PMID- 33662802
OWN - NLM
STAT- MEDLINE
DCOM- 20210514
LR  - 20210514
IS  - 1872-7565 (Electronic)
IS  - 0169-2607 (Linking)
VI  - 202
DP  - 2021 Apr
TI  - Homogenized finite element models can accurately predict screw pull-out in 
      continuum materials, but not in porous materials.
PG  - 105966
LID - S0169-2607(21)00041-9 [pii]
LID - 10.1016/j.cmpb.2021.105966 [doi]
AB  - BACKGROUND AND OBJECTIVE: Bone screw fixation can be estimated with several test 
      methods such as insertion torque, pull-out, push-in and bending tests. A basic 
      understanding of the relationship between screw fixation and bone microstructure 
      is still lacking. Computational models can help clarify this relationship. The 
      objective of the paper is to evaluate homogenized finite element (hFE) models of 
      bone screw pull-out. METHODS: Experimental pull-out tests were performed on three 
      materials: two polyurethane (PU) foams having a porous microstructure, and a high 
      density polyethylene (HDPE) which is a continuum material. Forty-five titanium 
      pedicle screws were inserted to 10, 20, and 30 mm in equally sized blocks of all 
      three materials (N = 5/group). Pull-out characteristics i.e. stiffness (S), yield 
      force (F(y)), peak pull-out force (F(ult)) and displacement at F(ult) (d(ult)) 
      were measured. hFE models were created replicating the experiments. The screw was 
      modeled as a rigid body and 5 mm axial displacement was applied to the head of 
      the screw. Simulations were performed evaluating two different conditions at the 
      bone-screw interface; once in which the screw fitted the pilot hole exactly 
      ("free-stressed") and once in which interface stresses resulting from the 
      insertion process were taken into account ("pre-stressed"). RESULTS: The 
      simulations representing the pre-stressed condition in HDPE matched the 
      experimental data well; S, F(y), and F(ult) differed less than 11%, 2% and 0.5% 
      from the experimental data, respectively, whereas d(ult) differed less than 16%. 
      The free-stressed simulations were less accurate, especially stiffness (158% 
      higher than the pre-stressed condition) and d(ult) (30% lower than pre-stressed 
      condition) were affected. The simulations representing PU did not match the 
      experiments well. For the 20 mm insertion depth, S, F(y) and F(ult) differed by 
      more than 104%, 89% and 66%, respectively from the experimental values. Agreement 
      did not improve for 10 and 30 mm insertion depths. CONCLUSIONS: We found that hFE 
      models can accurately quantify screw pull-out in continuum materials such as 
      HDPE, but not in materials with a porous structure, such as PU. Pre-stresses in 
      the bone induced by the insertion process cannot be neglected and need to be 
      included in the hFE simulations.
CI  - Copyright (c) 2021. Published by Elsevier B.V.
FAU - Einafshar, Mohammadjavad
AU  - Einafshar M
AD  - Biomechanical engineering group, Department of Biomedical Engineering, Amirkabir 
      University of Technology, Tehran, Iran.
FAU - Hashemi, Ata
AU  - Hashemi A
AD  - Biomechanical engineering group, Department of Biomedical Engineering, Amirkabir 
      University of Technology, Tehran, Iran. Electronic address: a.hashemi@aut.ac.ir.
FAU - van Lenthe, G Harry
AU  - van Lenthe GH
AD  - Biomechanics Section, Department of Mechanical Engineering, KU Leuven, Leuven, 
      Belgium. Electronic address: harry.vanlenthe@kuleuven.be.
LA  - eng
PT  - Journal Article
DEP - 20210207
PL  - Ireland
TA  - Comput Methods Programs Biomed
JT  - Computer methods and programs in biomedicine
JID - 8506513
SB  - IM
MH  - Biomechanical Phenomena
MH  - Finite Element Analysis
MH  - Materials Testing
MH  - *Pedicle Screws
MH  - Porosity
MH  - Torque
OTO - NOTNLM
OT  - Bone analog
OT  - Bone screw
OT  - Finite element method
OT  - Pre-stress modeling
OT  - Pull-out test
OT  - Simulation of screw insertion
COIS- Declaration of Competing Interest The authors report no conflicts of interest. 
      The authors alone are responsible for the content and writing of this article.
EDAT- 2021/03/05 06:00
MHDA- 2021/05/15 06:00
CRDT- 2021/03/04 20:18
PHST- 2020/12/07 00:00 [received]
PHST- 2021/01/28 00:00 [accepted]
PHST- 2021/03/05 06:00 [pubmed]
PHST- 2021/05/15 06:00 [medline]
PHST- 2021/03/04 20:18 [entrez]
AID - S0169-2607(21)00041-9 [pii]
AID - 10.1016/j.cmpb.2021.105966 [doi]
PST - ppublish
SO  - Comput Methods Programs Biomed. 2021 Apr;202:105966. doi: 
      10.1016/j.cmpb.2021.105966. Epub 2021 Feb 7.