Bending strength and stress distribution of the interlocking intramedullary nails with high-thread wooden club-shaped nails versus traditional nails

doi:10.3969/j.issn.2095-4344.2017.23.016

Abstract

Abstract:

BACKGROUND: Interlocking intramedullary nailing is a main method for bone fractures, but traditional static intramedullary nails usually lead to nail breakage and loosening. Thereafter, we design a novel high-thread wooden club-shaped screw (HTWCSS) and explore its mechanical properties.

OBJECTIVE: To measure the bend strengths of HTWCSS, analyze its stress distribution, and to evaluate its biomechanical properties, thereby providing theoretical basis for its clinical application.

METHODS: The bend strength of HTWCSS and traditional nails were measured via three-point bending experiments. Transverse fractures of the middle tibia were simulated using finite element method, and then the force and stress distribution of the two different nails were analyzed.

RESULTS AND CONCLUSION: (1) The average maximum load of HTWCSS was 3.52 kN and 1.81 kN at span of 20 mm and 30 mm, respectively, which were larger than those of the traditional nails. (2) The average maximum displacement and the stress of HTWCSS were smaller than those of the traditional screws in finite element analysis, and the stress distribution was relatively dispersed. (3) The average maximum axial displacement and stress HTWCSS, traditional interlocking screws, wooden club-shaped screws and traditional screws were 131 MPa and 3.27 mm, 162 MPa and 4.07 mm, 26.5 MPa and 0.323 mm, and 34.3 MPa and 0.407 mm, respectively. (4) These results suggest that HTWCSS has relative high bend strength, and it is able to disperse stress and improve fatigue strength bend strength, further reduce screw broken.

中国组织工程研究杂志出版内容重点：人工关节；骨植入物；脊柱；骨折；内固定；数字化骨科；组织工程

Key words: Bone Nails, Finite Element Analysis, Biomechanics, Tissue Engineering

CLC Number:

R318

Xia Guan-ping, Wang Yong-qing, Dong Li-min, Liu Lei, Dong Yan-sheng, Wang Ye-lin. Bending strength and stress distribution of the interlocking intramedullary nails with high-thread wooden club-shaped nails versus traditional nails[J]. Chinese Journal of Tissue Engineering Research, 2017, 21(23): 3700-3705.

Figures/Tables 1

2.1 三点弯曲实验结果从实验结果可知，HTWCSS在跨度为20 mm和30 mm时能承受的平均最大载荷分别为3.52 kN和1.81 kN，均比通用锁钉承受的载荷要大，由于锁钉在骨折固定中的受力情况与工程问题上的简支梁相似，都是两端支撑中间受力的结构。由材料力学知识可知弯曲正应力是影响弯曲强度的主要因素。根据弯曲应力的计算公式如下： σ=My/Iz，或者σ=My/Iz=Fdy/Iz，在一般情况下，梁的最大正应力发生在弯矩最大的截面上，且距中性轴最远之处，其值为σmax=Mmaxymax/Iz，式中σ为横截面上任意一点处的应力，F为水平截面上承受的法向力，在这里为承受的载荷，Iz为截面惯性矩Iz=πd3/64，y为该点到中性轴的距离，在这里中性轴为螺钉的中轴线，由此可知应力法向压力成正比，由公式可知在其他条件一样的情况下，力越大，应力就越大。因而在同一挠度变形下前者HTWCSS比通用螺钉具有更高的抗弯曲强度。当HTWCSS的挠度到达一定程度时螺纹的丝底会发生裂缝，而通用锁钉相对能够发生较大的挠度变形而不发生破坏。实验中2种长度的两种锁钉载荷-位移平均值曲线见图3。 2.2 有限元分析结果从有限元分析得出的数据可知，两种模型在轴向载荷分别为250，500，1 000和1 500 N时，胫骨平台与锁钉的轴向最大位移值和最大应力值均依次变大。而使用HTWCSS的胫骨骨折模型比使用通用锁钉的轴向最大位移和最大应力值要小。而两种模型中，HTWCSS的最大位移和最大应力值也比通用锁钉的小，且其应力分布呈现的比后者也相对分散。其具体轴向最大位移结果见图4A，具体最大应力值见图4B。本实验中髓内钉与锁钉应力集中在远端第一锁钉处，HTWCSS与通用螺钉的有很大的区别，其具体平均最大位移见图4A，平均最大应力值见图4B。其中HTWCSS平均最大应力值为26.5 MPa，轴向平均最大位移为0.323 mm；通用锁钉平均最大应力值为34.3 MPa，轴向平均最大位移为0.407 mm。而使用HTWCSS的带锁髓内钉模型平均最大应力值为131 MPa，轴向平均最大位移为3.27 mm，使用通用锁钉的带锁髓内钉模型平均最大应力值为162 MPa，轴向平均最大位移为4.07 mm；以上结果表明在负载作用下HTWCSS比通用锁钉应力不易集中，抗疲劳性强，抗弯曲强度更高，对带锁髓内钉固定稳定性更可靠。髓内钉及锁钉的应力分布情况见图5，6。"

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