Objectives: To analyze the biomechanical stability of four kinds of internal fixation for the type Ⅰ Hangman fracture, type Ⅱ odontoid fracture and the C(2/3) disc injury by finite element (FE) analysis. Methods: Thin-section spiral computed tomography (0.5 mm) was performed on C(1) to C(3) region of cervical vertebra in healthy male volunteers.A three-dimensional hexahedral FE model of upper cervical spine was established by software (Mimics, GEOMAGICS, Pro/E and Ansys). Then the weakening of the strength of grid was performed to simulate the FE model of the type Ⅰ Hangman fracture, type Ⅱ odontoid fracture and the C(2/3) disc injury (FE/Fracture), the four internal fixation models: anterior cervical plate+ odontoid screw+ cage (FE/ACP+ OS+ cage), affixing rods from pedicle screws in C(2) to lateral mass screws in C(3)+ odontoid screw + cage (FE/C(2)PS+ C(3)LMS+ OS+ cage), affixing rods from pedicle screws in C(1) to pedicle screws in C(2) and lateral mass screws in C(3) (FE/C(1)PS+ C(2)PS+ C(3)LMS), anterior odontoid screw plate fixation system (FE/AOSP) were simulated on the FE/Fracture model.Flexion, extension, lateral bending and axial rotation were imposed on the FE/Intact, FE/Fracture and the four fixation models respectively. Results: The intact model of upper cervical spine (C(1)-C(3)) was established successfully, consisting of 259 641 nodes and 403 674 units.There was no significant difference among the FE/ACP+ OS+ cage, the FE/ C(2)PS+ C(3)LMS+ OS+ cage and the FE/AOSP of ROMC(1/2).During flexion, extension, left axial rotation and right axial rotation of ROMC(2)-C(3), the FE/AOSP decreased 70.7%, 74.4%, 38.9%, 41.1% respectively compared with the FE/C(1)PS+ C(2)PS+ C(3)LMS.The ROMC(2)-C(3) during flexion, extension, left lateral bending, right lateral bending, left axial rotation and right axial rotation in the FE/AOSP decreased for 82.2%, 82.8%, 73.2%, 64.8%, 72.2%, 81.5% respectively when compared with those in FE/ACP+ OS+ cage.The ROMC(2)-C(3) during flexion, extension, left lateral bending, right lateral bending, left axial rotation and right axial rotation in the FE/AOSP decreased 88.2%, 81.2%, 47.6%, 41.2%, 38.9%, 39.0% respectively when compared with those in FE/C(2)PS+ C(3)LMS+ OS+ cage.The stress concentrated on the connection between plate and screw in the FE/ACP+ OS+ cage, the FE/C(2)PS+ C(3)LMS+ OS+ cage and the FE/C(1)PS+ C(2)PS+ C(3)LMS, while it distributed evenly in the FE/AOSP. Conclusion: Anterior odontoid screw plate fixation system can be used to treat the type Ⅰ Hangman fracture, type Ⅱ odontoid fracture, and the C(2/3) disc injury and can reserve the function of atlanto-axial joint.
目的： 利用有限元分析评价四种内固定术治疗Ⅰ型Hangman骨折伴Ⅱ型齿状突骨折联合C(2/3)椎间盘损伤的生物力学性能。 方法： 选择1名30岁健康男性志愿者，采用16排螺旋CT对其C(1)～C(3)节段进行层厚0.5 mm的薄层扫描，利用Mimics、Geomagics、Pro/E及Ansys软件，建立正常C(1)～C(3)节段有限元模型(FE/Intact)。在FE/Intact模型基础上建立Ⅰ型Hangman骨折伴Ⅱ型齿状突骨折联合C(2/3)椎间盘损伤模型(FE/Fracture)；在FE/Fracture基础上分别建立4种内固定模型：前路钢板内固定模型＋齿状突螺钉＋C(2/3)椎间融合器固定模型(FE/ACP＋OS＋cage)；后路C(2/3)椎弓根侧块螺钉＋齿状突螺钉＋C(2/3)椎间融合器固定模型(FE/C(2)PS＋C(3)LMS＋OS＋cage)；后路C(1)～C(3)椎弓根侧块螺钉固定模型(FE/C(1)PS＋C(2)PS＋C(3)LMS)；齿状突螺钉钢板内固定模型(FE/AOSP)，对FE/Intact、FE/Fracture和4种内固定模型进行边界约束后，记录各内固定模型在不同工况下的Von Mises应力云图及最大应力值，计算三维活动度(ROM)。 结果： 建立了正常成年人C(1)～C(3)的三维有限元模型，包括403 674个单元，259 641个节点。在各工况下，FE/Fracture模型ROM较FE/Intact模型均增大，在C(1/2)节段，除FE/C(1)PS＋C(2)PS＋C(3)LMS的ROM值减小，其余3种固定模型在各个方向的ROM与健康颈椎的活动差异不大。在C(2/3)节段，FE/AOSP与FE/C(1)PS＋C(2)PS＋C(3)LMS相比，在前屈、后伸、左旋转、右旋转方向上的ROM分别减小70.7%、74.4%、38.9%、41.1%；FE/AOSP的ROM值较FE/ACP＋OS＋cage在前屈、后伸、左侧屈、右侧屈、左旋转和右旋转方向分别减小82.2%、82.8%、73.2%、64.8%、72.2%、81.5%。FE/AOSP的ROM值较在FE/C(2)PS＋C(3)LMS＋OS＋cage在前屈、后伸、左侧屈、右侧屈、左旋转和右旋转方向分别减小88.2%、81.2%、47.6%、41.2%、38.9%、39.0%。相较于其他3种内固定术在钉板或棒连接部位出现应力集中，AOSP组应力分布较均匀。 结论： FE/AOSP能够处理Ⅰ型Hangman骨折伴Ⅱ型齿状突骨折联合C(2/3)椎间盘损伤，同时能保留寰枢关节的生理活动功能。.
Keywords: Cervical vertebra; Finite element analysis; Hangman fracture; Internal fixation; Odontoid fracture.