Data Sheet 1_A biomechanical investigation of three fixation methods for unilateral denis type II sacral fractures using finite element analysis.docx

ObjectiveDue to its inherent high instability, the selection of fixation strategies for unilateral Denis type II sacral fractures remains a controversial challenge in the field of traumatic orthopedics. This study focuses on unilateral Denis type II sacral fractures. By applying three different fixation methods, it aims to explore their biomechanical properties and provide a theoretical basis for optimizing clinical fixation protocols.
MethodsA ligament-intact three-dimensional finite-element model of a right-sided Denis type II sacral fracture, including ipsilateral superior and inferior pubic rami fractures, was generated. Three fixation models were simulated: (1) S1/S2 transiliac-transsacral screw fixation (S1/S2-TTS); (2) unilateral L4/5 triangular osteosynthesis (UTOS); and (3) bilateral S2-alar-iliac screws combined with an iliosacral screw (BS2AI-ISS). Appropriate material properties, boundary conditions, and loading protocols were assigned. A 500 N axial compressive load superimposed with a 7.5 Nm torque was applied to simulate standing position and multiplanar spinal motion. Biomechanical parameters evaluated included vertical sacral stiffness, maximum von Mises stress within implants, and relative interfragmentary displacement (RID) at the fracture site.
ResultsSacrum vertical stiffness: All constructs significantly increased sacrum vertical stiffness compared with the intact model. Normalised stiffness values were 443.18% (S1/S2-TTS), 228.38% (UTOS) and 397.26% (BS2AI-ISS). Maximum implant von Mises stress: Under every loading mode, S1/S2-TTS exhibited the lowest and most evenly distributed stress (range 30.30–49.23 MPa). Maximum stresses ranked from lowest to highest: S1/S2-TTS < BS2AI-ISS < UTOS. Relative interfragmentary displacement: In standing position, mean RID were 0.0313 ± 0.0148 mm (S1/S2-TTS), 0.0736 ± 0.0314 mm (UTOS) and 0.0539 ± 0.0163 mm (BS2AI-ISS). Only the difference between S1/S2-TTS and UTOS reached statistical significance (p = 0.047). Similar patterns were observed in extension, left flexion and left rotation; no significant differences were found in right flexion or right rotation.
ConclusionThe present study demonstrates that BS2AI-ISS provides biomechanical stability comparable to both S1/S2-TTS and UTOS for unilateral Denis type II sacral fractures. Notably, BS2AI-ISS achieves this stability without compromising lumbar motion and irrespective of sacral morphologic variations. These findings suggest that BS2AI-ISS may serve as an effective alternative for managing unilateral Denis type II sacral fractures.

研究目的 由于单侧Denis Ⅱ型骶骨骨折（unilateral Denis type II sacral fracture）固有的高度不稳定性，其固定策略的选择在创伤骨科领域仍存在争议，是一项颇具挑战性的课题。本研究聚焦于单侧Denis Ⅱ型骶骨骨折，通过采用三种不同的固定方式，旨在探究其生物力学特性，为优化临床固定方案提供理论依据。
研究方法 构建了包含同侧耻骨上、下支骨折的右侧Denis Ⅱ型骶骨骨折且韧带完整的三维有限元模型。模拟了三种固定模型：(1) S1/S2经髂骨经骶骨螺钉固定（S1/S2 transiliac-transsacral screw fixation, S1/S2-TTS）；(2) 单侧L4/5三角骨固定术（unilateral L4/5 triangular osteosynthesis, UTOS）；(3) 双侧S2骶骨翼-髂骨螺钉联合髂骨螺钉固定（bilateral S2-alar-iliac screws combined with an iliosacral screw, BS2AI-ISS）。设置了适配的材料属性、边界条件及加载方案。施加500N轴向压缩载荷叠加7.5Nm扭矩，以模拟站立位及脊柱多平面运动。评估的生物力学参数包括骶骨垂直刚度、植入物内最大冯·米塞斯应力（von Mises stress）以及骨折部位的骨折块间相对移位（relative interfragmentary displacement, RID）。
研究结果 骶骨垂直刚度：所有固定结构均较完整模型显著提升了骶骨垂直刚度。归一化刚度值分别为443.18%（S1/S2-TTS组）、228.38%（UTOS组）和397.26%（BS2AI-ISS组）。植入物最大冯·米塞斯应力：在所有加载模式下，S1/S2-TTS组均表现出最低且分布最均匀的应力（范围30.30~49.23MPa）。最大应力由低到高排序为：S1/S2-TTS < BS2AI-ISS < UTOS。骨折块间相对移位：在站立位时，各组平均RID分别为0.0313±0.0148mm（S1/S2-TTS组）、0.0736±0.0314mm（UTOS组）和0.0539±0.0163mm（BS2AI-ISS组）。仅S1/S2-TTS组与UTOS组之间的差异具有统计学意义（p = 0.047）。在伸展、左侧屈曲及左侧旋转工况下也观察到了类似的结果；右侧屈曲或右侧旋转工况下则未发现显著差异。
研究结论 本研究表明，对于单侧Denis Ⅱ型骶骨骨折，BS2AI-ISS所提供的生物力学稳定性可与S1/S2-TTS及UTOS相媲美。值得注意的是，BS2AI-ISS在不影响腰椎活动度的前提下即可实现该稳定性，且不受骶骨形态变异的影响。上述研究结果提示，BS2AI-ISS或可作为治疗单侧Denis Ⅱ型骶骨骨折的有效替代方案。