胫骨平台后外侧骨折3种内固定方式的有限元分析

Finite element analysis of posterolateral fracture of tibial plateau using three types of internal fixation

背景:如今胫骨平台骨折的研究已由起初的内外侧"双轨道结构"逐步转型为"360°全方位立体结构",国内外学者们更关注平台后侧结构的稳定性、复位情况以及对复位后功能恢复的影响。后侧平台的内固定材料的选择仍无明确定论,存在较大争议。目的:探讨胫骨平台后外侧骨折3种内固定方式的生物力学特性。方法:通过计算机三维有限元技术,模拟胫骨平台后外侧1/2和后外侧1/4骨折。分别使用前侧2枚6.5 mm拉力螺钉、外侧4.5 mm L型钢板以及后侧3.5 mm T型钢板置入内固定骨折块。在胫骨平台中心处加载500 N纵向应力,比较3种内固定方式的生物力学状态。结果与结论:在1/2骨块模型中,前侧拉力螺钉与后侧钢板在各个方向上的位移较小,外侧钢板的位移较其他两种固定方式大。而在1/4骨块模型中,前侧拉力螺钉在各方向的位移优势更明显,后侧钢板的位移居次,外侧钢板的位移最大。1/2骨块上,前侧拉力螺钉的最大应力为36.523 MPa,外侧钢板为153.372 MPa,后侧钢板为115.922 MPa;而在骨块上的最大应力前侧拉力螺钉模型为4.309 MPa,外侧钢板为4.37 MPa,后侧钢板为3.124 MPa。1/4骨块上前侧拉力螺钉的最大应力为36.803 MPa,外侧钢板为153.336 MPa,后侧钢板为104.234 MPa;而在骨块上的最大应力前侧拉力螺钉模型为1.195 MPa,外侧钢板为0.827 MPa,后侧钢板为1.196 MPa。提示前侧拉力螺钉能够承担更大的应力,并在受到应力后位移变化较小,可提供较稳定的支持。而后侧钢板在骨块较大(1/2骨块)时,能够提供较强的稳定性,与拉力螺钉相仿;而在骨块较小(1/4骨块)时,稳定性不如前侧拉力螺钉。外侧钢板在固定胫骨平台后外侧骨折时,稳定性较差,不如前侧拉力螺钉和后侧钢板。

BACKGROUND： Studies on tibial plateau fractures had gradually focused on ＂360° stereochemical structure＂ from medial and lateral ＂double track structure＂ nowadays. Scholars pay great attention on the stability and reposition of posterior plateau and functional recovery after reduction. The choice of fixation material of posterior plateau was controversial. OBJECTIVE： To discuss the biomechanical characteristics of posterolateral fracture of tibial plateau using three types of internal fixation. METHODS： Using three-dimensional finite element analysis, we simulated 1/2 and 1/4 posterolateral tibial plateau fractures. Three types of internal fixation were used： two anterior 6.5 mm lag screws, lateral 4.5 mm L-shape plate, and posterior 3.5 mm T-shape plate. 500 N was loaded at the center of the tibial plateau vertically, and biomechanical status of three types of fixation was compared. RESULTS AND CONCLUSION： In 1/2 fracture model, anterior lag screw group and posterior plate group gained least displacement in all directions, as lateral plate group gained more. In 1/4 model, the advantage in displacement of anterior lag screw group was more apparent, the second was posterior plate group, and the last was lateral plate group. In 1/2 fracture model, the maximum stress of anterior lag screw was 36.523 MPa, which of lateral plate group was 153.372 MPa and posterior plate group was 115.922 MPa. The maximum stress left in the separate bone of lag screw group was 4.309 MPa, which of lateral plate group was 4.37 MPa and posterior plate group was 3.124 MPa. In 1/4 fracture model, the maximum stress of anterior lag screw was 36.803 MPa, which of lateral plate group was 153.336 MPa and posterior plate group was 104.234 MPa. The maximum stress left in the separate bone of lag screw group was 1.195 MPa, which of lateral plate group was 0.827 MPa and posterior plate group was 1.196 MPa. Results indicated that anterior lag screw could bear more stress and gained least displacement after loading, and the fixation was more stable. Posterior plate can give more stabilization when the separate bone was bigger（1/2）, similar to anterior lag screw. When the separate bone was smaller（1/4）, posterior plate model was less stable than anterior lag screw. Lateral plate model, with poor stabilization, was the worst choice in three types of fixation.