The impact of total lumbar disc replacement on segmental and total lumbar lordosis

BACKGROUND: One of the goals of total lumbar disc replacement is restoration of the physiological sagittal alignment. There is little evidence if this goal is reached in vivo and further affects the clinical outcome. METHODS: In 29 patients segmental lordosis and total lumbar lordosis were measured on X-rays pre- and postoperatively. The functional outcome was evaluated prospectively with the Visuell Analogue Scale, Oswestry Low Back Pain Disability Questionnaire and Short Form 36 Health Survey Questionnaire. FINDINGS: Total disc replacement increased segmental lordosis significantly while total lumbar lordosis remained unchanged. Preoperative segmental/total lumbar lordosis was physiological in 52%/91% of the patients. Postoperatively these values changed to 72% for segmental- and 94% for total lumbar lordosis. No difference could be observed in clinical outcome measures in patients with physiological and unphysiological segmental lordosis. INTERPRETATION: Monosegmental total disc replacement increases the segmental lordosis in most of the cases while preserving the total lumbar lordosis which produces a decrease of lordotic angle in the adjacent segment(s). Although short term clinical results are not affected, the segmental lordosis increase and adjacent segment(s) alteration may influence long term outcome.     

Movements in the lumbar spine during exercises of the upper extremities. A roentgenologic study in para- and tetraplegic patients.

Strengthening exercises during treatment of patients with unstable lumbar fractures produce a kyphotic or lordotic sagittal movement in the lumbar spine. These movements have been measured roentgenologically. Forward flexion exercises in the shoulder joints to 45 degrees produced a kyphotic movement, while forward flexion to 110 degrees and abduction exercises to 90 degrees produced a lordotic movement. Flexion of hips and knees to 45 degrees produced a kyphotic movement adding to the movements caused by the shoulder exercises. Increasing the load on the upper extremities produced an increase of all movements.     

单节段腰椎活动度对邻近节段运动的影响

背景：有研究报道腰椎融合后其邻近节段运动范围和压力会明显增大;但也有报道腰椎融合与动态固定非融合或正常腰椎相比,其邻近节段运动范围和压力未见明显增加,甚至出现减少。然而,腰椎的活动度多少到底对邻近节段会有什么影响呢？目的：观察单节段腰椎不同范围活动度对邻近关节运动范围的影响。方法：取6具新鲜成人L2～S2腰椎标本,依次对成人L4～L5椎体进行不同方式处理形成5种不同活动度状态：完整标本状态;部分失稳状态;动态固定状态;完全失稳状态;刚性固定状态。在脊柱三维运动试验机上,采用＂载荷控制＂法进行屈伸、侧弯和旋转等运动方向测试,分别将其他4个状态与完整标本状态进行比较。结果与结论：处理节段L4～L5椎体在各处理状态的下运动范围明显不同,形成了完全不同范围的活动度。与完整标本状态相比较,其他4个状态旋转时,上方邻近节段L3～L4的运动范围在刚性固定状态下明显减少;下方邻近节段L5～S1各方向和上方邻近节段L3～L4其余方向的运动范围无显著性差异。单节段腰椎刚性固定状态下,整个脊柱标本的运动范围明显减少。说明在＂载荷控制＂方法的实验下,单节段腰椎活动度多少对邻近节段的屈伸、侧弯等运动范围影响不明显,对上方邻近节段的旋转运动范围影响较大;腰椎刚性固定融合后,不一定要恢复到正常腰椎的活动范围,也许对预防邻近节段病有利。     

Precision measurement of segmental motion from flexion-extension radiographs of the lumbar spine

OBJECTIVE: To measure sagittal plane motion of lumbar vertebrae from lateral radiographic views. Previously identified factors of imprecision such as distortion in central projection, off-centre position, axial rotation, and lateral tilt of the spine were compensated. STUDY DESIGN: This study presents a new protocol to measure sagittal plane rotational and translational motion from lateral flexion-extension radiographs of the lumbar spine. BACKGROUND: Conventional methods to determine sagittal plane rotation and translation are prone to error from the distortional effects of the divergence of the radiographic beam and the measurement error inherent in constructing tangents to the contours of the vertebral body. High precision is attained by roentgen-stereophotogrammetric methods, but because of their invasive nature they can be applied only in exceptional cases. Agreement has been reached only in that measurement of sagittal plane motion from lumbar spine flexion-extension radiographs is inaccurate. Normal patterns of sagittal plane motion and the definition of what is an abnormal flexion-extension radiograph have not been settled. METHOD: Starting from an analysis of vertebral contours in the lateral view, geometric measures are identified which are virtually independent of distortion, axial rotation or lateral tilt. Applying a new protocol based on those geometric measures, the pattern of translational and rotational motion was determined from flexion-extension radiographs of 61 symptom-free, adult subjects. Measurement errors were quantified in a specimen experiment; a reproducibility study quantified inter- and intraobserver errors. RESULTS: Magnitude and sign of 'translation per degree of rotation' determined from a cohort of 61 adult subjects were very uniform for all levels of the lumbar spine. An auxiliary study evaluating a cohort of 10 healthy subjects where flexion-extension radiographs had been taken standing and side-lying showed no dependence of the rotation/translation pattern on posture. The error study demonstrated errors in angle ranging between 0.7 and 1.6 degrees and errors in displacement ranging between 1.2% and 2.4% of vertebral depth (the largest errors occurring at the L(5)/S(1) segment). Intra- and interobserver tests showed no or only negligibly small bias and an SD virtually equal to the measurement error multiplied by radical2. The relation of displacement to angle observed in the normal cohort can be used in individual cases to predict translational motion depending on the rotation actually performed. A comparison of the predicted translation (determined from normal controls) and the value actually measured allows translational hypo-, normal, or hypermobility to be quantified. Examples illustrate application of the new method in cases of normal, hypo-, and hypermobility and in the case of an instrumented spine. CONCLUSIONS: The results of this study show that precision of the measurement of rotational and translational motion can be considerably enhanced by making allowance for radiographic distortional effects and by minimizing subjective influence in the measurement procedure.     

Correction of thoracic kyphosis and lumbar lordosis in the treatment of idiopathic scoliosis treatment with Cotrel-Dubousset instrumentation

Background. The treatment of thoracic kyphosis and lumbar lordosis with the C-D method remains controversial. Material and methods. The lateral radiographs of 70 patients with King I, II, III, IV idiopathic scoliosis, treated with C-D instrumentation, were retrospectively analyzed. The average age was 14 +/- 1.8 years. Thoracic kyphosis between T2 and T12 and lumbar lordosis between L1 and L5 were measured. Results. Normalization of thoracic kyphosis occurred in 15 of the 22 hypokyphosis patients. The largest kyphosis correction (average +12 +/- 8 degrees ) was in the preoperative hypokyphosis group. A deep hyperkyphosis (average 64 degrees ) was found preoperatively in patients with postoperative hyperkyphosis. Kyphosis correction in the instrumented region was often reverse to the uninstrumented region correction. Lumbar lordosis remained normal in 29 (63%) and hypolordosis occurred in 14 (31%) of the 45 patients with normal preoperative lordosis. When instrumentation below L1 was performed, a greater decrease in lumbar lordosis was observed. Conclusions. The C-D method enables good kyphosis and lordosis correction in scoliotic patients, but problems may occur in greater deformities. Longer lumbar instrumentation may result in decreased lumbar lordosis.     

一种基于影像特征经皮椎体成形术生物力学稳定性评估的有限元模型

背景: 生物力学研究表明椎体成形术在注入骨水泥后单个骨质疏松椎体的硬度和强度有很大的增长, 但对于保持椎体力学稳定性所需骨水泥的体积和其注入位置还有待进一步研究。目的: 通过参数有限元模型比较椎体成形手术腰椎 L1- L2 的生物力学稳定性评估椎体成形术的有效性。设计: 非随机对照观察。单位: 北京神经外科研究所。材料: 选择 1 例 54 岁女性骨质疏松性导致腰椎 L1- L2 压缩性骨折患者, 经 CT 确诊, 该患者对实验项目知情同意。通过椎体成形手术前后CT 扫描, 分别得到了各 90 张连续切片, 层厚 1 mm, 每个像素的尺寸是 0.33 mm。方法: 实验于 2005- 10/2006- 06 在北京神经外科研究所完成。①三维有限元模型的创建: 通过整合 CT 和 MRI 图像的解剖结构, 建立了一种腰椎功能性脊椎单元的三维几何模型, 基于该几何模型对搜集到 90 张连续 CT 切片数据进行转换并对图像进行分割, 创建两种分别表示患者通过椎体成形手术前后的 L1～2 段椎体三维有限元模型。②模型评估: 在模型 L1 椎体的上表面分别施加 500,1 000,1 500,2 000,2 500 N 的轴向负载,观察有限元模型腰椎 L1～2 段的位移、应力、应变的分布变化情况; 观察骨水泥体积的增加对有限元椎体模型位移、应力、应变的分布的影响。主要观察指标: ①不同负载下有限元模型腰椎 L1～2 段的位移、应力、应变的分布变化情况。②骨水泥体积的增加对有限元椎体模型位移、应力、应变的分布的影响。结果: ①在轴向负载下 L1～2 段的应力应变随着负载的增大而增大, 在椎间盘的右侧部有很大的应力应变集中。而这一区域也是在负载情况下经常发生损伤的部位。在椎间盘上应力的大小取决于应用于椎体单元负载的大小。负载越大, 应力越大。②通过椎间盘上接触应力的增加, 随着骨水泥体积的增加导致了临近椎体的负载转移。结论: 建立了椎体成形手术前后 L1～2 段椎体三维有限元模型, 在有限元模型上计算腰椎 L1～2 相对位移可以说明椎体三维的生理状态。这一仿真计算也能清楚地显示椎体应力应变的分布和术前术后的变形。     

Comparison of axial and flexural stresses in lordosis and three buckled configurations of the cervical spine

OBJECTIVE: To calculate and compare combined axial and flexural stresses in lordosis versus buckled configurations of the sagittal cervical curve. DESIGN: Digitized measurements from lateral cervical radiographs of four different shapes were used to calculate axial loads and bending moments on the vertebral bodies of C2-C7.Background. Osteoarthritis and spinal degeneration are factors in neck and back pain. Calculations of stress in clinically occurring configurations of the sagittal cervical spine are rare. METHODS: Center of gravity of the head (inferior-posterior sella turcica) and vertebral body margins were digitized on four different lateral cervical radiographs: lordosis, kyphosis, and two "S"-shapes. Polynomials (seventh degree) and stress concentrations on the concave and convex margins were derived for the shape of the sagittal cervical curvatures from C1 to T1. Moments of inertia were determined from digitizing and the use of an elliptical shell model of cross-section. Moment arms from a vertical line through the center of gravity of the head to the atlas and scaled neck extensor moment arms from the literature were used to compute the vertical component of extensor muscle effort. Segmental lever arms were calculated from a vertical line through C1 to each vertebra. RESULTS: In lordosis, anterior and posterior stresses in the vertebral body are nearly uniform and minimal. In kyphotic areas, combined stresses changed from tension to compression at the anterior vertebral margins and were very large (6-10 times as large in magnitude) compared to lordosis. In kyphotic areas at the posterior vertebral body, the combined stresses changed from compression (in lordosis) to tension. CONCLUSIONS: The stresses in kyphotic areas are very large and opposite in direction compared to a normal lordosis. This analysis provides the basis for the formation of osteophytes (Wolff's Law) on the anterior margins of vertebrae in kyphotic regions of the sagittal cervical curve. This indicates that any kyphosis is an undesirable configuration in the cervical spine. Relevance. Osteophytes and osteoarthritis are found at areas of altered stress and strain. Axial and flexural stresses at kyphotic areas in the sagittal cervical spine are abnormally high.     

Strain behavior of malaligned cervical spine implanted with metal-on-polyethylene,metal-on-metal,and elastomeric artificial disc prostheses – A finite element analysis

BackgroundPostoperative alterations in cervical spine curvature (i.e. loss of lordotic angle) are frequently observed following total disc replacement surgery. However, it remains unclear whether such changes in lordotic angle are due to preoperative spinal deformities and/or prostheses design limitations. The objective of the study is to investigate strain and segmental biomechanics of the malaligned cervical spine following total disc replacement.MethodsThree disc prostheses were chosen, namely a metal-on-polyethylene, a metal-on-metal, and an elastomeric prosthesis, which feature different geometrical and material design characteristics. All discs were modelled and implanted into multi-segmental cervical spine finite element model (C3-C7) with normal, straight and kyphotic alignments. Comparative analyses were performed by using a hybrid protocol.FindingsThe results indicated that as the spine loses lordotic alignment, the prosthesis with elastomeric core tends to produce significantly larger flexion range of motion (difference up to 6.1°) than metal-on-polyethylene and metal-on-metal prostheses. In contrast, when the treated spine had normal lordotic alignment, the range of motion behaviors of different prostheses are rather similar (difference within 1.9°). Large localized strains up to 84.8% were found with the elastomeric prosthesis, causing a collapsed anterior disc space under flexion loads.InterpretationChanges in cervical spinal alignments could significantly affect the surgical-level range of motion behaviors following disc arthroplasty; the in situ performance was largely dependent on the designs of the artificial disc devices in particular to the material properties.     

矢向轴动态椎弓根钉棒系统固定腰椎失稳有限元分析

[目的]利用有限元方法对矢向轴动态椎弓根钉棒内固定系统固定腰椎失稳模型的生物力学特性进行评价,为此动态内固定系统临床应用提供生物力学基础和理论依据.[方法]采用预先获取的健康成年中国男性志愿者的腰椎CT数据建立腰椎正常模型及L4,5失稳模型.根据矢向轴动态椎弓根钉棒系统和坚强椎弓根钉棒系统的材料参数计算和构建有限元模型,并将其导入已通过验证的腰椎失稳模型,分别构建L4,5单节段动态固定模型和坚强固定模型.约束L5椎体下终板,在轴向500N载荷和10N·m力矩下分别模拟人体腰椎正常生理轴向载荷、前屈、后伸、侧弯和旋转五种工况,分别记录4种模型轴向载荷工况下L4,5轴向位移及后四种工况下L4,5固定节段及L3,4邻近节段活动度、椎间盘应力、邻近节段小关节的应力和器械应力,并进行分析比较.[结果]矢向轴动态椎弓根钉棒系统固定失稳腰椎可让固定节段椎间关节留有大于坚强固定组、小于完整脊柱组运动范围的适当活动度,对邻近节段腰椎活动度的影响也小于坚强固定组,同时固定节段椎间盘应力较坚强固定组大,器械应力却小于坚强椎弓根钉棒系统,邻近节段腰椎间盘及椎间小关节应力也小于坚强固定组.[结论]应用矢向轴动态椎弓根钉棒系统固定失稳腰椎,既保留了腰椎固定节段适当活动性,又能提供即刻的稳定性;同时该系统与脊柱合力承担载荷,能有效避免因术后应力遮挡及器械应力集中引起的内固定失效等并发症;它也能降低邻近节段椎间盘及椎间关节的应力,对邻近节段腰椎活动度影响也较坚强固定小,理论上有利于减少和预防邻近节段退变.     

Thoracolumbar And Lumbopelvic Spinal Alignment During The Deadlift Exercise: A Comparison Between Men And Women

BackgroundA neutral spinal alignment is considered important during the execution of the deadlift exercise to decrease the risk of injury. Since male and female powerlifters experience pain in different parts of their backs, it is important to examine whether men and women differ in spinal alignment during the deadlift.ObjectivesThe purpose of this study was to quantify the spinal alignment in the upper (thoracolumbar, T11-L2) and lower (lumbopelvic, L2-S2) lumbar spine during the deadlift exercise in male and female lifters. Secondary aims were to compare lumbar spine alignment during the deadlift to standing habitual posture, and determine whether male and female lifters differ in these aspects.Study DesignObservational, Cross-sectional.MethodsTwenty-four (14 men, 10 women) lifters performed three repetitions of the deadlift exercise using 70% of their respective one-repetition maximum. Spinal alignment and spinal range of motion were measured using three inertial measurement units placed on the thoracic, lumbar and sacral spine. Data from three different positions were analyzed; habitual posture in standing, and start and stop positions of the deadlift, i.e. bottom and finish position respectively.ResultsDuring the deadlift, spinal adjustments were evident in all three planes of movement. From standing habitual posture to the start position the lumbar lordosis decreased 13° in the upper and 20° in the lower lumbar spine. From start position to stop position the total range of motion in the sagittal plane was 11° in the upper and 22° in the lower lumbar spine. The decreased lumbar lordosis from standing habitual posture to the start position was significantly greater among men.ConclusionsMen and women adjust their spinal alignment in all three planes of movement when performing a deadlift and men seem to make greater adjustments from their standing habitual posture to start position in the sagittal plane.Level of Evidence3     

Predictive model of intersegmental mobility of lumbar spine in the sagittal plane from skin markers

This article describes a sagittal motion model that transforms skin marker coordinates into corresponding vertebral body coordinates. Coordinate data were obtained from 45 subjects with radiopaque skin markers over the vertebral spinous processes. Data of 30 subjects were used for model development while data of the other Fifteen subjects were used for model validation. The subjects were subjected to lateral spinal radiographs in positions of neutral, flexion, and extension. The model was developed by taking the non-linear difference between lumbar spinal profile and skin profile, the L₄ skin-fold, and the difference of L₁-S₁ skin distraction into consideration. Regression analysis shows high coefficients of determination (range, 62.43–99.86%; mean, 86.41%) in comparing the estimated position data with the actual data in all vertebral body positions. Based on the estimated coordinates, both the intersegmental joint angles and intersegmental joint mobilities were calculated. The result of this study using the non-invasive protocol and the transformation matrices demonstrated that the intersegmental sagittal motion of lumbar spine can be obtained with error ranged from 0.05 to 0.56 degrees.     

Comparison of effects of four interbody fusion approaches on the fused and adjacent segments under vibration

BackgroundWhich lumbar fusion approaches having fewer impacts on the lumbar spine, reducing the risk of complications and the most conducive to bone fusion under whole-body vibration is urgent to know.ObjectivesThis study researched the best approach under vibration by comparing the effects of four different approaches on the spine, especially regarding some significant indexes related to complications and outcomes.MethodsThe L1-L5 finite element model was modified to simulate anterior, posterior, trans-foraminal and direct lateral lumbar interbody fusion approaches with bilateral pedicle screw fixation at L4-L5 level.FindingsAnterior lumbar interbody fusion decreased the corresponding vibration amplitude of the dynamic response at adjacent segments compared with the other three approaches. Direct lateral lumbar interbody fusion decreased the maximum stress in the cage, the endplates at the fused level, and the maximum compressive stress at the interface between the cage and endplates. The maximum disc height and segmental lordosis of Direct lateral lumbar interbody fusion model were the highest among these fusion approaches.InterpretationAnterior lumbar interbody fusion may provide a more stable environment for the adjacent segments under vibration. Direct lateral lumbar interbody fusion may reduce the risk of subsidence, cage failure, and adjacent segment disease. Direct lateral lumbar interbody fusion may provide a more stable and suitable environment for vertebral cell growth and lead to better fusion outcomes. The findings may help us understand the effect of various fusion approaches on lumbar and provide some references for choosing a fusion approach.     

Belt effects on lumbar sagittal angles

OBJECTIVE: The study examined the belt effects on the change of lumbar sagittal angles. DESIGN: The effects of pelvic and lumbar belts on lumbar sagittal angles were examined both radiographically and videographically in standing, erect sitting, and slump sitting. BACKGROUND: The resulting changes of lumbar angles when wearing belts with different mechanical characteristics should be different. METHODS: Eighteen healthy male subjects participated in this study. L1/L3, L3/L5, L5/S1 and L1/S1 were measured with the aid of lateral radiographs. The external joint angles were also measured via the motion analysis system. RESULTS: Radiographic data revealed an interactive effect between working posture and the use of a belt (P<0.046) on the change of L1/S1. In standing, both belts increased L1/S1 by increasing almost all the lumbar vertebral angles. In erect sitting, wearing lumbar belt had no effect but the pelvic belt decreased L1/S1 mainly through a decrease in L1/L3. In sitting slump with trunk flexion of 15 degrees, both belts increased L1/S1 and restricting the movement of the pelvis. CONCLUSIONS: Belt effect to the change of lumbar sagittal angles in posture which involve knee flexing and/or trunk flexing seems not as the same as in standing posture. RELEVANCE: This study related internal vertebral angles and externally measured trunk angles with lumbar and pelvic belt usage.     

Somatic features and parameters of anterior-posterior spinal curvature in 7-year-olds with particular posture types

Background. One of the key elements in the examination and evaluation of body posture is defining the shape and size of anterior-posterior curvature of the spine and the location of symmetrical bone points in the trunk area. The aim of our study was to determine which somatic features and parameters of spinal curvature in the sagittal plane show statistically significant differences among children with given types of body posture. Material and methods. We examined 298 children (146 boys and 152 girls) attending four primary schools in Wroclaw, Poland. The examinations were carried out in specially prepared darkened rooms, using computer equipment to evaluate body posture. Results. The most significant similarities regardless of gender were observed in the inclination of the lumbosacral spine (a) and the angle of thoracic kyphosis, as well as in the size and index of thoracic kyphosis. The highest values in these parameters were found in children with lordotic posture, in whom the lowest values were found in the inclination of the upper thoracic segment (g) and the angle and size of lumbar lordosis. However, in children with kyphotic posture the most significant differences were observed in the length of thoracic kyphosis, and the least significant in the actual length of lumbar lordosis. Conclusions. The size parameters and indexes of anterior-posterior spinal curvature appeared to be the least differentiating factors among posture types. The strongest similarity of posture types was found in somatic features and weight-height ratios.     

脊柱外固定器治疗相邻双节段腰椎骨折的生物力学测试

背景：胸腰椎骨折固定后相邻节段退变发生的一个重要因素是相邻运动节段出现过度活动,导致该节段应力集中,并且相邻节段的头侧较尾侧更容易发生退变,固定节段数量越多,相邻节段的应力越集中,退变概率越大。目的：通过对相邻双节段腰椎爆裂性骨折经皮椎弓根螺钉外固定进行生物力学测试,评价脊柱外固定器的即刻生物力学稳定性以及上位相邻椎体的运动范围退变情况。方法：选取6具新鲜成年猪脊柱标本（T14-S1,猪胸椎共有14个椎体）。每具标本均按以下顺序进行生物力学测试：正常组、骨折组（L3,L4椎体制作成爆裂性骨折模型）、外固定组（L2,L5椎体行脊柱外固定器固定）、内固定组（取出脊柱外固定器后行L2,L5椎体传统开放后路内固定）。测试标本的固定节段（L2-L5）和上位相邻节段（L1）应用跨相邻2伤椎4钉外固定与内固定后的前屈、后伸、侧屈、轴向旋转角位移运动变化。结果与结论：骨折组各方位角位移运动范围均大于正常组,差异有显著性意义（P〈0．05）;两种固定状态下固定节段（L2-L5）各方位角位移运动范围均显著小于正常状态和骨折状态,差异有显著性意义（P＜0．01）,且两种固定状态下各方位的即刻稳定指数比较,差异均无显著性意义（P〉0．05）;与正常组比较,两种固定状态上位椎体（L1）的各方位角位移运动范围均增加;外固定组与正常组上位椎体（L1）三维运动范围比较：前屈、后伸时差异无显著性意义（P〉0．05）,侧屈、旋转时差异均有显著性意义（P〈0．01）;内固定组与正常组比较：前屈、后伸、侧屈、旋转时差异均有显著性意义（P＜0．01）。结果可见应用脊柱外固定器治疗相邻双节段腰椎爆裂性骨折,其即刻生物力学稳定性与传统开放后路内固定系统相当;两种固定方式均能引起上位正常相邻椎体侧屈、旋转的角位移增加,但脊柱外固定器较传统内固定在前屈、后伸时不会引起上位相邻椎体的运动范围显著增加。     

Force-deformation response of the lumbar spine: a sagittal plane model of posteroanterior manipulation and mobilization

OBJECTIVE: To develop a mathematical model capable of describing the static and dynamic motion response of the lumbar spine to posteroanterior forces. DESIGN: Static, impulsive and oscillatory forces with varying thrust angles and offsets were applied to the model, and the resulting motion responses were compared to experimental data published for spinal mobilization and manipulation of prone-lying subjects. BACKGROUND: Methods are sought to improve understanding of the dynamic force-induced displacement response of the lumbar spine during spinal mobilization and manipulation treatment. METHODS: The thorax, pelvis and five lumbar vertebrae were represented as seven rigid structures and eight flexible joint structures. Flexible joint structures were modeled using spring and damper elements with three displacement degrees-of-freedom (posterior-anterior and axial displacement, and flexion-extension rotation). The resulting 21 degrees-of-freedom lumped parameter model was solved in modal space. RESULTS: The fundamental natural frequency of vibration was 5.24 Hz. Simulations performed using 100 N static and dynamic posteroanterior forces applied to the L3 vertebrae indicated that peak L3 segmental displacements were up to 2.40 mm (impulsive) and 8.23 mm (oscillatory at 2 Hz). Appreciable axial displacements (0.41 mm) and flexion-extension rotations (1.49 degrees ) were also observed for oscillatory forces at L3. The posteroanterior motion response of the lumbar vertebrae was relatively insensitive to both the thrust force angle and thrust force offset, but axial displacements and flexion-extension rotations showed a large change (2-fold or greater) for thrust angles greater than -5 degrees (caudal) in comparison to vertical thrusts. Intersegmental motion responses for static, impulsive and oscillatory loads were more comparable than their segmental counterparts. CONCLUSIONS: The model predicts lumbar segmental and inter-segmental motion responses to manipulative forces that are otherwise difficult to obtain experimentally. RELEVANCE: This study assists clinicians to understand the biomechanics of posteroanterior forces applied to the lumbar spine of prone-lying subjects. Of particular clinical relevance is the finding that greater spinal mobility is possible by targeting specific load-time histories.     

人工椎间盘置换对腰椎小关节应力影响的三维有限元分析

背景:近年来随着对脊柱生物力学研究的深入,人工椎间盘被认为是治疗腰椎退行性变较理想的方法,但目前对人工腰椎间盘的生物力学研究还非常有限.目的:建立腰椎运动节段人工椎间盘置换的三维有限元模型并进行生物力学分析,观察人工椎间盘置换对腰椎小关节应力的影响.方法:在已建立的正常腰椎运动节段三维有限元模型的基础上去除L4～5椎间盘、上下终板的有限元单元,加入SB-Chaite Ⅲ型人工椎间盘的有限元模型,保留L4～5椎间隙的纤维环及相关韧带,形成L4～5运动节段人工椎间盘置换的三维有限元模型.对三维有限元模型在垂直压缩、前屈、后伸、侧弯等不同载荷下进行生物力学分析,记录小关节的应力,并与正常运动节段三维有限元模型相应部位的应力进行对比.结果与结论:生物力学分析结果显示,人工椎间盘置换后:①垂直压缩时上下椎体、双侧小关节内应力与正常节段相比差异无显著性意义(P > 0.01).②前屈、后伸时上下椎体前、后方及双侧小关节内应力与正常节段相比差异无显著性意义(P > 0.01).③侧弯时上下椎体左右两侧及双侧小关节内应力与正常节段相比差异无显著性意义(P > 0.01).提示人工腰椎间盘置换后小关节应力可保持在正常运动节段的水平,人工腰椎间盘置换可以达到腰椎生物力学性能重建的目的.     

A rigid body model of the dynamic posteroanterior motion response of the human lumbar spine

BACKGROUND: Clinicians apply posteroanterior (PA) forces to the spine for both mobility assessment and certain spinal mobilization and manipulation treatments. Commonly applied forces include low-frequency sinusoidal oscillations (<2 Hz) as used in mobilization, single haversine thrusts (<0.5 seconds) as imparted in high-velocity, low-amplitude (HVLA) manipulation, or very rapid impulsive thrusts (<5 ms) such as those delivered in mechanical-force, manually-assisted (MFMA) manipulation. Little is known about the mechanics of these procedures. Reliable methods are sought to obtain an adequate understanding of the force-induced displacement response of the lumbar spine to PA forces. OBJECTIVE: The objective of this study was to investigate the kinematic response of the lumbar spine to static and dynamic PA forces. DESIGN: A 2-dimensional modal analysis was performed to predict the dynamic motion response of the lumbar spine. METHODS: A 5-degree-of-freedom, lumped equivalent model was developed to predict the PA motion of the lumbar spine. Lumbar vertebrae were modeled as masses, massless-spring, and dampers, and the resulting equations of motion were solved by using a modal analysis approach. The sensitivity of the model to variations in the spring stiffness and damping coefficients was examined, and the model validity was determined by comparing the results to oscillatory and impulsive force measurements of vertebral motion associated with spine mobilization and 2 forms of spinal manipulation. RESULTS: Model predictions, based on a damping ratio of 0.15 (moderate damping) and PA spring stiffness coefficient ranging from 25 to 60 kN/m, showed good agreement with in vivo human studies. Quasi-static and low-frequency (<2.0 Hz) forces at L3 produced L3 segmental and L3-L4 intersegmental displacements up to 8.1 mm and 3.0 mm, respectively. PA oscillatory motions were over 2.5-fold greater for oscillatory forces applied at the natural frequency. Impulsive forces produced much lower segmental displacements in comparison to static and oscillatory forces. Differences in intersegmental displacements resulting from impulsive, static, and oscillatory forces were much less remarkable. The latter suggests that intersegmental motions produced by spinal manipulation may play a prominent role in eliciting therapeutic responses. CONCLUSIONS: The simple analytical model presented in this study can be used to predict the static, cyclic, and impulsive force PA displacement response of the lumbar spine. The model provides data on lumbar segmental and intersegmental motion patterns that are otherwise difficult to obtain experimentally. Modeling of the PA motion response of the lumbar spine to PA forces assists in the understanding the biomechanics of therapeutic PA forces applied to the lumbar spine and may ultimately be used to validate chiropractic technique procedures and minimize risk to patients receiving spinal manipulative therapy.