锁定钛板螺孔塞的设计与线性静力有限元分析

Design and linear statics finite element analysis of screw hole filler for titanium locking plate system

目的设计胫骨近端外侧锁定钛板螺孔塞，建立胫骨近端骨折固定有限元模型，通过线性静力有限元分析了解螺孔塞设计理念的可行性与价值。方法设计螺孔塞后，对正常胫骨进行CT扫描，通过数字骨科技术建立胫骨折、腓骨、髌韧带、近端外侧锁定钛板以及螺孔塞理想化数字模型，装配后建立“稳定腓骨使用螺孔塞”、“稳定腓骨不使用螺孔塞”、“不稳定腓骨使用螺孔塞”、“不稳定腓骨不使用螺孔塞”4种骨折内固定有限元分析模型，对4种模型分别施加相同的26组载荷，进行线性静力分析。记录并比较4种模型骨折面相对位移最大值、骨折面相对位移平均值、内固定最大VonMises应力、骨折面最大接触应力、钛板．骨界面最大接触应力、骨折面最大接触力、钛板一骨界面最大接触力。结果使用塞子与不使用塞子在骨折面相对位移最大值、骨折面相对位移平均值、内固定最大VonMises应力、钛板与骨面最大接触压力方面差异有统计学意义（P〈0．05），而在骨折面最大接触压力方面差异无统计学意义（P〉0．05）；不稳定腓骨使用螺孔塞情况下对内固定最大VonMises应力改善更为显著，差异有统计学意义（P〈0．05）。结论使用螺孔塞小幅增加钛板与骨面接触力，减少了内固定最大VonMises应力、模型整体最大位移、骨折面相对与平均位移，而对骨折面接触压力影响并不明显，能改善骨折内固定生物力学环境，具备深入研究价值。

Objective To investigate the conceptual feasibility and biomechanical advantages of our self-designed screw hole filler for a lateral bamboo-raft-type titanium locking plate in a digital model of prox- imal tibial fracture using linear statics finite element analysis. Methods A nut-type screw hole filler was designed. Four different idealized finite element models of proximal tibial fracture fixed by a lateral bam- boo-raft-type anatomic locking plate were established on the basis of three-dimensional CT reconstruction and digital orthopedic techniques. The first one was assembled with the filler and stabilized fibula, the second with stabilized fibula but without the filler, the third with the filler and unstabilized fibula, and the fourth with unstabilized fibula but without the filler. Linear statics finite element analyses were conducted for the 4 models under the same 26 groups of loads. The 4 models were compared in terms of maximum relative displacement on fracture surface, average relative displacement on fracture surface, maximum Von Mises stress of internal fixation, maximum contact stress on fracture surface, maximum contact stress between plate and tibial surface, maximum contact pressure on fracture surface, and maximum contact pressure between plate and tibial sur- face. Outcomes of the analyses for the 4 models were harvested and treated with Wilcoxon Signed Ranks Test. Results There were significant differences between using filler and not using filler in maximum relative displacement on fracture surface, average relative displacement on fracture surface, maximum Von Mises stress of internal fixation and maximum contact pressure between plate and tibial surface （ P 〈 0. 05）, but no sig- nificant difference was found in maximum contact pressure on fracture surface （ P 〉 0. 05） . The model as- sembled with the filler and unstabilized fibula led to the greatest improvement in maximum Von Mises stress of internal fixation （ P 〈 0. 05） . Conclusions Since use of nut-type screw hole filler may increase the contact pressure between plate and bone surface, reduce the maximum Von Mises stress of internal fixation, the maximum displacement of the whole model, and the relative and average displacements on fracture surface, but has insignificant effect on the contact pressure on fracture surface, it improves the biomechanical perfor- mance of internal fixation. The filler deserves further study.