三维有限元分析比较三种内固定物对骨盆后环损伤的治疗效果

发布时间：2018-09-11 08:57

【摘要】：骨盆骨折是临床中较为严重的骨折类型,多由交通车祸伤、高处坠落伤等高能量损伤所致。张英泽等对骨折的临床创伤流行病学研究中发现,骨盆骨折的发病率在全身骨折发病率中约占4.21%,且主要为中青年患者。其中不稳定性骨盆骨折占68.3%,常合并周围血管、神经及膀胱、直肠、子宫等重要脏器的损伤,致残率及致死率高。随着近十年内固定技术的发展,内固定复位治疗骨盆骨折成为了最常用的治疗手段。但内固定的选择多种多样,每种内固定方式的优缺点和手术适应症各不相同,因此选择合适的内固定方式仍是骨科医师面临的重点和难点。与此同时,骨盆是躯体与下肢的力学转换中心。因此,骨盆创伤手术治疗的首要目的是恢复骨盆生物力学功能。一般来说,内固定物的临床疗效和生物力学特性应该通过体外生物力学实验进行验证。然而尸体骨盆标本不易获得,难以收集或制作足够多的标本,易因样本量不足导致力学实验结果产生较大误差。同时,实体生物力学实验无法测量骨骼内部力学特性,这些都对骨盆生物力学研究带来了一定的局限性。随着计算机技术和数字化医学的发展,有限元分析在生物力学方面已得到越来越广泛的应用。有限元分析法通过化整为零、集零为整的基本思想,利用多形态网格来分割各个复杂研究区域,并根据需要布置所需节点,对骨盆这类复杂物体结构具有很好的适用性;同时有限元方法能够了解模型各部位受力时的内部应力和应变改变。这些使有限元分析在生物力学研究方面具有无法比拟的优势,使其成为人类骨盆生物力学研究最常用的手段。目前临床上常用的治疗骶骨纵行骨折、骶髂关节脱位等内固定技术主要有骶髂螺钉(iliosacral screw,ISS)、张力带接骨板(tension band plate,TBP)和骶髂棒等。这些内固定器械都有一定的局限性,如ISS技术进行内固定复位技术需要医生具有较高的手术技巧,螺钉和导针的置入均需在透视的引导进行,可能使医生和患者X线暴露时间增加;TBP在固定前需预弯钢板,而重复预弯钢板会降低钢板强度甚至造成钉孔损伤。此外,TBP术后感染率较高。针对上述问题,张英泽教授及其课题组根据骨盆后环的解剖形态设计了微创可调式接骨板(minimally invasive adjustable plate,MIAP),可微创植入并通过调节螺杆长度以复位骨盆后环骨折。本研究通过建立高度仿真的有限元模型,模拟骨盆骨折或脱位,从以下几个部分比较了三种内固定物对于骨盆生物力学功能的恢复效果、骨折固定的稳定性以及内固定物的生物力学相容性。第一部分有限元分析不同边界条件对骨盆生物力学载荷传递的影响目的:建立包括髂骨、骶骨、近端股骨和主要韧带在内的完整骨盆有限元模型。随后通过应变片测量不同载荷下骨盆标本表面的应变值以验证有限元模型。最终利用验证成功的有限元模型分析不同边界条件和髋关节接触条件对骨力学载荷传递的影响。方法:取1具成年女性非骨质疏松性完整骨盆及近侧l/3股骨标本。模拟双足站立骨盆中立位,将标本固定于BOSE生物力学试验机。于骶1椎体、骶1椎体近骶髂关节的部位、骶2椎体、骶2椎体近骶髂关节的部位、髂耻线中点和临近坐骨大切迹粘贴电阻应变片,应用WS3811型数字应变仪记录标本在100~500N时(间隔为100N)垂直载荷下选定位点的应变值。随后选取成年健康女性1名,经CT扫描,层厚0.3mm,影像资料以医学数字成像和交互(Digital Imaging and Communications in Medicine,DICOM)格式保存。应用Mimics、Geomagic Studio、Solid Works、Abaqus等软件建立完整骨盆的三维有限元模型。根据三种不同髋关节接触条件和边界条件分别建立模型I、模型II和模型III。模型I在股骨头和髋臼上建立接触面,并将其设为“Contact Condition”,以研究将髋关节设为滑动关节对于应力分布的影响。模型II将双侧髋关节设定为绑定连接。模型III的髋关节处不包含股骨。模型I和模型II约束股骨末端,模型III约束两侧的髋臼运动中心。向骶骨表面垂直加载100~500N载荷,计算骨盆的应力分布情况。为了更精确的研究不同边界条件下骨盆载荷传递,我们除比较了验证试验中的6个位点外,检测了另外3个骨盆表面的解剖学位点的应力:髋臼臼顶、髋臼后壁和骨盆前部靠近耻骨联合的位点。结果:我们应用线性回归分析对骨盆标本和骨盆有限元模型的每个对应点的应变值进行了比较来验证有限元模型的有效性。回归方程和相关系数分别是:y=1.019x-1.114,R2=0.97。同时,随着载荷水平增加,线性回归的相关系数从100N时的R2=0.90升高至500N时的R2=0.98,说明高载荷比低载荷的线性回归性更好。此外,我们发现回归方程的理论斜率随加载力的升高而更加趋近于1,说明加载越高,有限元分析与生物力学实验结果越接近。关于载荷传递,三个模型的应力分布均沿着髂耻线传递,每个模型的最大应力均位于骶髂骨间韧带。比较三个模型应力值,在耻骨联合附近的位点,模型III分别比模型I和II分别下降了39.1%和48.52%。此外,模型II和III在髋臼臼顶区域的应力值比模型I分别减少了390.53%和103.61%。同时,模型II髋臼后壁的应力值比模型I和III分别分别高出了197.15%和305.17%。结论:包含有完整骨结构和主要韧带的骨盆三维有限元模型可以很好的模拟出正常的骨盆生物力学特性。同时,髋关节处的边界条件、接触条件和骨盆近端股骨解剖结构对生物力学预测结果具有很大影响。第二部分三种内固定治疗骶骨骨折的稳定性和生物力学相容性目的:通过有限元分析模拟双足站立位、前屈和侧弯姿态,分别比较2枚ISS、TBP和MIAP治疗垂直不稳定型骨盆骨折后骨盆生物力学功能的恢复、骨折固定的稳定性以及内固定物的生物力学相容性。方法:根据之前的实验数据建立完整的骨盆有限元模型,分别置入三种不同的内固定器械。随后对骶骨施加500N垂直载荷、500N垂直载荷加10Nm前向扭矩和500N垂直载荷加10Nm右向扭矩,以分别模拟双足站立姿态、前屈姿态和侧弯姿态。为了研究不同内固定下骨盆载荷的传递,我们设置了6个测量点,用以测量骨盆的应力传递,分别为:骶1椎体中点;骶1椎体水平骶髂关节处;骶2椎体骶髂关节处;髂耻线中点;髋臼臼顶和耻骨联合旁。同时,测量在不同姿态下骨盆模型中骶骨和内固定物的最大位移值、应力值及骶骨骨折断端的应力值,并进行比较。结果:三种内固定物都可以有效的恢复受损骨盆的生物力学传递功能。但是MIAP降低了在骶2椎体水平骶髂关节区域的应力集中。同时,不同运动状态对应力分布无明显影响。在站立状态下,TBP模型内固定物的最大应力分别比ISS和MIAP模型高出了167.47%和53.41%;TBP模型应力遮蔽现象分别比ISS和MIAP模型高出343.42%和68.2%;TBP固定方式的受损骶骨的垂直位移仅比ISS和MIAP模型分别高出了5.83%和9.48%;MIAP模型受损骶骨的最大应力值与ISS和TBP模型相比分别降低了15.84%和8.84%;同时,结果显示TBP模型的骨折表面应力明显高于MIAP和ISS模型,在骶2和骶3椎体尤为明显。侧弯和前屈状态下,各结果的趋势与站立状态相同。结论:这三种内固定物的生物力学稳定性无显著差异;然而,ISS和MIAP内固定方式的疲劳断裂、螺钉松动风险以及应力遮蔽现象均低于TBP内固定方式。同时,MIAP和ISS固定相比于TBP固定,减少了骶骨上的应力集中,更有助于愈合过程,尤其是在骶2和骶3椎体骨折断端。第三部分三种内固定治疗骶髂关节脱位的稳定性和生物力学相容性目的:通过有限元分析模拟双足站立位,分别比较2枚ISS、TBP和MIAP配合重建钢板治疗单侧骶髂关节脱位合并耻骨联合分离骨盆后骨盆生物力学功能的恢复、骨折固定的稳定性以及内固定物的生物力学相容性。方法:根据之前实验数据建立完整的骨盆有限元模型,随后将三个有限元模型中左半骨盆的所有支持韧带和耻骨联合韧带去除,以获得垂直和旋转不稳定模型。分别模拟置入三种不同的内固定器械,随后对骶骨施加500N垂直载荷以模拟双足站立姿态。为了研究不同内固定下骨盆的载荷传递,我们设置了6个测量点用以测量骨盆的应力传递,分别为:骶1椎体中点;骶1椎体水平骶髂关节处;骶2椎体骶髂关节处;髂耻线中点;髋臼臼顶和耻骨联合旁。同时,测量骨盆模型中骶骨和内固定物的最大位移值、应力值及骨盆前环重建钢板的应力值,并进行比较。结果:应力云图显示,ISS、TBP和MIAP模型可以有效恢复受损骨盆的生物力学传递功能。对6个应力测量位点进行分析后,发现MIAP降低了在骶2椎体水平骶髂关节区域的应力集中。在ISS、TBP和MIAP模型中,最大Von Mises应力都集中于骨盆后环内固定物的螺钉上,并且ISS模型中骨盆后环内固定物的Von Mises应力最大值比在TBP模型和MIAP模型中分别高出了13.6%和21.12%。骨盆后环内固定物与骶骨间的Von Mises应力差异值越大代表应力遮蔽现象越明显,ISS模型中的应力差值分别比TBP模型和MIAP模型中高出了7.91%和14.72%。MIAP内固定物的最大垂直位移仅比ISS模型和TBP模型分别高出4.46%和1.74%。ISS固定方式中受损骶骨的最大垂直位移仅比TBP和MIAP模型分别高出了0.85%和6.25%。ISS模型中骶骨的Von Mises应力最大值比在TBP模型和MIAP模型中分别高出了26.11%和35.35%。同时,TBP和MIAP模型中受损骶骨的Von Mises应力最大值均位于骶髂关节下部,而ISS模型的则位于螺钉与第2骶椎棘突相连接处。我们比较了三种内固定物对于骨盆前屈稳定性的恢复,TBP模型组的前屈角度比ISS组与MIAP组分别提高了288.18%和256.56%。结论:这三种内固定的生物力学稳定性以及应力遮蔽现象均无显著差异。然而,TBP和MIAP内固定方式的疲劳断裂和螺钉松动风险低于ISS内固定方式。此外,ISS和MIAP固定方式对于前屈旋转的稳定性比TBP固定方式具有明显的优越性。
[Abstract]:Pelvic fracture is a serious type of fracture in clinic, which is mostly caused by high-energy injuries such as traffic accidents and high-altitude falling injuries. With the development of internal fixation technology in recent ten years, internal fixation and reduction has become the most commonly used treatment for pelvic fractures. However, the choice of internal fixation varies, the advantages and disadvantages of each internal fixation method and the surgical adaptation. In general, the clinical efficacy and biomechanical properties of the internal fixator should be considered. However, cadaver pelvic specimens are difficult to obtain, collect or make enough specimens, which may lead to large errors in mechanical experimental results due to insufficient sample size. At the same time, solid biomechanical experiments can not measure the internal mechanical properties of bones, which bring about pelvic biomechanical research. With the development of computer technology and digital medicine, finite element analysis has been used more and more widely in biomechanics. Finite element analysis (FEA) divides various complex research areas by means of the basic idea of turning the whole into zero and integrating the zero into the whole. At the same time, the finite element method can understand the internal stress and strain changes of each part of the model. These make the finite element analysis have incomparable advantages in biomechanical research, making it the most commonly used means of human pelvic biomechanical research. The commonly used internal fixation techniques for the treatment of sacroiliac fracture and dislocation include iliosacral screw (ISS), tension band plate (TBP) and sacroiliac rod. Screw and guide needle placement should be guided by fluoroscopy, which may increase X-ray exposure time of doctors and patients. TBP should be pre-bent before fixation, and repeated pre-bent plates can reduce the strength of the plate and even cause nail hole damage. In addition, the infection rate after TBP is high. To solve these problems, Professor Zhang Yingze and his team based on the posterior pelvic ring. A minimally invasive adjustable plate (MIAP) was designed for minimally invasive pelvic fracture reduction by adjusting the screw length. The first part is the finite element analysis of the effects of different boundary conditions on the biomechanical load transfer of the pelvis. Objective: To establish a complete finite element model of the pelvis including the ilium, sacrum, proximal femur and main ligament. The finite element model was validated by measuring the strain on the surface of pelvic specimens under different loads with strain gauges. Finally, the effects of different boundary conditions and hip contact conditions on the mechanical load transfer were analyzed by the validated finite element model. The specimens were recorded at 100-500N intervals (intervals of 100N) by using the WS3811 digital strain gauge. Then a healthy adult female was selected and CT scanned with a slice thickness of 0.3 mm. The image data were stored in the format of Digital Imaging and Communications in Medicine (DICOM). Mimics, Geomagic Studio, Solid Works, Abaqus and other software were used to establish a complete pelvic three-dimensional finite. Model I, model II, and model III were established according to three different hip contact conditions and boundary conditions. Model I established contact surfaces on the femoral head and acetabulum and set them as "Contact Condition" to study the effect of setting the hip as a sliding joint on stress distribution. The hip joint of model III does not contain the femur. Model I and model II constrain the femoral end and model III constrain the acetabular motion center on both sides. Out of the six sites, the stresses at the other three anatomical points on the pelvic surface were measured: the acetabular apex, the posterior wall of the acetabulum and the anterior part of the pelvis near the pubic symphysis. The regression equation and correlation coefficients are y = 1.019x-1.114 and R2 = 0.97, respectively. Meanwhile, with the increase of load level, the correlation coefficient of linear regression increases from R2 = 0.90 at 100N to R2 = 0.98 at 500N, indicating that high load is better than low load. The results of finite element analysis and biomechanics experiment show that the higher the load is, the closer the stress distribution of the three models is to the one of 1. As for the load transfer, the stress distribution of the three models is transmitted along the iliopubic line, and the maximum stress of each model is located in the sacroiliac ligament. In addition, the stress values of model II and III were 390.53% and 103.61% lower than those of model I, respectively. Meanwhile, the stress values of posterior wall of model II were 197.15% and 305.17% higher than those of model I and III, respectively. Normal pelvic biomechanical properties can be well simulated. At the same time, the boundary conditions at the hip joint, contact conditions and anatomical structure of the proximal femur of the pelvis have a great impact on the biomechanical prediction results. Part II Stability and biomechanical compatibility of the three internal fixations in the treatment of sacral fractures. Purpose: To simulate by finite element analysis Two ISS, TBP and MIAP were used to compare the pelvic biomechanical recovery, fracture fixation stability and biomechanical compatibility of the internal fixator after treatment of vertically unstable pelvic fractures. Different instrumentations were then applied to the sacrum under 500N vertical load, 500N vertical load plus 10Nm forward torque, 500N vertical load plus 10Nm right torque to simulate standing posture, forward bending posture and lateral bending posture respectively. The stress transfer was measured at the center of the sacral 1 vertebral body, the horizontal sacroiliac joint of the sacral 1 vertebral body, the sacroiliac joint of the sacral 2 vertebral body, the middle point of the iliopubic line, the acetabular apex and the parapubic symphysis. Three kinds of internal fixator can effectively restore the biomechanical transfer function of the injured pelvis. However, MIAP reduces the stress concentration in the sacroiliac joint area at the level of the sacral 2 vertebral body. At the same time, different motion states have no significant effect on the stress distribution. In standing state, the maximum stress of the TBP model is higher than that of ISS and MIAP models, respectively. The stress shielding phenomena of TBP model were 343.42% and 68.2% higher than that of ISS and MIAP model respectively; the vertical displacement of damaged sacrum of TBP model was only 5.83% and 9.48% higher than that of ISS and MIAP model; the maximum stress of damaged sacrum of MIAP model was 15.84% and 8.84% lower than that of ISS and TBP model, respectively; meanwhile, the results showed that the vertical displacement of damaged sacrum of TBP model was only 5.83% and 9.48% higher than that of ISS and MIAP model. The results showed that the fracture surface stress of TBP model was significantly higher than that of MIAP and ISS models, especially in sacral 2 and sacral 3 vertebrae. At the same time, MIAP and ISS fixation, compared with TBP fixation, reduce the stress concentration on the sacrum and are more conducive to healing process, especially at the broken ends of sacral 2 and sacral 3 vertebral fractures. Finite element analysis was used to simulate bipedal standing position. Two ISS, TBP and MIAP were compared with reconstruction plate in the treatment of unilateral sacroiliac joint dislocation combined with pubic symphysis separation. In the finite element model, all the supporting ligaments and the pubic symphyseal ligaments in the left half of the pelvis were removed to obtain the vertical and rotational instability models. Six measuring points were set up to measure pelvic stress transfer: sacral 1 vertebral body point; sacroiliac joint of sacral 1 vertebral body; sacroiliac joint of sacral 2 vertebral body; sacroiliac joint of sacroiliac 2 vertebral body; midpoint of iliopubic line; acetabular apex and pubic symphysis. Results: Stress nephogram showed that ISS, TBP and MIAP models could effectively restore the biomechanical transfer function of the injured pelvis. After analysis of six stress measurement sites, MIAP reduced the stress concentration in the sacroiliac joint region at the level of the sacral 2 vertebra. In ISS, TBP and MIAP models, the maximum Vo was found. The Von Mises stress in ISS model was 13.6% and 21.12% higher than that in TBP model and MIAP model, respectively. The maximum vertical displacement of MIAP was only 4.46% and 1.74% higher than that of ISS and TBP, respectively. The maximum vertical displacement of damaged sacrum in ISS was only 0.85% and 6.25% higher than that of TBP and MIAP, respectively. Mises stress maxima were 26.11% and 35.35% higher in the TBP and MIAP models, respectively. Meanwhile, the Von Mises stress maxima of the damaged sacrum in the TBP and MIAP models were located at the lower sacroiliac joint, while the ISS model was located at the joint of the screw and the second sacral spinous process. The flexion angles of TBP model group were 288.18% and 256.56% higher than those of ISS and MIAP groups, respectively.
【学位授予单位】：河北医科大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：R687.3

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