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.     

Biomechanical evaluation of an injectable radiopaque polypropylene fumarate cement for kyphoplasty in a cadaveric osteoporotic vertebral compression fracture model

Vertebral compression fractures cause pain, deformity, and disability. Polypropylene fumarate (PPF) has shown promise as an injectable cement for bone defects but little is known about its performance for kyphoplasty. The purpose of this study was to evaluate the biomechanical performance of PPF for kyphoplasty in simulated anterior compression fractures in cadaveric vertebral bodies. Thirty-one vertebral bodies (T9 to L4) from osteoporotic cadaveric spines were disarticulated, stripped of soft tissue and compressed on a materials testing machine to determine pretreatment strength and stiffness. All fractures were repaired with inflatable balloon tamps and either polymethylmethacrylate or PPF-30 (containing 30% barium sulfate by dry weight) cement and then retested. Strength restoration with PMMA and PPF-30 were 120% and 104%, respectively, of the pretreatment strengths. For stiffness, PMMA and PPF-30 restored vertebral bodies to 69% and 53%, respectively, of the initial values. There was no significant difference in treatment with either PMMA or PPF-30. The biopolymer PPF-30 exhibits mechanical properties similar to PMMA in a cadaveric kyphoplasty model. PPF biopolymer may be a suitable alternative for kyphoplasty.     

An ex vivo biomechanical evaluation of an inflatable bone tamp used in the treatment of compression fracture

STUDY DESIGN: Ex vivo biomechanical study using osteoporotic cadaveric vertebral bodies. OBJECTIVES: To determine if the inflatable bone tamp (tamp) restores height to compressed vertebral bodies and to compare the biomechanical properties of isolated, fractured osteoporotic vertebral bodies treated by kyphoplasty (tamp) or vertebroplasty. SUMMARY OF BACKGROUND DATA: Previous biomechanical studies have shown that vertebroplasty increases vertebral body strength and restores vertebral body stiffness, but does not restore vertebral body height lost as a result of compression fracture. METHODS: Compression fractures were experimentally created in 16 osteoporotic VBs assigned to either the tamp or percutaneous vertebroplasty group. The tamp treatment consisted of inserting balloon-like devices into the vertebral body, inflating the bone tamp, and filling the void with Simplex P (Howmedica, Rutherford, NJ) bone cement. The percutaneous vertebroplasty treatment consisted of directly injecting Cranioplastic bone cement (CMW, Blackpool, UK) into the vertebral body. Pre- and posttreatment heights were measured, and the repaired vertebral bodies were recompressed to determine posttreatment strength and stiffness values. RESULTS: The tamp treatment resulted in significant restoration (97%) of vertebral body height lost after compression, whereas percutaneous vertebroplasty treatment resulted in a significantly lower restoration of lost height (30%) (P < 0.05). Both treatments resulted in significantly stronger vertebral bodies relative to their initial state (P < 0.05). The tamp treatment restored vertebral body stiffness to initial values, but the percutaneous vertebroplasty treatment did not (P < 0.05). CONCLUSIONS: Tamp treatment resulted in significantly greater height restoration than did percutaneous vertebroplasty, without loss of vertebral body strength or stiffness.     

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 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     

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。     

椎体后凸成形术中灌注不同凝固状态骨水泥对骨质疏松性椎体压缩性骨折绵羊椎体生物力学的影响

目的 探讨椎体后凸成形术中灌注不同凝固状态骨水泥对骨质疏松性椎体压缩性骨折(OVCF)绵羊椎体强度和刚度的影响.方法 选取成年绵羊8只,获得L1～5椎体40个,随机分为4组,每组10个.采用3％稀盐酸浸泡和双侧椎弓根微泵灌注法制作骨质疏松椎体模型,再将骨质疏松椎体置于衡翼生物力学机上并压缩其高度的1/4制作压缩骨折椎体模型.制备骨水泥灌注通道后,用球囊经双侧椎弓根复位骨折椎体,在C形臂X线机透视下,对照组(A组)不灌注骨水泥,其余各组分别在聚甲基丙烯酸甲酯(PMMA)骨水泥粉液混合后2 min(骨水泥稀薄期,B组)、4 min(骨水泥黏稠期,C组)、6 min(骨水泥凝固期,D组)灌注骨水泥.室温放置24 h待骨水泥凝固.分别于术前和术后测量各组椎体的强度和刚度.结果 术前4组椎体强度和刚度组间比较,差异均无统计学意义(P>0.05).A组术后椎体强度低于术前,B、C、D组术后椎体强度均高于术前,差异有统计学意义(P<0.05).4组术后椎体刚度均低于术前,差异有统计学意义(P<0.05).B、C、D组术后椎体强度和刚度均高于A组,差异有统计学意义(P<0.05);B、C组术后椎体强度和刚度均高于D组,差异有统计学意义(P<0.05);B组和C组术后椎体强度和刚度差异无统计学意义(P>0.05).结论 OVCF绵羊采用椎体后凸成形术治疗,注入稀薄期和黏稠期骨水泥的椎体强度和刚度均高于注入凝固期骨水泥的椎体.注入不同凝固状态骨水泥均可增强椎体强度,但椎体刚度均恢复不到未骨折时期状态.     

PKP术中不同比例灌注骨水泥椎体生物力学分析

目的 利用乙二胺四乙酸二钠（EDTA-Na2）脱钙法制备离体椎体骨质疏松模型,在万能材料试验机上垂直压缩制成椎体压缩骨折模型,行椎体后凸成形术（percutaneous kyphoplasty,PKP）后再进行生物力学实验,分析按照球囊扩张容积的不同比例灌注骨水泥后椎体的生物力学性能变化,为临床治疗提供参考性资料.方法 选取新鲜成年猪胸腰段椎体36个,甲醛浸泡24 h,再以EDTA-Na2脱钙20 d,制成骨质疏松椎体模型,随机分成A、B、C、D4组,每组9个椎体,检测各组椎体骨矿密度,并依次放在万能材料试验机上行垂直压缩,测出椎体最大压缩强度及压缩刚度,记录各组椎体压缩前、后的椎体前缘高度.之后将各组分别进行聚甲基丙烯酸甲酯灌注椎体成形,按照球囊扩张容积的不同比例灌注聚甲基丙烯酸甲酯,记录球囊扩张容积、球囊压力、成型后椎体前缘高度及骨水泥渗漏椎体个数.之后进行第二次加载测试,按初始方法压缩椎体,记录此时椎体最大压缩强度和刚度.结果 PKP前四组间的椎体前缘高度、骨密度、椎体最大压缩强度及压缩刚度均无统计学意义（P＞0.05）;各组在PKP前、后的椎体最大压缩强度和压缩刚度的比较有统计学意义（P＜0.01）;PKP后A、B组间的椎体最大压缩强度和刚度比较无统计学意义（P＞0.05）,A、B两组分别与C、D组间的椎体最大压缩强度和刚度的比较有统计学意义（P＜0.01）;PKP后四组间椎体高度恢复值比较无统计学意义（P＞0.05）;A、B两组的骨水泥渗漏率为0,C、D两组的骨水泥渗漏率分别为22.22%及44.44%.结论 PKP中按照球囊扩张容积的0.8～1倍灌注骨水泥即可有效恢复骨质疏松性压缩骨折椎体的生物力学性能,又能减少骨水泥的渗漏;PKP中按照球囊扩张容积的0.8～1倍灌注骨水泥可以部分恢复压缩椎体的高度,其与高比例灌注组无明显差别;球囊扩张容积可以作为PKP中骨水泥灌注剂量的参考指标.     

Initial outcome and efficacy of "kyphoplasty" in the treatment of painful osteoporotic vertebral compression fractures.

STUDY DESIGN: An Institutional Review Board-approved Phase I efficacy study of inflatable bone tamp usage in the treatment of symptomatic osteoporotic compression fractures. OBJECTIVES: To evaluate the safety and efficacy of inflatable bone tamp reduction and cement augmentation, "kyphoplasty," in the treatment of painful osteoporotic vertebral compression fractures. SUMMARY OF BACKGROUND DATA: Osteoporotic compression fractures can result in progressive kyphosis and chronic pain. Traditional treatment for these patients includes bed rest, analgesics, and bracing. Augmentation of vertebral compression fractures with polymethylmethacrylate, "vertebroplasty," has been used to treat pain. This technique, however, makes no attempt to restore the height of the collapsed vertebral body. Kyphoplasty is a new technique that involves the introduction of inflatable bone tamps into the vertebral body. Once inflated, the bone tamps restore the vertebral body back toward its original height while creating a cavity that can be filled with bone cement. PATIENTS AND METHODS: Seventy consecutive kyphoplasty procedures were performed in 30 patients. The indications included painful primary or secondary osteoporotic vertebral compression fractures. Mean duration of symptoms was 5.9 months. Symptomatic levels were identified by correlating the clinical data with MRI findings. Perioperative variables and bone tamp complications or issues were recorded and analyzed. Preoperative and postoperative radiographs were compared to calculate the percentage height restored. Outcome data were obtained by comparing preoperative and latest postoperative SF-36 data. RESULTS: At the completion of the Phase I study there were no major complications related directly to use of this technique or use of the inflatable bone tamp. In 70% of the vertebral bodies kyphoplasty restored 47% of the lost height. Cement leakage occurred at six levels (8.6%).SF-36 scores for Bodily Pain 11.6-58.7, (P = 0.0001) and Physical Function 11.7-47.4, (P = 0.002) were among those that showed significant improvement. CONCLUSIONS: The inflatable bone tamp was efficacious in the treatment of osteoporotic vertebral compression fractures. Kyphoplasty is associated with early clinical improvement of pain and function as well as restoration of vertebral body height in the treatment of painful osteoporotic compression fractures.     

Die Wertigkeit der Ballonkyphoplastie bei der osteoporotischen Wirbelkörperfraktur

BACKGROUND DATA: Patients with osteoporotic vertebral compression fractures frequently complain of pain and a loss of function and mobility. Such fractures are associated with an increased mortality. The common treatment with bed rest, bracing or osteosynthesis does not lead to satisfying results. With two new surgical techniques, vertebroplasty and kyphoplasty, an internal stabilisation of osteoporotic vertebral fractures is possible. METHODS: All patients were treated by kyphoplasty. With a minimal invasive dorsal approach, an inflatable bone tamp is placed in the fractured vertebral body. This tamp can restore the vertebral body height and create a cavity, which is filled with bone cement under low pressure. The advantage of kyphoplasty compared to vertebroplasty is the restoration of the vertebral height and a decreased cement leakage rate. We performed a prospective, interdisciplinary study with a follow-up of 12 months. We treated 192 vertebral fractures in 102 patients. Augmentation was performed with polymethylmethacrylate in 138 cases and with a new injectable calcium phosphate-cement in 54 vertebral bodies. Outcome data were obtained with two different spine-scores and by the radiomorphometric evaluation of x-rays before and after treatment. RESULTS: We noticed a significant improvement in pain and function in 89% of the patients. All patients showed a regain of vertebral height of on average 17%. In 7% of all treated vertebral bodies, we noticed cement leakage, which was, however, far below the rates published for vertebroplasty (20-70%). There were two complications, bleeding due to an unknown coagulopathy and a violation of the myelon by malpunction. CONCLUSION: Kyphoplasty is a reliable and minimally invasive method for stabilizing fractured osteoporotic vertebral bodies. Improvement of pain and function and a regain in height of the treated vertebral body can be accomplished.     

Biomechanical efficacy of unipedicular versus bipedicular vertebroplasty for the management of osteoporotic compression fractures.

STUDY DESIGN: Cadaveric study on the biomechanics of osteoporotic vertebral bodies augmented and not augmented with polymethylmethacrylate cement. OBJECTIVES: To determine the strength and stiffness of osteoporotic vertebral bodies subjected to compression fractures and 1) not augmented, 2) augmented with unipedicular injection of cement, or 3) augmented with bipedicular injection of cement. SUMMARY OF BACKGROUND DATA: Percutaneous vertebroplasty is a relatively new method of managing osteoporotic compression fractures, but it lacks biomechanical confirmation. METHODS: Fresh vertebral bodies (L2-L5) were harvested from 10 osteoporotic spines (T scores range, -3.7 to -8.8) and compressed in a materials testing machine to determine intact strength and stiffness. They were then repaired using a transpedicular injection of cement (unipedicular or bipedicular), or they were unaugmented and recrushed. RESULTS: Results suggest that unipedicular and bipedicular cement injection restored vertebral body stiffness to intact values, whereas unaugmented vertebral bodies were significantly more compliant than either injected or intact vertebral bodies. Vertebral bodies injected with cement (both bipedicular and unipedicular) were significantly stronger than the intact vertebral bodies, whereas unaugmented vertebral bodies were significantly weaker. There was no significant difference in loss in vertebral body height between any of the augmentation groups. CONCLUSIONS: This study suggests that unipedicular and bipedicular injection of cement, as used during percutaneous vertebroplasty, increases acute strength and restores stiffness of vertebral bodies with compression fractures.     

Vertebro-/Kyphoplasty History, Development, Results

Abstract Many investigations prove the significant analgetic effect of vertebral augmentation. The reasons for the decrease in pain are found in the stabilization of fracture fragments as well as the toxic-thermic effect of polymethylmethacrylate (PMMA), used in the majority of cases. The techniques, primarily in use since 1984, can be divided in vertebro- and kyphoplasty. Vertebroplasty is the direct injection of PMMA into the trabecular vertebral body, while kyphoplasty uses an inflatable bone tamp to create a cavity which is filled with highly viscous cement allowing a certain degree of vertebral height restoration. Both techniques are used percutaneously. Indications for augmentation are painful osteoporotic vertebral fractures, metastatic osteolyses, and painful or destabilizing vertebral hemangiomas. In this article, an overview of the techniques and the history of their development is provided. The materials used for augmentation, the possibilities, limits, and complications of the techniques are discussed.     

气囊扩张椎体后凸成形术的初步报告

目的:初步评价气囊扩张后突成形术治疗骨质疏松性椎体压缩骨折的手术操作、安全性、及疗效。方法:观察21例骨质疏松患者,30节椎体,新鲜骨折24椎节,陈旧性骨折6椎节,均有局部腰背疼痛,无神经症状。C-arm透视下,两侧同时经皮穿刺,气囊扩张骨折复位后,骨水泥灌注入椎体。随访4～7月。记录患者局部止痛的疗效,骨折的复位,及并发症等情况。结果:完全止痛14例,部分止痛7例,24节新鲜骨折气囊扩张的复位率是28.2％,6节陈旧性骨折复位率是2.1％。并发症2例,骨水泥外漏到椎间隙。其他椎体再次骨折2例,余无疼痛复发及椎体高度丢失。结论:气囊扩张后突成形术能恢复脊柱的稳定性,部分矫正脊柱后突,止痛疗效好,创伤小,并发症少,值得推广。     

The biomechanics of vertebroplasty. The effect of cement volume on mechanical behavior.

STUDY DESIGN: Ex vivo biomechanical study using osteoporotic cadaveric vertebral bodies. OBJECTIVE: To determine the association between the volume of cement injected during percutaneous vertebroplasty and the restoration of strength and stiffness in osteoporotic vertebral bodies, two investigational cements were studied: Orthocomp (Orthovita, Malvern, PA) and Simplex 20 (Simplex P with 20% by weight barium sulfate content; Stryker-Howmedica-Osteonics, Rutherford, NJ). SUMMARY OF BACKGROUND DATA: Previous biomechanical studies have shown that injections of 8-10 mL of cement during vertebroplasty restore or increase vertebral body strength and stiffness; however, the dose-response association between cement volume and restoration of strength and stiffness is unknown. METHODS: Compression fractures were experimentally created in 144 vertebral bodies (T6-L5) obtained from 12 osteoporotic spines harvested from female cadavers. After initial strength and stiffness were determined, the vertebral bodies were stabilized using bipedicular injections of cement totaling 2, 4, 6, or 8 mL and recompressed, after which post-treatment strength and stiffness were measured. Strength and stiffness were considered restored when post-treatment values were not significantly different from initial values. RESULTS: Strength was restored for all regions when 2 mL of either cement was injected. To restore stiffness with Orthocomp, the thoracic and thoracolumbar regions required 4 mL, but the lumbar region required 6 mL. To restore stiffness with Simplex 20, the thoracic and lumbar regions required 4 mL, but the thoracolumbar region required 8 mL. CONCLUSION: These data provide guidance on the cement volumes needed to restore biomechanical integrity to compressed osteoporotic vertebral bodies.     

低压力应用单一球囊治疗多椎体骨质疏松性脊柱压缩骨折

目的探讨低压力应用单一球囊治疗多个椎体骨质疏松性脊柱压缩骨折的疗效。方法共治疗13例患者37个椎体,均为女性,年龄65～79岁,平均72.3岁。均为骨质疏松性脊柱压缩骨折,压缩骨折椎体后壁均完整。在C型臂X线机引导下行单一球囊多椎体后凸成形术。结果13例手术顺利完成。椎体前缘、中部及后缘平均高度分别由术前的(1.9±0.5)cm,(1.5±0.5)cm,(2.6±0.5)cm增至术后的(2.1±0.4)cm,(2.2±0.4)cm,(2.8±0.5)cm,椎体前缘、中部高度差异有显著统计学意义,P值均小于0.01。Cobb角由术前的(31.3±14.1)°矫正至术后的(24.8±11.3)°。术后平均随访17.3个月,患者疼痛均较术前改善或消失,无临床并发症发生。结论通过降低球囊扩张压力,避免了球囊破损,为患者减少了经济负担。同时,骨水泥填充量相应减小,减少了骨水泥渗漏,又可以避免因大幅度提高患椎弹性模量和刚度造成相邻椎体压缩骨折。     

Spinal loads after osteoporotic vertebral fractures treated by vertebroplasty or kyphoplasty

Vertebroplasty and kyphoplasty are routine treatments for compression fractures of vertebral bodies. A wedge-shaped compression fracture shifts the centre of gravity of the upper body anteriorly and generally, this shift can be compensated in the spine and in the hips. However, it is still unclear how a wedge-shaped compression fracture of a vertebra increases forces in the trunk muscle and the intradiscal pressure in the adjacent discs. A nonlinear finite element model of the lumbar spine was used to estimate the force in the trunk muscle, the intradiscal pressure and the stresses in the endplates in the intact spine, and after vertebroplasty and kyphoplasty treatment. In this study, kyphoplasty represents a treatment with nearly full fracture reduction and vertebroplasty one without restoration of kyphotic angle although in reality kyphoplasty does not guarantee fracture reduction. If no compensation of upper body shift is assumed, the force in the erector spine increases by about 200% for the vertebroplasty but by only 55% for the kyphoplasty compared to the intact spine. Intradiscal pressure increases by about 60 and 20% for the vertebroplasty and kyphoplasty, respectively. In contrast, with shift compensation of the upper body, the increase in muscle force is much lower and increase in intradiscal pressure is only about 20 and 7.5% for the vertebroplasty and kyphoplasty, respectively. Augmentation of the vertebral body with bone cement has a much smaller effect on intradiscal pressure. The increase in that case is only about 2.4% for the intact as well as for the fractured vertebra. Moreover, the effect of upper body shift after a wedge-shaped vertebral body fracture on intradiscal pressure and thus on spinal load is much more pronounced than that of stiffness increase due to cement infiltration. Maximum von Mises stress in the endplates of all lumbar vertebrae is also higher after kyphoplasty and vertebroplasty. Cement augmentation has only a minor effect on endplate stresses in the unfractured vertebrae. The advantages of kyphoplasty found in this study will be apparent only if nearly full fracture reduction is achieved. Otherwise, differences between kyphoplasty and vertebroplasty become small or vanish. Our results suggest that vertebral body fractures in the adjacent vertebrae after vertebroplasty or kyphoplasty are not induced by the elevated stiffness of the treated vertebra, but instead the anterior shift of the upper body is the dominating factor.     

胸腰椎骨质疏松性骨折自固化磷酸钙骨水泥椎体成形的实验研究

目的探讨自固化磷酸钙骨水泥(calciumphosphatecement,CPC)注射椎体成形术后对胸腰椎骨质疏松性骨折椎体的力学影响。方法自愿捐赠的4具甲醛固定的老年尸体,取胸腰椎骨质疏松标本,平均年龄69岁,男、女各2具。每具标本随机取6个椎体,制备24个单椎体标本,建立前屈方向加载单椎体骨折模型。将CPC粉末与固化液以2.5g∶1ml调和制备CPC骨水泥,对骨折标本行CPC成形强化,每个椎体注射CPC约4ml。分别进行骨折前、成形后屈曲压缩力学检测。结果骨质疏松椎体标本骨折前最大载荷为1954±46N,位移长度为5.60±0.70mm,刚度为349±18N/mm;骨折间隙CPC填塞成形后最大载荷为2285±34N,位移为5.35±0.60mm,刚度为427±10N/mm,各指标骨折前和成形后比较差异均有统计学意义(P<0.05)。CPC加强成形后单椎体的承载能力强度较骨折前提高16.92%,刚度较骨折前提高22.31%。结论椎体内注射CPC能明显恢复骨质疏松骨折椎体的力学性能。     

Vertebral body stenting: a new method for vertebral augmentation versus kyphoplasty

Vertebroplasty and kyphoplasty are well-established minimally invasive treatment options for compression fractures of osteoporotic vertebral bodies. Possible procedural disadvantages, however, include incomplete fracture reduction or a significant loss of reduction after balloon tamp deflation, prior to cement injection. A new procedure called “vertebral body stenting” (VBS) was tested in vitro and compared to kyphoplasty. VBS uses a specially designed catheter-mounted stent which can be implanted and expanded inside the vertebral body. As much as 24 fresh frozen human cadaveric vertebral bodies (T11-L5) were utilized. After creating typical compression fractures, the vertebral bodies were reduced by kyphoplasty (n = 12) or by VBS (n = 12) and then stabilized with PMMA bone cement. Each step of the procedure was performed under fluoroscopic control and analysed quantitatively. Finally, static and dynamic biomechanical tests were performed. A complete initial reduction of the fractured vertebral body height was achieved by both systems. There was a significant loss of reduction after balloon deflation in kyphoplasty compared to VBS, and a significant total height gain by VBS (mean ± SD in %, p < 0.05, demonstrated by: anterior height loss after deflation in relation to preoperative height [kyphoplasty: 11.7 ± 6.2; VBS: 3.7 ± 3.8], and total anterior height gain [kyphoplasty: 8.0 ± 9.4; VBS: 13.3 ± 7.6]). Biomechanical tests showed no significant stiffness and failure load differences between systems. VBS is an innovative technique which allows for the possibly complete reduction of vertebral compression fractures and helps maintain the restored height by means of a stent. The height loss after balloon deflation is significantly decreased by using VBS compared to kyphoplasty, thus offering a new promising option for vertebral augmentation.     

椎体后凸成形术与椎体成形术生物力学比较

目的比较椎体后凸成形术（KP）与椎体成形术（VP）对骨质疏松性椎体压缩骨折（OVCF）椎体力学性能的影响。方法5具尸体取20个胸腰段骨质疏松单椎体标本,按配对设计,分配为球囊扩张椎体后凸成形术组（KP组）和椎体成形术组（VP组）。经轴向加载压缩25%,制成椎体压缩骨折,记录制成骨折时的最大载荷及刚度数据。KP组将椎体压缩骨折标本行球囊扩张椎体后凸成形术;VP组将椎体压缩骨折标本行椎体成形术。然后将骨水泥强化治疗的椎体再次经万能力学试验机轴向加载,记录治疗后最大载荷及刚度数据。结果KP组和VP组骨折治疗后椎体最大载荷均分别明显高于骨折前（P〈0.01）,而椎体刚度差异无统计学意义（P〉0.05）。KP组与VP组间比较治疗后椎体最大载荷差异无统计学意义（P〉0.05）,椎体刚度差异无统计学意义（P〉0.05）。结论KP和VP均可明显增加OVCF椎体的抗压强度和恢复刚度。     

An ex vivo biomechanical evaluation of a hydroxyapatite cement for use with vertebroplasty.

STUDY DESIGN: Comparative ex vivo biomechanical study. OBJECTIVE: To determine the strength and stiffness of osteoporotic vertebral bodies subjected to compression fractures and stabilized via bipedicular injections of the following: 1) Simplex P (Stryker-Howmedica-Osteonics, Rutherford, NJ), 2) Simplex P formulated consistent with the practice of vertebroplasty (F2), or 3) BoneSource (Stryker-Howmedica-Osteonics). SUMMARY OF BACKGROUND DATA: Little is known about the mechanical stabilization afforded by new materials proposed for use with vertebroplasty. METHODS: Vertebral bodies (T8-T10 and L2-L4) from each of 10 fresh spines were harvested from female cadavers (81 +/- 12 years), screened for bone density (t score, -3.8 +/- 1.1; bone mineral density, 0.75 +/- 15 g/cm2), disarticulated, and compressed to determine initial strength and stiffness. The fractured vertebral bodies were stabilized via bipedicular injections of 4 mL (thoracic) or 6 mL (lumbar) and then recrushed. RESULTS: Vertebral bodies repaired with Simplex P resulted in significantly greater strength (P < 0.05) relative to their prefracture states, those repaired with BoneSource resulted in the restoration of initial strength for both the thoracic and lumbar level, and those repaired with F2 resulted in significantly greater strength (P < 0.05) in the thoracic region and restoration of strength in the lumbar region. All cement treatments resulted in significantly less stiffness compared with initial values. CONCLUSIONS: All three materials tested restored or increased vertebral body strength, but none restored stiffness. Both new materials show promise for use in percutaneous vertebroplasty, but they need clinical evaluation.