不同前路内固定方式治疗枢椎椎体横行骨折合并Hangman骨折稳定性的有限元分析

The biomechanical study of different kinds of anterior internal fixation for the transverse fracture associated with Hangman′s fractures of the axis: a finite-element analysis

目的：应用有限元分析评价三种C2~C3前路内固定方式治疗枢椎椎体横行骨折合并Hangman骨折的生物力学稳定性，为临床手术方式选择提供理论参考。方法：选择1位35岁健康男性志愿者，采用16排螺旋CT对枕骨底（C0）~C3节段进行层厚0.5mm的薄层扫描，利用Mimics 10.01、Hypermesh V 10.0及ABAQUS 6.11软件，建立正常颈椎C0~C3节段三维六面体网格有限元模型（FE/Intact）并进行有效性验证。在已验证的C0~C3节段模型上通过弱化网格单元强度的方法模拟建立枢椎椎体横行骨折合并Hangman骨折模型（FE/Fracture）并进行验证；在FE/Fracture上分别建立三种C2~C3前路内固定模型：前路C2/3椎间盘切除、cage植骨融合＋长钢板螺钉内固定模型（FE/cage＋ACFLP）；前路齿状突螺钉固定＋C2/3椎间盘切除、cage植骨融合＋短钢板螺钉内固定模型（FE/AOSF＋cage＋ACFSP）；前路齿状突螺钉固定＋C2/3椎间盘切除、cage植骨融合＋长钢板螺钉内固定模型（FE/AOSF＋cage＋ACFLP），对FE/Intact、FE/Fracture和三种内固定模型进行边界约束后分别施加前屈、后伸、侧屈、旋转四种生理载荷，比较各模型在不同工况下三维活动的角位移（ROM）及骨折端节点位移变化。结果：建立的FE/Intact外观逼真，几何相似性好，经验证有效。在相同条件下FE/Fracture模型三维活动度较FE/Intact模型明显增大，在前屈、后伸、侧屈及旋转方向上的ROM分别增加至FE/Fracture模型的244.7％、203.3％、188.9％、200％；FE/AOSF＋cage＋ACFLP在前屈、后伸、侧屈、旋转方向上的ROM分别为FE/Intact的60.5％、70％、66.7％、62.5％；FE/AOSF＋cage＋ACFSP在各方向的ROM分别为FE/Intact的118.4％、123.3％、148.1％、175％；FE/cage＋ACFLP在各方向上的ROM分别为FE/Intact的123.7％、143.3％、122.2％、137.5％。FE/AOSF＋cage＋ACFLP稳定性最强，骨折端位移最小；FE/AOSF＋cage＋ACFSP稳定性较差，其在侧屈和旋转方向上ROM及骨折端位移最大；FE/cage＋ACFLP在前屈及后伸方向上提供的稳定性最差，骨折端的位移最大。结论：FE/AOSF＋cage＋ACFLP固定可为枢椎椎体横行骨折合并Hangman骨折提供较强的生物力学稳定性，达到固定融合C2~C3节段和骨折断端以重建上颈椎稳定性的目的。

Objectives： To explore the biomechanical stability of three kinds of anterior internal fixation for the transverse fracture associated with Hangman′s fractures of the axis by finite element（FE） analysis, and to provide theoretical reference for the clinical surgery. Methods： Thin-section spiral computed tomography（0.5mm） was performed on occiput（C0） to C3 region. A three-dimensional hexahedral FE model of upper cervical spine was established by software（Mimics 10.01, Hypermesh V 10.0 and ABAQUS 6.11）, and the finite element model of intact（FE/Intact） was verified with availability. Then the weakening of the strength of grid was performed to simulate the finite element model of the transverse fracture associated with Hangman′s fractures of the axis（FE/Fracture） and was verified with availability, the three internal fixation models： anterior C2/3 discectomy＋cage bone grafting＋anterior cervical fusion and long plate（FE/cage＋ACFLP）, anterior odontoid screw fixation＋C2/3 discectomy cage bone grafting＋anterior cervical fusion and short plate（FE/AOSF＋cage＋ACFSP）, anterior odontoid screw fixation＋C2/3 discectomy cage bone grafting＋ anterior cervical fusion and long plate（FE/AOSF＋cage＋ACFSP） were simulated on the FE/Fracture model. Flexion, extension, lateral bending and axial rotation were imposed on the FE/Intact, FE/Fracture and the three fixation models respectively. The ROM of different models and the displacement of fracture end were compared. Results： The model of FE/Intact was established clearly with good geometric similarity and realistic appearance, which was verified with availability. The ROM of FE/Fracture increased obviously compared with the FE/Intact under the same loading conditions, and the ROM of C2/3 in flexion-extension, lateral bending and axial rotation increased 244.7％, 203.3％, 188.9％, 200％ respectively. The ROM of C2/3 of the FE/AOSF＋ cage＋ACFLP in flexion-extension, lateral bending and axial rotation was 60.5％, 70％, 66.7％, 62.5％ of the FE/Intact respectively; the ROM of C2/3 of the FE/AOSF＋cage＋ACFSP increased 118.4％, 123.3％, 148.1％, 175％ respectively in flexion-extension, lateral bending and axial rotation compared with the FE/Intact, and the ROM of the FE/cage＋ACFLP was 123.7％, 143.3％, 122.2％, 137.5％ of the FE/Intact. The FE/AOSF＋ cage＋ACFLP presented with highest stability and the displacement of the fracture end was the least; FE/AOSF＋cage＋ACFSP had least stability, especially in bending and rotation, and the displacement of fracture end was the biggest, the ROM of FE/cage＋ACFLP and the displacement of fracture end was the highest in respectively flexion-extension. Conclusions： The FE/AOSF＋cage＋ACFLP is effective for the transverse fracture of the axis associated with Hangman′s fractures, which can ensure good stability.