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Finite Element Modeling of Stress Distribution in Intervertebral Spacers of Different Surface Geometries
Author(s) -
Lee Jae Hyup,
Baek MyongHyun,
Kim Young Eun,
Seo JunHyuk,
Song Dong Ryul,
Ryu HyunSeung,
Lee ChoonKi,
Chang BongSoon
Publication year - 2013
Publication title -
artificial organs
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.684
H-Index - 76
eISSN - 1525-1594
pISSN - 0160-564X
DOI - 10.1111/aor.12107
Subject(s) - finite element method , compressive strength , isosceles triangle , materials science , stress (linguistics) , fracture (geology) , composite material , structural engineering , mathematics , geometry , engineering , linguistics , philosophy
Intervertebral disc spacers using bioactive ceramics have been used to treat degenerative spinal disease. Tooth‐shaped spacers are commonly used to prevent migration, but there is a possibility of fracture when inserted or after insertion. Intervertebral disc spacers with either an isosceles triangle‐shaped tooth ( T 1) or a right triangle‐shaped tooth ( T 2) were used as a control group. The design factors for the experimental group were modified to prevent fractures induced by stress concentration, and the surfaces of the spacers were designed as either an isosceles triangle‐shaped valley ( V 1) or a right triangle‐shaped valley ( V 2). Linear analysis using finite element model ( FEM ) was performed, and V on M ises stress distribution was calculated by applying 1000 N of uniformly distributed load. Samples of the V 2 design were made with bioactive glass‐ceramics ( BGS ‐7) and evaluated for compressive strength, fatigue degree, and impact strength. V on M ises stress was highest at the first tooth from the posterior side for the control group and at the center for the experimental group. Compared with the control group, the experimental group showed 18.4% and 82.5% reduction ( V 1 vs. T 1 and V 2 vs. T 2, respectively) in the maximum stress at the bottom of the valleys. The FEM analysis revealed that the V 2 design had the most even load distribution. The V 2 samples with bioactive glass‐ceramics were evaluated for compressive strength, and all six samples were not fractured up to 24 000 N. However, the average impact strength was 19.42 kN, suggesting that momentary force caused damage at a lower load than compression with a steady speed. The BGS ‐7 intervertebral disc spacer with V 2 design was not fractured during the fatigue test at maximum pressure of 8000 N, R ≥10, 5 Hz, and 5 million cycles. These data confirm that the BGS ‐7 spacer with the V 2 design may be clinically applicable. Collectively, the modified surface geometry of the experimental group significantly lowered V on M ises stress values at the bottom of the valleys, and thus the possibility of fracture by compressive load was greatly reduced. Also, impact during insertion was confirmed to cause fracture more easily, as the impact strength was lower than the compressive strength in the experimental group.