三种充填材料应用于山羊经皮椎体成形术的组织学评价

经皮椎体成形术（PVP）充填材料性能的优劣直接关系到PVP的成败，我们在山羊骨质疏松症（OP）模型上行PVP．充填聚甲基丙烯酸甲酯（PMMA）、可注射型的自固化磷酸钙人工骨（CPC）和复合重组人类骨形态发生蛋白-2（rhBMP-2）的CPC（rhBMP-2／CPC）三种材料。并行光镜观察，为寻找理想的PVP充填材料提供组织学依据。     

复合rhBMP-2可注射磷酸钙骨水泥在椎体成形术中应用的实验研究

目的 探讨自主研发的复合rhBMP-2可注射磷酸钙骨水泥(复合材料)替代注射型聚甲基丙烯酸甲酯(PMMA)应用于猕猴椎体成形术的可行性.方法 将4只成年猕猴分为Ⅰ、Ⅱ两组,每组2只.每组猕猴T10～L7的20个椎体经皮穿刺,按处理方法不同分为复合材料组(A组,8个椎体)、可注射型PMMA组(B组,6个椎体)和手术空白对照组(C组,6个椎体).分别于术后即刻和术后1、2,4、6个月行放射学检查.Ⅰ组于术后2个月、Ⅱ组于术后6个月处死,取出单个椎体,每个椎体取含材料骨样本2份,1份用于光镜检查,另1份用于扫描电镜.观察两种材料强化椎体的早期和后期效果和变化.结果 A组2个月时材料部分降解,未见界面缝隙、纤维增生、炎性浸润或硬化骨痂现象,大量类骨质形成并长人材料,可见新生血管;6个月后大部分材料吸收完全,大部分软骨钙化形成成熟骨组织,有完整的骨小梁及哈佛系统.B组2个月时未见材料降解,中度炎性浸润,纤维组织膜包裹,界面缝隙明显,未见新骨生长;6个月时,炎性浸润消失,纤维界膜变薄,界面缝隙变窄,仍无材料降解和新骨生长.C组2个月后椎体骨隧道被新生骨质填充,骨小梁排列紊乱,边界硬化骨痂形成;6个月后,骨小梁排列整齐,边界骨痂消失,不能辨认,骨重建完成.结论 复合rhBMP-2的注射型磷酸钙骨水泥植入椎体后能够获得良好的诱导生长活性,材料降解和新骨替代同步,周期接近于正常椎体的骨愈合,可望替代PMMA获得椎体成形后早期和远期更好的组织学效果.     

磷酸钙骨水泥在椎体成形术中的实验研究

目的 :模仿椎体成形术观察磷酸钙骨水泥 /聚甲基丙烯酸甲酯植入椎体后与椎体界面间的组织学差异。方法 :将PMMA和CPC植入到犬椎体 ,通过X线、CT、光镜、扫描电镜观察 2种材料与椎体界面间的微观结构变化。结果 :PMMA与椎体之间的结合是单纯的机械连接未能达到生物机械固定 ,CPC与骨界面间无排异反应的表现 ,是直接的骨小梁与生物材料之间的生物连接。结论 :磷酸钙骨水泥是椎体成形术中的一种比较理想的替代材料     

丝素蛋白增强型磷酸钙复合rhBMP-2用于绵羊腰椎椎体间融合的实验研究

目的 评价可注射丝素蛋白增强型磷酸钙(silk fibroin/calcium phosphate cement,SF/CPC)复合人重组骨形态发生蛋白-2(recombinant human bone morphogenetic protein-2,rhBMP-2)应用于绵羊腰椎椎体间融合的效果.方法 24只绵羊均建立L1.2、L3.4和L5.6前路椎体间融合模型.每只绵羊的3个腰椎间隙随机植入SF/CPC、CPC/rhBMP-2、SF/CPC/rhBMP-2和自体髂骨中的3种.分别于术后6个月和12个月各处死12只绵羊.每个时段均获得36个腰椎手术节段,每种材料9个节段.通过大体观察、手触检测、CT扫描、非破坏性生物力学测试和组织学观察分析脊柱融合状况.结果 术后6个月时,手触检测SF/CPC、CPC/rhBMP-2、SF/CPC/rhBMP-2以及髂骨的融合率分别为0、33.33%(3/9)、55.56%(5/9)和77.78%(7/9);12个月时为11.11%(1/9)、44.44%(4/9)、77.78%(7/9)和77.78%(7/9).生物力学显示6个月时,前屈、后伸、左屈和右屈的融合刚度:髂骨＞SF/CPC/rhBMP-2＞CPC/rhBMP-2＞SF/CPC;12个月时SF/CPC/rhBMP-2刚度与髂骨相近,SF/CPC最小.组织学定量表明:6个月时,髂骨新生骨量＞SF/CPC/rhBMP-2＞CPC/rhBMP-2＞SF/CPC;而钙磷残留量依次增多;12个月时,SF/CPC/rhBMP-2新生骨量与髂骨相近;SF/CPC最少;钙磷残留量依次增多.结论 SF/CPC/rhBMP-2人工骨具有骨传导和骨诱导性,降解与成骨能力匹配,是一种理想的脊柱融合材料.     

丝素蛋白增强型磷酸钙复合rhBMP-2用于绵羊腰椎椎体间融合的实验研究

目的 评价可注射丝素蛋白增强型磷酸钙(silk fibroin/calcium phosphate cement,SF/CPC)复合人重组骨形态发生蛋白-2(recombinant human bone morphogenetic protein-2,rhBMP-2)应用于绵羊腰椎椎体间融合的效果.方法 24只绵羊均建立L1.2、L3.4和L5.6前路椎体间融合模型.每只绵羊的3个腰椎间隙随机植入SF/CPC、CPC/rhBMP-2、SF/CPC/rhBMP-2和自体髂骨中的3种.分别于术后6个月和12个月各处死12只绵羊.每个时段均获得36个腰椎手术节段,每种材料9个节段.通过大体观察、手触检测、CT扫描、非破坏性生物力学测试和组织学观察分析脊柱融合状况.结果 术后6个月时,手触检测SF/CPC、CPC/rhBMP-2、SF/CPC/rhBMP-2以及髂骨的融合率分别为0、33.33%(3/9)、55.56%(5/9)和77.78%(7/9);12个月时为11.11%(1/9)、44.44%(4/9)、77.78%(7/9)和77.78%(7/9).生物力学显示6个月时,前屈、后伸、左屈和右屈的融合刚度:髂骨＞SF/CPC/rhBMP-2＞CPC/rhBMP-2＞SF/CPC;12个月时SF/CPC/rhBMP-2刚度与髂骨相近,SF/CPC最小.组织学定量表明:6个月时,髂骨新生骨量＞SF/CPC/rhBMP-2＞CPC/rhBMP-2＞SF/CPC;而钙磷残留量依次增多;12个月时,SF/CPC/rhBMP-2新生骨量与髂骨相近;SF/CPC最少;钙磷残留量依次增多.结论 SF/CPC/rhBMP-2人工骨具有骨传导和骨诱导性,降解与成骨能力匹配,是一种理想的脊柱融合材料.     

丝素蛋白增强型磷酸钙复合rhBMP-2用于绵羊腰椎椎体间融合的实验研究

目的 评价可注射丝素蛋白增强型磷酸钙(silk fibroin/calcium phosphate cement,SF/CPC)复合人重组骨形态发生蛋白-2(recombinant human bone morphogenetic protein-2,rhBMP-2)应用于绵羊腰椎椎体间融合的效果.方法 24只绵羊均建立L1.2、L3.4和L5.6前路椎体间融合模型.每只绵羊的3个腰椎间隙随机植入SF/CPC、CPC/rhBMP-2、SF/CPC/rhBMP-2和自体髂骨中的3种.分别于术后6个月和12个月各处死12只绵羊.每个时段均获得36个腰椎手术节段,每种材料9个节段.通过大体观察、手触检测、CT扫描、非破坏性生物力学测试和组织学观察分析脊柱融合状况.结果 术后6个月时,手触检测SF/CPC、CPC/rhBMP-2、SF/CPC/rhBMP-2以及髂骨的融合率分别为0、33.33%(3/9)、55.56%(5/9)和77.78%(7/9);12个月时为11.11%(1/9)、44.44%(4/9)、77.78%(7/9)和77.78%(7/9).生物力学显示6个月时,前屈、后伸、左屈和右屈的融合刚度:髂骨＞SF/CPC/rhBMP-2＞CPC/rhBMP-2＞SF/CPC;12个月时SF/CPC/rhBMP-2刚度与髂骨相近,SF/CPC最小.组织学定量表明:6个月时,髂骨新生骨量＞SF/CPC/rhBMP-2＞CPC/rhBMP-2＞SF/CPC;而钙磷残留量依次增多;12个月时,SF/CPC/rhBMP-2新生骨量与髂骨相近;SF/CPC最少;钙磷残留量依次增多.结论 SF/CPC/rhBMP-2人工骨具有骨传导和骨诱导性,降解与成骨能力匹配,是一种理想的脊柱融合材料.     

复合重组人类骨形态发生蛋白-2的磷酸钙骨水泥应用于椎体成形术的体外生物力学评价

目的 通过将复合重组人类骨形态发生蛋白-2的注射型磷酸钙人工骨(rhBMP-2/CPC)应用于体外经皮椎体成形术(PVP),评价其生物力学性能.方法 5具完整老年脊柱标本(T10～L2),游离成30个椎体,随机分为3组:I组为空白对照组(n=10);Ⅱ组为PMMA组(n=10);Ⅲ组为rhBMP-2/CPC组(n=10).G形臂监视下,Ⅱ、Ⅲ组经双侧椎弓根分别充填PMMA及BMP-2/CPC 5 ml,注射后摄轴位X线片了解骨水泥分布情况,测试3组椎体静态压缩下的最大抗压强度及刚度.结果 平均最大载荷和刚度分别为:I组:(1595.6±165.0)N和(934.8±120.2)N/mm;Ⅱ组:(3025.4±210.2)N和(1570.7±190.0)N/mm;Ⅲ组:(2778.8±156.5)N和(1361.9±230.5)N/mm;最大载荷:I～Ⅲ组之间均差异有统计学意义(P＜0.05).刚度:I～Ⅲ组之间差异有统计学意义(P＜0.05).结论 rhBMP-2/CPC可以恢复骨质疏松椎体的力学性能.     

负载重组人骨形态发生蛋白2的α型半水硫酸钙/纳米羟基磷灰石复合植骨材料的成骨性能研究

目的:评价负载重组人骨形态发生蛋白2(rh BMP-2)的α型半水硫酸钙/纳米羟基磷灰石(α-CSH/n HA)复合植骨材料的成骨性能。方法:制备可注射性α-CSH/n HA/rh BMP-2复合材料,取12只成年绵羊,分别经左侧椎弓根在L1~L6椎体上制作直径6mm、深15mm的6个洞形缺损,第一只绵羊的椎体缺损随机分为3组,其余羊的椎体都按此进行分组,即L2、L5为实验组,L1、L4为对照组,L3、L6为空白对照组。实验组植入α-CSH/n HA/rh BMP-2复合材料;对照组植入可注射性磷酸钙骨水泥(CPC);空白对照组不植入任何材料。术后4、8、12周各处死4只动物,取椎体标本分别行X线及micro-CT扫描,观察缺损修复情况;行生物力学检查,测定椎体压缩强度和压缩模量;行组织学观察比较新骨生成率。结果:术后4周时,实验组压缩强度及压缩模量与CPC组的差异无统计学意义(P0.05),实验组和对照组均显著性高于空白对照组(P0.05);术后8周和12周时实验组和对照组均显著性高于空白对照组(P0.05),实验组显著性高于对照组(P0.05)。影像学及组织学结果显示,术后4周时,实验组复合材料大部分已降解,密度稍低于正常骨,可见大量纤细短小、尚未塑形的新生骨小梁,边缘有大量成骨细胞环绕;对照组CPC材料呈高密度充满整个缺损,未见明显降解吸收征象,材料与骨的界限明显,缺损边缘有少量幼稚骨小梁形成;空白对照组缺损较大,边缘整齐,几乎看不到有新骨生成。术后8周时,实验组复合材料完全降解,缺损内新生骨小梁数量增多,增粗变长,且开始早期塑形;对照组材料开始部分降解,在边缘和中心降解区可见明显新骨形成,新生骨小梁数量较实验组少;空白对照组缺损修复不明显,边缘只可见少量新生骨小梁。术后12周时,实验组缺损完全被新生骨小梁充满,骨小梁趋于成熟,结构与正常骨小梁相似,密度与正常骨接近,很难与正常部位区分;对照组CPC大量降解,只残留一小团块状和零星的材料,缺损边缘修复明显,新生骨小梁长入残余材料内,将其分割成岛屿状;空白对照组缺损依然较大,呈低密度影清晰可见,新骨生成很少。结论:α-CSH/n HA/rh BMP-2复合材料在绵羊体内具有良好的成骨活性,是较好的微创植骨材料。     

rhBMP-2/CPC对骨质疏松骨缺损的治疗作用的研究

目的 探讨磷酸钙骨水泥复合rhBMP-2对骨质疏松骨缺损的治疗作用.方法 以卵巢切除法对10只成年山羊去势,低钙膳食6个月后建立骨质疏松模型;手术去除每只动物L2、L4椎体部分侧方骨质,造成约5 mm×10 mm×10mm大小骨缺损,将动物随机分成2组,一组植入rhBMP-2/CPC作为实验组,另一组植入CPC作为对照组;术后1周、9周分别采用双能x线吸收骨密度仪检测手术椎体骨密度、CT三维成像观察骨缺损愈合情况,术后9周手术椎体进行牛物力学检测,制作椎体不脱钙切片进行骨组织计量学分析.结果 术后骨密度检测实验组与对照组间差异无显著性,但实验组在骨缺损愈合状况、骨小梁微结构及骨牛物力学性能等方面均显著优于对照组.结论 应用rhBMP-2/CPC能改善局部骨质疏松,促进骨质疏松骨缺损愈合,达到治疗骨质疏松骨折骨缺损的目的 .     

不同充填材料强化椎体在骨质疏松性椎体压缩骨折中的应用

目的分别以聚甲基丙烯酸甲酯骨水泥(PMMA)和注射型自固化磷酸钙人工骨(CPC)作为强化椎体的充填材料,采用椎体成形术和膨胀式椎体成形器(Sky)后凸成形术治疗骨质疏松性椎体压缩骨折,观察其临床疗效。方法对45例骨质疏松性椎体压缩骨折患者采用以下4种方法治疗:椎体成形术 PMMA(15例17个椎体),椎体成形术 CPC(13例16个椎体),Sky后凸成形术 PMMA(8例8个椎体),Sky后凸成形术 CPC(9例10个椎体)。根据患者术前和术后侧位X线片计算椎体高度压缩率和恢复率、椎体后凸角度和恢复率,并采用VAS(vasual analogscale)进行术前和术后疼痛评分。结果所有患者均未出现并发症。Sky后凸成形术椎体高度恢复率和后凸角度恢复率优于椎体成形术。椎体增强材料充填剂量各组间无显著性差异。椎体成形术与Sky后凸成形术手术时无显著性差异。VAS评分术前各组无显著性差异,术后充填PMMA者优于充填CPC者,术后6周两者间无显著性差异。结论用PMMA和CPC强化椎体是一种微创、安全、有效治疗骨质疏松性椎体压缩骨折的方法,应根据患者的具体情况选择治疗方法和椎体充填材料。     

经皮椎体成形术自固化磷酸钙人工骨充填治疗骨质疏松性胸腰椎压缩性骨折

目的探讨应用经皮椎体成形术(PVP)自固化磷酸钙人工骨(CPC)充填治疗骨质疏松性胸腰椎压缩性骨折的临床疗效。方法自2004年1月起,对26例29个椎体骨质疏松性胸腰椎压缩骨折患者,采用术中手法复位、PVP自固化CPC充填治疗。结果26例患者经单侧或双侧椎弓根穿刺椎体成形术成功治愈。胸腰椎自固化CPC平均充填量为4.6mL。术中CPC渗漏者5例5个椎体。无一例出现严重并发症。经3～8个月(平均4.6个月)随访,术后所有患者疼痛消失。除3例椎体高度丢失15%外,其余椎体高度平均恢复达正常的80%。结论PVP自固化CPC充填治疗骨质疏松性胸腰椎压缩性骨折是一种安全、简单、有效的方法。     

Biomechanical evaluation of kyphoplasty and vertebroplasty with calcium phosphate cement in a simulated osteoporotic compression fracture

 Kyphoplasty and vertebroplasty with polymethylmethacrylate (PMMA) have been used for the treatment of osteoporotic vertebral compression fractures. We performed kyphoplasty and vertebroplasty with α-tricalcium phosphate cement (CPC) and PMMA to compare the biomechanical properties. Thirty osteoporotic vertebrae were harvested from nine embalmed cadavers. We randomized the vertebrae into four treatment groups: (1) kyphoplasty with CPC; (2) kyphoplasty with PMMA; (3) vertebroplasty with CPC; and (4) vertebroplasty with PMMA. Prior to injecting the cement, all vertebrae were compressed to determine their initial strength and stiffness. They were then recompressed to determine their augmented strength and stiffness. Although the augmented strength was greater than the initial strength in all groups, there was no significant difference between the two bone cements for either kyphoplasty or vertebroplasty. The augmented stiffness was significantly less than the initial stiffness in the kyphoplasty groups, but the difference between the two cements did not reach significance. In the vertebroplasty groups, the augmented stiffness was not significantly different from the initial stiffness. There was no significant difference between the two bone cements for either procedure when cement volume and restoration of anterior height were assessed. We concluded that kyphoplasty and vertebroplasty with CPC were viable treatment alternatives to PMMA for osteoporotic vertebral compression fractures. Received: July 18, 2002 / Accepted: November 6, 2002 Offprint requests to: S. Tomita     

Experimental vertebroplasty using osteoconductive granular material

STUDY DESIGN: Osteoporotic human cadaveric thoracic vertebral bodies and vertebral bodies from mature sheep were used as model systems to assess coral resorption and new bone formation after injection of coral granules. OBJECTIVE: To evaluate the use of natural coral exoskeleton, an osteoconductive material, for the filling of vertebral bodies. SUMMARY OF BACKGROUND DATA: Percutaneous injection of polymethylmetacrylate (PMMA) is often proposed for prophylactically stabilizing osteoporotic vertebral bodies at risk for fracture or augmentation of vertebral bodies that have already fractured. Recently, the possibility of using osteoconductive materials in granular formulation was assessed in pilot studies. METHODS: As a first step, the possibility of injecting coral granules percutaneously within osteoporotic human cadaveric thoracic vertebral bodies was assessed. As a second step, cavities were drilled into vertebral bodies of 10 mature ewes and were either left empty (control group) or filled with coral alone (CC) or coral supplemented with fibrin sealant (CC+FS). Quantitative evaluation of coral resorption and new bone formation was made 2 months and 4 months after implantation. RESULTS: The distribution of coral granules injected into human cadaveric thoracic vertebral bodies was homogenous as assayed radiographically. In the experimental animal model, osteogenesis was increased in cavities filled with coral in comparison with cavities left empty at both 2 months and 4 months (P < 0.005 and P < 0.02, respectively). Surprisingly, supplementation of coral with a fibrin sealant had no positive influence on osteogenesis (P < 0.0008 at 2 months; P < 0.002 at 4 months). In addition, it led to an increase in coral resorption by as soon as 2 months (P < 0.0008). CONCLUSION: These results demonstrate the osteoconductivity of coral in granular form for vertebral filling. Interestingly, interconnectivity between adjacent bone trabeculae and newly formed bone was restored; however, its mechanical significance remains to be determined. Further investigations are needed to evaluate the efficacy of coral in osteopenic animals and in relieving pain.     

Augmentation of mechanical properties in osteoporotic vertebral bones – a biomechanical investigation of vertebroplasty efficacy with different bone cements

Recent clinical trials have reported favorable early results for transpedicular vertebral cement reinforcement of osteoporotic vertebral insufficiencies. There is, however, a lack of basic data on the application, safety and biomechanical efficacy of materials such as polymethyl-methacrylate (PMMA) and calciumphospate (CaP) cements. The present study analyzed 33 vertebral pairs from five human cadaver spines. Thirty-nine vertebrae were osteoporotic (bone mineral density < 0.75 g/cm2), 27 showed nearly normal values. The cranial vertebra of each pair was augmented with either PMMA (Palacos E-Flow) or experimental brushite cement (EBC), with the caudal vertebra as a control. PMMA and EBC were easy to inject, and vertebral fillings of 20-50% were achieved. The maximal possible filling was inversely correlated to the bone mineral density (BMD) values. Cement extrusion into the spinal canal was observed in 12% of cases. All specimens were subjected to axial compression tests in a displacement-controlled mode. From load-displacement curves, the stiffness, S, and the maximal force before failure, Fmax, were determined. Compared with the native control vertebrae, a statistically significant increase in vertebral stiffness and Fmax was observed by the augmentation. With PMMA the stiffness increased by 174% (P = 0.018) and Fmax by 195% (P = 0.001); the corresponding augmentation with EBC was 120% (P = 0.03) and 113% (P = 0.002). The lower the initial BMD, the more pronounced was the augmentation effect. Both PMMA and EBC augmentation reliably and significantly raised the stiffness and maximal tolerable force until failure in osteoporotic vertebral bodies. In non-porotic specimens, no significant increase was achieved.     

Biomechanical comparison of vertebral augmentation with silicone and PMMA cement and two filling grades

Purpose

Vertebral augmentation with PMMA is a widely applied treatment of vertebral osteoporotic compression fractures. Subsequent fractures are a common complication, possibly due to the relatively high stiffness of PMMA in comparison with bone. Silicone as an augmentation material has biomechanical properties closer to those of bone and might, therefore, be an alternative. The study aimed to investigate the biomechanical differences, especially stiffness, of vertebral bodies with two augmentation materials and two filling grades.

Methods

Forty intact human osteoporotic vertebrae (T10–L5) were studied. Wedge fractures were produced in a standardized manner. For treatment, PMMA and silicone at two filling grades (16 and 35 % vertebral body fill) were assigned to four groups. Each specimen received 5,000 load cycles with a high load range of 20–65 % of fracture force, and stiffness was measured. Additional low-load stiffness measurements (100–500 N) were performed for intact and augmented vertebrae and after cyclic loading.

Results

Low-load stiffness testing after cyclic loading normalized to intact vertebrae showed increased stiffness with 35 and 16 % PMMA (115 and 110 %) and reduced stiffness with 35 and 16 % silicone (87 and 82 %). After cyclic loading (high load range), the stiffness normalized to the untreated vertebrae was 361 and 304 % with 35 and 16 % PMMA, and 243 and 222 % with 35 and 16 % silicone augmentation. For both high and low load ranges, the augmentation material had a significant effect on the stiffness of the augmented vertebra, while the filling grade did not significantly affect stiffness.

Conclusions

This study for the first time directly compared the stiffness of silicone-augmented and PMMA-augmented vertebral bodies. Silicone may be a viable option in the treatment of osteoporotic fractures and it has the biomechanical potential to reduce the risk of secondary fractures.     

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。     

A rat osteoporotic spine model for the evaluation of bioresorbable bone cements.

BACKGROUND CONTEXT: As the aging population increases, the rising prevalence of osteoporosis-related spine fractures will have a dramatic impact on health care. At present, mainstay treatment relies on systemic medications intended to prevent diminishing bone mineral density (BMD) and bone mass. However, an adjunctive treatment strategy is to target specific areas of the skeletal system that are prone to clinically significant osteoporotic fractures. We term this strategy the "local treatment of osteoporosis" or osteoplasty. Potential use of osteoplasty involves the percutaneous injection of bioresorbable and bioactive bone cements into bones at risk of sustaining osteoporotic fractures. Calcium sulfate (CaSO(4)) is among the candidate bioresorbable bone cements with the material attributes desirable for potential application with osteoplasty, yet previous studies on the osteoconductive properties of CaSO(4) have been limited to animal models exhibiting normal bone biology and architecture. However, osteoporotic bone physiology may potentially interfere with the material properties of common osteoconductive biomaterials, such as that of CaSO(4). To further test this hypothesis, a suitable animal model is needed to evaluate the in vivo behavior of potential biomaterials in osteoporotic bone. PURPOSE: The purpose of this study is to evaluate the caudal (proximal tail) rat vertebral body as an appropriate system for the in vivo evaluation of bone cement performance in the osteoporotic spine. STUDY DESIGN: (1) Micro-computed tomography radiomorphometry study and (2) biomechanical vertebral compression analysis. METHODS: Female Sprague Dawley rats were ovarectomized (OVX) at age 8 weeks and subsequently maintained on a low-calcium diet for 3 months. Normal nonovarectomized female rats (NL) of similar age and size were maintained on regular rodent feed. Micro-CT analysis was performed on both the lumbar and caudal vertebrae (levels 5-7) of both groups. The following bone radiomorphometric parameters were determined: bone mineral density (BMD), average cortical thickness (ACT), average trabecular thickness (TbTh), and average trabecular spacing (TbSp). Strength and stiffness of both NL and OVX vertebral bodies were assessed under axial compression at 0.1 mm/s, whereas displacement (mm) and force (N) were measured at 10 Hz until completion to failure. After the implantation of an injectable form of CaSO(4) bone cement into caudal vertebrae, radiomorphometric analysis of cement volume, based on its unique CT absorption profile, was performed over the 8-week time period, as well as the subsequent bone response of both NL and OVX caudal vertebrae to CaSO4. RESULTS: OVX caudal vertebrae showed an 18% decrease in BMD, a 28% decrease in diaphyseal ACT, a 55% decrease in TbTh, and a 2.4-fold increase in TbSp compared with NL (p<.05). Additionally, lumbar vertebrae exhibited a 21% decrease in BMD, a 24% decrease in anterior body ACT, a 48% decrease in TbTh, and a 4.7-fold increase in TbSp (p<.05). Failure testing of OVX caudal vertebral bodies revealed a 29% decrease in strength and a 60% decrease in stiffness compared with NL (p<.01). After implantation into OVX caudal vertebrae, CaSO(4) cement exhibited a 50% decrease in initial cement volume at 2 weeks and complete resorption by 4 weeks, whereas CaSO(4) injected into NL vertebrae exhibited a 79% decrease in initial cement volume at 4 weeks, trace amounts at 6 weeks, and complete resorption by 8 weeks. At 8 weeks, NL vertebrae implanted with CaSO(4) cement exhibited increased cortical bone thickness compared with NL sham vertebrae. This CaSO(4) cement-mediated bone augmentation was altered in osteoporotic vertebrae that exhibited porous irregular cortical bone not noted in cement-treated NL vertebrae or OVX sham vertebrae. CONCLUSIONS: Future investigation of potential biomaterials intended for the local treatment of osteoporosis will require their study within an appropriate osteoporosis animal model. The OVX rat caudal spine exhibits pathologic bone changes consistent with the osteoporosis phenotype, including decreased BMD, diminished trabecular network density, cortical thinning, and decreased mechanical strength. These derangements in bone microarchitecture and physiology may contribute toward the accelerated cement resorption and altered bone response to CaSO4 observed in this study. Important advantages of the OVX rat caudal spine are the rapid and minimally invasive surgical exposure of the vertebral body and the ease of cement injection. We propose that the OVX rat caudal spine represents a valuable and cost-effective tool in the armamentarium of investigators evaluating biomaterials designed for implantation into the osteoporotic spine.     

The use of an injectable, biodegradable calcium phosphate bone substitute for the prophylactic augmentation of osteoporotic vertebrae and the management of vertebral compression fractures.

STUDY DESIGN: A biomechanical study comparing two materials for augmentation of osteoporotic vertebral bodies and vertebral bodies after compression fracture. OBJECTIVES: To compare an injected, biodegradable calcium phosphate bone substitute with injected polymethylmethacrylate bone cement for strengthening osteoporotic vertebral bodies and improving the integrity of vertebral compression fractures. SUMMARY OF BACKGROUND DATA: Injection of polymethylmethacrylate bone cement into fractured vertebral bodies has been used clinically. However, there is concern about thermal damage to the neural elements during polymerization of the polymethylmethacrylate bone cement as well as its negative effects on bone remodeling. Biodegradable calcium phosphate bone substitutes have been studied for enhancement of fixation in fractured vertebrae. METHODS: Forty fresh osteoporotic thoracolumbar vertebrae were used for two separate parts of this study: 1) injection into osteoporotic vertebrae: intact control (n = 8), calcium phosphate (n = 8), and polymethylmethacrylate bone cement (n = 8) groups. Each specimen then was loaded in anterior compression until failure; 2) injection into postfractured vertebrae: calcium phosphate (n = 8) and polymethylmethacrylate bone cement (n = 8) groups. Before and after injection, the specimens were radiographed in the lateral projection to determine changes in vertebral body height and then loaded to failure in anterior bending. RESULTS: For intact osteoporotic vertebrae, the average fracture strength was 527 +/- 43 N (stiffness, 84 +/- 11 N/mm), 1063 +/- 127 N (stiffness, 157 +/- 21 N/mm) for the group injected with calcium phosphate, and 1036 +/- 100 N (stiffness, 156 +/- 8 N/mm) for the group injected with polymethylmethacrylate bone cement. The fracture strength and stiffness in the calcium phosphate bone substitute group and those in the polymethylmethacrylate bone cement group were similar and significantly stronger than those in intact control group (P < 0.05). For the compression fracture study, anterior vertebral height was increased 58.5 +/- 4.6% in the group injected with calcium phosphate and 58.0 +/- 6.5% in the group injected with polymethylmethacrylate bone cement as compared with preinjection fracture heights. No significant difference between the two groups was found in anterior vertebral height, fracture strength, or stiffness. CONCLUSION: This study demonstrated that the injection of a biodegradable calcium phosphate bone substitute to strengthen osteoporotic vertebral bodies or improve vertebral compression fractures might provide an alternative to the use of polymethylmethacrylate bone cement.     

Biomechanical evaluation of vertebroplasty using calcium sulfate cement for thoracolumbar burst fractures

OBJECTIVE: To evaluate the biomechanical performance of vertebroplasty using calcium sulfate cement for thoracolumbar burst fractures. METHODS: Sixteen bovine thoracolumbar spines (T11-L1) were divided into 4 groups (A,B,C and D). After burst-fracture model was created, 12 vertebral bodies in Groups A, B and C were augmented with calcium sulfate cement (CSC), calcium phosphate cement (CPC) and polymethylmethacrylate (PMMA) bone cement, respectively. Each anterior vertebral body height was measured with a caliper at 4 time points: intact conditions (HInt), post-fracture (HFr), post-reduction (HRe) and post-vertebroplasty (HVP). The filling volume of 3 different bone cements was also measured. Each vertebral body was compressed at 0.5 mm/s using a hinged plating system on a materials testing machine to 50% of the post-vertebroplasty height to determine strength and stiffness. Difference was checked using t test or One-way ANOVA. RESULTS: The average strike energy was 66.2 J. Vertebroplasty with different cements could sustain vertebral height.The average filling volume of bone cement in 3 groups was 4.35 ml (CSC), 3.72 ml (CPC) and 3.95 ml (PMMA), respectively, and there was no statistically significant difference among them (P larger than 0.05). Vertebroplasty with PMMA completely restored strength (116%) and stiffness (105%). CSC or CPC partly recovered vertebral strength and stiffness. However, greater strength restoration was got with CSC (1659 N) as compared with CPC (1011N, P less than 0.01). Regarding stiffness, differences between CSC (140 N/mm+/-40 N/mm)and the other two bone cements (CPC:148 N/mm+/-33 N/mm, PMMA:236 N/mm+/-97 N/mm) were not significant (P larger than 0.05). CONCLUSIONS: For a burst-fracture of calf spine, use of CSC for vertebroplasty yields similar vertebral stiffness as compared with PMMA or CPC. Although augmentation with CSC partly obtains the normal strength, this treatment still can be applied in thoracolumbar burst fractures with other instrumental devices in light of its bioactivation.