不同椎弓根螺钉固定及骨水泥强化方法在骨质疏松骶骨上锚定强度的比较

目的:通过比较不同椎弓根螺钉固定及骨水泥强化方法在骨质疏松骶骨上的锚定强度,探讨骶骨椎弓根螺钉松动后的理想补救技术.方法:应用11具成人新鲜骶骨标本,经骨密度测试确认为骨质疏松后,在同一骶骨标本上,依次建立5种骶骨螺钉固定模型,A组,单皮质椎弓根螺钉固定(左侧):B组,双皮质椎弓根螺钉固定(右侧);C组,PMMA钉道强化后单皮质椎弓根螺钉固定(建立于A组螺钉拔出后);D组,PMMA钉道强化后侧翼钉固定(右侧);E组,后凸成形技术支持下的PMMA强化后侧翼钉固定(左侧).应用MTS材料测试机进行轴向拔出测试,记录各种骶骨螺钉固定技术的最大拔出力并进行比较.结果:11具标本的骨密度为0.55～0.79g,cm~2,平均0.71±0.08g/cm~2.A～E组最大拔出力分别为508±128N、685±126N、846±230N、543±121N和702±144N.A组与D组间无显著性差异(P>0.05),且均显著低于B、C和E组(P<0.05);B组与E组间无显著性差异(P>0.05),但两组的拔出力均显著低于C组(P<0.05).结论:在骨质疏松患者的骶骨固定中,双皮质骶骨椎弓根钉较单皮质具有更高的锚定强度.骶骨椎弓根钉一旦发生松动,PMMA钉道强化和后凸成形技术支持下的PMMA强化后的侧翼钉固定均可成为理想的补救手段.     

骨质疏松程度对骶骨椎弓根螺钉固定的生物力学影响

目的:评价骨质疏松程度对骶骨椎弓根螺钉固定强度的影响.方法:25具骨质疏松成人新鲜尸体骶骨标本,按尸体腰椎骨密度(BMD)值分为A组(n=9,BMD 0.70～0.79g/cm2)、B组(n=8,BMD 0.60～0.69异/cm2)和C组(n=8,BMD＜0.60g,cm2).在同一标本的S1左侧置入双皮质椎弓根螺钉,右侧置入单皮质椎弓根螺钉时用聚甲基丙烯酸甲酯(PMMA)骨水泥强化.4h后使用MTS实验机对螺钉尾部进行30～250N的头尾方向循环加载2000次后,测定椎弓根螺钉的下沉位移和轴向拔出力.2000次载荷中螺钉下沉超过2mm定义为锚定失败.结果:A组和B组螺钉均未出现锚定失败;C组双皮质椎弓根螺钉锚定失败6例(75%),PMMA强化单皮质椎弓根螺钉锚定失败5例(63%).A组双皮质螺钉固定的下沉位移和轴向最大拔出力与PMMA强化螺钉固定比较无显著性差异(P＞0.05);B组.PMMA强化螺钉固定的下沉位移显著低于双皮质螺钉固定,轴向最大拔出力显著高于双皮质固定(P＜0.05).A组双皮质螺钉固定和PMMA强化螺钉固定的下沉位移均显著低于B组(P＜0.05),A组双皮质螺钉同定的轴向最大拔出力显著高于B组(P＜0.05).A组PMMA强化螺钉固定的轴向最大拔出力与B组比较无显著性差异(P＞0.05).C组内同定失败病例中,PMMA强化螺钉固定的承载次数显著高于双皮质螺钉固定(P＜0.05).结论:BMD≥0.70g/cm2时双皮质骶骨椎弓根螺钉同定和PMMA强化单皮质骶骨椎弓根螺钉固定可获得同等的锚定强度,BMD值为0.60～0.69g/cm2时PMMA强化单皮质骶骨椎弓根螺钉同定的锚定强度显著高于双皮质螺钉固定,BMD值＜0.60g/cm2时两种锚定方式均容易导致早期松动.术前行腰椎BMD检查可指导选择骶骨螺钉同定方式.     

聚甲基丙烯酸甲酯强化对骨质疏松椎弓根螺钉固定的生物力学作用

目的探讨聚甲基丙烯酸甲酯 (polymethylmethacrylate,PMMA)骨水泥强化椎弓根螺钉的方法和评价 PMMA强化骨质疏松椎弓根螺钉后的生物力学性质。方法 6具新鲜老年女性胸腰段骨质疏松脊柱标本 (T10～ L5),使用双能 X线骨密度吸收仪测试每个椎体的骨密度,随机取 16个椎体 (32侧椎弓根 ),一侧椎弓根拧入 CCD螺钉,测量最大旋入力偶矩后拔出螺钉作为正常对照组,用 PMMA骨水泥强化椎弓根螺钉作为修复固定组,行螺钉拔出试验;另一侧经导孔直接强化椎弓根螺钉后拔出作为强化固定组,记录三组螺钉的最大轴向拔出力。结果椎体平均骨密度为 (0.445± 0.019)g/cm2;螺钉最大旋入力偶矩为（ 0.525± 0.104） Nm;正常对照组螺钉最大轴向拔出力为 (271.5± 57.3)N;修复固定组为 (765.9± 130.7)N;强化固定组为 (845.7± 105.0)N。 PMMA骨水泥强化或修复骨质疏松椎弓根螺钉后最大抗压力明显高于强化前,差异有非常显著性意义 (P< 0.01)。结论 PMMA骨水泥强化骨质疏松椎弓根螺钉能显著增加螺钉在椎体内的稳固性。     

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。     

髂骨螺钉松动四种翻修技术的生物力学比较

目的:比较松质骨填塞钉道、增加螺钉长度、传统聚甲基丙烯酸甲酯(polymethylmethacrylate,PMMA)强化钉道和外板开窗PMMA强化钉道四种方法翻修松动髂骨螺钉后的固定强度,探讨髂骨螺钉松动的理想补救手段。方法:8具成人防腐尸体骨盆标本,经双能X光吸收法测定骨密度后,将直径7.5mm髂骨短钉(长度为70mm)分别置入左右髂骨(A组),通过MTS材料实验机向螺钉尾部施加100～300N垂直循环载荷2000次后,测试髂骨螺钉的轴向拔出力。用松质骨紧密填塞两侧钉道后,在左侧钉道内置入短钉(B组),右侧钉道置入长度为100mm的髂骨长钉(C组),重复上述测试。将左侧钉道内注满PMMA后,再次置入髂骨短钉(D组);将另1枚髂骨短钉置入右侧钉道,以螺钉中点为中心沿螺钉轴线的髂骨外板处开窗,高度20mm、长度40mm、深度至内板皮质,灌注PMMA(E组);D组和E组重复上述测试。记录各组髂骨螺钉的轴向最大拔出力并进行比较。结果:8具标本的骨密度为0.75～0.91g/cm2,平均为0.85±0.05g/cm2。A～E组的最大拔出力分别为1174±542N、261±89N、769±317N、1954±623N和1820±659N,D组与E组比较无显著性差异(P0.05),D组与E组显著高于A、B和C组(P0.05),C组显著高于B组(P0.05),B组和C组显著低于A组(P0.05)。结论:松质骨填塞钉道和增加螺钉长度不能恢复髂骨螺钉的锚定强度;外板开窗PMMA强化和传统PMMA强化后置钉可使髂骨螺钉获得更高的锚定强度;从微创角度,外板开窗PMMA强化可能成为髂骨螺钉松动的理想补救手段。     

PMMA提高椎体钉固定强度的体外实验研究

[目的]探讨骨水泥(PMMA)强化后椎体钉穿透单侧椎体固定的可行性。[方法]选用新鲜成人尸体标本32个,按骨密度分为骨质正常组和骨质疏松组分别进行实验。实验组为骨水泥(PMMA)强化后椎体钉穿单侧椎体皮质固定;对照组为无骨水泥强化,椎体钉穿透双侧椎体皮质固定。应用螺钉拔出实验,记录螺钉最大拔出力。[结果]在骨质正常组中,PMMA组和对照组拉出力分别为1758.42±32.63N和843.25±65.35N,增加109%±33%。在骨质疏松组中,PMMA组和对照组拉出力分别为811.19±188.58N和374.21±77.66N,增加122%±56%。差异有显著性P<0.01。[结论]应用PMMA固化椎体钉,减少手术并发症是可行的。     

胸椎椎弓根螺钉固定失败经椎弓根外入路补救的力学测试

目的 比较胸椎椎弓根螺钉椎弓根入路，椎弓根外入路置钉以及置钉失败后椎弓根入路，椎弓根外入路补救置钉的抗拔出力。方法 4具书本脊柱标本（T6-11）分解为单椎体（附双侧肋骨）24个。根据配对随机分组的原则进行标本分组，测试各组的抗拔出力，将椎弓根入路置钉组成的抗拔出力结果作为对照组数据。结果 椎弓根入路补救组抗拔出力和椎弓根入路组，椎弓根外入路组差异无显著性（P〉0.05）。结论椎弓根螺钉穿破内侧壁导致的胸椎椎弓根螺钉固定失败，可选择椎弓根外入路的方式进行补救。     

枢椎骨密度分布规律的研究及对内固定影响

目的研究枢椎椎弓根、椎体的骨密度分布规律及其对内固定的影响。方法取30枚人尸体骨干骨标本,测量每一块枢椎的椎弓根、椎体的骨密度,对比两者骨密度的大小,得出枢椎两部位的骨密度分布规律。分别以椎体中心点矢状位、椎弓根背侧中点冠状位为扫描中心,用双能射线法分别测量其椎体、椎弓根骨密度,从前路打入椎弓根钉,以椎体为中心打入椎体螺钉,生物力学测量仪测量其椎弓根钉、椎体钉拔出力。结果测得椎弓根螺钉抗拔出力519.31 N,椎体螺钉拔出力455.14 N。结论①椎弓根的骨密度高于椎体骨密度;②骨密度与螺钉拔出力有相关性;③枢椎两部位的骨密度分布规律：椎弓根骨密度〉椎体骨密度,是造成椎弓根钉拔出力优于椎体钉的原因之一。     

经骶1-2侧块螺钉固定的最大拔出力测定

【摘要】 目的：测量经骶1-2侧块螺钉固定的最大拔出力,初步探讨该内固定方法的有效性。方法：8具甲醛溶液固定湿润成人骶骨标本,采用双能X线吸收测定仪（dual-energy X-ray absorptiometry, DEXA）测定S1椎体骨密度。在同一骶骨标本上随机置入3种骶骨螺钉：经骶1-2侧块螺钉（A组）、S1椎弓根螺钉（B组）、S1前外骶骨翼螺钉（C组）。将标本固定于858型MTS材料试验机上,对螺钉施加轴向拔出力,根据3种骶骨螺钉轴向拔出实验的数据绘制力（N）-位移（mm）曲线,取曲线的顶点作为最大拔出力数值。应用SPSS 16.0统计软件对3组骶骨螺钉的最大拔出力数值行方差分析。结果：8具骶骨标本S1椎体骨密度为0.43～0.74g/cm3,平均0.641±0.275g/cm3。3种骶骨螺钉固定的螺钉即刻平均最大拔出力：A组为379.62±73.10N,B组为829.12±170.74N,C组为230.62±98.52N,3组之间两两比较差异有统计学意义（P＜0.05）。结论：经骶1-2侧块螺钉固定的最大拔出力低于S1椎弓根螺钉固定,但高于S1前外骶骨翼螺钉固定,当S1椎弓根螺钉固定不能施行时,骶1-2侧块螺钉固定可作为一种有效的选择。     

直入式注入PMMA骨水泥强化椎弓根钉内固定生物力学研究

【摘要】 目的 分析直入式骨水泥注入椎体强化方法在体外提高螺钉稳定性的效果。方法采用新鲜尸体脊柱标本共24个椎体,一侧椎弓根采用直入式注入PMMA骨水泥强化椎弓根钉固定作(试验组),另一侧椎弓根采用常规椎弓根螺钉固定(对照组),两侧进行最大轴向拔出力试验、最大旋出力矩试验、周期抗屈试验生物力学测试,比较两组测试结果。结果〓骨水泥强化组中螺钉的稳定性均显著强于单纯常规椎弓根螺钉组(P < 0.05)。结论〓应用PMMA行椎体强化椎弓根钉固定有利于增强对椎弓根钉的把持力,可有效防止椎弓根钉的松动及脱落,具有良好的临床效果。     

The effects of cyclic loading on pull-out strength of sacral screw fixation: an in vitro biomechanical study

STUDY DESIGN: The pull-out strength of sacral screw fixation after cyclic loading was tested using young human cadaveric specimens. OBJECTIVES: To evaluate the effects of fatigue loading on the pull-out strength of medial and lateral unicortical and bicortical sacral screws and to correlate the pull-out strength with sacral bone density and the screw insertion torque. SUMMARY OF BACKGROUND DATA: The immediate biomechanical effects of depth of penetration, screw orientation, and bone density on sacral screw fixation have been studied in aged cadaveric specimens. The effect of cyclic loading on the pull-out strength of sacral screw fixation is unknown, however, and data from young specimens is rare. METHODS: Eleven fresh specimens of human sacrum were used in this study. Bone mineral density at the vertebral body and the ala were determined by peripheral quantitative computed tomography. Seven-millimeter compact Cotrel-Dubousset sacral screws were inserted into the sacrum anteromedially and anterolaterally, both unicortically and bicortically, and the insertion torque for each screw was measured. Cyclic loading from 40 to 400 N was applied to each screw at a frequency of 2 Hz up to 20,000 cycles. Pull-out tests were conducted after completion of the fatigue tests. RESULTS: The average bone density was 0.38 +/- 0.08 g/mL at the S1 body and 0.24 +/- 0.05 g/mL at the S1 ala. The insertion torque and average pull-out force after cyclic loading were significantly higher for bicortical fixation than for unicortical fixation for a particular screw alignment. The pull-out strength and insertion torque of medially oriented fixation was always higher than that for lateral fixation, however, regardless of whether the insertion was unicortical or bicortical. The pull-out force of unicortical and bicortical medial screw fixations after cyclic loading showed significant linear correlations with both the insertion torque and the bone mineral density of the S1 body. CONCLUSIONS: In a young population, screw orientation (anterolateral or anteromedial) was more important in determining pull-out strength than screw depth (unicortical or bicortical) after fatigue loading, anteromedially directed screws being significantly stronger than laterallyplaced screws. Bone mineral density of the S1 body andinsertion torque were good preoperative and intraoperative indicators of screw pull-out strength.     

骶骨螺钉四种固定方式的生物力学分析

目的 研究骶骨螺钉固定在承受周期性载荷后的拔出强度,评价前内、前外侧和单、双边皮累钉固定的生物力学作用。方法 对１１具新鲜成人尸体的骶骨行定量ＣＴ（ＱＣＴ）扫描以确定Ｓ１椎体和骶骨翼的骨矿物质密度。ＣＣＤ骶骨螺钉分别放置在骶骨的前内、前是和单、双边皮质等四个位置上,测量螺钉固定时旋入的力矩。对螺钉施加４０～４００Ｎ的垂直周期载荷、载荷频率为２Ｈｚ,加载桨数为２００００次。然后行螺钉拔出试验,获得螺     

枢椎后路3种螺钉固定技术生物力学测试的对比研究

目的：评价单皮质和双皮质枢椎椎弓根螺钉、枢椎侧块螺钉和枢椎椎板螺钉的固定强度,为临床选择后路螺钉的固定方式提供生物力学依据。方法：利用30具新鲜尸体枢椎标本,进行单皮质和双皮质的枢椎椎弓根螺钉、枢椎侧块螺钉、枢椎椎板螺钉固定,测试比较其螺钉拔出强度。结果：双皮质枢椎椎弓根螺钉的拔出力量最大,为（1255.8±381.9）N;单皮质枢椎椎弓根螺钉[（901.8±373.3）N]、双皮质枢椎侧块螺钉[（776.1±306.8）N]和双皮质枢椎椎板螺钉[（640.8±302.9）N]之间差异无统计学意义。结论：枢椎后路螺钉固定宜首选椎弓根螺钉,枢椎侧块螺钉和枢椎椎板螺钉可作为枢椎后路补充固定技术,且以双皮质骨固定为宜。     

Biomechanical study of pedicle screw fixation in severely osteoporotic bone.

BACKGROUND CONTEXT: Obtaining adequate purchase with standard pedicle screw techniques remains a challenge in poor quality bone. The development of alternate insertion techniques and screw designs was prompted by recognition of potential fixation complications. An expandable pedicle screw design has been shown to significantly improve fixation compared to a conventional screw in poor quality bone. PURPOSE: The purpose of this study was to determine if polymethylmethacrylate (PMMA) bone cement augmentation of an expandable pedicle screw can further improve fixation strength compared to the expandable screw alone in severely osteoporotic bone. A technique for cement insertion into the pedicle by means of the cannulated central portion of the expandable screw is also described. STUDY DESIGN: The axial pullout strength, stiffness and energy absorbed of cemented and noncemented expandable pedicle screws was determined in cadaveric vertebrae. METHODS: Twenty-one fresh unembalmed vertebrae from the thoracolumbar spine were used. Radiographs and bone mineral density measurements (BMD) were used to characterize bone quality. Paired cemented and noncemented pedicle screw axial pullout strength was determined through mechanical testing. Mechanical pullout strength, stiffness and energy to failure was correlated with BMD. RESULTS: Overall, there was a 250% increase in mean pullout strength with the cemented expandable screw compared with a noncemented expandable screw including a greater than twofold increase in pullout strength in the most severely osteoporotic bone. The mean stiffness and energy absorbed to failure was also significantly increased. A cemented conventional screw achieved a pullout strength similar to the noncemented expandable screw. CONCLUSIONS: PMMA cement augmentation of the expandable pedicle screw may be a viable clinical option for achieving fixation in severely osteoporotic bone.     

Polymethylmethacrylate augmentation of the pedicle screw: the cement distribution in the vertebral body

Many studies have proven that the polymethylmethacrylate (PMMA) augmentation of the pedicle screw can significantly increase stiffness and strength of spinal fixation. Some major complications have also been reported. However, there are no reports discussing cement distribution and its morphology in the osteoporotic vertebral body, which is critical in the analysis of the biomechanical strength of the pedicle screw and the risk of cement leakage after pedicle screw augmentation. In this study, we used computed tomography (CT) to evaluate the cement distribution in the osteoporotic vertebral body after PMMA augmentation of a pedicle screw and to analyze the factors leading to cement leakage. Two groups of patients were studied. Group A consisted 25 osteoporotic patients (mean age of 73 years) with spinal instrumentation who had a total of 145 pedicle screws and cement augmentation with biopsy needles. Group B consisted of 23 osteoporotic patients (mean age of 74.6 years) with spinal instrumentation who had a total of 125 cannulated pedicle screws with cement augmentation. All patients had CT evaluation of the cement distribution in the vertebral body after the surgery. The cement distribution in the vertebrae was divided into four zones in the axial CT view: anterior one-third, middle third, and posterior third of vertebral body, and the pedicle. The morphology of the cement distribution around the pedicle screw was defined as scattered type or concentrate type. The leakage pattern was divided to anterior–lateral, posterior–lateral, and canal leakage. The correlations among bone mineral density (BMD), the cement leakage rate, and cement distribution morphology were also analyzed. The results showed that most augmented pedicle screws had cement extension into three of the four zones of the vertebral body (66.3%), followed by two zones (20%), all four zones (11.5%), and only one zone (2.2%). Overall, 123 screws (84.8%) in Group A and 108 screws (86.4%) in Group B had cement concentrate type distribution. The cement leakage rate in Group A is 18.3% and 13.6% in Group B. Patients with a BMD <0.6 g/cm² had significantly higher rates of cement leakage and tended toward a scattered cement distribution. There was only one patient who had a symptomatic leakage (sciatica) in Group B. We concluded that the cement distribution after pedicle screw augmentation with biopsy needle or cannulated screw technique was mostly localized in three zones of the vertebral body, and patients with lower BMD had a higher risk of cement leakage and scattered cement distribution.     

geneX骨水泥强化骨质疏松椎体椎弓根钉的生物力学研究

目的评估骨质疏松情况下geneX骨水泥强化椎弓根钉的固定强度。方法应用微量注射泵对30个新鲜小牛腰椎标本注射稀盐酸建立骨质疏松椎体模型。60个椎弓根分为四组:geneX骨水泥组,硫酸钙骨水泥(CSC)组,聚甲基丙烯酸甲酯骨水泥(PMMA)组,对照组。随机选择一侧注射2.5 ml骨水泥,然后置入螺钉;另一侧行正常螺钉固定对照,应用材料试验机进行轴向拔出力测试,记录各组的轴向最大拔出力和能量吸收值并进行比较。结果 geneX组与CSC组两组拔出力及能量吸收值比较,差异无统计学意义(P>0.05),两组均显著低于PMMA组(P<0.05),两组均显著高于对照组(P<0.05)。结论 geneX骨水泥强化椎弓根钉可显著提高椎弓根固定强度,geneX骨水泥可用作椎弓根强化螺钉的填充材料。     

Loosening of sacral screw fixation under in vitro fatigue loading.

Sacral screw fixation is frequently used for fusion of the lower lumbar spine, but sacral screws appear to offer less secure fixation than lumbar pedicle screws, and failure due to loosening under fatigue loading is common. The aim of this study was to examine in vitro the stability of medial and lateral bicortical and unicortical sacral screw fixation under a physiologically relevant fatigue-loading pattern. Bone mineral density, screw insertion torque, and screw-fixation stiffness were measured prior to cyclic loading between 40 and 400 N compression at 2 Hz for 20,000 cycles. The screw-fixation stiffness was measured every 500 cycles, and the axial pullout strength of the screws was recorded following loading. All of the lateral insertions loosened under the applied loading, but some of the medial insertions remained stable. Medial insertions proved stiffer and stronger than lateral insertions, and bicortical fixations were stronger than unicortical fixations. Bone mineral density and insertion torque were correlated with screw stiffness and pullout strength, although better correlation was found for insertion torque than bone mineral density. Bone mineral density is a good preoperative indicator of sacral screw-fixation strength, and insertion torque is a good intraoperative indicator. An insertion torque greater than 1.5 Nm is suggested as an indicative value for a stable medial unicortical insertion, whereas an insertion torque greater than 2 Nm suggests a stable medial bicortical insertion. It appears that, apart from the choice of technique (screw orientation and depth), minimizing the load on the screws during the initial part of the fusion process is also critical to maintain stability of the fused section and to obtain a solid fusion mass.