Lumbar facet joint and intervertebral disc loading during simulated pelvic obliquity

Background contextIntervertebral disc and facet joints are the two primary load-bearing structures of the lumbar spine, and altered loading to these structures may be associated with frontal plane spinal deviations.PurposeTo determine the load on the lumbar facet joint and intervertebral disc under simulated frontal plane pelvic obliquity combined loading, an in vitro biomechanical study was conducted.Study design/settingAn in vitro biomechanical study using a repeated-measures design was used to compare L4–L5 facet joint and intervertebral disc loading across pure moment and combined loading conditions.MethodsEight fresh-frozen lumbosacral specimens were tested under five loading conditions: flexion/extension, lateral bending, axial rotation using pure moment bending (±10 Nm), and two additional tests investigating frontal plane pelvic obliquity and axial rotation (sacrum tilted left 5° and at 10° followed by a ±10-Nm rotation moment). Three-dimensional kinematics, facet load, and intradiscal pressures were recorded from the L4–L5 functional spinal unit.ResultsSagittal and frontal plane loading resulted in significantly smaller facet joint forces compared with conditions implementing a rotation moment (p<.05). The facet joint had the highest peak load during the 10° combined loading condition (124.0±30.2 N) and the lowest peak load in flexion (26.8±16.1 N). Intradiscal pressure was high in lateral flexion (495.6±280.9 kPa) and flexion (429.0±212.9 kPa), whereas intradiscal pressures measured in rotation (253.2±135.0 kPa) and 5° and 10° combined loading conditions were low (255.5±132.7 and 267.1±127.1 kPa, respectively).ConclusionsFacet loading increased during simulated pelvic obliquity in frontal and transverse planes, whereas intradiscal pressures were decreased compared with sagittal and frontal plane motions alone. Altered spinopelvic alignment may increase the loads experienced by spinal tissue, especially the facet joints.     

The instant axis of rotation influences facet forces at L5/S1 during flexion/extension and lateral bending

Because the disc and facets work together to constrain spinal kinematics, changes in the instant axis of rotation associated with disc degeneration or disc replacement may adversely influence risk for facet overloading and arthritis. The relationships between L5/S1 segmental kinematics and facet forces are not well defined, since previous studies have separated investigations of spinal motion and facet force. The goal of this cadaveric biomechanical study was to report and correlate a measure of intervertebral kinematics (the centrode, or the path of the instant axis of rotation) and the facet forces at the L5/S1 motion segment while under a physiologic combination of compression and anterior shear loading. Twelve fresh-frozen human cadaveric L5/S1 joints (age range 50–64 years) were tested biomechanically under semi-constrained conditions by applying compression plus shear forces in several postures: neutral, and 3° and 6° of flexion, extension and lateral bending. The experimental boundary conditions imposed compression and shear representative of in vivo conditions during upright stance. The 3-D instantaneous axis of rotation (IAR) was calculated between two consecutive postures. The facet joint force was simultaneously measured using thin-film sensors placed between both facet surfaces. Variations of IAR location and facet force during motion were analyzed. During flexion and extension, the IAR was oriented laterally. The IAR intersection with the mid-sagittal plane moved cephalad relative to S1 endplate during flexion (P=0.010), and posterior during extension (P=0.001). The facet force did not correlate with posture (P=0.844). However, changes in the facet force between postures did correlate with IAR position: higher IARs during flexion correlated with lower facet forces and vice versa (P=0.04). During lateral bending, the IAR was oblique relative to the main plane of motion and translated parallel to S1 endplate, toward the side of the bending. Overall, the facet force was increased on the ipsilateral side of bending (P=0.002). The IAR positions demonstrate that the L5 vertebral body primarily rotates forward during flexion (IAR close to vertebral body center) and rotates/translates backward during extension (IAR at or below the L5/S1 intervertebral disc). In lateral bending, the IAR obliquity demonstrated coupling with axial torsion due to resistance of the ipsilateral facet.     

Cervical facet joint kinematics during bilateral facet dislocation

Previous biomechanical models of cervical bilateral facet dislocation (BFD) are limited to quasi-static loading or manual ligament transection. The goal of the present study was to determine the facet joint kinematics during high-speed BFD. Dislocation was simulated using ten cervical functional spinal units with muscle force replication by frontal impact of the lower vertebra, tilted posteriorly by 42.5°. Average peak rotations and anterior sliding (displacement of upper articulating facet surface along the lower), separation and compression (displacement of upper facet away from and towards the lower), and lateral shear were determined at the anterior and posterior edges of the right and left facets and statistically compared (P < 0.05). First, peak facet separation occurred, and was significantly greater at the left posterior facet edge, as compared to the anterior edges. Next, peak flexion rotation and anterior facet sliding occurred, followed by peak facet compression. The highest average facet translation peaks were 22.0 mm for anterior sliding, 7.9 mm for separation, 9.9 mm for compression and 3.6 mm for lateral shear. The highest average rotation of 63° occurred in flexion, significantly greater than all other directions. These events occurred, on average, within 0.29 s following impact. During BFD, the main sagittal motions included facet separation, flexion rotation, anterior sliding, followed by compression, however, non-sagittal motions also existed. These motions indicated that unilateral dislocation may precede bilateral dislocation.     

脊柱三维运动对腰髓核摘除术后小关节的作用机制

目的观测髓核摘除术后腰椎小关节的应力分布变化。方法取新鲜青壮年尸体下腰椎标本6具,在L4下关节突、L5上下关节突、S1上关节突分别贴横形和竖形微细应变片进行力学测试。首先在髓核摘除前测量各应变片在轴向加压、前屈、后伸、侧屈、旋转工况下的应变值;然后在所有标本上行单侧L5/S1开窗髓核摘除术,在同样加载条件下测量应变值;最后在所有标本对侧行L5/S1开窗髓核摘除术形成双侧髓核摘除,重复加载测量应变值。结果轴向加压工况时3种实验力学状态应变量均无差异;前屈工况时L5下关节突竖形应变量髓核摘除前与双侧髓核摘除状态差异有统计学意义;后伸工况时L5上、下关节突竖形应变量双侧髓核摘除状态与其它2种实验力学状态相比差异均有统计学意义;侧屈工况时3种实验力学状态应变量均无差异;旋转工况时L4下关节突竖形片应变量髓核摘除前与单侧髓核摘除相比、单侧髓核摘除与双侧髓核摘除状态比较差异均有统计学意义,L5下关节突横行片应变量双侧髓核摘除状态与其它2种实验力学状态比较差异有统计学意义,S1上关节突竖形片应变量髓核摘除前与双侧髓核摘除状态比较差异有统计学意义。结论单侧开窗髓核摘除术后邻近关节突稳定性保存良好,但是双侧开窗髓核摘除术后下腰椎邻近节段关节突在前屈、后伸、旋转运动时与髓核摘除前比较应变量显著增高,稳定性下降,需要给予适当的稳定措施。     

Normal range-of-motion of trapeziometacarpal joint

PurposeThe range-of-motion of the trapeziometacarpal joint is difficult to assess clinically. The purpose of our study was to constitute a range-of-motion database from normal active trapeziometacarpal joints.Material and methodsTwo hundred hands from 101 healthy subjects (50 female and 51 male) with a mean age of 23.1 years (range: 22 to 35 years) have been evaluated. An optoelectronic device (Polaris^®) was used to analyse the thumbs range-of-motion. Splints were fitted so as to isolate the trapeziometacarpal joint and retroreflective markers were placed both on the splints and on the thumb. After active flexion–extension, abduction–adduction, axial rotation and circumduction, the different range-of-motion parameters were calculated.ResultsThe mean range-of-motion of the trapeziometacarpal joint was 41° for flexion–extension, 51° for abduction–adduction and 21° for axial rotation. Comparisons between female and male subjects showed significant differences concerning flexion–extension, abduction–adduction axial rotation and circumduction. No significant differences were noted between right and left hands except for the abduction–adduction movement.Discussion and conclusionOne hundred and one healthy subjects were analysed for the development of a database of normal active range-of-motion parameters of the trapeziometacarpal joint, with an in vivo protocol. This database should allow comparing the range-of-motion of patients with osteoarthritic trapeziometacarpal joint and assessing surgical outcome.     

A biomechanical study of lumbar fusion based on a three-dimensional nonlinear finite element method

Biomechanical analyses under compression, flexion, and extension loading were performed to evaluate the stability of interbody, posterolateral, posterior, and facet fusions using a nonlinear three-dimensional finite element method. The effects of facet fusion on other lumbar fusions were also examined. A three-dimensional L4-L5 motion segment model was developed that took into consideration the material nonlinearities of ligaments and annular fibers and the contact nonlinearities of facet joints. Of all models of fusion, maximum rigidity was obtained in the interbody fusion model. In the posterolateral, posterior, and facet fusion models under compression, axial displacement and flexion rotation were induced. In combination with facet fusion, the interbody, posterolateral, and posterior fusion models demonstrated a decrease in axial displacement of about 6%, 1%, and 5%, respectively, under compression and a decrease in rotation angle of about 22%, 12%, and 48%, respectively, under flexion-extension loading. Stress concentration moved principally toward the fusion site, indicating increased load transfer across the fusion mass. Our findings suggest that a more solid fixation can be expected from lumbar fusion--especially in posterior fusion--if facet fusion is performed.     

Biomechanical contribution of spinal structures to stability of the lumbar spine—novel biomechanical insights

Background ContextThe contribution of anatomical structures to the stability of the spine is of great relevance for diagnostic, prognostic and therapeutic evaluation of spinal pathologies. Although a plethora of literature is available, the contribution of anatomical structures is still not well understood.PurposeWe aimed to quantify the biomechanical relevance of each of the passive spinal structure trough deliberate biomechanical test series using a stepwise reduction approach on cadavers.Study designBiomechanical cadaveric study.MethodsFifty lumbar spinal segments originating from 22 human lumbar cadavers were biomechanically tested in a displacement-controlled stepwise reduction study: the intertransverse ligaments, the supraspinous and interspinous ligaments, the facet joint capsules (FJC), the facet joints (FJ), the ligamentum flavum (LF), the posterior longitudinal ligament (PLL), and the anterior longitudinal ligament were subsequently reduced. In the intact state and after each transection step, the segments were physiologically loaded in flexion, extension, axial rotation (AR), lateral bending (LB) and with anterior (AS), posterior (PS) and lateral shear (LS). Thirty-two specimens with only minor degeneration, representing a reasonably healthy subpopulation, were selected for the here presented evaluation. Quantitative values for load and spinal level dependent contribution patterns for the anatomical structures were derived.ResultsSmall variability between of the contribution patterns are observed. The intervertebral disc (IVD) is exposed to about 67% of the applied load in LB and during shear loading, but less by load in flexion, extension and AR (less than 35%). The FJ&FJC are the main stabilizers in AR with 49%, but provide only 10% of the stability in extension. Beside the IVD, the LF and the PLL contribute mainly in flexion (22% and 16%, respectively), while the ALL plays a major role during extension (40%) and also contributes during LB (15%). The contribution of the intertransverse ligaments and the supraspinous and interspinous ligaments are very small in all loading directions (<2% and <6%, respectively).ConclusionThe IVD takes the main load in LB and absorbs shear loading, while the FJ&FJC stabilize AR. The ALL resists extension while LF and PLL stabilize flexion. With the small variability of contribution patterns, suggesting distinct adaptation of the structures to one another, the biomechanical characteristics of one structure have to be put in context of the whole spinal segment.CLINICAL SIGNIFICANCEThe novel information on load distribution helps predict the biomechanical consequences of surgical procedures in more detail.     

后部结构对腰椎前屈／后伸稳定性的影响

目的：探讨小尾寒羊L5／6后部结构分级切除对腰椎前屈／后伸稳定性的影响。方法：利用改良的定位移生物力学测试方法,对L5／L6后部结构依次分级切除：Ⅰ正常→Ⅱ全椎板减压→Ⅲ左侧关节突切除1／2→Ⅳ左侧关节突全部切除→Ⅴ右侧关节突切除1／2→Ⅵ右侧关节突全部切除,Instron8874试验机依次测试标本前屈／后伸椎间运动的变化。结果：全椎板减压和左侧关节突的全部切除对于前屈／后伸的稳定性影响不大（P〉0．05）;当再切除右侧关节突1／2时,稳定性影响明显（P〈0.05）。结论：在保证手术视野的情况下,腰椎后路手术力求做到微创,尽量保留后部结构的完整性。     

The effect of disc degeneration and facet joint osteoarthritis on the segmental flexibility of the lumbar spine

STUDY DESIGN: A biomechanical and imaging study of human cadaveric spinal motion segments. OBJECTIVE: To investigate the effect of both disc degeneration and facet joint osteoarthritis on lumbar segmental motion. SUMMARY OF BACKGROUND DATA: Spinal degeneration includes the osteoarthritic changes of the facet joint as well as disc degeneration. Disc degeneration has been reported to be associated with spinal motion. The association of facet joint osteoarthritis with lumbar segmental motion characteristics and the combined influence of disc degeneration and facet osteoarthritis has not yet been investigated. METHODS: A total of 110 lumbar motion segments (52 female, 58 male) from 44 human lumbar spines were studied (mean age = 69 years). Magnetic resonance images were used to assess the disc degeneration from Grade I (normal) to Grade V (advanced) and the osteoarthritic changes in the facet joints in terms of cartilage degeneration, subchondral sclerosis, and osteophytes. Disc height, endplate size, and facet joint orientation and width also were measured from the computed tomographic images. Rotational movements of the motion segment in response to the flexion, extension, lateral bending, and axial rotational moments were measured using a three-dimensional motion analysis system. RESULTS: Female motion segments showed significantly greater motion (lateral bending: P < 0. 001, flexion: P < 0.01, extension: P < 0.05) and smaller endplate size (P < 0.001) than male ones. The segmental motion increased with increasing severity of disc degeneration up to Grade IV, but decreased in both genders when the disc degeneration advanced to Grade V. In male segments, the disc degeneration-related motion changes were significant in axial rotation (P < 0.001), lateral bending (P < 0.05), and flexion (P < 0.05), whereas female segments showed significant changes only in axial rotation (P < 0.001). With cartilage degeneration of the facet joints, the axial rotational motion increased, whereas the lateral bending and flexion motion decreased in female segments. In male segments, however, motion in all directions increased with Grade 3 cartilage degeneration and decreased with Grade 4 cartilage degeneration. Subchondral sclerosis significantly decreased the motion (female: axial rotation, P < 0. 05; extension, P < 0.05 vs.- male:flexion,P < 0.05). Severity of osteophytes had no significant association with the segmental motion. CONCLUSION: Axial rotational motion was most affected by disc degeneration, and the effects of disc degeneration on the motion were similar between genders. Facet joint osteoarthritis also affected segmental motion, and the influence differed for male and female spines. Further studies are needed to clarify whether the degenerative process of facet joint osteoarthritis differs between genders and how facet joint osteoarthritis affects the stability of the spinal motion segment.     

Biomechanik der interspinösen Platzhalter

Interspinous spacers are commonly used to treat lumbar spinal stenosis or facet joint arthritis. The aims of implanting interspinous devices are to unload the facet joints, restore foraminal height, and provide stability especially in extension but still allow motion. This paper summarizes several in vitro studies, which compared four different interspinous implants – Coflex?, Wallis, DIAM?, and X-STOP – in terms of their three-dimensional primary stability, the intradiscal pressure, and stability after cyclic loading. 24 human lumbar spine specimens were divided into four equal groups and tested with pure moments in flexion/extension, lateral bending, and axial rotation: intact, after decompression with hemifacetectomy, and after implantation. Implantation had similar biomechanical effects with all four implants. In extension, they overcompensated the instability caused by the defect and restricted extension to about 50% compared to the intact state. In contrast, in flexion, lateral bending, and axial rotation the values of the range of motion stayed similar compared to the defective state. Intradiscal pressure after implantation was similar to that of the intact specimens in flexion, lateral bending, and axial rotation but much smaller during extension; 50,000 load cycles increased the range of motion in all motion planes by no more than 20%, but in extension motion this was still less than in the intact state.     

A biomechanical evaluation of an interspinous device (Coflex) used to stabilize the lumbar spine

A biomechanical study of an interspinous stabilization spinal implant (Coflex) was carried out using eight human lumbar L4/L5 motion segments. Each motion segment was tested in compression, then flexion/extension, then lateral bending, and then axial rotation at five conditions: 1) intact; 2) partial destabilization (by cutting the supraspinous and interspinous ligaments, the ligamentum flavum, the facet capsules, and 50% of the inferior bony facet bilaterally); 3) stabilization with the Coflex device; 4) complete destabilization with total laminectomy; and 5) stabilization with pedicle screws and rods. The most important result is that the motion segment after destabilization and insertion of the Coflex device does not allow significantly more or less motion than the intact specimen in either flexion/extension or axial rotation. Thus the Coflex offers nonrigid fixation and can return a partially destabilized specimen back to the intact condition in terms of motion in flexion/extension and axial rotation.     

腰椎关节突关节骨性关节炎对腰椎稳定性的影响

目的探讨腰椎退变过程中,腰椎间盘退变、关节突关节骨性关节炎与腰椎稳定性之间的关系.方法对78名腰椎退变患者进行腰椎MRI和动力位X线摄影.腰椎不稳分为椎间角度运动不稳、旋转不稳和椎间位移不稳,其中椎间位移不稳细分为前向不稳、后向不稳和前后向不稳.腰椎间盘退变依据矢状位T2加权像分为5级;关节突关节骨性关节炎依据水平位T1加权像分为4级.对资料进行统计分析.结果腰椎椎间角度运动不稳和前后向椎间位移不稳与关节突关节骨性关节炎存在显著负相关,前向椎间位移不稳与腰椎关节突关节骨性关节炎和椎间盘退变呈显著正相关,腰椎矢状面旋转不稳与腰椎关节突关节骨性关节炎无显著相关.结论腰椎间盘退变和腰椎关节突关节骨性关节炎可影响腰椎运动节段的稳定性.     

Biomechanical effects of sequential resection of the posterior ligamentous complex on intradiscal pressure and resistance to compression forces

ObjectiveThe aim of this biomechanical experimental study was to evaluate the resistance of each posterior ligamentous complex structure of the thoracic and lumbar spine to compression forces and to measure the shifting load to the intervertebral disc when each PLC structure was interrupted.MethodThe study was conducted on 4 groups for thoracic and lumbar region as intact, supraspinous ligament interrupted, interspinous ligament/ligamentum flavum combination interrupted and facet joint capsule interrupted. Pre and post anterior vertebral body height, the highest compression force and pressure changes in the intervertebral disc during 40 N loading were measured.ResultsA significantly different degree of resistance to compression force was determined in each posterior ligamentous complex structure in the thoracic and lumbar spine samples. The combination of interspinous ligament and ligamentum flavum was found to be the most effective structure to resist compression forces (p = 0.001 in both groups). The effect of the supraspinous ligament in thoracic and lumbar segments was found to be similar to that of the interspinous ligament and ligamentum flavum combination (p = 0.008 and p = 0.006, respectively). The least effective structure was observed to be the facet joint capsule. Compression forces were significantly increased in the intervertebral disc as a result of the disruption of supraspinous ligament (p = 0.0032 and p = 0.0029, respectively in thoracic and lumbar segments) and combination of interspinous ligament/ligamentum flavum (p = 0.0019 and p = 0.0021, respectively in thoracic and lumbar segments).ConclusionThe interspinous ligament/ligamentum flavum combination and supraspinous ligament are the largest contributor to resisting applied compression moments in the sheep thoracic and lumbar spine. As a result of the loss of resistance to compression forces, there will be a shift of a great proportion of this force onto the intervertebral disc.Level of evidenceLevel V.     

Human lumbar facet joint capsule strains: I. During physiological motions.

BACKGROUND CONTEXT: The lumbar facet joint capsule is innervated with nociceptors and mechanoreceptors, and is thought to play a role in low back pain as well as to function proprioceptively. PURPOSE: In order to examine the facet capsule's potential proprioceptive role, relationships between intracapsular strain and relative spine position were examined. STUDY DESIGN/SETTING: Lumbar facet joint capsule strains were measured in human cadaveric specimens during displacement-controlled motions. METHODS: Ligamentous lumbar spine specimens (n=7) were potted and actuated without inducing a moment at the point of application. Spines were tested during physiological motions of extension, flexion, left and right lateral bending. Intervertebral angulations (IVA) were measured using biaxial inclinometers mounted on adjacent vertebrae. Joint moments were determined from the applied load at T12 and the respective moment arms. Capsule plane strains were measured by optically tracking the displacements of infrared reflective markers glued to capsule surfaces. Statistical differences (p<.05) in moment, IVA and strain were assessed across facet joint levels using analysis of variance and comparison of linear regressions. RESULTS: The developed moments and IVAs increased monotonically with increasing displacements; the relationships were highly correlated for all four motion types. Although highly variable among specimens, principal strains also increased monotonically in magnitude with increasing displacements during extension and flexion, but were more complex during lateral bending. At a given joint level, the absolute magnitudes of principal strains and IVA were largest during the same motion type. CONCLUSIONS: Distinct patterns in principal strains and IVA were identified during physiological motions, lending biomechanical support to the theory that lumbar facet joint capsules could function proprioceptively.     

后部结构分级切除对下腰椎稳定性影响的实验研究

目的 探讨小尾寒羊L5,6后部结构分级切除对腰椎稳定性的影响.方法 选取14只小尾寒羊,截取L4～L7脊柱标本.实验前摄正、侧位X线片以排除脊柱疾患,CT定位关节突关节分级切除.对L5,6节段后部结构依次分级切除如下:Ⅰ正常→Ⅱ全椎板减压→Ⅲ左侧关节突切除1/2→Ⅳ左侧关节突全部切除→Ⅴ右侧关节突切除1/2→Ⅵ右侧关节突全部切除→结束.利用Instron 8874液压伺服动态生物力学测试系统依次测试标本六个自由度上椎间运动的变化,计算平均刚度.利用SPSS 11.5行单因素方差分析,检验水准α值取0.05.结果 全椎板减压和左侧关节突的全部切除对于前屈或后伸的稳定性影响不大;当再切除右侧关节突1/2时,前屈或后伸的平均刚度比正常时分别下降32.33%和30.83%.腰椎后路结构的切除对于腰椎侧弯的稳定性影响不大.全椎板减压即出现左和右扭转失稳,平均刚度分别比正常时下降26.13%和26.20%,关节突关节与扭转的稳定性亦具有重要意义,特别是对对侧扭转的稳定性.结论 行腰椎后路手术时,在保证手术视野的情况下,力求做到微创,尽量保留后部结构的完整性.     

Posterior lumbar interbody fusion using posterolateral placement of a single cylindrical threaded cage

STUDY DESIGN: An in vitro biomechanical study of posterior lumbar interbody fusion (PLIF) with threaded cages was performed on 18 bovine lumbar functional spinal units. OBJECTIVES: To compare the segmental stiffness among PLIF with a single long posterolateral cage, PLIF with a single long posterolateral cage and simultaneous facet joint fixation, and PLIF with two posterior cages. SUMMARY OF BACKGROUND DATA: In most cases, PLIF with threaded cage techniques needs bilateral facetectomy, extensive exposure, and retraction of the cauda equina. Posterior element deficiency is detrimental to postoperative segmental stiffness. METHODS: All specimens were tested intact and with cage insertion. Group 1 (n = 12) had a long threaded cage (15 x 36 mm) inserted posterolaterally and oriented counter anterolaterally on the left side by posterior approach with left unilateral facetectomy. Group 2 (n = 6) had two regular-length cages (15 x 24 mm) inserted posteriorly with bilateral facetectomy. Six specimens from Group 1 were then retested after unilateral facet joint screw fixation in neutral (Group 3). Similarly, the other six specimens from Group 1 were retested after fixation with a facet joint screw in an extended position (Group 4). Nondestructive tests were performed in pure compression, flexion, extension, lateral bending, and torsion. RESULTS: The PLIF procedure involving a single cage (Group 1) had a significantly higher stiffness than PLIF with two cages (Group 2) in left and right torsion (P < 0.05). Group 1 had higher stiffness values than Group 2 in pure compression, flexion, and left and right bending, but differences were not significant. Group 3 had a significant increase in stiffness in comparison with Group 1 for pure compression, extension, left bending, and right torsion (P < 0.05). For Group 4, the stiffness significantly increased in comparison with Group 1 for extension, flexion, and right torsion (P < 0.05). Although there was no significant difference between Groups 3 and 4, Group 4 had increased stiffness in extension, flexion, right bending, and torsion. CONCLUSIONS: Posterior lumbar interbody fusion with a single posterolateral long threaded cage with unilateral facetectomy enabled sufficient decompression while maintaining most of the posterior elements. In combination with a facet joint screw, adequate postoperative stability was achieved.     

腰椎弓根延长术对关节突关节力学影响的有限元分析

目的 探讨腰椎椎弓根延长术对关节突关节生物力学的影响,分析关节突关节发生异常应力变化前椎弓根的最大延长长度。方法 取1名腰椎健康志愿者的CT图像,建立L₃~L₅正常腰椎的有限元模型,在其基础上构建L₄椎弓根延长术后模型,L₃椎体上表面均施加垂直于水平面400 N的压力,模拟正常人腰椎所承载重力,固定支撑L₅椎体下表面。通过建立不同椎弓根延长长度的术后模型,分析在力矩为5 Nm时L_3/4的应力分布云图及相应的应力-应变曲线,得出相同力矩下L_3/4关节突关节应力极值随椎弓根延长长度变化的曲线图。结果 施加5 Nm力矩下,L_3/4小关节左旋工况下应力先随延长长度的增加而增加,在椎弓根延长3.8 mm时达到最大,为9.133 MPa;随后,L_3/4小关节的应力骤然减小,曲线发生不可逆变化。结论 力矩加载为5 Nm时腰椎弓根延长术的最大延长距离为3.8 mm,临床应结合腰椎管狭窄的严重程度,选择减压所需的延长长度,取得更好的手术疗效。     

Mechanism of facet load transmission as a hypothesis for low-back pain

Low-back pain has a complex and multi-faceted etiology. The articular facets have been shown to be load-bearing structures and may be a site for low-back pain. The aim of this paper is to establish the mechanism for the transmission of axial load across a facet joint and to propose a facet-related hypothesis for low-back pain. The mechanism of load transmission was studied by two methods. Lumbar segments were instrumented with an intervertebral load cell (IVLC) to measure disc load so that facet load could be deduced. The applied load was moved 10 mm anteriorly and 12.5 mm posteriorly from the center of the vertebral body. The facets then were separated from the body and loaded axially to determine their stiffness in tension and compression and to observe the failure mode of the joint. It was shown optically that compressive loading of the isolated facet joints was equivalent to spinal extension and tensile loading to spinal flexion. Lastly, a finite element model of a lumbar motion segment was developed to simulate the transmission of facet load and to study the effects of disc degeneration on facet loads. Results of the study on six lumbar segments revealed that the normal facets carried 3-25%. If the facet joint was arthritic, the load could be as high as 47%. Experiments on isolated facet joints revealed that they behaved as a stiffening spring in compression and were weak in tension.(ABSTRACT TRUNCATED AT 250 WORDS)     

Combined flexion and compression negatively impact the mechanical integrity of the annulus fibrosus

Purpose

To observe the effect of static flexion, in combination with compression, on the intralamellar and interlamellar matrix properties of the annulus fibrosus.

Methods

C3/C4 cervical functional spinal units of porcine specimens were selected. Following preloading, all specimens were loaded under 1200 N axial compression in either a neutral or static end range flexion posture (15º) for 2 h. Following loading, six annulus samples were dissected from each disc: four single-layer and two multi-layer samples. The multi-layer samples underwent peel tests to quantify the mechanical properties of the interlamellar matrix while the single-layer samples underwent tensile tests to quantify the mechanical properties of the intralamellar matrix. Statistical comparisons between properties were performed to determine differences between postural condition, extraction location, and extraction depth.

Results

Flexion elicited a decrease in lamellar adhesive strength (p = 0.045) and in single-layer failure strain (p = 0.03) when compared to a neutral posture. Flexion also had extraction depth-specific effects namely increased intralamellar matrix stiffness in the inner annulus when compared to neutral (p = 0019). Flexion also resulted in a significant decrease in toe region strain for the inner region of the annulus (p = 0.035). The inner region of the annulus was shown to have a significant increase in stress at 30% strain when compared to the outer region after flexion (p = 0.041).

Conclusion

The current findings suggest that the mechanical properties of the interlamellar and intralamellar matrices are sensitive to flexion, creating an environment that promotes an increased potential for damage to occur.

     

斜扳时完整腰椎三维立体运动的研究

实验对象为Ｌ＿（１～５）的完整腰椎标本，设计了平行光脊柱三维运动测量系统，改进加载方法以更好模拟脊柱推拿手法，设置７个腰椎特定点，将观察图像动态变化输入计算机系统，应用工程系统力学中刚体转移计算理论进行计算，获得腰椎及其后部结构在模拟推拿加载时的三维运动量。根据右旋时完整腰椎的三维运动结果，发现在左侧卧位斜扳时，右侧关节突等构成神经根管壁结构发生定向位移，在各节段可以不同，但其主运动轴位移的结果可直接扩大神经根管，或牵拉，紧张小关节囊韧带和黄韧带而扩大神经根管。