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  脊柱外科杂志  2017, Vol.15 Issue(3): 177-181   PDF    
骨水泥注入量对经皮椎体后凸成形术后相邻椎体应力影响的有限元分析
徐建彪1, 张伟学2, 王鸿晨2, 杜传超1, 王占长1, PORTER Daniel1    
1. 清华大学第一附属医院骨科, 北京 100016;
2. 北京市仁和医院骨科, 北京 102600
摘要: 目的 采用三维有限元法分析骨水泥注入量对椎体后凸成形术(PKP)后患椎相邻椎体生物力学的影响。 方法 经PKP治疗的骨质疏松性椎体压缩性骨折(OVCF)患者69例,根据骨水泥注入量分为低剂量(> 2.0 mL且<3.0 mL)组(22例)、中剂量(≥3.0 mL且<6.0 mL)组(28例)、高剂量(≥6 mL)组(19例),采用视觉模拟量表(VAS)评分评价术前、术后的疼痛程度。收集患者手术前后的CT数据,利用Mimics 10.01和Abaqus 6.8软件建立三维有限元模型,在患椎的上终板分别施加0.3 MPa(低压力)、1.0 MPa(中压力)、4.0 MPa(高压力)的轴向压力,观察不同载荷下的应力改变。 结果 所有患者术后VAS评分与术前相比均明显降低,差异有统计学意义(P<0.05);3组患者术后VAS评分差异无统计学意义(P>0.05)。骨水泥渗漏5例(7.25%),均未出现神经症状;低剂量组1例,中剂量组2例,高剂量组2例,3组间差异无统计学意义(P>0.05)。末次随访未发现相邻椎体再发骨折。在低压力(中立位)时,患椎下位椎体的应力较术前增加约22%,上位椎体的应力增加约15%。在中压力(正常活动)、高压力(突然摔倒)时,高剂量组患椎上、下位椎体的应力较低压力时均明显增加,差异有统计学意义(P<0.05),而中剂量组和低剂量组的患椎上、下位椎体的应力与低压力时相比,差异无统计学意义(P>0.05)。 结论 PKP术后可引起患椎上、下相邻节段生物力学的改变,相邻椎体所受的应力随着轴向负荷和骨水泥注入量的增加呈增加趋势。
关键词: 胸椎     腰椎     骨折, 压缩性     骨质疏松     经皮椎体后凸成形术    
Biomechanical finite element analysis of adjacent vertebral stress changes after percutaneous kyphoplasty with different amounts of bone cement
XU Jian-biao1, ZHANG Wei-xue2, WANG Hong-chen2, DU Chuan-chao1, WANG Zhan-chang1, PORTER Daniel1    
1. Department of Orthopaedics, First Hospital of Tsinghua University, Beijing 100016, China;
2. Department of Orthopaedics, Beijing Renhe Hospital, Beijing 102600, China
Abstract: Objective To explore the biomechanical effects of different amount of bone cement on adjacent vertebral bodies after percutaneous kyphoplasty (PKP). Methods Totally 69 patients with osteoporotic vertebral compression fractures (OVCF) who underwent PKP were included and divided into 3 groups according to the amount of bone cement:low dose (> 2.0 mL and < 3.0 mL) group (n=22), medium dose (≥ 3.0 mL and < 6.0 mL) group (n=28), and high dose (≥ 6 mL) group (n=19).The outcome was evaluated by visual analogue scale (VAS) score.The three-dimensional finite element models of 69 patients were built based on CT scan data by the Mimics 10.01 and Abaqus 6.8 software.Different axial pressures (0.3, 1.0, and 4.0 MPa) were put on the superior endplate, and the stress on the adjacent vertebrae was analyzed. Results All patients had a decrease in VAS score post-operation compared to pre-operation, with a significant difference (P < 0.05).There was no significant difference in postoperative VAS score between the 3 groups (P> 0.05).Bone cement leak occurred in 5 patients (7.25%), and none of them had neurological symptoms; 1 cases in the low dose group, 2 cases in the medium dose group and 2 cases in the high dose group, and difference between the 3 groups was not statistically significant (P>0.05).No adjacent vertebral body fracture was found in the final follow-up.At low pressure (neutral position), the pressure in the lower vertebra increased by about 22% compared with pre-operation; and upper vertebral body stress increased by about 15%.At medium pressure (normal activities) and high pressure (suddenly falls down), stress of the vertebral body in high dose group were significantly increased than neutral position with a statistical difference (P < 0.05), while those in low and medium dose groups showed no difference compared with that at neutral pressure (P>0.05). Conclusion PKP changes the biomechanical distribution on adjacent vertebrae.With the increases of axial pressure and the amount of bone cement, the biomechanical effect has the increasing trend.
Key words: Thoracic vertebrae     Lumbar vertebrae     Fractures, compression     Osteoporosis     Percutaneous kyphoplasty    

骨质疏松椎体压缩性骨折(OVCF)是骨质疏松症的常见并发症。经皮椎体后凸成形术(PKP)是治疗OVCF的有效手段[1-2],但近年的研究表明,PKP术后存在相邻椎体骨折的风险[3-4]。本研究采用三维有限元法分析不同骨水泥量对患椎相邻椎体生物力学的影响,为临床提供理论支持。

1 资料和方法1.1 一般资料

本研究共纳入2011年8月—2015年2月在清华大学第一附属医院骨科行PKP治疗的OVCF患者69例。纳入标准:① 持续胸背部、腰背部疼痛,可伴有胸肋部疼痛,平卧休息时疼痛减轻甚至消失,体位改变时疼痛明显;② 体格检查可见胸腰部骨折部压痛、叩击痛,一般无下肢神经损伤表现;③ X线及CT示椎体楔形变,无明显脊髓压迫;④ MRI表现为新鲜椎体骨折,即患椎在T1加权像上显示低信号,在T2加权及压脂像上显示高信号;⑤ 骨密度检测T≤-2.5。排除标准:① 多节段椎体骨折;② 经检查存在手术禁忌证,无法耐受PKP治疗的患者。入选病例均为单椎体骨折,病变节段:T11骨折10例,T12骨折22例,L1骨折21例,L2骨折16例。所有患者均采用PKP治疗,术后均给予规范化的抗骨质疏松治疗。根据术中骨水泥注入量分为3组:低剂量(≥2.0 mL且 < 3.0 mL)组22例,中剂量(≥3.0 mL且 < 6.0 mL)组28例,高剂量(≥6 mL)组19例。

1.2 建模及加载

应用三维重建软件Mimics 10.01对CT扫描图像进行三维模型重建和赋值。患椎相邻的椎体应用通用电气公司生产的64排螺旋CT进行薄层扫描,层厚1 mm,图像以dicom格式保存。CT扫描范围为患椎上、下各一椎体。将dicom格式的图像导入Mimics 10.01软件建立骨结构的三维模型,对椎间盘、韧带、终板等结构进行补建,使用Geomagic软件对图像进行优化,使用有限元软件Ansys 11.0建立模型。参照已发表的有限元分析相关研究文献设定不同成分材料参数[3, 5]。应用Abaqus 6.8软件对骨水泥区域体网格化,椎体网格化后再重新导入Mimics 10.01软件中赋予其材料属性(骨水泥弹性模量4 000 MPa,泊松比0.33,可以与其他组织明显分离)。人体在正常直立位时椎体轴向压力约为0.3 MPa(1 mmHg=0.133 kPa),故本研究模拟人体中立位(低压力)、正常活动(中压力)及突然摔倒(高压力)时的椎体受力情况[6],在患椎的上终板分别施加0.3 MPa(低压力)、1.0 MPa(中压力)、4.0 MPa(高压力)的轴向压力,观察其相邻椎体不同载荷下的力学变化。

1.3 观察指标

使用视觉模拟量表(VAS)[6]在术前和术后2 d进行疼痛评分;根据PKP术后正、侧位X线片观察骨水泥渗漏情况,统计骨水泥渗漏率;以末次随访为终点计算再发骨折率。三维模型重建主要的力学分析指标为VonMises应力,单位为MPa,观察PKP不同骨水泥注入量对相邻终板在不同轴向压力下应力分布的影响。

1.4 统计学处理

采用SPSS 13.0软件对数据进行统计学分析。计量资料采用x±s表示,组内术前、术后VAS评分和不同压力下的应力分布比较采用配对t检验,组间术前、术后VAS评分比较行单因素方差分析;计数资料(骨水泥渗漏率及再发骨折率)的比较采用χ2检验。以P < 0.05为差异有统计学意义。

2 结果2.1 临床结果

术前骨密度T值,低剂量组为-3.5±0.7,中剂量组为-3.2±0.5,高剂量组为-3.4±0.6,三组间差异无统计学意义,具有可比性。发生骨水泥渗漏5例,渗漏率7.25%,均未出现神经症状;其中低剂量组1例,中剂量组2例,高剂量组2例,3组间骨水泥渗漏率差异无统计学意义(P > 0.05)。术后1 d,患者腰痛消失或部分缓解,可离床活动。术后2 d,患者的VAS评分均较术前明显降低,差异有统计学意义(P < 0.05);3组间术前、术后VAS评分差异无统计学意义(P > 0.05,表 1)。随访12~24(16.5±3.5)个月。末次随访时未出现疼痛症状复发、椎体高度严重丢失及相邻椎体再骨折。

表 1 各组VAS评分 Table 1 VAS score in each group
2.2 有限元分析结果

在低压力(中立位)时,患椎下位椎体终板的应力较术前增加约22%(低剂量组为16%,中剂量组为18%,高剂量组为31%),上位椎体终板的应力增加约15%(低剂量组为11%,中剂量组为12%,高剂量组为21%)。在中压力(正常活动)、高压力(突然摔倒)时,高剂量组的患椎上、下位椎体的应力变化较低压力(中立位)时均明显增加,差异有统计学意义(P < 0.05);中剂量组和低剂量组的患椎上、下位椎体的应力变化虽较低压力时有所增加,但差异无统计学意义(P > 0.05,表 23)。

表 2 上位相邻椎体终板的应力分布 Table 2 Stress distribution of upper adjacent vertebral endplate

表 3 下位相邻椎体终板的应力分布 Table 3 Stress distribution of lower adjacent vertebral endplate
3 讨论

PKP是缓解OVCF患者疼痛、恢复脊柱正常生理曲度的有效方法。众多研究显示,PKP术后相邻椎体骨折率增加[7-9]。目前,对PKP引起相邻椎体骨折的原因尚未有统一的认识,有学者认为仅仅是骨质疏松症的自然进展,骨水泥的量与相邻椎体骨折无明显关系[10-11];也有学者认为是PKP后骨水泥椎体强化使相邻椎体受力增加所致[2]。有关PKP术中骨水泥的注入量一直存在争议,目前尚无统一的标准[12-15]。本研究通过三维有限元的方法探讨PKP术中骨水泥注入量对患椎相邻椎体生物力学的影响。

OVCF最常见的发生部位是胸腰段,通常是T11~L2,这主要与胸腰段的解剖位置有关,其处于活动较多的腰椎与相对固定的胸椎之间[16]。本研究中所有患者均为T11~L2节段的OVCF。本研究中三维模型构建参考已发表的相关文献[3, 17-19],较为符合真实的人体生物力学要求,能够真实模拟不同情况下椎体的受力情况。

理论上注入更多的骨水泥能够更好地恢复椎体的高度,更有效地缓解患者的疼痛,但众多研究发现,临床止痛效果与骨水泥量无明显相关性[20-21]。本研究亦发现,注入不同剂量骨水泥的患者其术前、术后VAS评分改变差异无统计学意义,说明骨水泥量并未影响患者的术后临床效果。有研究认为,注入2.0~6.0 mL骨水泥就可达到良好的止痛效果[22],也有学者研究发现,PKP术后相同剂量的骨水泥在椎体中均匀分布的患者脊柱稳定性优于偏侧分布[23]。由于高黏度骨水泥的渗漏率要明显低于低黏度骨水泥,且高黏度骨水泥较低黏度骨水泥在椎体中分布更为均匀[24],本研究采用高黏度骨水泥注入,术后复查发现骨水泥均基本均匀分布,仅5例发生骨水泥渗漏。

本研究发现随着轴向负荷的增加,相邻椎体所受的VonMises应力呈增加趋势;随着骨水泥量的增加,相邻椎体所受的VonMises应力呈增加趋势。Liebschner等[25]认为大量的骨水泥能够增加骨水泥的刚度,较高的骨水泥刚度使脊柱纵轴方向过量的应力传递至相邻椎体终板,并通过终板传递至相邻椎体。同时患者术后康复运动的强度随着疼痛缓解而增加,从而进一步增加相邻椎体的压力负荷。Polikeit等[26]通过有限元模型发现,即使少量的骨水泥亦可使相邻椎体应力分布显著改变。上述原因可能导致术后相邻椎体骨折的发生概率增加。本研究发现,在中压力(正常活动)、高压力(突然摔倒)时,高剂量组患椎上、下位椎体的应力较低压力(中立位)均明显增加,差异具有统计学意义。本研究末次随访未发现相邻椎体骨折,可能与术后规范化抗骨质疏松治疗有关。

综上,本研究发现,骨水泥量并未明显影响患者的术后临床效果;PKP术后可引起患椎上、下相邻节段生物力学的改变,且随着轴向负荷和骨水泥量的增加,相邻椎体所受的应力均呈增加趋势。本研究为单中心回顾性研究,且病例数较少,结果仍有待于前瞻性、大样本、多中心随机对照研究进一步证实。

参考文献
[1] Chen B, Li Y, Xie D, et al. Comparison of unipedicular and bipedicular kyphoplasty on the stiffness and biomechanical balance of compression fractured vertebrae[J].Eur Spine J, 2011, 20(8): 1272–1280. DOI:10.1007/s00586-011-1744-3
[2] 王清泽, 王相利, 张金锋, 等. 椎体成形术与非手术治疗骨质疏松性椎体压缩性骨折安全性的Meta分析[J].脊柱外科杂志, 2016, 14(5): 306–311.
[3] Rotter R, Schmitt L, Gierer P, et al. Minimum cement volume required in vertebral body augmentation-A biomechanical study comparing the permanent SpineJack device and balloon kyphoplasty in traumatic fracture[J].Clin Biomech(Bristol, Avon), 2015, 30(7): 720–725. DOI:10.1016/j.clinbiomech.2015.04.015
[4] Martinčič D, Brojan M, Kosel F, et al. Minimum cement volume for vertebroplasty[J].Int Orthop, 2015, 39(4): 727–733. DOI:10.1007/s00264-014-2620-7
[5] Sun K, Liebschner MA. Evolution of vertebroplasty:a biomechanical perspective[J].Ann Biomed Eng, 2004, 32(1): 77–91. DOI:10.1023/B:ABME.0000007793.49771.6d
[6] Huskisson EC. Measurement of pain[J].Lancet, 1974, 2(7889): 1127–1131.
[7] Bliemel C, Oberkircher L, Buecking B, et al. Higher incidence of new vertebral fractures following percutaneous vertebroplasty and kyphoplasty-fact or fiction?[J].Acta Orthop Belg, 2012, 78(2): 220–229.
[8] Berlemann U, Ferguson SJ, Nolte LP, et al. Adjacent vertebral failure after vertebroplasty. A biomechanical investigation[J].J Bone Joint Surg Br, 2002, 84(5): 748–752. DOI:10.1302/0301-620X.84B5.11841
[9] Baroud G, Bohner M. Biomechanical impact of vertebroplasty. Postoperative biomechanics of vertebroplasty[J].Joint Bon, Spine, 2006, 73(2): 144–150. DOI:10.1016/j.jbspin.2005.02.004
[10] Kim DJ, Kim TW, Park KH, et al. The proper volume and distribution of cement augmentation on percutaneous vertebroplasty[J].J Korean Neurosurg Soc, 2010, 48(2): 125–128. DOI:10.3340/jkns.2010.48.2.125
[11] Kaufmann TJ, Trout AT, Kallmes DF. The effects of cement volume on clinical outcomes of percutaneous vertebroplasty[J].AJNR Am J Neuroradiol, 2006, 27(9): 1933–1937.
[12] Kolb JP, Kueny RA, Püschel K, et al. Does the cement stiffness affect fatigue fracture strength of vertebrae after cement augmentation in osteoporotic patients?[J].Eur Spine J, 2013, 22(7): 1650–1656. DOI:10.1007/s00586-013-2809-2
[13] Kim JM, Shin DA, Byun DH, et al. Effect of bone cement volume and stiffness on occurrences of adjacent vertebral fractures after vertebroplasty[J].J Korean Neurosurg Soc, 2012, 52(5): 435–440. DOI:10.3340/jkns.2012.52.5.435
[14] Sun G, Jin P, Li M, et al. Percutaneous vertebroplasty for pain management in spinal metastasis with epidural involvement[J].Technol Cancer Res Treat, 2011, 10(3): 267–274. DOI:10.7785/tcrt.2012.500202
[15] Kwon HM, Lee SP, Baek JW, et al. Appropriate cement volume in vertebroplasty:a multivariate analysis with short-term follow-up[J].Korean J Neurotrauma, 2016, 12(2): 128–134. DOI:10.13004/kjnt.2016.12.2.128
[16] Holub O, López A, Borse V, et al. Biomechanics of low-modulus and standard acrylic bone cements in simulated vertebroplasty:a human ex vivo study[J].J Biomech, 2015, 48(12): 3258–3266. DOI:10.1016/j.jbiomech.2015.06.026
[17] Yan L, Chang Z, Xu Z, et al. Biomechanical effects of bone cement volume on the endplates of augmented vertebral body:a three-dimensional finite element analysis[J].Chin Med J(Engl), 2014, 127(1): 79–84.
[18] 费琦, 王炳强, 杨雍, 等. 计算机模拟椎体成形对邻近节段力学影响的有限元分析[J].中国组织工程研究与临床康复, 2011, 15(26): 4757–4762. DOI:10.3969/j.issn.1673-8225.2011.26.003
[19] 杨小彬, 贺宝荣, 郝定均, 等. 不同骨水泥量在PKP术后对相邻节段生物力学影响的有限元分析[J].中国骨与关节损伤杂志, 2016, 31(1): 40–43. DOI:10.7531/j.issn.1672-9935.2016.01.013
[20] Luo J, Daines L, Charalambous A, et al. Vertebroplasty:only small cement volumes are required to normalize stress distributions on the vertebral bodies[J].Spine (Phila Pa 1976), 2009, 34(26): 2865–2873. DOI:10.1097/BRS.0b013e3181b4ea1e
[21] 张阳, 单建林, 李放, 等. 骨水泥椎间渗漏与椎体成形术术后再发椎体压缩骨折相关性研究[J].脊柱外科杂志, 2013, 11(5): 279–282.
[22] Lien SB, Liou NH, Wu SS. Analysis of anatomic morphometry of the pedicles and the safe zone for through-pedicle procedures in the thoracic and lumbar spine[J].Eur Spine J, 2007, 16(8): 1215–1222. DOI:10.1007/s00586-006-0245-2
[23] Garfin SR, Buckley RA, Ledlie J. Balloon Kyphoplasty Outcomes Group. Balloon kyphoplasty for symptomatic vertebral body compression fractures results in rapid, significant, and sustained improvements in back pain, function, and quality of life for elderly patients[J].Spine(Phila Pa 1976), 2006, 31(19): 2213–2220. DOI:10.1097/01.brs.0000232803.71640.ba
[24] 徐超, 伊力哈木·托合提, 李国华, 等. 高粘度与低粘度骨水泥PVP治疗骨质疏松椎体压缩骨折的疗效和并发症[J].中国脊柱脊髓杂志, 2014, 24(10): 900–905. DOI:10.3969/j.issn.1004-406X.2014.10.07
[25] Liebschner MA, Rosenberg WS, Keaveny TM. Effects of bone cement volume and distribution on vertebral stiffness after vertebroplasty[J].Spine(Phila Pa 1976), 2001, 26(14): 1547–1554. DOI:10.1097/00007632-200107150-00009
[26] Polikeit A, Nolte LP, Ferguson SJ. The effect of cement augmentation on the load transfer in an osteoporotic functional spinal unit:finite-element analysis[J].Spine (Phila Pa 1976), 2003, 28(10): 991–996.