膨胀式脊柱椎弓根螺钉固定的生物力学研究

目的:测试膨胀式椎弓根螺钉(expansivepediclescrew,EPS)的骨-器械界面强度及耐疲劳强度,评价EPS的脊柱后路固定强度。方法:100个新鲜小牛腰椎随机分成A、B、C三组,以USS,Tenor,CDH螺钉为对照螺钉,分别对EPS进行最大旋出力矩实验、轴向拔出实验和翻修实验,记录最大旋出力矩(Tmax)、最大轴向拔出力(Fmax)和翻修后最大轴向拔出力。并在超高分子聚乙烯材料上对螺钉进行150万次的周期载荷疲劳实验。结果:EPS的Tmax、Famx显著大于三种对照螺钉(P<0.01)。EPS翻修时的Fmax亦显著高于对照螺钉(P<0.05)。150万次周期载荷疲劳实验完成后,四种螺钉均未出现疲劳折断现象。结论:EPS较目前常使用的非膨胀椎弓根螺钉有更好的脊柱固定作用及翻修性能,其耐疲劳强度与其它三种螺钉相当。     

新型经皮椎弓根螺钉系统的设计与生物力学测试

目的 评估新型经皮椎弓根螺钉系统设计的合理性和临床操作可行性.方法 取6具经甲醛处理的完整尸体标本,模拟临床手术操作安放新型经皮椎弓根螺钉系统(A组),以传统经皮椎弓根螺钉系统为对照(B组).应用新型经皮椎弓根螺钉系统在新鲜小牛腰椎压缩性骨折模型上行撑开操作.分别以单向螺钉、改良螺钉和万向螺钉跨节段固定骨折,测量固定节段的三维稳定性.结果 A组平均手术时间(38.2±6.20)min,B组(56.4±12.8)min,差异有统计学意义(P<0.05).A组螺钉位置优良率91.7%,B组95.8%,差异无统计学意义.新型椎弓根螺钉系统对三种螺钉均具有良好的撑开功能,改良螺钉和单向螺钉主要撑开椎体前柱,两者差异无统计学意义;万向螺钉主要撑开椎体中、后柱,对前柱撑开效果较其他两种螺钉差(P<0.05).三组固定节段在完整状态和骨折状态的屈伸、左右侧弯及旋转运动范围无统计学差异.改良螺钉和单向螺钉固定后固定节段有相似的三维稳定性;万向螺钉屈伸稳定性较改良螺钉差(P<0.05),而侧弯和旋转稳定性与其他两组接近.结论 改良螺钉能有效撑开椎体前柱,螺钉-棒系统可对固定节段提供稳定性.新型经皮椎弓根螺钉系统具有临床操作可行性.     

强化膨胀式椎弓根螺钉翻修作用的生物力学评价

目的测试骨水泥强化膨胀式椎弓根螺钉(augmentation expansive pedicle screwfixa-tion with polymethyl methacrylate,AEPS),未强化的膨胀式椎弓根螺钉(expansive pedicle screw,EPS),CDH椎弓根螺钉翻修后的最大轴向拔出力,评价AEPS螺钉的翻修效应。方法24个新鲜小牛腰椎随机分成三组,AEPS组、EPS组、CDH组,每组8个椎体,三组椎体的椎弓根处均预先植入直径6.5mm CDH螺钉,拔出螺钉造成螺钉松动脱出的脊柱模型,然后分别植入AEPS、EPS、CDH螺钉,再次拔出螺钉,记录翻修后最大轴向拔出力。结果AEPS、EPS、CDH螺钉翻修后的最大拔出力分别为(2723.3±565.4)、(2216.3±475.6)和(1321.4±346.7)N,AEPS和EPS螺钉最大拔出力均显著高于CDH螺钉(P<0.05),AEPS轴向拔出力高于EPS螺钉,但差异无统计学意义(P>0.05)。结论AEPS与EPS螺钉具有相当的翻修作用。     

椎弓根螺钉生物力学研究新进展

椎弓根螺钉作为一种较为优良的脊柱内固定手段，近几年来已越来越广泛地应用于临床实践中。本文就生物力学研究与椎弓根螺钉最新进展进行综述。     

骨粘合剂强化椎弓根螺钉稳定的生物力学研究

如何提高骨质疏松患者椎弓根螺钉固定在椎体内的稳定性，已成为临床骨科亟待解决的难题。本文从生物力学角度综述了椎弓根强化固定的国外研究进展。     

几种椎弓根钉内固定器的生物力学测试与临床应用

目的通过生物力学测试和临床应用,对四种椎弓根内固定器进行评价.方法取24具新鲜猪的胸腰椎脊柱标本,制作成严重前中柱损伤模型,比较四种椎弓根内固定器械在轴向压缩、弯曲和扭转实验中的生物力学稳定性及椎弓根螺钉的握持能力.依据术前、术后X线片及CT片,分别测量178例胸腰椎骨折患者伤椎的前缘高度、后缘高度、后凸角度、椎管内径.结果池氏椎弓根螺钉抗拔出力及其安放后的标本抗侧屈及抗扭转能力较Dick钉、AF钉、RF钉强(P<0.05).池氏钉后凸矫正率为92.0%±20.5%,前缘矫正率为81.3%±10.7%,后缘矫正率为69.7%±8.3%,椎管内径改善率为89.4%±15.1%.经统计学处理较Dick钉、AF钉有显著差异(P<0.05).结论新型椎弓根钉内固定器(池氏钉)整复固定性能更强.     

通用型脊柱内固定系统椎弓根螺钉的生物力学测试

目的测试自行设计的通用型脊柱内固定系统(generalspinesystem,GSS)椎弓根螺钉以及SOCON和CCD螺钉置入正常成人椎体标本的最大轴向拔出力及最大旋入力矩,评价GSS螺钉对椎弓根的锚固作用。方法将27个正常成人腰椎椎体标本随机分为3组,每组9个椎体(18侧椎弓根),分别置入GSS、SOCON和CCD椎弓根螺钉,行螺钉拔出试验,测试并记录螺钉的最大旋入力矩和最大轴向拔出力。结果三组螺钉的最大旋入力矩分别为(1.83±0.27)Nm、(2.09±0.51)Nm和(1.66±0.34)Nm,最大轴向拔出力分别为(1131.0±255.4)N、(1034.0±262.3)N和(886.1±152.9)N。GSS螺钉最大轴向拔出力最大,且与CCD螺钉相比差异有非常显著性意义(P<0.01)。结论GSS螺钉具有很强的椎弓根锚固作用。     

枢椎棘突螺钉与椎弓根螺钉固定的生物力学拔出力比较

目的 比较枢椎棘突螺钉和椎弓根螺钉的生物力学拔出力强度.方法 取8具新鲜尸体枢椎标本(C2).于椎体两侧随机进行枢椎棘突螺钉和椎弓根螺钉固定,置入直径为4.0 mm的皮质骨螺钉.枢椎棘突螺钉进钉点选择为棘突的基底部、棘突及椎板的交界处,进钉角度为水平置钉,螺钉由对侧棘突基底部穿出,形成双层皮质固定;枢椎椎弓根螺钉在直视椎弓根下置钉.置钉后行拔出强度实验,比较2种螺钉的最大轴向拔出力强度.结果 枢椎棘突螺钉的平均拔出力强度为(387.56±137.73)N,稍小于枢椎椎弓根螺钉的平均拔出强度(465.25±214.32)N,差异无统计学意义(t=-0.862,P =0.403);枢椎棘突螺钉的平均钉道长度为(21.42±1.14) mm,稍短于枢椎椎弓根螺钉的(23.16±1.01) mm,差异有统计学意义(t=4.368,P ＜0.05). 结论 枢椎棘突螺钉具有椎弓根螺钉相近的生物力学拔出力强度,枢椎棘突螺钉在生物力学上具有应用可行性.     

颈椎经关节椎弓根螺钉固定与标准椎弓根螺钉固定的生物力学比较

目的 比较颈椎经关节椎弓根螺钉固定和标准椎弓根螺钉固定的拔出强度.方法 取10具新鲜尸体颈椎标本(C_3～T_1),游离成三个颈椎运动节段(C_(3,4),C_(5,6),C_7T_1).在椎体两侧随机进行经关节椎弓根螺钉固定或标准椎弓根螺钉固定,置入直径3.5 mm皮质骨螺钉.经关节椎弓根螺钉固定以上位椎骨侧块外下象限中点为进钉点,在直视椎弓根下,螺钉在冠状面内倾约45°、矢状面尾倾约50°.由上位椎骨下关节突经关节突关节、下位椎骨的椎弓根,进入下位椎骨的椎体内.标准椎弓根螺钉固定以侧块外上象限中点为进钉点,在直视椎弓根下,螺钉方向参考CT测量结果 ,尽量与椎弓根倾斜角度保持一致,在横断面上内倾约45°、矢状面上螺钉指向椎体的上1/3.在生物力学试验机上行拔出强度试验,比较两种螺钉固定的最大轴向拔出力.结果 颈椎经关节椎弓根螺钉固定平均最大轴向拨出力为(694±42)N,标准椎弓根螺钉固定为(670±36)N,两者比较差异有统计学意义(P<0.05).结论 颈椎后路经关节椎弓根螺钉固定的拔出强度大干标准椎弓根螺钉固定,从生物力学强度方面考虑经关节椎弓根螺钉固定可以作为标准椎弓根螺钉固定的一种补充方法.     

颈椎经关节椎弓根螺钉固定与标准椎弓根螺钉固定的生物力学比较

Objective To compare biomechanical pullout strength of cervical transfacet pedicle screws to that of standard pedicle screws. Methods Ten fresh human cadaveric cervical spines were harvested. On one side, transfacet pedicle screws were placed at the C3,4, C5,6, and C7T1 levels. On the other side, pedicle screws were, placed at the C3, C5, and C7 levels. The screw insertion technique at each level was randomized for right or left. The starting point for the transfacet pedicle screw insertion was about located at the midpoint of the inferolateral quadrant of the lateral mass and the direction of the screw was about 50° caudally in the sagittal plane and about 45° medially in the axial plane. Screws were placed across the facet joint and the pedicle into the body of the caudal vertebra. The entry points for pedicle screw was located at the midpoint of the superolateral quadrant of the lateral mass and the direction of the screw was about 45° toward the midline in the transverse plane and toward the upper third of the vertebral body in the sagittal plane. The pedicle screws were oriented along the axis of the pedicle in an effort to avoid violations of the cortical wall. All the screw insertions were based on direct observation and the CT scan on the pedicles. After screw placement, axial pullout testing was performed. Results The mean pullout strength for the transfacet pedicle screws was (694±42) N. This compares with (670±36) N for the pedicle screws (P< 0.05). The greatest difference at a single level in pullout strength was observed at the C5,6 level, with a mean difference of 38 N. Conclusion Transfacet pedicle screws exhibited statistically greater pullout strength to pedicle screws. At each level the transfacet pedicle screws exhibited greater pullout strength than the pedicle screws. Posterior transarticular pedicle screw fixation in the cervical spine affords an alternative to standard screw placement for plate fixation and cervical stabilization.     

Biomechanical evaluation of an expansive pedicle screw in calf vertebrae

incetheintroductionofthetranspedicularscrewsystembyBoucher ,1theapplicationofthissysteminthetreatmentofdegenerativedisordersandunstablefractures ,tumorsofthespinehasbecomeverypopularinthelasttwodecades.2 Looseningandfailureofthescrewsareamongthemostcommoncomplicationsreported ,especiallyforosteoporosis .3Thesefailuresoftenleadtonon union ,sagittalcollapseoftheconstructandpainfulkyphosis .Revisionisoftennecessary .Increasingthediameterand/orlengthofthepediclescrewseemstobethebestsolution .Howe…     

Biomechanical evaluation of an expansive pedicle screw in calf vertebrae

The main objective of the present study is to evaluate biomechanically a newly designed expansive pedicle screw (EPS) using fresh pedicles from calf lumber vertebrae in comparison with conventional pedicle screws, (CDH) CD Horizon, Universal Spine System pedicle screw (USS) and Tenor (Sofamor Denek). Pull-out and turning-back tests were performed on these pedicle screws to compare their holding strength. Additionally, revision tests were undertaken to evaluate the mechanical properties of EPS as a rescue revision screw. A fatigue simulation test using a perpendicular load up to 1,500,000 cycles was also carried out. The results showed that the turning back torque (Tmax) and pull-out force (Fmax) of EPS screws were significantly greater than those of USS, Tenor and CDH screws (6.5×40 mm). In revision tests, the Fmax of both types of EPS screws (6.5×40 mm; 7.0×40 mm) were significantly greater than that of CDH, USS, and Tenor screws (P<0.05). Furthermore, no screws were broken or bent at the end of fatigue tests. The findings from the current study suggest that expansive pedicle screws can significantly improve the bone purchase and the pull-out strength compared to USS, Tenor and CDH screws of similar dimensions before and after a failure simulation.     

Design and biomechanical study of a modified pedicle screw

Objective： In pedicle screw fixation, the heads of monoaxial screws need to be directed in the same straight line to accommodate the rod placement by backing out during operation, which decreases the insertional torque and internal fixation strength. While polyaxial screws facilitate the assembly of the connecting rod, but its ball-in-cup locking mechanism reduces the static compressive bending yield strength as compared with monoaxial screws. Our study aimed to assess the mechanical performance of a modified pedicle screw.
Methods： In this study, the tail of the screw body of the modified pedicle screw was designed to be a cylindershaped structure that well matched the inner wall of the screw head and the screw head only rotated around the cyclinder. Monoaxial screws, modified screws and polyaxial screws were respectively assembled into 3 groups ofvertebrectomy models simulated by ultra high molecular weight polyethylene （UHMWPE） blocks. This model was developed according to a standard for destructive mechanical testing published by the American Society for Testing Materials （ASTM F1717-04）. Each screw design had 6 subgroups, including 3 for static tension, load compression and torsion tests, and the rest for dynamic compression tests. In dynamic tests, the cyclic loads were 25%, 50%, and 75% of the compressive bending ultimate loads respectively. Yield load, yield ultimate load, yield stiffness, torsional stiffness, cycles to failure and modes of failure for the 3 types of screws were recorded. The results of modified screws were compared with those ofmonoaxial and polyaxial screws.
Results： In static tests, results of bending stiffness, yield load, yield torque and torsional stiffness indicated no significant differences between the modified and monoaxial screws （P〉0.05）, but both differed significantly from those ofpolyaxial screws （P〈0.05）. In dynamic compression tests, both modified and monoaxial screws showed failures that occurred at the insertion point of screw body into the UHMWPE block, while the polyaxial screw group showed screw body swung up and down the screw head because of loosening of the ball-in-cup mechanism.
Conclusions： The modified screw is well-designed and biomechanically improved. And it can provide sufficient stability for segment fixation as monoaxial screws.     

短节段腰椎滑脱复位固定器的生物力学评价

目的评价腰椎滑脱复位固定器(HOIST)的生物力学性能。方法采用7具新鲜成人尸体脊柱标本(L2～S2),Panjabi法制作腰椎滑脱模型,固定器械分别为HOIST器械和DICK器械。应用脊柱三维运动稳定测试仪对标本进行前屈,后伸,右、左侧弯及左、右轴向旋转6个方位的运动范围(ROM)测试;在858MTS实验机上进行疲劳实验。实验分为完整状态组、L4滑脱组、HOIST器械固定组、HOIST器械疲劳组和DICK器械组。结果滑脱状态的ROM明显大于其他4个状态(P<0.05);HOIST器械固定疲劳前后的标本(L4,5)在6个方位的ROM明显较完整状态小(P<0.05);HOIST器械固定疲劳前后以及DICK器械固定三个状态间的ROM(除左轴向旋转外)差异无显著性意义(P>0.05)。结论HOIST器械在力学性能上能满足生理需要,且具有良好的疲劳后稳定性。     

椎弓根螺钉不同翻修方法的生物力学研究

目的：研究增加螺钉直径和长度、钉孔内植骨以及聚四氟乙烯膨胀螺栓强化这四种椎弓根螺钉翻修方法所各自产生的最大轴向拔出力和最大置入扭矩变化，以确定椎弓根螺钉的最佳翻修方法。方法：将6具成人T10～L5椎体标本，分为：(1)增加椎弓根螺钉直径组，(2)延长椎弓根螺钉长度组，(3)增加直径 延长长度组，(4)植骨组，(5)聚四氟乙烯膨胀螺栓组，(6)退出后再置组。将最初置入的直径5．0mm、长40mm螺钉时所测得的最大扭矩和最大轴向拔出力作为对照组数据；记录翻修螺钉最大扭矩和最大轴向拔出力与相应对照组数据之间的变化量，各组之间结果行统计学分析。结果：在增加螺钉直径和(或)长度的方法中，当螺钉直径增加2mm且长度增加10mm时，扭矩和最大轴向拔出力的增加最明显，分别为37．06％和18．22％；螺钉直径增加2mm，扭矩增加20．15％，最大轴向拔出力增加19．99％；螺钉直径增加1mm、长度增加5mm，扭矩增加19．23％，最大轴向拔出力增加10．07％；螺钉长度单纯增加5mm与10m，扭矩分别下降32．80％和14．02％，最大轴向拔出力分别下降27.36％和增加43．25％；钉孔内植骨后再置入螺钉，扭矩和轴向拔出力分别下降了14．99％和29．34％；聚四氟乙烯膨胀螺栓强化后再置入螺钉，扭矩显著增加，而轴向拔出力下降了37．40％；螺钉退出后再置，扭矩下降了34．22％。结论：螺钉直径增加2mm对椎弓根螺钉翻修最有效，其次为螺钉直径增加1mm、长度增加5mm。钉孔内植骨的方法不可取。聚四氟乙烯膨胀螺栓强化的翻修方法需进一步研究。     

可吸收陶瓷改善椎弓根螺钉稳定性的体外生物力学试验

目的探讨在椎弓根螺钉置入时添加可吸收陶瓷Biobon对椎弓根螺钉稳定性的影响。方法采用28个L3～L5椎体标本,将椎弓根螺钉按标准操作分别置入两侧椎弓根,随机在其中一侧加Biobon。对其中16个椎体测试螺钉最大轴向拔出力F-max和螺钉拔出过程中达到最大轴向拔出力时的能量吸收值E-F-max及螺钉拔出一个螺距2.0mm时的能量吸收值E-2mm。另外12个椎体作梯增负荷的周期抗屈试验。结果同未加Biobon组比较,加入Biobon组的F-max增加了79.7%。E-F-max和E-2mm也分别增加了83.1%和68.2%,两组差异有非常显著性意义Wilcoxon检验,P<0.01。周期抗屈试验中,添加Biobon可使螺钉耐受更强的负荷或在同等负荷下仅产生较小的位移。结论在椎弓根螺钉置入时添加Biobon能显著提高其初始稳定性。     

四种骶骨钉固定技术的生物力学比较

目的通过骨质疏松骶骨标本对4种骶骨椎弓根钉（双皮质、三皮质、标准骨水泥强化和终板下骨水泥强化）载荷后的下沉位移进行比较。方法取自11具新鲜骨质疏松尸体的骶骨标本用于实验。采用DEXA测定骨密度后在同一骶骨的左右侧随机置入直径7mm的双皮质和三皮质骶骨椎弓根钉。使用MTS试验机对螺钉进行30～250N压力加载2000次后取出螺钉。钉道内注入骨水泥（polymethylmethacrylate,PMMA）,将比双皮质或三皮质固定短5mm的螺钉再次置人（分别定义为标准和终板下PMMA强化）,并重复上述加载。记录加载后螺钉的下沉位移,进行比较。结果11具标本的骨密度为0．55～0．78g／cm^2,平均0．7lg／cm^2。三皮质和标准PMMA强化椎弓根钉间的下沉位移差异无统计学意义,此2种固定技术的下沉位移显著低于双皮质固定。终板下PMMA强化椎弓根钉的下沉位移显著低于其他固定技术。结论在骨质疏松状态下PMMA强化可显著提高骶骨钉一骨界面的结合强度。在上述4种骶骨固定技术中终板下PMMA强化椎弓根钉可获得最坚强的锚定。