Lenke 1AN型青少年特发性脊柱侧凸不同置棒顺序矫形的有限元分析

Different inserting rod sequences in Lenke 1AN adolescent idiopathic scoliosis: a finite element analysis

[目的]建立Lenke1AN型青少年特发性脊柱侧凸的三维有限元模型,分析三种不同置钉模式中凹侧螺钉的应力分布。[方法]建立一个T2~S5脊柱侧凸的三维有限元模型,在凹侧置入椎弓根螺钉,按照不同的置棒方式进行矫形模拟。A组模拟从顶椎开始,再依次向上和向下置棒;B组从中立椎开始,然后依次向上,再从中立椎下方开始置棒;C组从中立椎开始,然后依次向下,再从中立椎上方开始置棒,最后分析椎弓根螺钉及连接棒的等效应力。[结果]研究表明A组连接棒上的等效应力相对稳定,而B组和C组应力变化较大。虽然无论何种置棒顺序,都可以得到相同的脊柱侧凸矫正效果,但是A组连接棒上应力分布变化较小,而且最大应力小。[结论]三种置棒顺序都可以得到较好的脊柱侧凸矫正效果,A组椎弓根钉及连接棒断裂风险最低。

[Objective] To develop a patient-specific Lenke 1AN scoliosis finite element (FE) model, and using this model to analyze the three-dimensional corrective forces and stress distributions which acting at each screw located on the concave side with the three different setting rod sequences.[Methods] A T2~S5 scoliosis FE model was successfully developed and vali dated. Pedicle screws were inserted from T3 to L4 on the concave side, then three different sequences of rod placement were mimicked. In the A group the rod was inserted on the pedicle screw at the apical vertebra firstly, and then on the screws above and below the apical vertebra alternately, whereas the B group had the rod placed on the pedicle screw at the neutral vertebra firstly, then upward and finally downward on the remaining screws, and the C group had the rod inserted on the pedicle screw at the neutral vertebra firstly, then downward and finally upward on the remaining screws. The maximum von Mises stress was ana lyzed.[Results] The main thoracic (MT) curve and thoracic kyphosis (TK) of three groups were the same. However, the stresses on the rod in the A group were significantly less changed compared with those in the B and C groups in the process of locking rod to the screws.[Conclusion] Whatever the sequence of the rod placement applied, the same outcome of scoliosis correction do achieve by this instrumentation. By comparison, that rod is inserted on the pedicle screw at the apical vertebra firstly, and then on the screws above and below alternately has the lest stress variation on the links, which im plies the lowest risk of pedicle screws and rod failure.