国人枢椎椎板螺钉固定的可行性研究
摘要
目的目前临床上常用的上颈椎融合固定技术(Harms、Magerl技术等)发生椎动脉损伤的危险比较高,枢椎椎板螺钉固定技术与椎弓根钉内固定相比,具有操作简单、血管损伤几率小等优点。本文从枢椎椎板螺钉固定技术的要素,确定研究的主要内容和范围,测量国人枢椎的解剖学及影像学参数,建立寰枢椎三维有限元模型,探讨枢椎椎板螺钉固定的可行性和有效性。
方法(1)解剖学测量组(Group A):测量96例(男51例,女45例)成人枢椎干燥骨标本的解剖学数据。影像学测量组(Group B):测量112例(男58例,女54例)健康成人的影像学数据。所测量参数：枢椎椎板长度、厚度和高度,棘突根部的高度,进钉点到侧块外缘及椎板外缘的距离、椎板棘突角。(2)应用VTK (Visualization Toolkit)三维图像处理软件处理1名健康成年男性寰枢椎CT图像,获得寰枢椎三维几何模型,并赋以非均质材料后导入大型有限元分析软件ABAQUS中,构建寰椎侧块-枢椎椎板螺钉固定的有限元模型,分析中立、前屈／后伸、侧弯、平移、旋转等状态下寰枢侧块螺钉-枢椎椎板螺钉所受应力变化情况。
结果(1)结果显示除了椎板棘突角以外的其他各项参数男性大于女性(P<0.05)。枢椎椎板长度、椎板厚度、椎板高度、棘突根部高度、进钉点至侧块外缘及椎板外缘的距离、椎板棘突角,解剖学测量(Group A)结果分别为1.81±0.51cm,0.62cm±0.15cm,1.36cm±0.69cm1.21±0.16cm,3.22±0.13cm,2.85±0.16cm,45.0°±5.0°；影像学测量(Group B)结果则分别为1.79±0.32cm,0.66cm±0.15cm,1.60cm±0.23cm,1.18±0.33cm,3.32±0.45cm,2.44±0.41cm,46.89°±4.89°。45%椎板厚度小于6mm,椎板长度小于2.5cm,5%进钉点至椎板外缘的距离大于3.0cm,进钉点至侧块外缘的距离2.5～4.0cm,只有5%大于4.0cm。双侧椎板参数无显著性差异。(2)所建立有限元模型中,椎骨包含130982个节点,83776个单元,螺钉包含52381个节点,32306个单元,逼真地描绘了寰枢椎的结构特点。有限元分析结果显示在中立、屈伸、侧弯、旋转和前后平移等不同运动状态下,螺钉应力分布与寰枢椎沿钉道受力对应,主要集中在螺钉的骨-钉交界处和钉棒连接处,应力沿螺钉轴向方向逐渐减小。在各种运动状态下,最大应力均产生在螺钉置入点周围,寰椎侧块螺钉承受的应力最大。
结论(1)国人枢椎具备椎板螺钉内固定条件,术前影像学测量可为枢椎椎板准确置钉提供可靠参数,一般可置入直径3.5mm、长度>20mm的螺钉,建议术前行影像学检查确定患者是否适合椎板螺钉技术及选择合适规格的螺钉。我们提出了一种新的更精确的影像学测量方法。(2)在不同运动状态下,螺钉应力分布与寰枢椎沿钉道受力对应,主要集中在螺钉的骨-钉交界处和钉棒连接处,最大应力均产生在螺钉置入点周围。寰椎侧块-枢椎椎板螺钉固定的有限元模型能有效模拟寰枢椎运动的生物力学状态,方便了进一步的生物力学研究。(3)枢椎椎板螺钉技术提供了一种安全有效的寰枢椎固定方式,具有临床应用的可行性与安全性。
Objectives. Different atlantoaxial fusion techniques are used for instability of the upper cervical spine. C2 laminar screws are becoming an increasingly used method of fixation, avoiding the fixation through the C2 pedicle and eliminating the risk of vertebral artery injury. In this research, we performed the anatomical and CT measurement of C2 lamina in North Chinese people and established an anatomic detailed finite element model of C1-C2 complex in order to provide the anatomical and radiographic data and to verify the clinical applicability of trans-lamina screws in North Chinese people.
Methods. (1) 96 dry samples of cadaveric atlas were measured with vernier calipers and protractors (group A). The parameters included the length of C2 laminar, the height of C2 laminar, the thickness of C2 lamina, the height of spinous process root the length from entry point to lateral border of lateral mass, the length from entry point to lateral border of lamina and the angle between lamina and spinous process(°). Radiographic measurements were then performed on 112 volunteers and all measurements were repeated from these images (group B). Correlation coefficients were calculated to determine the ability of radiographic measurement to accurately determine these measurements. (2) The coordinate data of the vertebras were obtained from the CT scan images of Chinese healthy male adult volunteers' cervical spine, VTK(Visualization Toolkit) software was used to preprocess and establish the geometry model of the C1-C2 cervical spine. The geometry model was meshed by ABAQUS software. Some material parameters were defined from other available material parameters using proportion and function scale method. The changes of theoretical stress in different position of atlas were analyzed when the skull was in neutral position, flexion/extension, right and left lateral bending, axial rotation and anterior-posterior (AP) translation.
Results. (1) The data of males were significant higher than those of female (P<0.05) except angle A (P>0.05) according to our anatomic and radiographic measurement. The thickness in 45 percent specimens is less than 6mm. The length of lamina in all specimens is less than 2.5cm, while length from entry point to rim of lamina is more than 3cm only in 5 percent specimens. The length from entry point to the lateral rim of lateral mass range from 2.5-4cm, however only 5% percent is longer than 4cm. There was no significant difference in the data of bilateral lamina (P>0.05).There was no significant difference of age, height in group A and B. The data of group B have no significant statistic difference with those of group A. (2) The model of C1-C2 complex consists of 130982 nodes and 83776 elements, that of the rod-cantilever construction is composed of 52381 nodes and 32306 elements. The data indicates that C1 lateral mass-C2 intralaminar screw-rod fixation significantly reduced the C1-C2 motion in flexion/extension, lateral bending and axial rotation compared to the intact cases. The results showed that there was concentration of stress at the upper bone-screw interface and the inferior transition area between rod and screw in extension. Stress concentration in flexion positions occurred in both the upper rod-screw transition area and bone-screw interface. In rotation positions the inferior conjunction of screw-rod has stress convergence, the stress of the screw system is well-distributed.
Conclusion. (1) This result demonstrates that the radiographic measurement method we used is simple, accurate and reliable. The preoperative radiographic evaluation is very important to determine the suitable size of screws. The appropriate diameter of screws is 3mm to 3.5mm in Chinese people. It is safe to use less than 30mm longer screws in Chinese people. (2) The finite element model of the atlantoaxial spine realistically simulates the atlantoaxial motion, which can simulate the natural condition and facilitate the further biomechanical research. (3) This novel fixation method could be used as an option for atlantoaxial instability of posterior approach techniques.
方法(1)解剖学测量组(Group A):测量96例(男51例,女45例)成人枢椎干燥骨标本的解剖学数据。影像学测量组(Group B):测量112例(男58例,女54例)健康成人的影像学数据。所测量参数：枢椎椎板长度、厚度和高度,棘突根部的高度,进钉点到侧块外缘及椎板外缘的距离、椎板棘突角。(2)应用VTK (Visualization Toolkit)三维图像处理软件处理1名健康成年男性寰枢椎CT图像,获得寰枢椎三维几何模型,并赋以非均质材料后导入大型有限元分析软件ABAQUS中,构建寰椎侧块-枢椎椎板螺钉固定的有限元模型,分析中立、前屈／后伸、侧弯、平移、旋转等状态下寰枢侧块螺钉-枢椎椎板螺钉所受应力变化情况。
结果(1)结果显示除了椎板棘突角以外的其他各项参数男性大于女性(P<0.05)。枢椎椎板长度、椎板厚度、椎板高度、棘突根部高度、进钉点至侧块外缘及椎板外缘的距离、椎板棘突角,解剖学测量(Group A)结果分别为1.81±0.51cm,0.62cm±0.15cm,1.36cm±0.69cm1.21±0.16cm,3.22±0.13cm,2.85±0.16cm,45.0°±5.0°；影像学测量(Group B)结果则分别为1.79±0.32cm,0.66cm±0.15cm,1.60cm±0.23cm,1.18±0.33cm,3.32±0.45cm,2.44±0.41cm,46.89°±4.89°。45%椎板厚度小于6mm,椎板长度小于2.5cm,5%进钉点至椎板外缘的距离大于3.0cm,进钉点至侧块外缘的距离2.5～4.0cm,只有5%大于4.0cm。双侧椎板参数无显著性差异。(2)所建立有限元模型中,椎骨包含130982个节点,83776个单元,螺钉包含52381个节点,32306个单元,逼真地描绘了寰枢椎的结构特点。有限元分析结果显示在中立、屈伸、侧弯、旋转和前后平移等不同运动状态下,螺钉应力分布与寰枢椎沿钉道受力对应,主要集中在螺钉的骨-钉交界处和钉棒连接处,应力沿螺钉轴向方向逐渐减小。在各种运动状态下,最大应力均产生在螺钉置入点周围,寰椎侧块螺钉承受的应力最大。
结论(1)国人枢椎具备椎板螺钉内固定条件,术前影像学测量可为枢椎椎板准确置钉提供可靠参数,一般可置入直径3.5mm、长度>20mm的螺钉,建议术前行影像学检查确定患者是否适合椎板螺钉技术及选择合适规格的螺钉。我们提出了一种新的更精确的影像学测量方法。(2)在不同运动状态下,螺钉应力分布与寰枢椎沿钉道受力对应,主要集中在螺钉的骨-钉交界处和钉棒连接处,最大应力均产生在螺钉置入点周围。寰椎侧块-枢椎椎板螺钉固定的有限元模型能有效模拟寰枢椎运动的生物力学状态,方便了进一步的生物力学研究。(3)枢椎椎板螺钉技术提供了一种安全有效的寰枢椎固定方式,具有临床应用的可行性与安全性。
Objectives. Different atlantoaxial fusion techniques are used for instability of the upper cervical spine. C2 laminar screws are becoming an increasingly used method of fixation, avoiding the fixation through the C2 pedicle and eliminating the risk of vertebral artery injury. In this research, we performed the anatomical and CT measurement of C2 lamina in North Chinese people and established an anatomic detailed finite element model of C1-C2 complex in order to provide the anatomical and radiographic data and to verify the clinical applicability of trans-lamina screws in North Chinese people.
Methods. (1) 96 dry samples of cadaveric atlas were measured with vernier calipers and protractors (group A). The parameters included the length of C2 laminar, the height of C2 laminar, the thickness of C2 lamina, the height of spinous process root the length from entry point to lateral border of lateral mass, the length from entry point to lateral border of lamina and the angle between lamina and spinous process(°). Radiographic measurements were then performed on 112 volunteers and all measurements were repeated from these images (group B). Correlation coefficients were calculated to determine the ability of radiographic measurement to accurately determine these measurements. (2) The coordinate data of the vertebras were obtained from the CT scan images of Chinese healthy male adult volunteers' cervical spine, VTK(Visualization Toolkit) software was used to preprocess and establish the geometry model of the C1-C2 cervical spine. The geometry model was meshed by ABAQUS software. Some material parameters were defined from other available material parameters using proportion and function scale method. The changes of theoretical stress in different position of atlas were analyzed when the skull was in neutral position, flexion/extension, right and left lateral bending, axial rotation and anterior-posterior (AP) translation.
Results. (1) The data of males were significant higher than those of female (P<0.05) except angle A (P>0.05) according to our anatomic and radiographic measurement. The thickness in 45 percent specimens is less than 6mm. The length of lamina in all specimens is less than 2.5cm, while length from entry point to rim of lamina is more than 3cm only in 5 percent specimens. The length from entry point to the lateral rim of lateral mass range from 2.5-4cm, however only 5% percent is longer than 4cm. There was no significant difference in the data of bilateral lamina (P>0.05).There was no significant difference of age, height in group A and B. The data of group B have no significant statistic difference with those of group A. (2) The model of C1-C2 complex consists of 130982 nodes and 83776 elements, that of the rod-cantilever construction is composed of 52381 nodes and 32306 elements. The data indicates that C1 lateral mass-C2 intralaminar screw-rod fixation significantly reduced the C1-C2 motion in flexion/extension, lateral bending and axial rotation compared to the intact cases. The results showed that there was concentration of stress at the upper bone-screw interface and the inferior transition area between rod and screw in extension. Stress concentration in flexion positions occurred in both the upper rod-screw transition area and bone-screw interface. In rotation positions the inferior conjunction of screw-rod has stress convergence, the stress of the screw system is well-distributed.
Conclusion. (1) This result demonstrates that the radiographic measurement method we used is simple, accurate and reliable. The preoperative radiographic evaluation is very important to determine the suitable size of screws. The appropriate diameter of screws is 3mm to 3.5mm in Chinese people. It is safe to use less than 30mm longer screws in Chinese people. (2) The finite element model of the atlantoaxial spine realistically simulates the atlantoaxial motion, which can simulate the natural condition and facilitate the further biomechanical research. (3) This novel fixation method could be used as an option for atlantoaxial instability of posterior approach techniques.
引文
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