacement through the Anterior Approach in Animal Model: A Biomechanical and In Vivo Evaluation of a Successful Goat Model

This was an in vitro and in vivo study to develop a novel artificial cervical vertebra and intervertebral complex (ACVC) joint in a goat model to provide a new method for treating degenerative disc disease in the cervical spine. The objectives of this study were to test the safety, validity, and effectiveness of ACVC by goat model and to provide preclinical data for a clinical trial in humans in future. We designed the ACVC based on the radiological and anatomical data on goat and human cervical spines, established an animal model by implanting the ACVC into goat cervical spines in vitro prior to in vivo implantation through the anterior approach, and evaluated clinical, radiological, biomechanical parameters after implantation. The X-ray radiological data revealed similarities between goat and human intervertebral angles at the levels of C2-3, C3-4, and C4-5, and between goat and human lordosis angles at the levels of C3-4 and C4-5. In the in vivo implantation, the goats successfully endured the entire experimental procedure and recovered well after the surgery. The radiological results showed that there was no dislocation of the ACVC and that the ACVC successfully restored the intervertebral disc height after the surgery. The biomechanical data showed that there was no significant difference in range of motion (ROM) or neural zone (NZ) between the control group and the ACVC group in flexion-extension and lateral bending before or after the fatigue test. The ROM and NZ of the ACVC group were greater than those of the control group for rotation. In conclusion, the goat provides an excellent animal model for the biomechanical study of the cervical spine. The ACVC is able to provide instant stability after surgery and to preserve normal motion in the cervical spine.     

四个节段以上伴椎间不稳颈椎病手术治疗的分析

目的:分析四个节段以上同时伴有椎间不稳的多节段颈椎病的手术入路及手术方法。方法:回顾性分析2008年10月-2012年12月收治的符合入选标准的颈椎病患者64例,其中A组33例,采用传统颈前路分节段开窗减压植骨内固定术;B组31例,采用改良颈后路单开门椎管减压轴侧植骨Arch钛板内固定术。采用日本矫形外科学会(JOA)评分标准和疼痛视觉模拟(VAS)评分标准对患者术后疗效进行评价,并对两组患者的术中出血量、手术时间、住院日数、颈椎活动度、颈椎曲度进行比较。结果:所有患者手术均顺利,A组患者的手术时间为(150.7±30.3)min,B组为(90.8±22.2)min,较A组明显缩短,差异具有统计学意义(P0.05)。A组患者的术中失血量为(320±50)m L,B组为(180±45)m L,较A组明显减少,差异具有统计学意义(P0.05)。此外,B组患者的住院时间显著短于短于A组(P0.05)。两组患者术后切口均I期愈合,出院时JOA评分及VAS评分均较术前明显改善(P0.05)。出院后6个月时,A组患者的Ishihara指数较术前显著改善(2.2±1.6),而B组无明显改善,A、B两组比较差异具有统计学意义(P0.05);A组患者的活动度丢失(4.2±3.3)°,B组活动度丢失(4.0±2.9)°,两组比较差异无统计学意义(t=0.26,P0.05)。结论:颈前路及颈后路手术方式治疗四个节段以上伴有椎间不稳颈椎病的患者均可获得理想的临床疗效,但颈后路手术方式的手术时间短,术中出血量少,住院周期短,安全性高,适应症广,是治疗四个节段以上颈椎病伴椎间不稳首选的手术方式。     

Determination of patient-specific multi-joint kinematic models through two-level optimization

Dynamic patient-specific musculoskeletal models have great potential for addressing clinical problems in orthopedics and rehabilitation. However, their predictive capability is limited by how well the underlying kinematic model matches the patient's structure. This study presents a general two-level optimization procedure for tuning any multi-joint kinematic model to a patient's experimental movement data. An outer level optimization modifies the model's parameters (joint position and orientations) while repeated inner level optimizations modify the model's degrees of freedom given the current parameters, with the goal of minimizing errors between model and experimental marker trajectories. The approach is demonstrated by fitting a 27 parameter, three-dimensional, 12 degree-of-freedom lower-extremity kinematic model to synthetic and experimental movement data for isolated joint (hip, knee, and ankle) and gait (full leg) motions. For noiseless synthetic data, the approach successfully recovered the known joint parameters to within an arbitrarily tight tolerance. When noise was added to the synthetic data, root-mean-square (RMS) errors between known and recovered joint parameters were within 10.4 degrees and 10 mm. For experimental data, RMS marker distance errors were reduced by up to 62% compared to methods that estimate joint parameters from anatomical landmarks. Optimized joint parameters found using a loaded full-leg gait motion differed significantly from those found using unloaded individual joint motions. In the future, this approach may facilitate the creation of dynamic patient-specific musculoskeletal models for predictive clinical applications.     

Biomechanical study of pediatric human cervical spine: a finite element approach

Although considerable effort has been made to understand the biomechanical behavior of the adult cervical spine, relatively little information is available on the response of the pediatric cervical spine to external forces. Since significant anatomical differences exist between the adult and pediatric cervical spines, distinct biomechanical responses are expected. The present study quantified the biomechanical responses of human pediatric spines by incorporating their unique developmental anatomical features. One-, three-, and six-year-old cervical spines were simulated using the finite element modeling technique, and their responses computed and compared with the adult spine response. The effects of pure overall structural scaling of the adult spine, local component developmental anatomy variations that occur to the actual pediatric spines, and structural scaling combined with local component anatomy variations on the responses of the pediatric spines were studied. Age- and component-related developmental anatomical features included variations in the ossification centers, cartilages, growth plates, vertebral centrum, facet joints, and annular fibers and nucleus pulposus of the intervertebral discs. The flexibility responses of the models were determined under pure compression, pure flexion, pure extension, and varying degrees of combined compression-flexion and compression-extension. The pediatric spine responses obtained with the pure overall (only geometric) scaling of the adult spine indicated that the flexibilities consistently increase in a uniform manner from six- to one-year-old spines under all loading cases. In contrast, incorporation of local anatomic changes specific to the pediatric spines of the three age groups (maintaining the same adult size) not only resulted in considerable increases in flexibilities, but the responses also varied as a function of the age of the pediatric spine and type of external loading. When the geometric scaling effects were added to these spines, the increases in flexibilities were slightly higher; however, the pattern of the responses remained the same as found in the previous approach. These results indicate that inclusion of developmental anatomical changes characteristic of the pediatric spines has more of a predominant effect on biomechanical responses than extrapolating responses of the adult spine based on pure overall geometric scaling.     

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.     

CINERADIOGRAPHIC STUDIES OF THE NORMAL CERVICAL SPINE

By considering the cervical spine as several segments with relatively different motions, an understanding of the total possible motions of the cervical spine can be more easily attained.Reversal of the cervical lordosis is a normal part of the flexion action and can result from positioning of the patient for radiographic studies.The effect of standing or sitting postures, and methods of initiating flexion of the neck should be considered in the evaluation of routine flexion and extension studies.Evaluation of individual cervical segments may be accomplished by the use of different methods of initiating flexion.     

Comparison of the anatomical morphology of cervical vertebrae between humans and macaques: related to a spinal cord injury model

Non-human primates are most suitable for generating cervical experimental models, and it is necessary to study the anatomy of the cervical spine in non-human primates when generating the models. The purpose of this study was to provide the anatomical parameters of the cervical spine and spinal cord in long-tailed macaques (Macaca fascicularis) as a basis for cervical spine-related experimental studies. Cervical spine specimens from 8 male adult subjects were scanned by micro-computed tomography, and an additional 10 live male subjects were scanned by magnetic resonance imaging. The measurements and parameters from them were compared to those of 12 male adult human subjects. Additionally, 10 live male subjects were scanned by magnetic resonance imaging, and the width and depth of the spinal cord and spinal canal and the thickness of the anterior and posterior cerebrospinal fluid were measured and compared to the relevant parameters of 10 male adult human subjects. The tendency of cervical parameters to change with segmental changes was similar between species. The vertebral body, spinal canal, and spinal cord were significantly flatter in the human subjects than in the long-tailed macaques. The cerebrospinal fluid space in the long-tailed macaques was smaller than that in the human subjects. The anatomical features of the cervical vertebrae of long-tailed macaques provide a reference for establishing a preclinical model of cervical spinal cord injury.     

Model-guided derivation of lumbar vertebral kinematics in vivo reveals the difference between external marker-defined and internal segmental rotations

This study investigated whether the external marker-defined spine inter-segmental rotation is different from the internal vertebral rotation, and explored how to estimate the latter from limited surface measurement. A kinematic model was first created to elucidate analytically the relation between the external and internal rotations. A novel approach guided by the model was proposed for deriving vertebral centers of rotation (CORs) from measured planar trajectories of skin-surface markers. The approach involved a recursive procedure for establishing local (anatomical) coordinate systems, and an optimization routine that identified the maximum-likelihood circles best fitting the marker trajectories in local coordinate systems. An experiment with 10 subjects (5 males and 5 females) was conducted to test the approach along with the model. Skin-surface markers were strategically placed over individual spinous processes and other body landmarks, and recorded by an opto-electronic system while sagittally symmetric load-lifting movements were being performed. For the majority (89%) of measured motions, the COR locations for lumbar vertebrae (L2-L5) were derived successfully: solutions resulting from the optimization routine met a convergence criterion governed by the model, and were in agreement with existing data from radiographic or cadaveric studies. Empirical results confirmed the differences between the external marker-defined inter-segmental motions and corresponding internal vertebral rotations (1.1-5.8 degrees on average, all statistically significant). The study demonstrated the necessity and viability of quantifying internal vertebral kinematics when utilizing non-invasive marker-based measurement for spine-related clinical diagnosis and biomechanical modeling.     

A multi-body model for comparative study of cervical traction simulation – development,improvement and validation

A computer simulation model was developed to study the dynamic behavior of the cervical spine during cervical traction therapy in inclined and sitting traction positions. The model improved upon an old model with additional components to represent the behavior of the intervertebral discs and the posterior ligaments. The simulation result of the new model was compared against the cervical traction data from a radiographic experiment in both positions. The simulation results of the old model and new model were compared to illustrate the improvement. Using the new model, we compared the timing response of cervical traction in the inclined and sitting positions.     

哈萨克族成人腰稚间盘高度的放射学测量及其临床意义

目的：为人工椎间盘的设计提供形态学依据。方法：对56例哈萨克族成人腰椎（L）间盘高度进行放射学测量。结果：56例哈萨克族L1-2椎间盘高度男女性之间差异无统计学意义（P〉0．05）,L3-5椎间盘高度男、女性之间差异有统计学意L（P〈0．005-0．001）;哈萨克族与汉族腰椎间盘高度之间差异均有统计学意义（P〈0．005）。结论：哈萨克族腰椎间盘高度均大于汉族,临床上可通过对腰椎间盘间高度的测量,为人工椎间盘假体设计提供参数．     

Cervical spine vertebral and facet joint kinematics under whiplash.

Whiplash injuries sustained during a rear-end automobile collision have significant societal impact. The scientific literature on whiplash loading is both diverse and confusing. Definitive studies are lacking to describe the local mechanisms of injury that induce either acute or chronic pain symptoms. A methodology has been presented to quantify the kinematics of the cervical spine components by inducing controlled whiplash-type forces to intact human head-neck complexes. The localized facet joint kinematics and the overall segmental motions of the cervical spine are presented. It is anticipated that the use of this methodology will assist in a better delineation of the localized mechanisms of injury leading to whiplash pain.     

应用反向滤过及迭代重建方法评估标准放射剂量与低剂量颈椎 CT图像质量的对比研究

目的：利用反向滤过重建（filtered back-projection,FBP）及迭代重建（iterative reconstruction,IR）方法评估标准剂量及低剂量 对颈椎CT 图像质量的影响。方法：40 例受检对象行颈椎CT 检查,将其随机分为两组：标准剂量组（SD,120 kVp, 275 mAs）及低 剂量组（LD,120 kVp,150 mAs）,随机选择管电流值,所有数据均行FBP 及IR 重建。测量C3 C4 及C6 C7 椎间盘水平椎间盘、脊 神经、脊髓、韧带以及周围软组织的图像噪声值（Image noise,IN）,信噪比（signal-to-noise,SNR）及对比信噪比（contrast-to-noise, CNR）。结果：在测量的各椎间盘水平,迭代重建的信噪比及对比噪声比要明显高于反向滤过重建方法,并有效的降低了图像噪 声。低剂量迭代重建图像与标准剂量反向滤过图像相比无明显统计学意义。排除剂量及扫描层面的影响,椎间盘、脊神经及韧带 的图像质量,迭代重建评分要明显高于反向滤过重建,结果具有统计学差异;而低剂量迭代重建图像质量评分与标准剂量反向滤 过重建相比无明显差异。软组织及椎体的图像质量,迭代重建图像质量评分要低于反向滤过重建方法,结果具有统计学差异;而 低剂量迭代重建图像质量评分与标准剂量反向滤过重建相比无明显差异。整体病例图像质量评分,迭代重建方法要高于反向滤 过重建方法,低剂量迭代重建方法要高于标准剂量反向滤过重建方法。结论：应用低剂量扫描方式以及迭代重建方法进行颈椎 CT 检查可以为临床提供较好的图像质量,对于椎间盘、脊神经、脊髓显示较好,对于周围软组织以及椎体来说,图像质量相对较 差,同时可以降低大约40%的放射剂量。     

The effect of axial compression and distraction on cervical facet mechanics during anterior shear,flexion, axial rotation,and lateral bending motions

The subaxial cervical facets are important load-bearing structures, yet little is known about their mechanical response during physiological or traumatic intervertebral motion. Facet loading likely increases when intervertebral motions are superimposed with axial compression forces, increasing the risk of facet fracture. The aim of this study was to measure the mechanical response of the facets when intervertebral axial compression or distraction is superimposed on constrained, non-destructive shear, bending and rotation motions. Twelve C6/C7 motion segments (70 ± 13 yr, nine male) were subjected to constrained quasi-static anterior shear (1 mm), axial rotation (4°), flexion (10°), and lateral bending (5°) motions. Each motion was superimposed with three axial conditions: (1) 50 N compression; (2) 300 N compression (simulating neck muscle contraction); and, (3) 2.5 mm distraction. Angular deflections, and principal and shear surface strains, of the bilateral C6 inferior facets were calculated from motion-capture data and rosette strain gauges, respectively. Linear mixed-effects models (α = 0.05) assessed the effect of axial condition. Minimum principal and maximum shear strains were largest in the compressed condition for all motions except for maximum principal strains during axial rotation. For right axial rotation, maximum principal strains were larger for the contralateral facets, and minimum principal strains were larger for the left facets, regardless of axial condition. Sagittal deflections were largest in the compressed conditions during anterior shear and lateral bending motions, when adjusted for facet side.     

应用反向滤过及迭代重建方法评估标准放射剂量与低剂量颈椎CT图像质量的对比研究

目的：利用反向滤过重建（filtered back-projecfion,FBP）及迭代重建（iterative reconstruction,IR）方法评估标准剂量及低剂量对颈椎CT图像质量的影响。方法：40例受检对象行颈椎CT检查,将其随机分为两组：标准剂量组（SD,120kVp,275mAs）及低剂量组（LD,120kVp,150mAs）,随机选择管电流值,所有数据均行FBP及IR重建。测量C3C4及C6C7椎间盘水平椎间盘、脊神经、脊髓、韧带以及周围软组织的图像噪声值（Imagenoise,IN）,信噪比（signal—to—noise,SNR）及对比信噪比（contrast—to—noise,CNR）。结果：在测量的各椎间盘水平,迭代重建的信噪比及对比噪声比要明显高于反向滤过重建方法,并有效的降低了图像噪声。低剂量迭代重建图像与标准剂量反向滤过图像相比无明显统计学意义。排除剂量及扫描层面的影响,椎间盘、脊神经及韧带的图像质量,迭代重建评分要明显高于反向滤过重建,结果具有统计学差异;而低剂量迭代重建图像质量评分与标准剂量反向滤过重建相比无明显差异。软组织及椎体的图像质量,迭代重建图像质量评分要低于反向滤过重建方法,结果具有统计学差异;而低剂量迭代重建图像质量评分与标准剂量反向滤过重建相比无明显差异。整体病例图像质量评分,迭代重建方法要高于反向滤过重建方法,低剂量迭代重建方法要高于标准剂量反向滤过重建方法。结论：应用低剂量扫描方式以及迭代重建方法进行颈椎CT检查可以为I临床提供较好的图像质量,对于椎间盘、脊神经、脊髓显示较好,对于周围软组织以及椎体来说,图像质量相对较差,同时可以降低大约40％的放射剂量。     

Evaluation of Euler's angles with a least squares method for the study of lumbar spine motion

To analyse intervertebral movements, methods with a high level of accuracy are required. Stereoradiographic methods have been used for a number of years to describe intervertebral movements, but their major problem is to identify the same anatomical landmarks, not only on the pair of radiographs used for three-dimensional reconstruction, but also on all the pairs used to analyse the displacements. To minimize the errors due to the incorrect identification of anatomical landmarks, a least squares method to resolve the parameters of Euler's angles was validated by means of measurements made on a spine obtained from a cadaver. The accuracy of this method varied between 0.69° and 0.71° in rotation and between 0.28 mm and 0.77 mm in translation. In addition, this method significantly corrected the position of the anatomical landmarks. Euler's angles, used with a least squares estimate, can provide accurate and precise results.