Background

The presence of screw tunnels in the femoral neck is a problem for patients with proximal femoral fractures after removal of internal fixation. The question of how much does the existence of the screw tunnels affect the strength of the femur and whether the patient needs to be protected with an adjunctive device has been controversial. The objective of this finite element analysis was to determine (1) whether the screw tunnels affects normal weight bearing after removal of internal fixation of a proximal femur fracture, (2) which screw tunnels parameters affect the weight bearing capacity of the entire femur.

Hypothesis

The presence of the screw tunnels reduces the load-bearing capacity of the femur, and the arrangement, diameter and wall thickness of the screw tunnels affect the load-bearing capacity of the femur.

Materials and methods

Twenty patients who underwent surgical treatment for proximal femur fracture at our hospital were included in the study. Computed tomography (CT) values of the screw tunnel wall in the femur after removal of internal fixations were analysed. Mimics v16.0 and Hypermesh v13.0 software programs were used to generate 3-dimensional (3D) tetrahedral finite element models of the proximal femur with different screw tunnel numbers, diameters, thicknesses, and arrangements. An acetabulum exerting a vertical pressure load of 600 N on the femoral head was simulated and the force on various parts of the femur in each model was calculated.

Results

There was no difference in the Hounsfield Units of the tunnel walls and cortical bone of the proximal femur (893.48 ± 61.28 vs. 926.34 ± 58.43; p = 0.091). In each of the 3D models, the cancellous bone was the first structure to reach maximal stress. The compressive strength of the femur decreased with increasing thickness of the screw tunnel wall and decreased with increasing tunnel diameter. The femoral neck model with the inverted triangle screw tunnel arrangement had the highest compressive strength.

Discussion

The femoral neck with screw tunnels can withstand day-to-day stress without special intervention. For femoral neck fractures fixed with cannulated screws, inverted triangle screws are recommended; For a single screw tunnel in the femoral neck, the larger the diameter of the femoral neck internal screw channel, the weaker the load-bearing capacity of the femur.

Level of evidence

III; well-designed computational non-experimental study.

中文翻译：

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螺钉隧道对螺钉取出后股骨近端强度的影响：有限元分析

背景

股骨颈螺钉隧道的存在是股骨近端骨折患者取出内固定后的一个问题。螺钉隧道的存在对股骨强度的影响有多大以及是否需要使用辅助装置保护患者一直存在争议。本有限元分析的目的是确定 (1) 螺钉隧道是否影响股骨近端骨折内固定移除后的正常负重，(2) 哪些螺钉隧道参数影响整个股骨的负重能力。

假设

螺钉隧道的存在降低了股骨的承重能力，螺钉隧道的排列、直径和壁厚影响股骨的承重能力。

材料和方法

20例在我院接受手术治疗的股骨近端骨折患者被纳入研究。分析拆除内固定后股骨螺钉隧道壁的计算机断层扫描 (CT) 值。Mimics v16.0 和 Hypermesh v13.0 软件程序用于生成具有不同螺钉隧道数量、直径、厚度和排列的股骨近端的 3 维 (3D) 四面体有限元模型。 模拟了在股骨头上施加 600 N 垂直压力载荷的髋臼，并计算了每个模型中股骨各个部位的力。

结果

隧道壁和股骨近端皮质骨的亨斯菲尔德单位没有差异（893.48  ±  61.28 对 926.34  ±  58.43；p  =  0.091）。在每个 3D 模型中，松质骨是第一个达到最大应力的结构。股骨的抗压强度随着螺钉隧道壁厚度的增加而降低，并随着隧道直径的增加而降低。具有倒三角螺钉隧道布置的股骨颈模型具有最高的抗压强度。

讨论

带螺钉隧道的股骨颈无需特殊干预即可承受日常压力。对于空心螺钉固定的股骨颈骨折，推荐使用倒三角螺钉；对于股骨颈单螺钉通道，股骨颈内螺钉通道直径越大，股骨的承重能力越弱。

证据等级

三；精心设计的计算非实验研究。