五种内固定方式用于不同Pauwels分型股骨颈骨折的有限元分析
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摘要
研究背景：
股骨由于其在运动及承重中的重要作用,为历年来运动医学和骨科学的研究热点。股骨颈骨折具有多发性和多样性,其治疗的并发症较多,因此针对股骨颈骨折治疗的方式层出不穷,然并未得到较好的解决,其因而成为临床上治疗的难题。
股骨颈骨折占髋部骨折的50%～60%,高发于老年患者,多合并不同程度的骨质疏松,女性多于男性。其治疗方式的选择受到多种因素的影响,包括年龄、骨折类型、精神因素等,股骨颈骨折主要包括内固定、半髋或全髋关节置换术。关节置换术为股骨颈骨折的终末治疗方法,一般患者首选内固定治疗,给股骨头一个恢复的机会。目前主流观点认为,对于小于60岁的患者,如无明确股骨头缺血征象,首选内固定治疗；对于80岁以上的移位型骨折患者,最好行髋关节置换术；60～80岁之间的患者则根据患者的伤情、骨折类型、精神因素及是否合并其他系统性疾病来综合选择治疗方式。目前可选用的内固定方式比较多,最常用的有空心钉,DHS,股骨近端钢板等。
Pauwels分型根据骨折线的夹角将骨折分为3型,Pauwels Ⅰ型骨折线小于300,Pauwels Ⅱ型骨折骨折线为30°～50°,Pauwels Ⅲ型骨折骨折线为大于50°。骨折线的夹角度数越大,即骨折线越垂直,骨折端所受到的剪式应力越大,骨折越不稳定,不愈合率随之增加。此种分型以往并未得到重视,然而由于近年来骨折不愈合及股骨头缺血性坏死的研究不断深入,较多学者对此分型的不同疗效进行了相关研究。
FEM具有强大的建模功能,在动静状态下能够对具有复杂的几何形状、材料参数和不同受力条件下的物体进行模拟仿真研究,其已经越来越多的被应用到人体生物力学中。
目的：
1.利用数字化技术,建立股骨颈骨折的三维数字虚拟仿真模型及有限元模型,并同时通过尸体标本验证有限元模型的有效性；
2.依据三维绘图软件绘制5种不同类型的股骨颈内固定模型,分别为上下平行的两枚空心拉力螺钉、“倒品字”形排列的三枚空心拉力螺钉模型、“倒品字”形排列的三枚全螺纹拉力螺钉模型、股骨颈锁定钢板模型、InterTan钉板系统模型,并建立5种内固定方式固定三种不同Pauwels股骨颈骨折的有限元模型；
3.以Ansys软件分析比较5种内固定方式对三种不同Pauwels分型的股骨颈骨折的应力分布、位移部分、生命周期,综合评价每种内固定的固定特点,通过比较不同内固定方式生物力学稳定性,为临床应用提供理论依据；
方法：
1.数字化股骨三维有限元模型的构建：经X线检查证实髋部无骨折、畸形、肿瘤等骨质破坏,采用Philips/Brilliance64排螺旋CT行股骨扫描,扫描参数：管电压120kV,管电流100mA,自股骨大转子上方,层厚0.625mm,共获取二维CT图像489层。数据以DICOM格式保存,输入个人计算机的Mimics10.01软件,经自动或手动阈值分割后三维重建出完整股骨的三维结构,再以点云输出并导出的STL格式数据导入Geomagic Studio10.0软件,根据在多边形阶段提取设定的特征和编辑的曲面片自动拟合成NURBS曲面,以Iges格式输出保存。同时,建立股骨颈Pauwels-Ⅱ型骨折模型,骨折线为50°,并以“倒品字”拉力螺钉固定。根据骨骼、内固定两种不同的材料属性,不计关节之间的摩擦,而将软骨忽略,肌肉及肌腱应力则简化处理。假设为骨折面完全断裂并处于接触状态,摩擦系数为0.2。将股骨三维有限元模型内外髁下缘全部节点的自由度约束为0作为边界条件,即远端各节点在x、y、z轴上的位移为0。采用目前常用的简化模型,即仅考虑骨盆髋臼窝作用于股骨头上的力,对于肌肉力,仅取大转子附近的外展肌力(臀中肌与梨状肌)和股外侧肌力外展肌作为有限元分析的外载荷,予以轴向600N应力,平均作用于股骨头与髋臼接触面,沿轴向向下,然后设置好网格划分密度生成网格并设置算例属性进行运算。
2.有限元模型有效性验证：取1具成人尸体的股骨颈标本,去除标本周围的软组织,保存完整的骨性结构,X线片检查排除肿瘤、骨折等病变,骨密度测试值为1.17g/cm2。用双层塑料袋密封在-80℃冷冻备用。测试前24h取出,室温下自然解冻后根据股骨颈Pauwels-Ⅱ型骨折模拟截骨,骨折线为50。,并以空心螺钉固定。股骨颈空心钉：空心钉全长90mm,直径6.5mm,螺纹部分长20mm,空心钉中空部分直径2.5mm。空心钉固定为“倒品字”固定,螺钉互相平行,且尽量分离。将骨折内固定模型固定于电子万能动静态材料试验机上,股骨远端双髁连线与水平面平行,所得股骨轴线与矢状线呈23。夹角,分别于梨状窝及大转子外侧固定尼龙线(拉伸弹性模量分别为9.7N/mm2和0.15N/mm2)予以固定,固定强度为10MPa。其后予以股骨头垂直方向600N应力,通过压敏片记录八个点的应力值,测量三次,取平均值,并与有限元分析结果进行比较。
3.内固定三维模型的绘制：本研究共涉及4种内固定结构,分别为,空心拉力螺钉、全螺纹空心螺钉、股骨颈锁定钢板、InterTan钉板系统。其中空心钉全长90mm,直径6.5mm,螺纹位于螺钉远端,螺纹部分长20mm,空心钉中空部分直径2.5mm;全螺纹空心螺钉,空心钉全长90mm,直径7.3mm,近端及远端螺纹为松质骨螺纹,近端自螺钉尾端始长约35mm,远端自螺钉部分长25mm,螺钉中部25mm为皮质骨螺纹,空心钉中空部分直径2.5mm；股骨颈锁定钢板,其结构包括一块倒三角形的解剖型钢板及三枚锁定螺钉；钢板上方两个万向锁定孔,下方一个锁定孔,锁定孔的斜率为140。,每个锁定孔上方为克式针孔；锁定螺钉钉3枚,两枚直径6mm,长度85～90mm,为半螺纹松质骨拉力螺钉,远端螺纹长度为20mm,中空部直径为2.0mm；另一枚为全螺纹螺钉,长度90～100mm,直径6.5mm,中空部直径为2.5mm；InterTan钉板系统数据由(Smith&Nephew公司,英国)提供,应用proE4.0(PTC,美国)三维绘图软件对其进行三维虚拟重建。
4.骨折内固定有限元模型建立及分析：根据Pauwels三种骨折类型建立三种股骨颈骨折有限元模型,同时建立5种内固定模型,分别为：a：两枚拉力螺钉模型b：三枚“倒品字”形排列拉力螺钉模型c：三枚“倒品字”型排列全螺纹空心螺钉；d：股骨颈锁定钢板的内固定模型e：InterTan钉板系统固定模型。均将绘制的内固定三维实体模型与股骨模型导入有限元分析前处理软件Hypermesh10.0中进行装配完成,生成节点和单元后导入有限元分析软件Ansys13.0进行处理分析,所有模型均采用solid185单元(材料赋值及边界约束同方法一)。通过5种指标对5种内固定模型(a-e)的力学性能进行综合分析：①内固定的应力分布位置及应力峰值；②股骨的应力分布位置及应力峰值；③内固定位移分布和峰值；④股骨的位移分布和峰值；⑤骨及内固定的疲劳测试：予0.5Hz频率,600N的垂直方向应力行疲劳测试,计算达到骨及内固定达到屈服的压力次数。
结果：
1.基于CT扫描数据,利用Mimics、Geomagic Studio、UG软件,建立股骨颈骨折的三维数字仿真模型,这种方法可行、有效,建模速度较快,且对人体无损害。三维有限元法是生物力学研究的一种理论方法,可以模拟各种结构的几何模型,赋予各种组织的生物材料属性,能很好的反映其生物力学特性的总体趋势,因而可以作为标本实验生物力学研究方法很好的补充。本研究利用人体股骨CT数据,借助Mimics、Geomagic Studio、Hypermesh、Anasys等软件,建立了股骨颈骨折的的有限元模型与正常人体具有良好的几何相似性。通过尸体模型进行了有效性验证,证明本模型具有良好的物理相似性,更能够准确和完整地模拟股骨颈骨折的其受力特点,有利于对其进行生物力学分析。
2.Pauwels Ⅰ型股骨颈骨折,5种模型的应力峰值均集中于骨折线处的内固定下方,其中模型b、c、e分布较为均匀,模型a、d分布较为集中,其峰值为a:136.90MPa; b:52.47MPa; c:27.16MPa:d:118.69MPa; e:50.40MPao所有模型的位移均集中于股骨头处,其峰值为：a:1.49mm; b:1.62mm; c:1.33mm:d:1.40mm; e:0.89mm.通过疲劳测试得出,内固定在1e6时均未发生屈服,骨端的生命周期分别为：a：1.5367e5次；b：1.8578e5次；c：1.9458e5次；d：1.2111e5次；e：1.769e5次。
3.Pauwels Ⅱ型股骨颈骨折,5种模型应力集中区域有所不同,模型a、d分布较为集中,应力集中区域主要位于近骨折线的内固定下方；模型b、c应力分布较为均匀；模型e应力主要集中于内固定上方螺钉处。其峰值为a：188.07MPa; b:88.96MPa; c:57.43MPa:d:167.92MPa; e:53.63MPa;所有模型的位移均集中于股骨头处,其峰值为：a:1.63mm; b:1.27mm; c:1.06mm: d:1.52mm; e:0.89mm,通过疲劳测试得出,内固定在1e6时均未发生屈服,骨端的生命周期分别为：a：1.5089e5次；b：1.1689e5次；c：1.849e5次；d：1.6932e5次；e：1.7964e5次。
4Pauwels Ⅲ型骨折,骨折端主要受力为垂直方向上的剪切力,5种模型应力集中区域有所不同,模型a、d分布较为集中,应力集中区域主要位于近骨折线的内固定下方；模型b、c应力分布较为均匀；模型e应力主要集中于内固定上方螺钉处。其峰值为a:210.91MPa; b:116.49MPa; c:62.56MPa:d:142.49MPa; e:65.72MPao所有模型的位移均集中于股骨头处,由图中可得出,其峰值为：a:1.59mm; b:1.61mm; C:1.33mm:d:1.48mm; e:0.91mm。内固定在1e6时均未发生屈服,骨端的生命周期分别为：a：1.4647e5次；b：1.3438e5次；c：1.9156e5次；d：1e6次；e：1.6254e5次。
结论：
股骨颈骨折Pauwels分型不同其生物力学特点各不相同,Pauwels Ⅰ型骨折断端压力较大,使用空心钉固定时骨折线不与螺钉方向垂直,预防股骨颈短缩为主要治疗目的。5种内固定方式均可以用于本型股骨颈骨折的治疗,使用带全螺纹的“倒品字”形排列的空心钉固定既能够达到较为稳定的生物力学稳定性,又能够有效防止股骨颈短缩,且具备微创的优点,可作为推荐治疗方式。Pauwels Ⅱ型骨折,垂直方向上的剪切力大于Pauwels Ⅰ型骨折,且螺钉方向与骨折线方向接近垂直,最容易产生股骨颈轴向的压力,骨折愈合过程中的动力加压作用较强。上下两枚螺钉固定其生物力学稳定性不佳,不推荐使用,三枚“倒品字”排列的以拉力螺钉固定时容易发生股骨颈短缩,而以全螺纹螺钉固定则可能使螺钉穿入髋臼内,股骨颈锁定钢板和InterTan钉板系统可作为首选固定方式。综合分析,本型骨折如骨质情况良好可选用“倒品字”型排列的空心钉治疗,而骨质疏松严重的患者则推荐使用股骨近端钉板系统治疗；Pauwels Ⅲ型骨折,骨折端主要受力为垂直方向上的剪切力,选用内固定方式时需要以维持骨折端的稳定为优先考虑原则,不推荐使用空心螺钉进行固定,推荐使用股骨颈锁定钢板或InterTan钉板系统进行治疗,如患者骨折碎裂严重或移位较多不推荐InterTan钉板系统,以免发生股骨头缺血性坏死。
Background
Femur plays an important role in movement and load-bearing, and has becoming a research hotspot of sports medicine and bone science. Because of the multiple and diversity of femoral neck fracture as well as more complications, the golden treatment has not defined yet. As a result, it is still a problem on the clinical treatment.
Femoral neck fracture is account for50%to60%of hip fracture, still with a high incidence in elderly patients, and more with a severe osteoporosis, women are more vulnerable than men. The choice of treatment can be affected by a variety of factors, including age, type of fracture, mental factors etc. The main treatment includes internal fixation, the hemiarthroplasty and total hip arthroplasty. The THA was the terminal choice for treatment, for most patients, it is advised to take the internal fixation as the first choice, to give a chance of a recovery to the femoral head. It is well convinced that, patients less than60years old, without a clear avascular signs, preferred internal fixation; hip arthroplasty for displaced fractures in patients over the age of80; Treatment of patients between the ages of60to80, according to the patient's injury, fracture classification, psychological factors, and whether combined with other systemic diseases to be comprehensive selection. The optional includes two cannulated screw, three cannulated screw, DHS, proximal femur locking plates, etc.
Pauwels type femoral neck fracture was based on the angle of the fracture line, the Pauwels type Ⅰ fracture line less than30°, Pauwels Ⅱ fractures fracture line at30°to50°Pauwels type Ⅲ fracture fracture line is greater than50°. Because as the Fracture line clip angle increased, the more vertical fracture line, the greater the shear-stress force, fracture are more unstable, as a result, fracture nonunion rate increases. Surgeons did not pay more attention to this fracture classification, but the situation changed with the research on the nonunion and avascular necrosis.
FEM has a powerful modeling and simulation with complex geometry, material parameters and objects under different loading conditions in the static and dynamic state, it has to be applied to a growing number of human biomechanics.
Objectives:
1. Use of digital technology, the establishment of a virtual simulation of three-dimensional digital model of femoral neck fractures and finite element model, and t to verify the validity of the finite element model by cadaver;
2. With the help of three-dimensional graphics software, five different types of femoral neck model were established, respectively, for the2low-angle screws,3low-angle lag screws (typically135°) in an inverted triangle position,3low-angle complete thread screws (typically135°) in an inverted triangle position, femoral neck locking plate and InterTan CHS model, the finite elements model were established as well.
3. To compare the stress distribution, displacement distribution and life circle between these models with the help of Ansys. Therefore, to make deep comprehensive evaluation of biomechanical feature on each kinds of fixation and provide a theoretical basis for clinical applications.
Methods:
1. Construction and verification of digital three-dimensional finite element model of femur:The including criteria is the hip without fracture, deformity, tumor, bone destruction confirmed by X-ray examination. The CT scan of femur was taken under Philips/Brilliance64-slice spiral CT. Scanning parameters:Tube voltage120kV, tube current of100mA over the greater trochanter, thickness0.625mm. About489slices has been obtained of a two-dimensional CT images. Data was saved with the. DICOM format to save, then input into the Mimics,10.01software, after automatic or manual threshold segmentation, three-dimensional reconstruction of a complete femur was established, and then export the STL format data import Geomagic Studio10.0software, based on the polygon stage extraction feature set and edit patches are automatically fitted NURBS surfaces, save as the iges format and then output. At the same time, the establishment of the femoral neck Pauwels-Ⅱ type fracture model, fracture line of50°and fixed with3low-angle lag screws (typically135°) in an inverted triangle position. According to the material properties of the bones and internal fixation, without taking into account the friction between the joints and cartilage, simplify the processing the muscle and tendon. Set the situation as that the fracture surface completely broken and is in the contact state, the friction coefficient of0.2. The DOF constraints and external condyle of the femur three-dimensional finite element model of the lower edge of all the nodes to0as the boundary conditions, i.e. the distal end of each node x, y, and z-axis displacement of0. Using simplified models, that the force on the femoral head from the pelvic acetabular fossa was only taken into consideration, take only the greater trochanter near abductor (gluteus medius muscle and piriformis) and vastus lateralis muscle force, external load force abductor as finite element analysis, be axial600N stress, average acting on the femoral head and acetabular contact surface axially down, then set mesh density generated grid and set an example attribute operator.
2. Finite element model validation:Take the body of an adult cadaver of the femoral neck, remove the soft tissue around, save the complete bone structure, X-ray examination to exclude tumors, fractures and other lesions, bone mineral density test value of1.17g/cm2.-80℃freezer spare sealed in double plastic bags, remove the natural thawing at room temperature24h before the test, fracture simulation osteotomy of the femoral neck Pauwels-II type fracture with the fracture line of50°, and fixed with cannulated screw. Femoral neck cannulated screw:cannulated screws total length of90mm, and diameter of6.5mm, the threaded portion of was20mm in length, hollow part of the diameter of2.5mm. The lag screws in an inverted triangle position and separated from each other. Specimen model was fixed in the the electronic universal dynamic static material testing machine, the distal femur bicondylar connection with the horizontal parallel proceeds the femur axis with the sagittal line showed a23°angle, piriform fossa and greater trochanter fixed by nylon thread (tensile elastic modulus of9.7N/mm2and0.15N/mm2), respectively to be fixed, the fixing strength of10MPa. Subsequently,600N force perpendicular to the direction of femoral head, record the stress on eight points around the femoral neck and three times each, and compared with finite element analysis results.
3. Three-dimensional model of the internal fixation:This study involved a total of four kinds of fixed structures, respectively, cannulated screws, fully threaded cannulated screws, femoral neck locking plate, InterTan CHS. The cannulated screw90mm in length and6.5mm in diameter, threaded in the screw distal threaded portion is20mm in length, cannulated screws hollow part of diameter2.5mm; fully threaded cannulated screws, cannulated screw90mm in length and diameter of7.3mm, the proximal and distalend threaded cancellous bone threaded proximal from screw end of the beginning to about35mm, remote from the screw part of a long25mm,25mm in the central screw cortical bone screw, cannulated screw hollow section diameter of2.5mm. The femoral neck locking plate, the structure including an inverted triangle anatomical plate and three locking screws; two universal locking hole of the steel plate above, a locking hole on the bottom, the locking hole with the slope140°;3locking screw nails, two of them were partially threaded cancellous lag screws, with diameter6mm, length85to90mm, distal threaded length of20mm, hollow part of a diameter of2.0mm; another one is fully threaded screws, length of90～100mm, diameter of6.5mm, the diameter of the hollow part of2.5mm; The parameter of InterTan CHS (Smith&Nephew, UK) provided by the company and reconstructed with proE4.0(PTC, USA).
4. Finite element modeling and analysis:Stimulated three types of Pauwels fractures to establish femoral neck fracture finite element model, while the establishment of five kinds of internal fixation model. Including:a:two cannulated screws model;:b:3low-angle lag screws in an inverted triangle position;c:3low-angle complete thread screws in an inverted triangle position, d:femoral neck locking plate; and d:InterTan CHS model. The femur and internal fixation model were import into Hypermesh10.0for assemble, and generate nodes and elements in finite element analysis software Ansys13.0for FEA, all the models are made of solid185unit. By the analysis of the five kinds of indicators on the mechanical properties of the five kinds of internal fixation model (a-e):①The stress distribution and peak stress on internal fixation;②the stress distribution location and peak stress on femur;③The displacement distribution of peak displacement on internal fixation;④The displacement distribution of and the peak displacement on the femur;⑤the life circle of bone and internal fixation:0.5Hz frequency,600N perpendicular to the direction of stress line fatigue test, calculated to reach the bone and internal fixation of the number of yield pressure.
Results:
1. Based on CT scan data using Mimics, Geomagic Studio, UG software,3D digital simulation to establish a femoral neck fracture model, this method is feasible and effective modeling faster, and no harm to the human body. The three-dimensional finite element method is a theoretical biomechanical research methods, geometric model can simulate a variety of structures, given the biological material properties of the various organizations, can reflect the overall trend of the biomechanical properties, which can be used as a specimen experiment, is a good supplement method to biomechanics research. In this study, the use of a human femur CT data, with Mimics, Geomagic Studio, Hypermesh, Anasys software, established the finite element model of normal human femoral neck fractures and has good geometric similarity. To discuss the model validation through the cadaver and demonstrated that the model has a good physical similarity, more accurate and complete simulation of its mechanical characteristics of femoral neck fracture, conducive to their biomechanical analysis.
2. Pauwels type-1femoral neck fractures, five models peak stress are concentrated in the internal fixation around the fracture line at the bottom of which model b, c, e, are more evenly distributed, model a, d distribution is more concentrated. Peak stress:a:136.90MPa; b:52.47MPa; c:27.16MPa:d:118.69MPa; e:50.40MPa. Displacement of all of the models are centralized in the femoral head at its peak:a:1.49mm; B:1.62mm; C:1.33mm:d:1.40mm; e:0.89mm. On fatigue testing within a fixed yield did not occur in1e6, the life cycle of the ends of the bones were:a:1.5367e5; b:1.8578e5times; c:1.9458e5times; d:1.2111e5times; e:1.769e5.
3. Pauwels type-2femoral neck fractures, stress concentration region differentiate from each models, a, d is more concentrated distribution, stress concentration areas mainly located near the fracture line and the internal fixation; model b, c, stress distribution is more even; Model e stress mainly fixed to the top of screw. Peak stress:a:188.07MPa; b:88.96MPa; c:57.43MPa:d:167.92MPa; e:53.63MPa. Displacement of all of the models are centralized in the femoral head at its peak:a:1.63mm; b:1.27mm; c:1.06mm:d:1.52mm; e:0.89mm. On fatigue testing within a fixed yield did not occur in Ie6, the life cycle of the ends of the bones were:a:1.5089e5次, b:1.1689e5次; c:1.849e5次; d:1.6932e5次; e:1.7964e5.
4. Pauwels type-3femoral neck fractures, fracture force as a shearing force in the vertical direction, five models stress concentration region is different, the stress distribution of model a, d are more concentrated located near the fracture line; model b, c stress more evenly distributed; model e stress is mainly concentrated in the internal fixation at the top of the screw. Peak stress:a:210.91MPa; b:116.49MPa; c:62.56MPa:d:142.49MPa; e:65.72MPa. Displacement of all of the models are centralized in the femoral head at its peak:a:1.59mm; b:1.61mm; c:1.33mm: d:1.48mm; e:0.91mm. On fatigue testing within a fixed yield did not occur in Ie6, the life cycle of the ends of the bones were:a:1.4647e5次; b:1.3438e5次; c:1.9156e5次; d:1e6次; e:1.6254e5.
Conclusion:
The biomechanics features is different with different types of Pauwels femoral neck fracture. The stress between fracure fragments is more high with Pauwels type-1fracture, fracture line can be not perpendicular to the screws, prevention of femoral neck shortening is the main therapeutic purposes. All internal fixation can be used for the treatment of this type of fractures, use with3low-angle complete thread screws in an inverted triangle position to achieve a more stable biomechanical stability, they can effectively prevent short femoral neck shortening, and have the advantages of minimally invasive, as recommended treatment. The Pauwels type-Ⅱ fractures, shear force is greater than in the vertical direction than Pauwels type-1fractures, the screw direction and the direction of the fracture line is closely to vertical, the most prone to the femoral neck axial pressure, has a strong dynamic compression effect and can help to achieve high fracture healing rates. Two screws has poor biomechanical stability, does not recommended,3lag screws in an inverted triangle position is easy caused femoral neck shortening, for complete threshed screw model, the screw appears more easy to penetrate into the acetabular joint. As a result, the femoral neck lock plates and InterTan CHS as the preferred fixed. Comprehensive analysis, the3lag screws in an inverted triangle position can be used in patients with good BMD, but for osteoporosis patient, proximal femoral screw and plate system are recommended. Pauwels type-3fractures, main force comes from the shearing force in the vertical direction, the principle of fixation is to maintain the stability of the fracture, two lag screws was not recommend in treating with these patient. On contrast, the femoral neck locking plate and InterTan CHS can be the recommended for treatment, but if patient with sever fractures fragmentation, in order to avoid avascular necrosis, femoral neck locking plate perhaps the only choice.
股骨由于其在运动及承重中的重要作用,为历年来运动医学和骨科学的研究热点。股骨颈骨折具有多发性和多样性,其治疗的并发症较多,因此针对股骨颈骨折治疗的方式层出不穷,然并未得到较好的解决,其因而成为临床上治疗的难题。
股骨颈骨折占髋部骨折的50%～60%,高发于老年患者,多合并不同程度的骨质疏松,女性多于男性。其治疗方式的选择受到多种因素的影响,包括年龄、骨折类型、精神因素等,股骨颈骨折主要包括内固定、半髋或全髋关节置换术。关节置换术为股骨颈骨折的终末治疗方法,一般患者首选内固定治疗,给股骨头一个恢复的机会。目前主流观点认为,对于小于60岁的患者,如无明确股骨头缺血征象,首选内固定治疗；对于80岁以上的移位型骨折患者,最好行髋关节置换术；60～80岁之间的患者则根据患者的伤情、骨折类型、精神因素及是否合并其他系统性疾病来综合选择治疗方式。目前可选用的内固定方式比较多,最常用的有空心钉,DHS,股骨近端钢板等。
Pauwels分型根据骨折线的夹角将骨折分为3型,Pauwels Ⅰ型骨折线小于300,Pauwels Ⅱ型骨折骨折线为30°～50°,Pauwels Ⅲ型骨折骨折线为大于50°。骨折线的夹角度数越大,即骨折线越垂直,骨折端所受到的剪式应力越大,骨折越不稳定,不愈合率随之增加。此种分型以往并未得到重视,然而由于近年来骨折不愈合及股骨头缺血性坏死的研究不断深入,较多学者对此分型的不同疗效进行了相关研究。
FEM具有强大的建模功能,在动静状态下能够对具有复杂的几何形状、材料参数和不同受力条件下的物体进行模拟仿真研究,其已经越来越多的被应用到人体生物力学中。
目的：
1.利用数字化技术,建立股骨颈骨折的三维数字虚拟仿真模型及有限元模型,并同时通过尸体标本验证有限元模型的有效性；
2.依据三维绘图软件绘制5种不同类型的股骨颈内固定模型,分别为上下平行的两枚空心拉力螺钉、“倒品字”形排列的三枚空心拉力螺钉模型、“倒品字”形排列的三枚全螺纹拉力螺钉模型、股骨颈锁定钢板模型、InterTan钉板系统模型,并建立5种内固定方式固定三种不同Pauwels股骨颈骨折的有限元模型；
3.以Ansys软件分析比较5种内固定方式对三种不同Pauwels分型的股骨颈骨折的应力分布、位移部分、生命周期,综合评价每种内固定的固定特点,通过比较不同内固定方式生物力学稳定性,为临床应用提供理论依据；
方法：
1.数字化股骨三维有限元模型的构建：经X线检查证实髋部无骨折、畸形、肿瘤等骨质破坏,采用Philips/Brilliance64排螺旋CT行股骨扫描,扫描参数：管电压120kV,管电流100mA,自股骨大转子上方,层厚0.625mm,共获取二维CT图像489层。数据以DICOM格式保存,输入个人计算机的Mimics10.01软件,经自动或手动阈值分割后三维重建出完整股骨的三维结构,再以点云输出并导出的STL格式数据导入Geomagic Studio10.0软件,根据在多边形阶段提取设定的特征和编辑的曲面片自动拟合成NURBS曲面,以Iges格式输出保存。同时,建立股骨颈Pauwels-Ⅱ型骨折模型,骨折线为50°,并以“倒品字”拉力螺钉固定。根据骨骼、内固定两种不同的材料属性,不计关节之间的摩擦,而将软骨忽略,肌肉及肌腱应力则简化处理。假设为骨折面完全断裂并处于接触状态,摩擦系数为0.2。将股骨三维有限元模型内外髁下缘全部节点的自由度约束为0作为边界条件,即远端各节点在x、y、z轴上的位移为0。采用目前常用的简化模型,即仅考虑骨盆髋臼窝作用于股骨头上的力,对于肌肉力,仅取大转子附近的外展肌力(臀中肌与梨状肌)和股外侧肌力外展肌作为有限元分析的外载荷,予以轴向600N应力,平均作用于股骨头与髋臼接触面,沿轴向向下,然后设置好网格划分密度生成网格并设置算例属性进行运算。
2.有限元模型有效性验证：取1具成人尸体的股骨颈标本,去除标本周围的软组织,保存完整的骨性结构,X线片检查排除肿瘤、骨折等病变,骨密度测试值为1.17g/cm2。用双层塑料袋密封在-80℃冷冻备用。测试前24h取出,室温下自然解冻后根据股骨颈Pauwels-Ⅱ型骨折模拟截骨,骨折线为50。,并以空心螺钉固定。股骨颈空心钉：空心钉全长90mm,直径6.5mm,螺纹部分长20mm,空心钉中空部分直径2.5mm。空心钉固定为“倒品字”固定,螺钉互相平行,且尽量分离。将骨折内固定模型固定于电子万能动静态材料试验机上,股骨远端双髁连线与水平面平行,所得股骨轴线与矢状线呈23。夹角,分别于梨状窝及大转子外侧固定尼龙线(拉伸弹性模量分别为9.7N/mm2和0.15N/mm2)予以固定,固定强度为10MPa。其后予以股骨头垂直方向600N应力,通过压敏片记录八个点的应力值,测量三次,取平均值,并与有限元分析结果进行比较。
3.内固定三维模型的绘制：本研究共涉及4种内固定结构,分别为,空心拉力螺钉、全螺纹空心螺钉、股骨颈锁定钢板、InterTan钉板系统。其中空心钉全长90mm,直径6.5mm,螺纹位于螺钉远端,螺纹部分长20mm,空心钉中空部分直径2.5mm;全螺纹空心螺钉,空心钉全长90mm,直径7.3mm,近端及远端螺纹为松质骨螺纹,近端自螺钉尾端始长约35mm,远端自螺钉部分长25mm,螺钉中部25mm为皮质骨螺纹,空心钉中空部分直径2.5mm；股骨颈锁定钢板,其结构包括一块倒三角形的解剖型钢板及三枚锁定螺钉；钢板上方两个万向锁定孔,下方一个锁定孔,锁定孔的斜率为140。,每个锁定孔上方为克式针孔；锁定螺钉钉3枚,两枚直径6mm,长度85～90mm,为半螺纹松质骨拉力螺钉,远端螺纹长度为20mm,中空部直径为2.0mm；另一枚为全螺纹螺钉,长度90～100mm,直径6.5mm,中空部直径为2.5mm；InterTan钉板系统数据由(Smith&Nephew公司,英国)提供,应用proE4.0(PTC,美国)三维绘图软件对其进行三维虚拟重建。
4.骨折内固定有限元模型建立及分析：根据Pauwels三种骨折类型建立三种股骨颈骨折有限元模型,同时建立5种内固定模型,分别为：a：两枚拉力螺钉模型b：三枚“倒品字”形排列拉力螺钉模型c：三枚“倒品字”型排列全螺纹空心螺钉；d：股骨颈锁定钢板的内固定模型e：InterTan钉板系统固定模型。均将绘制的内固定三维实体模型与股骨模型导入有限元分析前处理软件Hypermesh10.0中进行装配完成,生成节点和单元后导入有限元分析软件Ansys13.0进行处理分析,所有模型均采用solid185单元(材料赋值及边界约束同方法一)。通过5种指标对5种内固定模型(a-e)的力学性能进行综合分析：①内固定的应力分布位置及应力峰值；②股骨的应力分布位置及应力峰值；③内固定位移分布和峰值；④股骨的位移分布和峰值；⑤骨及内固定的疲劳测试：予0.5Hz频率,600N的垂直方向应力行疲劳测试,计算达到骨及内固定达到屈服的压力次数。
结果：
1.基于CT扫描数据,利用Mimics、Geomagic Studio、UG软件,建立股骨颈骨折的三维数字仿真模型,这种方法可行、有效,建模速度较快,且对人体无损害。三维有限元法是生物力学研究的一种理论方法,可以模拟各种结构的几何模型,赋予各种组织的生物材料属性,能很好的反映其生物力学特性的总体趋势,因而可以作为标本实验生物力学研究方法很好的补充。本研究利用人体股骨CT数据,借助Mimics、Geomagic Studio、Hypermesh、Anasys等软件,建立了股骨颈骨折的的有限元模型与正常人体具有良好的几何相似性。通过尸体模型进行了有效性验证,证明本模型具有良好的物理相似性,更能够准确和完整地模拟股骨颈骨折的其受力特点,有利于对其进行生物力学分析。
2.Pauwels Ⅰ型股骨颈骨折,5种模型的应力峰值均集中于骨折线处的内固定下方,其中模型b、c、e分布较为均匀,模型a、d分布较为集中,其峰值为a:136.90MPa; b:52.47MPa; c:27.16MPa:d:118.69MPa; e:50.40MPao所有模型的位移均集中于股骨头处,其峰值为：a:1.49mm; b:1.62mm; c:1.33mm:d:1.40mm; e:0.89mm.通过疲劳测试得出,内固定在1e6时均未发生屈服,骨端的生命周期分别为：a：1.5367e5次；b：1.8578e5次；c：1.9458e5次；d：1.2111e5次；e：1.769e5次。
3.Pauwels Ⅱ型股骨颈骨折,5种模型应力集中区域有所不同,模型a、d分布较为集中,应力集中区域主要位于近骨折线的内固定下方；模型b、c应力分布较为均匀；模型e应力主要集中于内固定上方螺钉处。其峰值为a：188.07MPa; b:88.96MPa; c:57.43MPa:d:167.92MPa; e:53.63MPa;所有模型的位移均集中于股骨头处,其峰值为：a:1.63mm; b:1.27mm; c:1.06mm: d:1.52mm; e:0.89mm,通过疲劳测试得出,内固定在1e6时均未发生屈服,骨端的生命周期分别为：a：1.5089e5次；b：1.1689e5次；c：1.849e5次；d：1.6932e5次；e：1.7964e5次。
4Pauwels Ⅲ型骨折,骨折端主要受力为垂直方向上的剪切力,5种模型应力集中区域有所不同,模型a、d分布较为集中,应力集中区域主要位于近骨折线的内固定下方；模型b、c应力分布较为均匀；模型e应力主要集中于内固定上方螺钉处。其峰值为a:210.91MPa; b:116.49MPa; c:62.56MPa:d:142.49MPa; e:65.72MPao所有模型的位移均集中于股骨头处,由图中可得出,其峰值为：a:1.59mm; b:1.61mm; C:1.33mm:d:1.48mm; e:0.91mm。内固定在1e6时均未发生屈服,骨端的生命周期分别为：a：1.4647e5次；b：1.3438e5次；c：1.9156e5次；d：1e6次；e：1.6254e5次。
结论：
股骨颈骨折Pauwels分型不同其生物力学特点各不相同,Pauwels Ⅰ型骨折断端压力较大,使用空心钉固定时骨折线不与螺钉方向垂直,预防股骨颈短缩为主要治疗目的。5种内固定方式均可以用于本型股骨颈骨折的治疗,使用带全螺纹的“倒品字”形排列的空心钉固定既能够达到较为稳定的生物力学稳定性,又能够有效防止股骨颈短缩,且具备微创的优点,可作为推荐治疗方式。Pauwels Ⅱ型骨折,垂直方向上的剪切力大于Pauwels Ⅰ型骨折,且螺钉方向与骨折线方向接近垂直,最容易产生股骨颈轴向的压力,骨折愈合过程中的动力加压作用较强。上下两枚螺钉固定其生物力学稳定性不佳,不推荐使用,三枚“倒品字”排列的以拉力螺钉固定时容易发生股骨颈短缩,而以全螺纹螺钉固定则可能使螺钉穿入髋臼内,股骨颈锁定钢板和InterTan钉板系统可作为首选固定方式。综合分析,本型骨折如骨质情况良好可选用“倒品字”型排列的空心钉治疗,而骨质疏松严重的患者则推荐使用股骨近端钉板系统治疗；Pauwels Ⅲ型骨折,骨折端主要受力为垂直方向上的剪切力,选用内固定方式时需要以维持骨折端的稳定为优先考虑原则,不推荐使用空心螺钉进行固定,推荐使用股骨颈锁定钢板或InterTan钉板系统进行治疗,如患者骨折碎裂严重或移位较多不推荐InterTan钉板系统,以免发生股骨头缺血性坏死。
Background
Femur plays an important role in movement and load-bearing, and has becoming a research hotspot of sports medicine and bone science. Because of the multiple and diversity of femoral neck fracture as well as more complications, the golden treatment has not defined yet. As a result, it is still a problem on the clinical treatment.
Femoral neck fracture is account for50%to60%of hip fracture, still with a high incidence in elderly patients, and more with a severe osteoporosis, women are more vulnerable than men. The choice of treatment can be affected by a variety of factors, including age, type of fracture, mental factors etc. The main treatment includes internal fixation, the hemiarthroplasty and total hip arthroplasty. The THA was the terminal choice for treatment, for most patients, it is advised to take the internal fixation as the first choice, to give a chance of a recovery to the femoral head. It is well convinced that, patients less than60years old, without a clear avascular signs, preferred internal fixation; hip arthroplasty for displaced fractures in patients over the age of80; Treatment of patients between the ages of60to80, according to the patient's injury, fracture classification, psychological factors, and whether combined with other systemic diseases to be comprehensive selection. The optional includes two cannulated screw, three cannulated screw, DHS, proximal femur locking plates, etc.
Pauwels type femoral neck fracture was based on the angle of the fracture line, the Pauwels type Ⅰ fracture line less than30°, Pauwels Ⅱ fractures fracture line at30°to50°Pauwels type Ⅲ fracture fracture line is greater than50°. Because as the Fracture line clip angle increased, the more vertical fracture line, the greater the shear-stress force, fracture are more unstable, as a result, fracture nonunion rate increases. Surgeons did not pay more attention to this fracture classification, but the situation changed with the research on the nonunion and avascular necrosis.
FEM has a powerful modeling and simulation with complex geometry, material parameters and objects under different loading conditions in the static and dynamic state, it has to be applied to a growing number of human biomechanics.
Objectives:
1. Use of digital technology, the establishment of a virtual simulation of three-dimensional digital model of femoral neck fractures and finite element model, and t to verify the validity of the finite element model by cadaver;
2. With the help of three-dimensional graphics software, five different types of femoral neck model were established, respectively, for the2low-angle screws,3low-angle lag screws (typically135°) in an inverted triangle position,3low-angle complete thread screws (typically135°) in an inverted triangle position, femoral neck locking plate and InterTan CHS model, the finite elements model were established as well.
3. To compare the stress distribution, displacement distribution and life circle between these models with the help of Ansys. Therefore, to make deep comprehensive evaluation of biomechanical feature on each kinds of fixation and provide a theoretical basis for clinical applications.
Methods:
1. Construction and verification of digital three-dimensional finite element model of femur:The including criteria is the hip without fracture, deformity, tumor, bone destruction confirmed by X-ray examination. The CT scan of femur was taken under Philips/Brilliance64-slice spiral CT. Scanning parameters:Tube voltage120kV, tube current of100mA over the greater trochanter, thickness0.625mm. About489slices has been obtained of a two-dimensional CT images. Data was saved with the. DICOM format to save, then input into the Mimics,10.01software, after automatic or manual threshold segmentation, three-dimensional reconstruction of a complete femur was established, and then export the STL format data import Geomagic Studio10.0software, based on the polygon stage extraction feature set and edit patches are automatically fitted NURBS surfaces, save as the iges format and then output. At the same time, the establishment of the femoral neck Pauwels-Ⅱ type fracture model, fracture line of50°and fixed with3low-angle lag screws (typically135°) in an inverted triangle position. According to the material properties of the bones and internal fixation, without taking into account the friction between the joints and cartilage, simplify the processing the muscle and tendon. Set the situation as that the fracture surface completely broken and is in the contact state, the friction coefficient of0.2. The DOF constraints and external condyle of the femur three-dimensional finite element model of the lower edge of all the nodes to0as the boundary conditions, i.e. the distal end of each node x, y, and z-axis displacement of0. Using simplified models, that the force on the femoral head from the pelvic acetabular fossa was only taken into consideration, take only the greater trochanter near abductor (gluteus medius muscle and piriformis) and vastus lateralis muscle force, external load force abductor as finite element analysis, be axial600N stress, average acting on the femoral head and acetabular contact surface axially down, then set mesh density generated grid and set an example attribute operator.
2. Finite element model validation:Take the body of an adult cadaver of the femoral neck, remove the soft tissue around, save the complete bone structure, X-ray examination to exclude tumors, fractures and other lesions, bone mineral density test value of1.17g/cm2.-80℃freezer spare sealed in double plastic bags, remove the natural thawing at room temperature24h before the test, fracture simulation osteotomy of the femoral neck Pauwels-II type fracture with the fracture line of50°, and fixed with cannulated screw. Femoral neck cannulated screw:cannulated screws total length of90mm, and diameter of6.5mm, the threaded portion of was20mm in length, hollow part of the diameter of2.5mm. The lag screws in an inverted triangle position and separated from each other. Specimen model was fixed in the the electronic universal dynamic static material testing machine, the distal femur bicondylar connection with the horizontal parallel proceeds the femur axis with the sagittal line showed a23°angle, piriform fossa and greater trochanter fixed by nylon thread (tensile elastic modulus of9.7N/mm2and0.15N/mm2), respectively to be fixed, the fixing strength of10MPa. Subsequently,600N force perpendicular to the direction of femoral head, record the stress on eight points around the femoral neck and three times each, and compared with finite element analysis results.
3. Three-dimensional model of the internal fixation:This study involved a total of four kinds of fixed structures, respectively, cannulated screws, fully threaded cannulated screws, femoral neck locking plate, InterTan CHS. The cannulated screw90mm in length and6.5mm in diameter, threaded in the screw distal threaded portion is20mm in length, cannulated screws hollow part of diameter2.5mm; fully threaded cannulated screws, cannulated screw90mm in length and diameter of7.3mm, the proximal and distalend threaded cancellous bone threaded proximal from screw end of the beginning to about35mm, remote from the screw part of a long25mm,25mm in the central screw cortical bone screw, cannulated screw hollow section diameter of2.5mm. The femoral neck locking plate, the structure including an inverted triangle anatomical plate and three locking screws; two universal locking hole of the steel plate above, a locking hole on the bottom, the locking hole with the slope140°;3locking screw nails, two of them were partially threaded cancellous lag screws, with diameter6mm, length85to90mm, distal threaded length of20mm, hollow part of a diameter of2.0mm; another one is fully threaded screws, length of90～100mm, diameter of6.5mm, the diameter of the hollow part of2.5mm; The parameter of InterTan CHS (Smith&Nephew, UK) provided by the company and reconstructed with proE4.0(PTC, USA).
4. Finite element modeling and analysis:Stimulated three types of Pauwels fractures to establish femoral neck fracture finite element model, while the establishment of five kinds of internal fixation model. Including:a:two cannulated screws model;:b:3low-angle lag screws in an inverted triangle position;c:3low-angle complete thread screws in an inverted triangle position, d:femoral neck locking plate; and d:InterTan CHS model. The femur and internal fixation model were import into Hypermesh10.0for assemble, and generate nodes and elements in finite element analysis software Ansys13.0for FEA, all the models are made of solid185unit. By the analysis of the five kinds of indicators on the mechanical properties of the five kinds of internal fixation model (a-e):①The stress distribution and peak stress on internal fixation;②the stress distribution location and peak stress on femur;③The displacement distribution of peak displacement on internal fixation;④The displacement distribution of and the peak displacement on the femur;⑤the life circle of bone and internal fixation:0.5Hz frequency,600N perpendicular to the direction of stress line fatigue test, calculated to reach the bone and internal fixation of the number of yield pressure.
Results:
1. Based on CT scan data using Mimics, Geomagic Studio, UG software,3D digital simulation to establish a femoral neck fracture model, this method is feasible and effective modeling faster, and no harm to the human body. The three-dimensional finite element method is a theoretical biomechanical research methods, geometric model can simulate a variety of structures, given the biological material properties of the various organizations, can reflect the overall trend of the biomechanical properties, which can be used as a specimen experiment, is a good supplement method to biomechanics research. In this study, the use of a human femur CT data, with Mimics, Geomagic Studio, Hypermesh, Anasys software, established the finite element model of normal human femoral neck fractures and has good geometric similarity. To discuss the model validation through the cadaver and demonstrated that the model has a good physical similarity, more accurate and complete simulation of its mechanical characteristics of femoral neck fracture, conducive to their biomechanical analysis.
2. Pauwels type-1femoral neck fractures, five models peak stress are concentrated in the internal fixation around the fracture line at the bottom of which model b, c, e, are more evenly distributed, model a, d distribution is more concentrated. Peak stress:a:136.90MPa; b:52.47MPa; c:27.16MPa:d:118.69MPa; e:50.40MPa. Displacement of all of the models are centralized in the femoral head at its peak:a:1.49mm; B:1.62mm; C:1.33mm:d:1.40mm; e:0.89mm. On fatigue testing within a fixed yield did not occur in1e6, the life cycle of the ends of the bones were:a:1.5367e5; b:1.8578e5times; c:1.9458e5times; d:1.2111e5times; e:1.769e5.
3. Pauwels type-2femoral neck fractures, stress concentration region differentiate from each models, a, d is more concentrated distribution, stress concentration areas mainly located near the fracture line and the internal fixation; model b, c, stress distribution is more even; Model e stress mainly fixed to the top of screw. Peak stress:a:188.07MPa; b:88.96MPa; c:57.43MPa:d:167.92MPa; e:53.63MPa. Displacement of all of the models are centralized in the femoral head at its peak:a:1.63mm; b:1.27mm; c:1.06mm:d:1.52mm; e:0.89mm. On fatigue testing within a fixed yield did not occur in Ie6, the life cycle of the ends of the bones were:a:1.5089e5次, b:1.1689e5次; c:1.849e5次; d:1.6932e5次; e:1.7964e5.
4. Pauwels type-3femoral neck fractures, fracture force as a shearing force in the vertical direction, five models stress concentration region is different, the stress distribution of model a, d are more concentrated located near the fracture line; model b, c stress more evenly distributed; model e stress is mainly concentrated in the internal fixation at the top of the screw. Peak stress:a:210.91MPa; b:116.49MPa; c:62.56MPa:d:142.49MPa; e:65.72MPa. Displacement of all of the models are centralized in the femoral head at its peak:a:1.59mm; b:1.61mm; c:1.33mm: d:1.48mm; e:0.91mm. On fatigue testing within a fixed yield did not occur in Ie6, the life cycle of the ends of the bones were:a:1.4647e5次; b:1.3438e5次; c:1.9156e5次; d:1e6次; e:1.6254e5.
Conclusion:
The biomechanics features is different with different types of Pauwels femoral neck fracture. The stress between fracure fragments is more high with Pauwels type-1fracture, fracture line can be not perpendicular to the screws, prevention of femoral neck shortening is the main therapeutic purposes. All internal fixation can be used for the treatment of this type of fractures, use with3low-angle complete thread screws in an inverted triangle position to achieve a more stable biomechanical stability, they can effectively prevent short femoral neck shortening, and have the advantages of minimally invasive, as recommended treatment. The Pauwels type-Ⅱ fractures, shear force is greater than in the vertical direction than Pauwels type-1fractures, the screw direction and the direction of the fracture line is closely to vertical, the most prone to the femoral neck axial pressure, has a strong dynamic compression effect and can help to achieve high fracture healing rates. Two screws has poor biomechanical stability, does not recommended,3lag screws in an inverted triangle position is easy caused femoral neck shortening, for complete threshed screw model, the screw appears more easy to penetrate into the acetabular joint. As a result, the femoral neck lock plates and InterTan CHS as the preferred fixed. Comprehensive analysis, the3lag screws in an inverted triangle position can be used in patients with good BMD, but for osteoporosis patient, proximal femoral screw and plate system are recommended. Pauwels type-3fractures, main force comes from the shearing force in the vertical direction, the principle of fixation is to maintain the stability of the fracture, two lag screws was not recommend in treating with these patient. On contrast, the femoral neck locking plate and InterTan CHS can be the recommended for treatment, but if patient with sever fractures fragmentation, in order to avoid avascular necrosis, femoral neck locking plate perhaps the only choice.
引文
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