颈椎终板结构的生物力学研究

目的 研究颈椎终板不同位点生物力学特性的分布规律。方法 运用人体新鲜颈椎标本66椎，对终板平面上的20个特定测试点进行压缩试验，用直径2mm的半球形压头以0.03mm/s的速度垂直终板平面下压2mm，由所得的压缩力-位移线计算最大压缩力及刚度，采用析因分析对实验数据进行统计处理。结果 （1）颈椎各节段之间最大压缩力及刚度的差异有显著性（P＜0.01)，且由上而下呈逐渐减小趋势。终板矢状方向中各点之间最大压缩力及刚度的差异有显著性（P＜0.01），且椎体后部是最大压缩力及刚度较大的区域；终板冠状方向上各点之间最大的压缩力及刚度（除下终板最大压缩力外）的差异均无显著性（P＞0.05)。（2）下颈椎相邻终板之间的最大压缩力及刚度的差异有显著性（P＜0.05），下终板的最大压缩力及刚度比上终板大。矢状方向上相邻板的最大压缩力差异有显著性（P＜0.05）。结论 颈椎上终板后都、下终板后外侧区是椎体力学强度最大的区域。在进行颈前路融合术时下颈椎较易发生塌陷，且塌陷多发生于颈椎上终板平面。     

The effects of bone density and disc degeneration on the structural property distributions in the lower lumbar vertebral endplates.

In this study, we hypothesized that vertebral bone density and disc degeneration would affect the structural property distributions of the lower lumbar vertebral endplates (L3-L5). The results may have implications for improving interbody implant designs to better resist subsidence. A 3 mm diameter hemispherical indenter was used to perform indentation tests at 0.2 mm/s to a depth of 3 mm at 27 standardized locations in 55 bony endplates of intact human lumbar vertebrae (L3-L5). The resulting load-displacement curves were used to extract the failure load and stiffness of each test site. Bone density was measured using lateral DEXA scans. Disc condition was determined using a four-point grading scale. Three-way analyses of variance were used to analyze the relationships between the data. The overall failure load decreased with bone mineral density (BMD) in the superior (p < 0.0001) and inferior (p = 0.011) lumbar endplates. In both endplates, the posterolateral regions were significantly stronger than more central regions. With increasing BMD, this difference became more pronounced in the superior endplates only (p = 0.005). Increased disc degeneration was associated with an overall failure load decrease in the inferior lumbar endplates (p = 0.002). The strength in the central regions of the superior endplates was reduced with increasing degeneration, but this was not observed peripherally (p = 0.001). Stiffness magnitude or distribution was not significantly affected by BMD or disc degeneration. The locations of the strongest regions of the endplate did not change with either bone density or disc degeneration. This implies that implant shapes designed using the basic structural property maps for the L3-L5 endplates are appropriate for use in patients with a wide range of pathologies, even though overall failure loads are generally lower in patients with reduced bone density and greater degrees of disc degeneration.     

颈椎椎间盘退变对终板结构生物力学特性的影响

目的研究颈椎椎间盘对终板结构生物力学特性的影响。方法50节颈椎标本,采用Nachemson椎间盘分级标准将标本分为4组,正常组(n=22)、Ⅰ度退变组(n=10)、Ⅱ度退变组(n=9)、Ⅲ度退变组(n=9),对每一终板平面上20个特定的测试点进行压缩实验,直径2mm的半球形压头以003mm/s的速度垂直于终板平面下压2mm,由所得的力─位移曲线计算出最大压缩力及刚度,采用单因素方差分析、析因分析、SNK检验及相关分析对实验数据进行统计学分析。结果颈椎椎间盘退变可导致颈椎终板最大压缩力及刚度的显著性减小(P<001),且存在负相关关系(分别为rs=-0429,P<0001;rs=-0244,P<0001);上终板随着椎间盘退变的加重终板平面中央承力逐渐变弱,外周承力逐渐增强,下终板的力学分布无明显改变。结论颈椎椎间盘退变是影响终板结构生物力学特性的重要因素,在进行颈椎前路融合术时应警惕由于椎间盘退变引起的“植入物沉陷”。     

腰椎终板骨折特点及相关因素的实验研究

目的 探讨腰椎椎体终板压迫骨折的特点及其影响因素。方法 19个尸体标本的腰椎运动节段（FSU）,根据X线检查来确定椎间盘的退变分级,在双能X线吸收仪器（DEXA）上测量椎体和椎体终板的骨密度（BMD）和骨矿含量（BMC）,然后分别承受过度负荷导致终板骨折,根据力-位移曲线来确定终板骨折和终板的极限负荷（FL）。终板骨折后,运动节段解剖为单独的椎体,观察终板骨折情况。结果 19个FSU标本中,16个发生肉眼可见的终板骨折,骨折仅仅发生在下位椎体的上终板,比率为84．2％,骨折均位于终板的中央部分或前部,表现为星形放射状、阶梯状、局部突入型等;终板的FL与椎体及终板的BMD、BMC呈正相关。同一个椎体内,上终板的BMD、BMC显著低于下终板,而同一个椎间盘周围,上终板的BMD高于下终板者,BMC却无差异。结论终板压迫骨折易发生于椎体的上终板;不同退变程度椎间盘邻近终板骨折的特点不同,但这种骨折在X线片上很难显现,终板的极限负荷与椎体终板的BMD、BMC呈正相关。     

Load shift of the intervertebral disc after a vertebroplasty: a finite-element study

Infiltrating osteoporotic cancellous bone with bone cement (vertebroplasty) is a novel surgical procedure to stabilize and prevent osteoporotic vertebral fractures. Short-term clinical and biomechanical results are encouraging; however, so far no reports on long-term results have been published. Our clinical observations suggest that vertebroplasty may induce subsequent fractures in the vertebrae adjacent to the ones augmented. At this point, there is only a limited understanding of what causes these fractures. We have previously hypothesized that adjacent fractures may result from a shift in stiffness and load following rigid augmentation. The purpose of this study is to determine the load shift in a lumbar motion segment following vertebroplasty. A finite-element (FE) model of a lumbar motion segment (L4-L5) was used to quantify and compare the pre- and post-augmentation stiffness and loading (load shift) of the intervertebral (IV) disc adjacent to the augmented vertebra in response to quasi-static compression. The results showed that the rigid cement augmentation underneath the endplates acted as an upright pillar that severely reduced the inward bulge of the endplates of the augmented vertebra. The bulge of the augmented endplate was reduced to 7% of its value before the augmentation, resulting in a stiffening of the IV joint by approximately 17%, and of the whole motion segment by approximately 11%. The IV pressure accordingly increased by approximately 19%, and the inward bulge of the endplate adjacent to the one augmented (L4 inferior) increased considerably, by approximately 17%. This increase of up to 17% in the inward bulge of the endplate adjacent to the one augmented may be the cause of the adjacent fractures.     

脊柱交界区终板抗压强度分布规律的生物力学研究

目的:探讨脊柱交界区终板不同位点抗压强度及其分布规律。方法:选用5具成年男性新鲜脊柱标本的颈胸段、胸腰段及腰骶段,共65个椎体125个终板,采用环形取点的方式,对每个终板平面的49个测试点用直径1.5mm的平底压头进行连续压缩加载试验,获得最大压缩力,所得数据进行统计分析。结果:以椎体为单位,颈胸段终板从C4开始抗压强度逐渐下降,至C7达到最低点,C7～T1明显升高。胸腰段各椎体终板的抗压强度呈依次上升趋势,腰骶段L3、L4终板抗压强度继续上升,L5出现降低,S1节段再次升高。颈胸段与胸腰段抗压强度均小于腰骶段(P<0.01)。上下终板抗压强度变化趋势相似。各段椎体抗压强度下终板强于上终板(P<0.01)。椎间隙相邻面上一椎体下终板的抗压强度大于下一椎体上终板(P<0.05)。由内至外,抗压强度逐渐增大(P<0.05)。颈胸段和腰骶段的后部终板抗压强度大于前部,而胸腰段为前部大于后部(P<0.05)。结论:不同节段终板的抗压强度分布规律不同,临床安放椎间置入物时需注意置入物的大小及放置位置。     

Variation of endplate thickness in the cervical spine

The purpose of the study was to investigate possible variation of thickness of the cervical spine endplate with respect to endplate orientation (superior or inferior endplate) and level distribution (C4–C7). Six human cervical spine segments C4–C7 were used to create six specimen of C4, C5, C6, and C7, respectively. The bony endplates of each vertebra were cleaned carefully from disc tissue without damaging the endplates. Six endplates with severe degenerative changes were excluded from the study. The posterior elements were removed, and a midaxial cut using a bone saw was performed through each vertebral body, thus producing a superior and inferior half. Each half-vertebra was then glued onto a piece of wood with the endplate oriented upwards and horizontally. For each specimen, four computed tomography scans were taken and thickness of the endplate was measured at five points on each scan perpendicular to the midaxial cut. Factorial analysis of variance (ANOVA) and Scheffe-test were used to detect significant differences. All peripheral regions were significantly thicker than the central point of the endplate if all measuring points were considered for statistical analysis, regardless of scan, endplate orientation or level (Scheffe-test, P<0.001). In both superior and inferior endplates, peripheral areas were thicker than the central region (Scheffe-test, P<0.001). For all levels, the endplate within the peripheral regions was thicker than within the central region and the difference reached significance for the superior and inferior endplate of C4, C5, and C6 and the inferior endplate of C7 (Scheffe-test, P<0.05). The peripheral regions of the cervical spine endplate are usually thicker than its central region, regardless of endplate orientation and level (C4, C5, C6, C7) distribution.     

Asymmetry between the superior and inferior endplates is a risk factor for lumbar disc degeneration

Endplate pathology plays an important role in the development of lumbar disc degeneration. Previous research paid little attention to differences between the superior and inferior endplates as a possible risk factor for disc degeneration. The purpose of this study was to test the hypothesis that asymmetry between the superior and inferior endplates is a risk factor for the development of lumbar disc degeneration. A total of 134 patients with lumbar disc herniation (LDH) and 100 healthy adults (“Controls”) underwent magnetic resonance imaging scans. Each disc was categorized as non‐degenerated (Pfirrmann grades I–II) or degenerated (Pfirrmann grades III–V) and get the following three groups: “Degenerated LDH” discs (n = 145), “Non‐degenerated LDH” discs (n = 525) and “Non‐degenerated Control” discs (n = 500). On mid‐sagittal image, the lumbar endplate morphology could be categorized into three types: Flat, concave, and irregular. Superior and inferior endplates of a given disc were “symmetric” if both were of the same type, and “asymmetric” if they were of different types. The proportion of asymmetric endplates at L4–5 was higher in the “Degenerated LDH” discs group (47%) than in the “Non‐degenerated LDH” discs group (21%) or “Non‐degenerated Control” discs group (7%) (p < 0.05). At L5‐S1 the proportions were 73%, 55%, and 38% (p < 0.05). Asymmetry of superior and inferior endplates in the mid‐sagittal plane is a risk factor for lumbar disc degeneration. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2469–2475, 2018.

     

The distribution of mineral density in the cervical vertebral endplates

Subsidence of various constructs into the vertebral body is a well-known complication in anterior fusion. Information on bone structure is needed, as a basis for improving these procedures. There are, however, no data available on the distribution of mineral density within vertebral endplates. In this study the regional distribution of mineralization within the cervical endplates with respect to endplate orientation (inferior and superior endplate) and level distribution (C3–C7) was examined by means of computed tomographic osteoabsorptiometry (CT-OAM). The distribution of mineralization in 80 cervical endplates of 8 spinal columns (4 male, 4 female, age range 38–62 years) in vertebrae C3–C7 was investigated by CT osteoabsorptiometry (CT-OAM). The subchondral mineralization distribution revealed considerable topographic differences within each endplate, whereby the areas of greatest density were found in the peripheral marginal zones with maxima in the posterolateral surface, whereas mineralization density was much lower in the central areas. The superior endplates showed an additional posteromedial maximum, whereas the inferior endplates showed an additional anterior mineralization maximum. Comparison of the distribution patters of inferior and superior endplates at different levels from C3 to C7 reveals a uniform increase of mineralization in the anterior portions from cranial to caudal. The mineralization distribution showed characteristic reproducible patterns. The maximal values occurred in the posterolateral parts, and can thus be considered a morphological substrate of high long-term loading. This can serve as a basis for improved prosthesis design and the anchorage point for various fusion techniques.     

Effect of implant design and endplate preparation on the compressive strength of interbody fusion constructs

STUDY DESIGN: A human cadaveric study on the compressive strength of different lumbar interbody fusion implants and endplate preparation techniques was performed. OBJECTIVES: To assess the axial compressive strength of an implant with peripheral endplate contact as opposed to full surface contact, and to assess whether removal of the central bony endplate affects the axial compressive strength. SUMMARY OF BACKGROUND DATA: The compressive strength of interbody fusion constructs has been compared between implants and bone grafts. Neither implant design nor endplate preparation has been shown to affect strength. Removal of the central bony endplate for bone grafts was noted to improve graft incorporation but also to facilitate subsidence. METHODS: A total of 44 vertebrae were tested in four experimental groups by combining two interbody implants (full-surface vs peripheral surface support) with two endplate preparation techniques (intact bony endplate vs removal of the central bony endplate). Specimens were tested to ultimate compressive failure using a 50 N/second ramped load. Yield strength and ultimate compressive strength were compared between groups using two-factor analysis of covariance. A P value less than 0.05 was considered significant. Stepwise linear regressions assessed the predictive power of age, bone mineral content, and the implant's normalized endplate coverage on yield strength and ultimate compressive strength. RESULTS: Neither implant design nor endplate preparation technique affected yield strength or ultimate compressive strength. Age, bone mineral content, and the normalized endplate coverage were strong predictors of yield strength (P < 0. 0001; r2 = 0.459) and ultimate compressive strength (P < 0.0001; r2 = 0.510). CONCLUSIONS: An implant with only peripheral support resting on the apophyseal ring offers axial mechanical strength similar to that of an implant with full support. Neither supplementary struts nor a solid implant face has any additional mechanical advantage, but reduces graft-host contact area. Removal of the central bony endplate is recommended because it does not affect the compressive strength and promotes graft incorporation.     

下腰椎软骨终板的形态测量及其临床意义

目的　探讨螺旋CT三维重建测量下腰椎软骨终板的方法 ,为下腰椎椎间盘疾病诊断及治疗提供一种定量检测指标。方法　福尔马林浸泡尸体脊柱标本 2 8例 ,分别采用螺旋CT扫描。扫描范围自L3 上缘至S2 上缘 ;扫描条件 :12 0Kv ,15 0mAs,成像矩阵 5 12× 5 12 ,FOV16cm ,层厚 1mm ,螺距 1 0 ,Pitch 1 0。利用O2图像工作站将原始扫描图像进行多平面重建(MPR) ,再在MPR重建的基础之上行曲面重建 (CPR) ,勾画出软骨终板的轮廓 ,然后测量软骨终板的最大矢状径、横径、面积、周径、形态。结果　L3 下缘至S1上缘软骨终板由类“心形”渐渐变为“椭圆形” ,作者还提供了L3 至S1软骨终板的所有测量参数。结论　螺旋CT三维重建方法用来评估椎间盘软骨终板简便、易行、可靠性好 ,为临床椎间盘疾病的诊断及治疗提供一种新的定量测量方法     

不同程度退变的软骨终板的影像学变化及其临床意义

目的：从影像学角度研究腰椎间盘不同程度退变时终板在矢状面和横断面的形态变化规律，探讨其临床意义。方法：本研究选取58例L4．5椎间盘呈退行性改变的影像学资料（MRI、CT）进行研究（其中椎间盘突出者34例），分别将其矢状位MRI T2WI成像采用MRI机内Mean／Curve测量软件测量L4．5运动节段退变的椎间盘与相应节段脑脊液平均信号强度比值，判断椎间盘退变程度进行分组。分为3组：轻度退变组17例，中度退变组17例，重度退变组24例。同时采用正中矢状位MRI T2WI成像分别测量相应椎间（L4．5）终板于矢状面上的凹陷角。另外借助L4．5椎间CT平扫成像测量其相邻终板的最大前后径和横径，计算终板的相对曲率，分析椎间盘在不同退变程度下椎体终板凹陷角及其相对曲率的变化规律，并探讨椎体终板的凹陷角与其相对曲率的相关性。结果：①椎体终板（L4下终板，L5上终板）凹陷角均随着相应椎间盘退变程度加重而增大，重度退变组与中度、轻度退变组（L4下终板、L5上终板）凹陷角差异均有统计学意义（P〈0．01）。②重度退变组与轻度退变组（L4下终板、L5上终板）相对曲率差异有统计学意义（P〈0．01），中度退变组与轻度退变组（L4下终板、L5上终板）相对曲率差异有统计学意义（P〈0．01），中度退变组与重度退变组（L4下终板、k上终板）相对曲率差异无统计学意义（P〉0．05）。⑧终板凹陷角与其相对曲率呈正相关关系（r：0．786，0．490）。结论：椎体终板的凹陷角与相对曲率随着椎间盘退变程度加重而发生相应变化，这种变化是腰椎间盘退变突出、椎间盘源性下腰痛的重要因素，且椎体终板的凹陷角与其相对曲率存在着相关关系，故可以通过凹陷角的变化判断其相对曲率的改变，评估椎间盘突出的概率。     

Influences of disc degeneration and bone mineral density on the structural properties of lumbar end plates

Background contextImplants subsidence is a frequent complication of interbody fusion, which can result in pain, deformity, nerve damage, and even failure of surgery. The end plates as the interface between implants and the vertebral bodies play a very important role in sharing the compression on the vertebral bodies. The information on the structural property distribution of the end plate and its relationship with bone mineral density (BMD) and disc degeneration will be of great significance for the reduction in implants subsidence and improvement in related operative procedures to increase the success rate of interbody fusion.PurposeTo investigate the structural property distribution of the lumbar end plate; the effects of disc degeneration on the biomechanical properties of the lumbar end plate; and the relationship between the biomechanical properties of the lumbar end plate and BMD.Study designA biomechanical study was conducted in human cadaveric lumbar spine models.MethodsIndentation tests were performed at 24 standardized test sites in 120 bony end plates of intact human vertebrae (L1–L5) using a 1.5-mm–diameter, hemispherical indenter at a speed of 0.2 mm/s. The failure load at each test site was determined using the load-displacement curve. Disc condition was evaluated using a four-point grading scale and bone density was measured using the lateral dual-energy radiograph absorptiometry scans. All end plates were divided into different disc degeneration groups based on the states of the adjacent degenerative discs and BMD groups according to BMD values of the corresponding vertebral bodies. The experimental results were statistically analyzed using the SPSS 15.0 with the disc degeneration and BMD being considered as independent factor, and the failure loads of the superior and inferior end plates were also compared.ResultsThe peripheral regions of lumbar end plates were stronger than the central regions (p<.05), with the posterolateral sites in front of vertebral pedicles being the strongest regions. The inferior lumbar end plates were found to be stronger than the superior lumbar end plates (p<.05). The disc degeneration was negatively correlated with the failure loads of the lumbar end plates (r_s=?0.563; p<.01). With increasing disc degeneration, the decreases of failure loads were nonuniform across the lumbar end plate, and the central region became weak with little strength change on the end plate periphery. The BMD was positively correlated with the failure loads of the lumbar end plates (r_s=0.812; p<.01). The failure loads decreased uniformly across the end plate surfaces as the BMD dropped, and the BMD decrease did not change the structural property distributions of lumbar end plates.ConclusionsPreoperative evaluation of the states of intervertebral discs and BMD of patients is necessary for predicting risks of implants subsidence after interbody fusion. For patients with or without disc degeneration or osteoporosis, the implants should be placed at the peripheral regions, especially the posterolateral sites, to acquire higher mechanical strength to reduce subsidence as much as possible.     

Structural features and thickness of the vertebral cortex in the thoracolumbar spine

STUDY DESIGN: The thickness and structure of the vertebral body cortex were examined from sections of human cadaveric vertebrae. OBJECTIVES: The objectives were to identify the principal structural features of the cortex, to directly measure the minimum and maximum thicknesses of the cortex in the thoracolumbar spine, and to compare regional variations in the structure of the cortex. SUMMARY OF BACKGROUND DATA: The thickness of the vertebral cortical shell contributes to the compressive strength of the vertebral body. There is little consensus concerning the thickness and morphology of vertebral shell and endplate along the spine in existing data. METHODS: Human T1, T5, T9, L1, and L5 vertebral bodies (mean age 70.4 years) from 20 cadaveric spines were sectioned and photographed. The minimum and maximum cortical thickness of the shells and endplates in the midsagittal plane were measured from magnified images. RESULTS: The anterior shell thickness was significantly greater than the posterior shell and both endplates. Endplate thickness was greatest in the lower lumbar vertebrae. There was a significant decrease in cortex thickness over the central portion of endplates and shells, with a mean minimum thickness of 0.40 mm and a mean maximum thickness of 0.86 mm, with an overall mean of 0.64 +/- 0.41 mm. Increased porosity was also observed along the central regions of the cortical shells. In the lower thoracic and lumbar spine, a double-layered endplate structure was observed. CONCLUSIONS: Invasive techniques provide the only means to directly resolve the thickness and distribution of bone in the vertebral cortex. The cortex thickness and structure varies along the endplates and the anterior and posterior surfaces of the vertebral body. The implications of the so called double-layered endplate structure are unknown, but indicate the need for further study.     

Regional variation in vertebral bone morphology and its contribution to vertebral fracture strength

Vertebral fractures may result in pain, loss of height, spinal instability, kyphotic deformity and ultimately increased morbidity. Fracture risk can be estimated by vertebral bone mineral density (BMD). However, vertebral fractures may be better defined by more selective methods that account for micro-architecture.

Our aim was to quantify regional variations in bone architecture parameters (BAPs) and to assess the degree with which regional variations in BAPs affect vertebral fracture strength. The influence of disc health and endplate thickness on fracture strength was also determined.

The soft tissue and posterior elements of 20 human functional spine units (FSU) were removed (T9 to L5, mean 74.45 ± 4.25 years). After micro-CT scanning of the entire FSU, the strength of the specimens was determined using a materials testing system. Specimens were loaded in compression to failure. BAPs were assessed for 10 regions of the vertebral cancellous bone. Disc health (glycosaminoglycan content of the nucleus pulposus) was determined using the degree of binding with Alcian Blue.

Vertebrae were not morphologically homogeneous. Posterior regions of the vertebrae had greater bone volume, more connections, reduced trabecular separation and more plate-like isotropic structures than their corresponding anterior regions. Significant heterogeneity also exists between posterior superior and inferior regions (BV/TV: posterior superior 12.6 ± 2.8%, inferior 14.6 ± 3%; anterior superior 10.5 ± 2.2%, inferior 10.7 ± 2.4%). Of the two endplates that abutted a common disc, the cranial inferior endplate was thicker (0.44 ± 0.15 mm) than the caudal superior endplate (0.37 ± 0.13 mm). Our study found good correlations between BV/TV, connective density and yield strength. Fracture risk prediction, using BV/TV multiplied by the cross sectional area of the endplate, can be improved through regional analysis of the underlying cancellous bone of the endplate of interest (R² 0.78) rather than analysis of the entire vertebra (R² 0.65) or BMD (R² 0.47). Degenerated discs lack a defined nucleus. A negative linear relationship between disc health and vertebral strength (R² 0.70) was observed, likely due to a shift in loading from the weaker anterior vertebral region to the stronger posterior region and cortical shell.

Our results show the importance of considering regional variations in cancellous BAPs and disc health when assessing fracture risk.     

Endplate deflection is a defining feature of vertebral fracture and is associated with properties of the underlying trabecular bone

Endplate deflection frequently occurs with vertebral failure, but the relationship between the two remains poorly defined. This study examined associations between endplate deflection under compressive loading and characteristics of the neighboring subchondral bone and intervertebral disc (IVD). Ten L1 vertebrae with adjacent IVDs were dissected, compressed axially in a stepwise manner to failure, and imaged with micro‐computed tomography before each loading step. From the images, deflection was measured across the surface of each endplate at each step. Trabecular microstructure and endplate volume fraction were evaluated in 5 mm regions just under the superior endplate. IVDs were assessed using computed tomography and histology. A marked increase in superior endplate deflection coincided with a drop in the load‐displacement curve. Endplate deflection was higher in regions with less robust bone microstructure (p < 0.009), though these associations tended to weaken as loading progressed. Immediately following the ultimate point, endplate deflection was higher in regions underlying the nucleus pulposus versus annulus fibrosus (p = 0.035), irrespective of disc grade (p = 0.346). These results indicate that a sudden increase in endplate deflection signals that the mechanical competence of the vertebra has been compromised. The mechanisms of endplate failure likely relate to anatomical features of the endplate, neighboring trabecular bone, and IVD. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:880–886, 2014.     

Sagittal geometry of the middle and lower cervical endplates

Purpose

Construct subsidence is a relatively common complication following anterior cervical fusion. Its occurrence has been revealed to be closely related to endplate-implant contact interface. But current literature focusing on the anatomy of cervical endplate is very scarce. The purpose of this morphometric study was to analyse the sagittal geometry, especially the concavity and slope, of vertebral endplates from C3 to C7 by employing data from CT scans.

Methods

Reformatted CT scans of 97 individuals were analyzed and endplate concavity depth, endplate concavity apex location, as well as endplate slope were measured in midsagittal plane. Those specific parameters were compared among different age and gender groups. Meanwhile, comparison between superior and inferior endplate of each vertebra was also performed.

Results

Age and gender did not influence endplate concavity depth, endplate concavity apex location, or endplate slope significantly (P > 0.05). Endplate concavity depths of superior endplates (range 0.9–1.2 mm) were significantly smaller than those of inferior endplates (range 2.1–2.7 mm). Endplate concavity apex was always located in the posterior half of the endplate, with the superior one ranged from 56 to 67 % and the inferior one 52 to 57 %. Average endplate slopes of superior endplates were between 4.5° and 9.0°, and average inferior endplate slopes ranged from 4.5° to 7.5°. Among all measured segments, C5 had the largest endplate slope values, while C7 the least.

Conclusions

Superior endplate is more flat than its inferior counterpart in middle and lower cervical spine, and the concavity apex is always located in the posterior half of the endplate. Endplate slope is correlated with cervical curvature, greater slope implying more significant lordosis. These sagittal endplate geometrical parameters should be taken into consideration when investigating implant subsidence following anterior cervical fusion.     

Geometry of thoracolumbar vertebral endplates of the human spine

Novel and better vertebral body replacement constructs are always desired by surgeons. Endplate geometry is crucial for the design of those implants, but current literature on that topic is very scarce. The authors present a morphometric study of thoracolumbar vertebral endplates, the goal of which was to analyze the geometry of endplates from T10 inferior to L3 superior by employing data from CT scans, as well as to verify the reliability of data derived from the CT measurement. Reformatted CT scans of 83 individuals were analyzed and sagittal concave angle, location of concave region, sagittal diameter of endplate, coronal concave angle, as well as transverse diameter of endplate were measured in midsagittal plane and specified coronal plane. The data of CT and cadaveric measurements of ten cadaveric specimens were also compared. Age and gender did not influence sagittal concave angle, location of concave region, and coronal concave angle significantly (P > 0.05). No significant difference has been revealed among each endplate for sagittal concave angle (range 162.5°–163.9°) and location of concave region (range 42.5–44.2%), either. Ranging between 170.9° and 175.7°, coronal concave angle was constantly larger in superior endplate than in inferior one. The sagittal and transverse endplate diameters of females were significantly smaller than those of males (P < 0.05), being about 88% of the latter one. The mean difference between CT and cadaveric measurements was small (Cronbach alpha > 0.8). Those morphologic parameters, especially the concavity of endplates, should be taken into consideration when designing novel vertebral body replacement constructs. CT measurement data could be used to calculate most suitable geometric parameters of those implants.     

Vertebral endplate fractures: an indicator of the abnormal forces generated in the spine after vertebroplasty.

Vertebroplasty alters spinal biomechanics and may lead to incident vertebral fractures. The endplate localization of prevalent and incident fractures was evaluated in 86 patients. In the absence of vertebroplasty, superior endplate fractures predominate. After the procedure, inferior endplate fractures are disproportionately common in adjacent vertebrae immediately above the treated level, potentially supporting a causative relationship between vertebroplasty and incident fractures. INTRODUCTION: To determine retrospectively whether new-onset fractures after vertebroplasty tend to cluster in the endplate immediately adjacent to the cemented vertebra. MATERIALS AND METHODS: Institutional Review Board approval and patient consent for use the use of medical records were obtained for this study. We performed a retrospective review of patients with new (incident) vertebral fractures after vertebroplasty. The median age for these patients was 72.5 years, and 58 (67.4%) were women. Fractures were diagnosed on the basis of MRI or bone scan and were catalogued based on their location within the vertebral body (superior endplate, inferior endplate, or holo-vertebral). Chi(2) and generalized estimating equation (GEE) analyses were used to compare the distribution of fracture subtypes among pre-existing (prevalent) and incident fractures. RESULTS: The patients had 313 prevalent osteoporotic vertebral fractures and were treated at 137 vertebral levels. Among prevalent fractures, superior endplate fractures predominated (57% superior, 11% inferior; p < 0.0001). After vertebroplasty, 186 incident fractures developed in these 86 patients. Seventy-seven (41%) of these incident fractures occurred adjacent to treated vertebrae. Nonadjacent, incident fractures, like prevalent fractures, occurred predominantly along superior endplate. Incident fractures immediately above treated levels, however, localized disproportionately to the inferior endplate (30% superior, 57% inferior; p < 0.0001). CONCLUSIONS: There are an increased number of inferior endplate fractures of the vertebral body immediately cephalad to the treated level.     

The gluteus maximus muscle: experimental and clinical considerations relevant to reconstruction in ambulatory patients

The gluteus maximus muscle and other haemodynamically related structures have been used for the reconstruction of significant defects in the perineum, sacrum, lumbar area and hip in 35 patients. The preservation of muscle function was achieved in all of 20 ambulatory patients and documented by gait analysis, muscle strength testing and EMG studies. Dye injection studies of the first perforating artery, inferior gluteal artery and superior gluteal artery led to the design of new flaps based on this arterial system. They include: medial advancements with extension above the sacrum, lateral advancements, lower gluteus advancements, the tensor fasciae latae gluteal extension and modifications of the gluteal thigh flap. These findings significantly increase our ability to close difficult wounds within the perineal, sacral, lumbar and trochanteric regions.