不同长度骶髂螺钉固定中央型骶骨纵行骨折的生物力学比较研究

Biomechanical comparisons of two sacroiliac screws with different lengths in the treatment of central sacral fractures in a finite element model

目的比较应用加长骶髂螺钉和长骶髂螺钉以不同方式固定中央型骶骨纵行骨折的生物力学特征，为临床应用提供参考依据。方法使用三维有限元方法，建立中央型骶骨纵行骨折（Tile C型骨盆损伤）模型，分别模拟7种不同长度骶髂螺钉固定方式，包括：（1）右侧1枚长骶髂螺钉对骶1进行固定（C1）；（2）右侧1枚长骶髂螺钉对骶2进行固定（C2）；（3）骶1和骶2各1枚长骶髂螺钉自右侧进行固定（C12）；（4）右侧1枚骶1长骶髂螺钉配合左侧1枚骶2长骶髂螺钉进行固定（C12双向）；（5）右侧1枚加长骶髂螺钉穿过骶1进行固定（J1）；（6）右侧1枚加长骶髂螺钉穿过骶2进行固定（J2）；（7）右侧2枚加长骶髂螺钉分别穿过骶1和骶2进行固定（j12）。对模拟站立位状态下骨盆后环的稳定性、多部位最大Von Mises应力（简称“最大应力”）、应力分布等指标进行量化和比较。结果骶1、骶2加长螺钉组合固定（J12）的后环-螺钉复合体的稳定性最优。螺钉最大应力受固定节段影响，骶1〉骶2〉骶1、骶2。双节段固定时，骶1、骶2两节段的骶髂螺钉最大应力相近，加长骶髂螺钉的最大应力小于长骶髂螺钉。加长骶髂螺钉固定模型的双侧骶髂关节最大应力均与正常骨盆相仿，长骶髂螺钉固定模型的左侧骶髂关节最大应力均大于正常骨盆。长骶髂螺钉较加长骶髂螺钉的钉-骨交界面最大应力大。螺钉应力分布方面，加长骶髂螺钉优于长骶髂螺钉，双节段固定优于单节段固定。双节段固定的骨盆应力分布与正常骨盆相差较小。结论使用骶1、骶2双节段加长骶髂螺钉组合固定Tile C型骨盆损伤的中央型骶骨纵行骨折，骨盆后环-螺钉复合体更稳定，螺钉应力较分散，骨盆应力分布更接近正常，内固定失效的风险较低，发生骶髂关节源性下腰痛的可能性较小。

Objective To compare the biomechanical characteristics of lengthened sacroiliac screw and long sacroiliac screw fixated in different ways for the treatment of central vertical sacral fractures to provide reference for clinical practice. Methods A finite element model with three dimensions of Tile type C pelvic ring injury （ central type Denis Ⅲ fracture of sacrum） was produced. The central sacral fractures were fixated with lengthened sacroiliac screw or long sacroiliac screw in 7 types of models respectively as follows. （1）One long sacroiliac screw was fixated in St segment from the right （C1） ; （2） One long sacroiliac screw was fixated in S2 segment from the right （C2） ; （3）Two long sacroiliac screws were fixated in S1 and S2 segments respectively from the right （C12） ; （4） One long sacroiliac screw was fixated in S1 segment from the right and one long sacroiliac screw was fixated in S2 segment from the left （C12hybrid） ; （5） One lengthened sacroiliac screw was fixated in S1 segment from the right （J1） ; （6） One lengthened sacroiliac screw was fixated in S2 segment from the right （J2） ; （ 7 ） Two lengthened sacroiliac screws were fixated in S1 and S2 segments respectively from the right （J12）. The shift and angle displacement of the central superior surface of sacrum in the case of standing on both feet were measured and compared. The maximum Von Mises stresses in different positions were measured. And various mechanical indices （ including stresses of various parts and stress distribution of screws and pelvis, etc） were also quantified and compared. Results The stability of the posterior ring-screw complex was optimal when the sacrum was fixated with S1 ＆ S2 lengthened sacroiliac screws. The maximum Von Mises stresses of screw were affected by sacral segments, namely, S1 〉 S2 〉 S1 ＆ S2. The maximum Von Mises stress of screws in S1 and S2 segments were similar. The maximum stress of the lengthened sacroiliac screw was lower than that of the long sacroiliac screw. The maximum Von Mises stress of bilateral sacroiliac joints in the lengthened sacroiliac screw fixation model was similar to that of normal pelvis. The maximum stress in the left sacroiliac joint of the long sacroiliac screw fixation model was larger than that of the normal pelvis. The maximum Von Mises stress of screw-bone interface of the long sacroiliac screw fixation model was larger than that of the lengthened sacroiliac screw fixation model. The screw stress distribution of the lengthened sacroiliac screw was superior to that of the long sacroiliac screw, and the screw stress distribution of the double segment fixation was superior to that of the single segment fixation. There was relatively less difference between the pelvic stress distribution of double segment fixation model and that of the normal pelvic model. Conclusion The fixation of S1 ＆ S2 lengthened sacroiliac screws utilized in central sacral fractures of Tile C pelvic ring injury results in a more stable posterior pelvic ring- screw complex, more dispersed screw stress and better pelvic stress distribution which is closed to normal, and can also reduce the risk of internal fixation failure as well as lower back pain.