重度骨质疏松条件下椎弓根螺钉内固定的可靠性研究

目的评价重度骨质疏松条件下椎弓根螺钉的稳定性,为椎弓根内固定在合并有重度骨质疏松症的患者中的选用提供力学理论基础。方法采用新鲜尸体脊柱标本,检测骨密度后,根据诊断标准,选用正常骨质的2具尸体标本、重度骨质疏松的4具尸体标本,分离T12~L5节段成单个椎体以备后用;然后在骨质正常椎体置入椎弓根螺钉12枚作对照组;在重度骨质疏松水平,分单纯置入椎弓根螺钉(pedicle screw,PS)、经磷酸钙骨水泥(calcium phosphate cement,CPC)强化钉道后置入椎弓根螺钉、经聚甲基丙烯酸甲酯(polymethylmethacrylate,PMMA)强化钉道后置入椎弓根螺钉三种方法置钉,依次为PS组、CPC/PS组和PMMA/PS组,进行螺钉轴向拔出实验,测最大拔出力、刚度和能量吸收值,对所测指标进行组间对比分析。结果重度疏松条件下,PS组、CPC/PS组和PMMA/PS各组最大拔出力、刚度、能量吸收值均显著低于对照组(P0.005);但是,PMMA/PS组三项指标均显著高于PS组、CPC/PS组(P0.001);PS组、CPC/PS组之间比较仅最大拔出力存在显著性差异(P0.05),刚度与能量吸收值差异无统计学意义(P0.05)。结论重度骨质疏松条件下,椎弓根螺钉固定强度明显下降,不宜单纯应用普通椎弓根螺钉行脊柱内固定治疗,采用普通骨水泥强化钉道后置钉可以提高椎弓根螺钉稳定性。     

骨质疏松对椎弓根螺钉稳定性影响 的实验研究

目的评价不同骨质疏松程度条件下,椎弓螺钉的稳定性,为椎弓根内固定在合并有骨质疏松 症的患者中的选用提供力学理论基础。方法采用新鲜尸体脊柱标本,根据骨密度检测结果,按临床 诊断标准分成骨质正常、骨量减少、骨质疏松和重度骨质疏松四个水平。然后,每个骨密度水平,植入 普通椎弓根螺钉24枚,进行螺钉轴向拔出实验,测定最大拔出力、刚度和能量吸收值三项指标,对所 测指标进行骨密度水平间的对比分析。结果骨密度水平从正常下降到重度疏松程度,最大拔出力、 刚度均随之下降,组间比较均存在显著性差异（孕<0.05 )。正常骨密度水平的能量吸收值显著高于 骨质疏松、重度疏松（孕<0.05 ),但与骨量减少水平相比并无统计学差异（孕>0.05 )。另外,骨量减少 水平的能量吸收值显著性高于重度骨质疏松水平（孕<0. 05 ),但与骨质疏松水平相比较无显著性差 异（P跃0.05 )。结论反映椎体骨质质量的骨密度是决定椎弓根螺钉稳定性的重要因素。     

骨密度对膨胀式椎弓根螺钉固定强度影响的力学研究北大核心CSCD

目的评价不同骨质疏松条件下膨胀式椎弓根螺钉(expansive pedicle screw,EPS)的稳定性,为其应用于合并有骨质疏松症的患者脊柱手术提供力学理论基础。方法取新鲜尸体脊柱(T12～L5)标本,根据骨密度检测结果,按临床骨质疏松程度诊断标准分成骨质正常、骨量减少、骨质疏松和重度骨质疏松4个水平,每个水平各2具标本12个椎体。于每个椎体两侧椎弓根分别植入普通椎弓根螺钉(conventional pedicle screw,CPS;CPS组)和EPS(EPS组)。采用AG-IS万能材料试验机,以5 mm/min匀速加载进行螺钉轴向拔出试验,测定最大拔出力、刚度和能量吸收值。结果两组随骨密度水平下降,最大拔出力及刚度均逐渐下降(P<0.05);CPS组能量吸收值逐渐下降(P<0.05),EPS组能量吸收值除正常骨质与骨量减少间比较、骨质疏松与重度疏松间比较差异无统计学意义(P>0.05)外,其余各密度水平间比较差异均有统计学意义(P<0.05)。同一骨密度水平EPS组最大拔出力均显著高于CPS组(P<0.05);除正常骨质水平外,同一骨密度水平EPS组刚度均显著高于CPS组(P<0.05);除骨量减少水平外,同一骨密度水平两组能量吸收值比较差异均无统计学意义(P>0.05)。骨质疏松水平EPS组最大拔出力、刚度、能量吸收值与骨量减少水平CPS组比较,差异均无统计学意义(P>0.05);但重度骨质疏松水平EPS组以上指标均显著低于骨量减少水平CPS组(P<0.05)。结论与CPS相比,EPS能明显提高固定强度,尤其对于骨量减少或骨质疏松患者。     

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。     

钉道强化提高椎弓根螺钉固定强度的生物力学研究

目的 评价椎弓根钉道局部强化技术及其结合膨胀式椎弓根螺钉提高椎弓根螺钉固定强度的效果.方法 通过自行设计及加工的钉道局部强化装置,向钉道周壁点状注入CaSO4骨水泥以强化椎弓根钉道.5具新鲜冻存人体脊柱标本,每具随机选取4个腰椎共20个腰椎标本,采用随机区组设计方法分为10个区组.设计四种固定方法:A组(普通椎弓根螺钉)、B组(普通椎弓根螺钉+钉道局部强化)、C组(膨胀式椎弓根螺钉+钉道局部强化)、D组(普通椎弓根螺钉+钉道内灌注CaSO4骨水泥),随机应用在每个区组的2个椎体共4个椎弓根钉道.分别测试每个椎弓根螺钉的最大轴向拔出力及能量吸收值.从剩余腰椎标本中任意取两个腰椎,应用钉道局部强化技术后利用Micro-CT观察钉道周壁微观结构变化.结果 C、D两组的最大轴向拔出力均值及能量吸收值均值高于A组(P＜0.01)及B组(P＜0.05),B组最大轴向拔出力均值及能量吸收值均值高于A组(P＜0.01),C、D两组之间的差异无统计学意义(P＞0.05).结论 钉道局部强化技术可显著提高椎弓根螺钉的固定强度,结合使用膨胀式椎弓根螺钉可进一步提高螺钉的固定强度.     

一种新型钉道强化椎弓根螺钉生物力学研究

[目的]探讨一种新型钉道强化椎弓根螺钉在骨质疏松椎体中的生物力学特性。[方法]从4具老年尸体中选取20个腰椎标本(L_(1～5)),均符合骨质疏松症诊断标准(T-2.5),采用随机分4组,每组5个椎体。分别为单纯普通椎弓根螺钉组(无强化组)、普通椎弓根螺钉强化组(普通强化组)、可注射空心椎弓根螺钉强化组(空心钉强化组)、新型钉道强化椎弓根螺钉强化组(新型强化组)。观察骨水泥分布情况,并测量各组螺钉最大轴向拔出力及不同螺钉的刚度。[结果]三种强化骨水泥的分布不同,普通强化组骨水泥主要分布于椎体前部;空心钉强化组骨水泥主要分布于椎体前部及部分中后部,新型强化组骨水泥主要分布于钉道周围,包括椎体前、中、后部及部分椎弓根部。生物力学测量最大轴向拔出力依次为:新型强化组空心钉强化组普通强化组无强化组,差异具有统计学意义(P0.05)。螺钉刚度依次为普通螺钉新型螺钉空心螺钉,差异有统计学意义(P0.05)。[结论]新型钉道强化椎弓根螺钉能够提高螺钉在骨质疏松椎体固定的稳定性,且骨水泥分布有所改善,螺钉的刚度适中。     

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.     

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。     

硫酸钙骨水泥强化去势绵羊体内椎弓根螺钉稳定性的动态生物力学研究

目的评价硫酸钙骨水泥(calciumsulfate cement,CSC)在去势绵羊体内强化椎弓根螺钉稳定性的动态效果。方法12只成年雌性绵羊行去势手术1年后,并测量去势前后腰椎骨密度。取去势绵羊的L2～L5双侧椎弓根为实验对象,其中一侧直接拧入椎弓根螺钉(空白组),另一侧向钉道内注入CSC(0.5ml)后,再拧入椎弓根螺钉(CSC组),两种方法左右完全随机。于术后1天,6周,12周,24周四个时间点各随机处死3只绵羊,分别测定各组中螺钉的轴向拔出力和拔出能量吸收值,对比分析同一时间点不同方法之间和同一方法的不同时间点之间的力学指标。结果去势1年后绵羊腰椎骨密度显著下降,差异具有统计学意义(P0.05),骨质疏松绵羊模型建立成功。空白组中各时间点之间的最大轴向拔出力(Fmax)和拔出能量吸收值(E)无显著性差异(P0.05),而CSC组中24周螺钉的Fmax和E显著高于同组的1天,6周和12周;同一时间点,CSC组螺钉的Fmax和E均显著高于对照组(P0.05)。结论CSC可以显著提高骨质疏松椎体内椎弓根螺钉的稳定性,强化螺钉的作用在体内是动态稳定的,并能进一步提高螺钉在体内的远期稳定性。在椎弓根螺钉强化方面,CSC可以作为PMMA的替代材料。     

体积骨密度与椎弓根螺钉稳定性的相关性及磷酸钙陶瓷的强化效应

目的探讨椎体松质骨体积骨密度对椎弓根螺钉稳定性的影响,以及添加磷酸钙陶瓷的效应.方法用pQCT测定16个腰椎的体积骨密度,将USS椎弓根螺钉分别置人两侧椎弓根,植入螺钉前随机在其中一侧钉道内添加磷酸钙陶瓷;测试螺钉最大轴向拔出力（F-max）,计算骨螺钉界面的剪切应力（η）.结果随体积骨密度提高,F-max和η亦逐次增加.无论是否添加磷酸钙陶瓷,F-max和体积骨密度始终呈较强的正相关关系（r=0.9056和0.9585,P＜0.05）.添加磷酸钙陶瓷后F-max和η均增加了约80%（Wilcoxon＇s test,P＜0.01）.结论椎弓根螺钉的稳定性与体积骨密度紧密相关,磷酸钙陶瓷有明显的强化效应.     

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.     

Augmentation of anterior vertebral body screw fixation by an injectable, biodegradable calcium phosphate bone substitute.

STUDY DESIGN: A biomechanical study to evaluate the effects of a biodegradable calcium phosphate (Ca-P) bone substitute on the fixation strength and bending rigidity of vertebral body screws. OBJECTIVES: To determine if an injectable, biodegradable Ca-P bone substitute provides significant augmentation of anterior vertebral screw fixation in the osteoporotic spine. SUMMARY OF BACKGROUND DATA: Polymethylmethacrylate (PMMA) augmented screws have been used clinically; however, there is concern about thermal damage to the neural elements during polymerization of the PMMA as well as its negative effects on bone remodeling. Injectable, biodegradable Ca-P bone substitutes have shown enhanced fixation of pedicle screws. METHODS: Sixteen fresh cadaveric thoracolumbar vertebrae were randomly divided into two groups: control (no augmentation) (n = 8) and Ca-P bone substitute augmentation (n = 8) groups. Bone-screw fixation rigidity in bending was determined initially and after 10(5) cycles, followed by pullout testing of the screw to failure to determine pullout strength and stiffness. RESULTS: The bone-screw bending rigidity for the Ca-P bone substitute group was significantly greater than the control group, initially (58%) and after cyclic loading (125%). The pullout strength for Ca-P bone substitute group (1848 +/- 166 N) was significantly greater than the control group (665 +/- 92 N) (P < 0.01). Stiffness in pullout for the Ca-P bone substitute groups (399 +/- 69 N/mm) was significantly higher than the control group (210 +/- 51 N/mm) (P < 0.01). CONCLUSION: This study demonstrated that augmentation of anterior vertebral body screw fixation with a biodegradable Ca-P bone substitute is a potential alternative to the use of PMMA cement.     

Improving the pullout strength of pedicle screws by screw coupling

The objective of this study was to determine the effect of pedicle screw coupling on the pullout strength of pedicle screws in the osteoporotic spine. The vertebral bone mineral density (BMD) of 33 cadaveric lumbar vertebrae were measured by quantitative computed tomography. Pedicle screws were inserted into each pedicle. The pullout strength and displacement of the screws, without coupling and with single or double couplers, were studied, and the relationship between pullout strength and BMD was analyzed. The average pullout strength of the pedicle screws without screw coupling was 909.3 +/- 188.6 N (n = 9), that coupled with a single coupler was 1,409.0 +/- 469.1 N (n = 9), and that with double couplers was 1,494.0 +/- 691.6 N (n = 9). The pullout strength of the screws coupled with single or double couplers was significantly greater than that of screws without couplers (p < 0.01); however, there was no significant difference between the groups of single and double couplers. The improvement of pullout strength by screw coupling was significant in a test group with BMD of more than 90 mg/ml (p < 0.01), but was not in the group with BMD less than 90 mg/ml (p = 0.55). These results suggest that the coupling of pedicle screws improves pullout strength; however, the effect tends to be less significant in severely osteoporotic spines.     

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.     

Pedicle screw augmentation with bone cement enforced Vicryl mesh

Achieving sufficient mechanical purchase of pedicle screws in osteoporotic or previously instrumented bone is technically and biologically challenging. Techniques using different kinds of pedicle screws or methods of cement augmentation have been used to address this challenge, but are associated with difficult revisions and complications. The purpose of this biomechanical trial was to investigate the use of biocompatible textile materials in combination with bone cement to augment pullout strength of pedicle screws while reducing the risk of cement extrusion. Pedicle screws (6/40 mm) were either augmented with standard bone‐cement (Palacos LV + G) in one group (BC, n = 13) or with bone‐cement enforced by Vicryl mesh in another group (BCVM, n = 13) in osteoporosis‐like saw bone blocks. Pullout testing was subsequently performed. In a second experimental phase, similar experiments were performed using human cadaveric lumbar vertebrae (n = 10). In osteoporosis‐like saw bone blocks, a mean screw pullout force of 350 N (±125) was significantly higher with the Bone cement (BC) compared to bone‐cement enforced by Vicryl mesh (BCVM) technique with 240 N (±64) (p = 0.030). In human cadaveric lumbar vertebrae the mean screw pullout force was 784 ± 366 N with BC and not statistically different to BCVM with 757 ± 303 N (p = 0.836). Importantly, cement extrusion was only observed in the BC group (40%) and never with the BCVM technique. In vitro textile reinforcement of bone cement for pedicle screw augmentation successfully reduced cement extrusion compared to conventionally delivered bone cement. The mechanical strength of textile delivered cement constructs was more reproducible than standard cementing. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:212–216, 2018.     

膨胀式椎弓根螺钉结合骨水泥强化钉道在严重骨质疏松脊柱手术中的应用

目的 探讨膨胀式椎弓根螺钉结合骨水泥强化钉道在治疗严骨质疏松性脊柱内固定手术中的早期疗效。方法 自2006年10月至2008年10月对20例需行内固定治疗同时合并严重骨质疏松的腰椎疾病患者采用膨胀式椎弓根螺钉结合骨水泥强化钉道进行脊柱后路稳定手术,其中男9例,女11例;年龄43～73岁,平均59岁。分别于术后1周、3个月、6个月、12个月及24个月摄动力位X线片及CT扫描,了解螺钉稳定性、骨水泥分布及脊柱融合情况。术前及术后3个月时应用日本矫形外科协会(JOA)不腰痛评分及视觉模拟评分(VAS)评价疗效。结果 本组共置人膨胀式椎弓根螺钉168枚。所有患者术后获12～ 38个月（平均26个月）随访。术前及术后3个月JOA评分平均分别为(11.4±2.6)分和(24.9±1.6)分,差异有统计学意义(t= 19.776,P=0.000);术前及术后3个月VAS评分分别为(7.0±1.4)分和(2.1±1.3)分,差异有统计学意义(t=11.470,P=0.000)。螺钉及骨水泥在椎体内位置稳定,周围骨小梁致密,未见明显透光带,无内固定松动移位迹象;后外侧融合节段植骨愈合良好,椎体间或椎板、关节突及棘突旁有连续性骨小梁形成,连接上下椎体。临床症状明显缓解,无早期及晚期感染等并发症发生,无临床复发。结论 对于合并严重骨质疏松的脊柱后路内固定手术,膨胀式椎弓根螺钉结合骨水泥强化钉道的方法能够极大地提高螺钉固定的稳定性。     

The Efficacy of Hydroxyapatite for Screw Augmentation in Osteoporotic Patients

The stability of screw constructs is of considerable importance in determining the outcome, especially in spinal osteoporosis. Polymethylmethacrylate (PMMA) has been proven as an effective material for increasing the pullout strength of pedicle screws inserted into the osteoporotic bones. However, PMMA has several disadvantages, such as its exothermic properties, the risk of neural injury in the event of extravasation, and difficulties in performing revision surgery. In the current study, we used hydroxyapatite (HA) cement for screw augmentation in spinal osteoporosis. We conclude that HA cement is a useful tool for screw augmentation and recommend it as a promising option for spinal instrumentation in osteoporotic patients.     

Mechanical evaluation of fracture fixation augmented with tricalcium phosphate bone cement in a porous osteoporotic cancellous bone model

OBJECTIVE: The purpose of this study was to examine the effects of resorbable bone cement on screw and plate-screw fracture fixation in a porous osteoporotic bone model. METHODS: Experiment 1: Screw pullout strength was assessed for 4 sets of 4.5-mm cortical screws inserted into a synthetic osteoporotic cancellous bone model, including screws inserted without cement augmentation (control), screws augmented with tricalcium phosphate (TCP) bone cement (Norian SRS; Synthes USA, Paoli, PA), and screws augmented with polymethylmethacrylate. Experiment 2: The effects of cement augmentation on plate-screw fixation strength were examined by performing cantilever bending tests on 4 sets of 8 plate-screw constructions, including nonaugmented and TCP-augmented standard and locked screw-plate constructions in a similar bone model. RESULTS: Experiment 1: Cement augmentation with both TCP and polymethylmethacrylate increased screw pullout strength from a porous osteoporotic cancellous bone model by about 4-fold (P < 0.05), and there was no significant difference between the 2 cements (P > 0.1). Experiment 2: Fixation strength was 1.5 times higher for locked plates compared with standard plates when neither was augmented with cement (P = 0.07). Cement augmentation with TCP improved fixation strength by 3.6 times for a standard plate-screw construction (P < 0.05) and 3.3 times for a locked plate-screw construction (P < 0.05). The most stable construction was the TCP-augmented locked plate, in which a 5-fold increase was observed compared with that of standard plates without TCP (P < 0.05). CONCLUSIONS: This study indicates augmenting screws with TCP cement during osteosynthesis improves fixation strength in an osteoporotic cancellous bone model. CLINICAL RELEVANCE:: In fracture situations in which osteoporotic bone makes screw and screw-plate fixation tenuous, screw augmentation with TCP cement should be considered as adjunct treatment.