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。     

骨密度对腰椎终板最大抗压强度影响的实验研究

目的:探讨腰椎骨密度(BMD)与腰椎终板生物力学性质的关系.方法:选用人体新鲜腰椎标本(L1～L5)7具,共35个椎体,用双能X线吸收骨密度仪(DEXA)测试每个椎体的BMD,游离成单个椎体,按骨质疏松试行诊断标准分成正常对照组(n=16)、骨密度减低组(n=10)和骨质疏松组(n=9),每个椎体上、下终板平面上设定24个特定测试点,用直径1.5mm的半球形压头以12mm/min的速度垂直于终板平面在每个测试点进行连续压缩加载试验,记录最大压缩力,并对数据进行统计学分析.结果:三组腰椎的骨密度分别为1.085±0.101g/cm2、0.781±0.095g/cm2和0.498±0.085g/cm2;平均最大抗压力分别为84.74±29.97N、74.98±23.57N和61.88±16.09N,三组间存在显著性差异(P＜0.01),最大压缩力与BMD呈明显的正相关关系(rs=0.632,P＜0.01).腰椎终板表面的最大抗压力点位于紧邻椎弓根的终板后外侧边缘,BMD对腰椎终板不同位点生物力学强度分布无明显影响.结论:椎体BMD是预测椎体生物力学特性的重要指标,建议术前常规查BMD,术中置入物应尽量放置于椎体终板的后外侧部以减少置入物沉陷的发生.     

不同终板准备方法对ProDisc-C颈椎人工椎间盘假体稳定性的影响

目的:探讨不同颈椎终板准备方法对颈椎人工椎间盘置换术后金属-骨界面刚度的影响,了解终板准备方法与人工椎间盘假体稳定性的关系。方法:取6具新鲜成人尸体颈椎标本,分离出C3～T1共35个椎体(1例C6～C7融合),剔除每个椎体上下面的椎间盘组织,显露出骨性终板,分为:去终板组17个,完全去除骨性终板;保留终板组18个,完整保留骨性终板。在所有椎体的上面安放相应大小的颈椎人工椎间盘(ProDisc-C)后用MTS-858生物力学实验机进行疲劳测试和屈服测试,得到金属-骨界面的刚度、位移和最大屈服压力,从其中1具颈椎标本取出4个椎体(每组各2个)切片行HE染色后用光镜观察金属-骨性界面。结果:疲劳前测试金属-骨界面刚度去终板组为1470±180N/mm,高于保留终板组的1260±170N/mm(P<0.0001);疲劳后测试两组刚度均有上升,去终板组刚度为1990±110N/mm,仍高于保留终板组的1680±140N/mm(P<0.0001)。疲劳前测试两组的终板位移分别为0.45±0.09mm和0.41±0.10mm,无显著性差异(P=0.15),疲劳后测试去终板组位移0.53±0.12mm小于保留终板组的0.66±0.14mm(P=0.005)。去终板组最大屈服压力为1110±350N,略小于保留终板组的1250±230N,但无显著性差异(P=0.27)。组织切片显示去终板组金属-骨界面贴合良好,而保留终板组金属-骨界面有明显的缝隙。结论:不同的终板准备方法会影响到假体金属-骨界面的刚度和稳定性。去终板组金属-骨界面的刚度和稳定性优于保留终板组,良好的金属-骨界面接触是颈椎人工椎间盘假体稳定的关键因素之一。     

腰骶椎终板生物力学特性的实验研究

目的:研究腰骶椎终板不同位点的生物力学特性及其分布规律。方法:选用成人新鲜尸体腰骶椎标本(L1～S1)5具,共30个椎体55个终板,应用电子万能实验机(型号CSS-2205)对终板平面49个测试点用直径1.5mm的平底压头以12mm/min的速度进行连续压缩加载实验,记录最大压缩力,并对数据进行统计分析。结果:(1)L1～S1上终板最大压缩力从68.81±8.12N增加至120.41±34.33N,各节段间差异有显著性(P<0.05);L1～L4下终板最大压缩力从78.66±5.57N增加至120.44±29.27,L5降为106.65±16.10N,各节段间差异有显著性(P<0.05)。(2)L1～S1上终板中央至外周最大压缩力从65.02±6.40N增加至110.61±10.63N,下终板中央至外周最大压缩力从68.09±9.43N增加至162.69±16.46N,差异有显著性(P<0.05);上终板前侧最大压缩力为87.30±6.42N,后侧为89.25±14.30N,下终板前侧最大压缩力107.63±4.84N,后侧最大压缩力109.82±18.66N,差异均无显著性(P>0.05)。(3)L3/4、L4/5上下终板的最大压缩力的差异均有显著性(P<0.05),余间隙差异无显著性。结论:L1～S1上终板强度逐渐增大;L1～L4下终板强度逐渐增大,L4～L5减小;腰骶椎上、下终板强度从中央至外周逐渐增大,前、后侧无差异;L3/4、L4/5间隙上位椎体下终板强度大于下位椎体上终板。     

动静力失衡对大鼠颈椎不同节段椎间盘退变影响的显微CT形态学和组织学研究

目的:评价大鼠动静力失衡颈椎退变模型对C4～C7各节段终板磨损面积、椎间高度和椎间盘退变的影响,并分析终板磨损面积和椎间高度与椎间盘退变的相关性.方法:24只3月龄雌性SD大鼠随机分为模型组(14只)和对照组(10只).对照组仅做皮肤切口;模型组大鼠横向切断颈背部肌肉以及韧带,制作大鼠动静力失衡颈椎退变模型.术后12周、18周、24周分三次取大鼠颈椎标本.标本取材后进行显微CT扫描以及番红O快绿染色.测量C4/5、C5/6、C6/7各个节段椎间高度,计算上述三个节段的终板磨损比例,并对椎间盘退变程度进行评分.应用SPSS 13.0比较不同组相同节段椎间盘的终板磨损率,椎间高度和退变评分,并分析终板磨损率与椎间盘退变之间的相关性.结果:显微CT扫描发现模型组术后12周各个节段软骨终板均出现明显的磨损,磨损主要位于终板的腹侧.颈椎节段越高,磨损程度越轻.术后18周、24周,模型组C5/6、C6/7软骨终板磨损比例明显大于对照组,有统计学意义(P＜0.05).术后各个时间点,模型组不同节段终板磨损率情况不同,其中C6/7节段明显大于C4/5节段(P＜0.05).组织学切片显示,软骨终板的形态学改变早期以磨损为主,晚期则出现了大量钙化.术后12周,模型组C5/6、C6/7椎间高度明显低于对照组,术后18周、24周时高度进一步下降.术后12周,模型组的各节段椎间盘退变评分明显高于对照组(P＜0.05).术后24周时,模型组C4/5退变评分为11.5±1.0分,C5/6为11.8±1.0分,C6/7为12.8±0.8分.不同节段椎间盘退变评分差异有显著性(P＜0.05),其中C6/7椎间盘退变评分最高,明显大于C4/5、C5/6节段(P＜0.05).相关分析显示:终板磨损比例与椎间盘高度、椎间盘退变评分具有明显的相关性.结论:在大鼠动静力失衡颈椎退变模型中C6/7终板磨损比例较大,椎间盘高度降低出现较早,组织学上椎间盘退变程度也较严重,是该模型椎间盘退变的主要节段.软骨终板的形态学改变与椎间高度的降低和椎间盘退变程度有明显的相关性.     

颈椎终板抗压强度分布规律的生物力学研究

[目的]研究颈椎终板不同位点抗压强度及其分布规律。[方法]选用5具成年男性新鲜颈椎标本(C3～7),共25个椎体50个终板。对终板平面49个测试点用直径1.5 mm的平底压头以12 mm/min的速度进行连续压缩加载试验,获得最大压缩力,进行统计分析。[结果](1)抗压强度自C3～7逐渐减小(P﹤0.05);(2)下终板抗压强度大于上终板(P=0.000);(3)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抗压强度(P<0.05);(4)随着压力点逐渐外移,抗压强度逐渐增大(P﹤0.05);(5)处于不同角度的压力点,其抗压强度存在差异(P=0.029);(6)终板后部强于前部(P=0.003)。上终板后部抗压强度大于前部(P=0.000)。[结论]颈椎终板抗压强度自C3～7逐渐减小,下终板强于上终板,外周大于中央,后部强于前部。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抗压强度。     

颈椎终板软骨细胞凋亡的检测及相关意义

目的检测颈椎终板软骨细胞的细胞凋亡指数,探讨其在椎间盘退变中可能的作用机制。方法颈椎间盘终板及髓核取自我院行颈椎前路手术的35例颈椎椎间盘退变患者（退变组）和19例颈椎外伤患者（外伤组）。光镜观察退变组和外伤组终板和髓核的细胞密度,TUNEL法检测两组终板软骨细胞和髓核细胞的细胞凋亡指数,咔唑分光光度法比较两组髓核蛋白多糖含量。结果退变组终板细胞密度较外伤组减少（P〈0.05）,TUNEL染色显示退变组终板细胞凋亡指数为（34.6±16.1）%,外伤组为（20.1±9.3）%,两组间比较差异有统计学意义（P〈0.05）。Pearson相关分析显示,颈椎终板TUNEL染色阳性细胞率与终板细胞密度、髓核蛋白多糖含量之间呈负相关（r=—0.805,P=0.001;r=—0.677,P=0.023）,与髓核TUNEL阳性细胞率之间呈正相关（r=0.758,P=0.003）。结论颈椎退变终板软骨细胞凋亡率较高,推测在椎间盘退变过程中可能发挥重要作用;软骨细胞凋亡可能与髓核细胞凋亡增加、终板细胞密度与髓核蛋白多糖含量降低密切相关。     

颈椎间盘退变对颈椎生物力学影响的有限元研究

目的建立人体颈椎C4-C5-C6节段颈椎间盘退变三维有限元模型,分析椎间盘退变对颈椎运动节段生物力学的影响。方法通过改变椎间盘材料特性和高度等参数,建立椎间盘轻度退变模型(LD)、中度退变模型(MD)和重度退变模型(SD)。在45 N垂直载荷下,分别对正常、轻、中、重度4种有限元模型进行生物力学测试,比较4种模型之间各项生物力学参数的差异。结果建立了C4-C5-C6节段颈椎间盘逐级退变三维有限元模型。45 N垂直载荷条件下,正常模型(ND)、MD、SD椎间盘轴向位移及向外膨出位移逐渐变小,LD椎间盘轴向位移及膨出位移比ND增大,四组模型纤维环轴向压缩应力逐渐增大,髓核内压力逐渐减小。ND、MD、SD关节突关节接触力逐渐减小,LD关节突关节接触力较ND轻度增大。结论椎间盘轻度退变时,颈椎稳定性下降。中、重度退变时,颈椎稳定性重新获得。从生物力学方面证明退变的椎间盘对维持颈椎的稳定性有一定的代偿作用。     

兔颈椎终板胶原结构变化对运动节段力学性能的影响

目的 通过测定兔退变颈椎运动节段力学参数的改变,观测其软骨终板胶原的超微结构变化,为退变的椎间盘显现异常力学特性作材料结构上的探讨。方法 将24只家兔随机分为对照组和模型组,模型组家兔保持45°低屈曲位5 h/d,取C5,6、C6,7进行生物力学测定,同时电镜观察终板胶原组织结构改变,总结分析终板材料的结构变化对运动节段力学性能的影响。结果 模型组终板抗扭强度、抗压强度、断裂时的最大形变都低于对照组,胶原排列从有序、致密、规整到紊乱、松散、溶解,并随造模进程的深入而加剧。结论 长时间的应力不均状态,造成椎间盘终板材料力学特性改变;终板胶原结构改变是颈椎间盘生物力学性能减退的原因之一。     

颈椎软骨终板钙化与颈椎间盘退变和椎体骨赘形成的关系

目的：研究颈椎软骨终板钙化与颈椎间盘退变和颈椎椎体骨赘形成的关系。方法：应用组织学方法观察颈前路环锯手术切下的18例脊髓型颈椎病和4例颈椎过伸性损伤致颈椎间盘突出患者的颈椎间盘及相邻的上下椎体标本,研究不同退变程度颈椎间盘软骨终板和椎间盘的形态学变化及椎体骨赘形成过程。结果：退变程度较轻或基本正常的颈椎间盘软骨终板结构良好,潮标清晰,退变程度较重的颈椎间盘软骨终板发生明显纤维化,潮标前移,钙化软骨和软骨下骨板增厚,退变颈椎间盘周边软骨终板潮标明显前移,钙化和骨化层增厚,形成突向外侧的椎体边缘的骨赘。结论：颈椎软骨终板的不断钙化和骨化导致颈椎间盘营养发生障碍可能是启动颈椎间盘退变的关键因素,退变椎体周边软骨终板的不断钙化和骨化是椎体骨赘形成的根本原因。     

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.     

Mapping the structural properties of the lumbosacral vertebral endplates

STUDY DESIGN: A biomechanical investigation using indentation tests in a human cadaveric model to seek variation in the structural properties across the lower lumbar and sacral endplates. OBJECTIVES: To determine 1) if there are regional differences in endplate strength and 2) whether any differences identified are affected by spinal level (lumbar spine vs. sacrum) or endplate (superior vs. inferior). SUMMARY OF BACKGROUND DATA: It has been postulated that some regions of the vertebral body may be stronger than others. Conclusive data, either supporting or disproving this theory, would be valuable for both spine surgeons and implant designers because one mode of failure of interbody implants is subsidence into one or both adjacent vertebrae. METHODS: Indentation tests were performed at 27 standardized test sites in 62 bony endplates of intact human vertebrae (L3-S1) using a 3-mm-diameter, hemispherical indenter with a test rate of 0.2 mm/sec to a depth of 3 mm. The failure load and stiffness at each test site were determined using the load-displacement curves. Three-way analyses of variance were used to analyze the resulting data. RESULTS: Both the failure load and stiffness varied significantly across the endplate surfaces (P < 0.0001), with posterolateral regions being stronger and stiffer than the central regions. Characteristic distributions were identified in the lumbar superior, lumbar inferior, and sacral endplates. The failure load distributions were found to differ in 1) the superior lumbar and sacral endplates (P = 0.0077), 2) the inferior lumbar and sacral endplates (P = 0.0014), and 3) the superior and inferior lumbar endplates (P < 0.0001). The sacral and inferior lumbar endplates were both found to be stronger than the superior lumbar endplates (sacrum, P = 0.054; inferior, P = 0.008) but were not themselves significantly different (P = 0.89). CONCLUSIONS: Highly significant regional strength and stiffness variations were identified in the lumbar and sacral endplates. The center of the bone, where implants are currently placed, is the weakest part of the lumbar endplates and is not the strongest region of the sacral endplate.     

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。     

Effect of endplate conditions and bone mineral density on the compressive strength of the graft-endplate interface in anterior cervical spine fusion

STUDY DESIGN: Destructive compression tests and finite element analyses were conducted to investigate the biomechanical strength at the graft-endplate interface in anterior cervical fusion. OBJECTIVES: To investigate the effect of endplate thickness, endplate holes, and bone mineral density of the vertebral body on the biomechanical strength of the endplate-graft interface in an anterior interbody fusion of the cervical spine. SUMMARY OF BACKGROUND: Subsidence of the graft into the vertebral body is a well-known complication in anterior cervical fusion. However, there is no information in the literature regarding the compressive strength of the graft-endplate interface in relation to the endplate thickness, holes in the endplate, and bone mineral density of the vertebral body. METHODS: Biomechanical destructive compression tests and finite element analyses were performed in this study. Cervical vertebral bodies (C3-C7) isolated from seven cadaveric cervical spines (age at death 69-86 years, mean 79 years) were used for compression tests. Bone mineral density of each vertebral body was measured using a dual energy radiograph absorptiometry unit. Endplate thickness was measured using three coronal computed tomography images of the middle portion of the vertebral body obtained using a computer-assisted imaging analysis. Then each vertebral body was cut into halves through the horizontal plane. A total of 54 specimens, consisting of one endplate and half of the vertebral body, were obtained after excluding eight vertebrae with gross pathology on plain radiograph. Specimens were assigned to one of three groups with different endplate conditions (Group I, intact; Group II, partial removal; and Group III, complete removal) so that group mean bone mineral density became similar. Each endplate was slowly compressed until failure using an 8-mm-diameter metal indenter, and the load to failure was determined as a maximum force on a recorded force-displacement curve. The effect on the strength of the graft-endplate interface of various hole patterns in the endplate was studied using a finite element technique. The simulatedhole patterns included the following: one large central hole, two lateral holes, two holes in the anterior and posterior portion of the endplate, and four holes evenly distributed from the center of the endplate. Stress distribution in the endplate was predicted in response to an axial compressive force of 110 N, and the elements with von Mises stress greater than 4.0 MPa were determined as failed. RESULTS: The endplate thickness and bone mineral density were similar at all cervical levels, and the superior and inferior endplates had similar thickness at all cervical levels. There was no significant association between bone mineral density and endplate thickness. Load to failure was found to have a significant association with bone mineral density but not with endplate thickness. However, load to failure tends to decrease with incremental removal of the endplate, and load to failure of the specimens with an intact endplate was significantly greater than that of the specimens with no endplate. Finite element model predictions showed significant influence of the hole pattern on the fraction of the upper endplate exposed to fracture stress. A large hole was predicted to be more effective than the other patterns at distributing a compressive load across the remaining area and thus minimizing the potential fracture area. CONCLUSION: Results of this study suggest that it is important to preserve the endplate as much as possible to prevent graft subsidence into the vertebral body, particularly in patients with poor bone quality. It is preferable to make one central hole rather than multiple smaller holes in the endplate for vascularity of the bone graft because it reduces the surface area exposed to fracture stresses.     

Correlation of cervical endplate strength with CT measured subchondral bone density

Cervical interbody device subsidence can result in screw breakage, plate dislodgement, and/or kyphosis. Preoperative bone density measurement may be helpful in predicting the complications associated with anterior cervical surgery. This is especially important when a motion preserving device is implanted given the detrimental effect of subsidence on the postoperative segmental motion following disc replacement. To evaluate the structural properties of the cervical endplate and examine the correlation with CT measured trabecular bone density. Eight fresh human cadaver cervical spines (C2–T1) were CT scanned and the average trabecular bone densities of the vertebral bodies (C3–C7) were measured. Each endplate surface was biomechanically tested for regional yield load and stiffness using an indentation test method. Overall average density of the cervical vertebral body trabecular bone was 270 ± 74 mg/cm³. There was no significant difference between levels. The yield load and stiffness from the indentation test of the endplate averaged 139 ± 99 N and 156 ± 52 N/mm across all cervical levels, endplate surfaces, and regional locations. The posterior aspect of the endplate had significantly higher yield load and stiffness in comparison to the anterior aspect and the lateral aspect had significantly higher yield load in comparison to the midline aspect. There was a significant correlation between the average yield load and stiffness of the cervical endplate and the trabecular bone density on regression analysis. Although there are significant regional variations in the endplate structural properties, the average of the endplate yield loads and stiffnesses correlated with the trabecular bone density. Given the morbidity associated with subsidence of interbody devices, a reliable and predictive method of measuring endplate strength in the cervical spine is required. Bone density measures may be used preoperatively to assist in the prediction of the strength of the vertebral endplate. A threshold density measure has yet to be established where the probability of endplate fracture outweighs the benefit of anterior cervical procedure.     

A morphological study of lumbar vertebral endplates: radiographic, visual and digital measurements

Purpose

Clinical observations suggest that endplate shape and size are related to complications of disc arthroplasty surgery. Yet, the morphology of the vertebral endplate has not been well defined. This study was conducted to characterize the morphology of lumbar vertebral endplates and to quantify their morphometrics using radiographic, visual and digital measures.

Methods

A total of 591 vertebral endplates from 76 lumbosacral spines of men were studied (mean age 51.3 years). The shape of the vertebral endplates was classified as concave, flat and irregular, and was evaluated from both radiographs and cadaveric samples. Each endplate was further digitized using a laser scanner to quantify diameters, surface area and concavity for the whole endplate and its components (central endplate and epiphyseal rim). The morphological characteristics and morphometrics of the vertebral endplates were depicted.

Results

In both radiographic and visual assessments, more cranial endplates (relative to the disc) were concave and more caudal endplates were flat at all disc levels (p < 0.001). On average, the mean concavity depth was 1.5 mm for the cranial endplate and 0.7 mm for the caudal endplate. From L1/2 down to L5/S1 discs, the vertebral endplate gradually changed into a more oval shape. The central endplate was approximately 70 % of the diameter of the whole endplate and the width of the epiphyseal rim varied from 3 to 7 mm.

Conclusions

There is marked morphological asymmetry between the two adjacent endplates of a lumbar intervertebral disc: the cranial endplate is more concave than the caudal endplate. The size and shape of the vertebral endplate also vary considerably between the upper and lower lumbar regions.     

椎间盘退变与终板内微血管形态改变的相关性研究

目的:通过观测大白兔椎间盘退变过程中椎间盘终板内的血管形态以及血流量的改变,探讨终板内微血管的改变与椎间盘退变之间的相关性。方法:选用40只新西兰大白兔随机分为2组,通过切除造模组20只免腰椎棘间、棘上韧带及棘突、关节突,造成力学失稳状态诱导形成椎间盘退变模型。分别在术后4、8个月通过扫描电镜、血流激光多普勒仪测定椎体终板内的血管形态以及血流量。结果:在椎间盘退变过程中,椎间盘终板内的血管芽形态逐渐被破坏,微血管数量相应减少,终板内的血流量也明显减少,同时终板内血流量中心部位(靠近髓核区域)血流量多于终板内周围区域的血流量。结论:椎体终板内微血管的改变可能是椎间盘退变的促进因素。     

Stiffness of the endplate boundary layer and endplate surface topography are associated with brittleness of human whole vertebral bodies

Stress magnitude and variability as estimated from large scale finite element (FE) analyses have been associated with compressive strength of human vertebral cancellous cores but these relationships have not been explored for whole vertebral bodies. In this study, the objectives were to investigate the relationship of FE-calculated stress distribution parameters with experimentally determined strength, stiffness, and displacement based ductility measures in human whole vertebral bodies, investigate the effect of endplate loading conditions on vertebral stiffness, strength, and ductility and test the hypothesis that endplate topography affects vertebral ductility and stress distributions. Eighteen vertebral bodies (T6-L3 levels; 4 female and 5 male cadavers, aged 40–98 years) were scanned using a flat-panel CT system and followed with axial compression testing with Wood's metal as filler material to maintain flat boundaries between load plates and specimens. FE models were constructed using reconstructed CT images and filler material was added digitally. Two different FE models with different filler material modulus simulating Wood's metal and intervertebral disc (W-layer and D-layer models) were used. Element material modulus to cancellous bone was based on image gray value. Average, standard deviation, and coefficient of variation of von Mises stress in vertebral bone for W-layer and D-layer models and also the ratios of FE parameters from the two models (W/D) were calculated. Inferior and superior endplate surface topographical distribution parameters were calculated. Experimental stiffness, maximum load and work to fracture had the highest correlation with FE-calculated stiffness while experimental ductility measures had highest correlations with FE-calculated average von Mises stress and W-layer to D-layer stiffness ratio. Endplate topography of the vertebra was also associated with its structural ductility and the distribution parameter that best explained this association was kurtosis of inferior endplate topography. Our results indicate that endplate topography variations may provide insight into the mechanisms responsible for vertebral fractures.     

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。