Impact of Screw Diameter and Length on Pedicle Screw Fixation Strength in Osteoporotic Vertebrae: A Finite Element Analysis

Biomechanical study. To quantitatively investigate the effect of screw size on screw fixation in osteoporotic vertebrae with finite element analysis (FEA). Osteoporosis poses a challenge in spinal instrumentation; however, the selection of screw size is directly related to fixation and is closely de...

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Bibliographic Details
Published in:Asian spine journal 2021, 15(5), , pp.566-574
Main Authors: Matsukawa, Keitaro, Yato, Yoshiyuki, Imabayashi, Hideaki
Format: Article
Language:English
Subjects:
Basic Study
Biomechanics
Bone density
Bone implants
Design optimization
Finite element analysis
Finite element method
fixation strength
Fractures
Load
Mechanical loading
Mechanical properties
Osteoporosis
pedicle screws
screw size
Spine
Surgery
Titanium alloys
Values
Vertebrae
정형외과학
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Summary:Biomechanical study. To quantitatively investigate the effect of screw size on screw fixation in osteoporotic vertebrae with finite element analysis (FEA). Osteoporosis poses a challenge in spinal instrumentation; however, the selection of screw size is directly related to fixation and is closely dependent on each surgeon's experience and preference. Total 1,200 nonlinear FEA with various screw diameters (4.5-7.5 mm) and lengths (30-50 mm) were performed on 25 patients (seven men and 18 women; mean age, 75.2±10.8 years) with osteoporosis. The axial pullout strength, and the vertebral fixation strength of a paired-screw construct against flexion, extension, lateral bending, and axial rotation were examined. Thereafter, we calculated the equivalent stress of the bone-screw interface during nondestructive loading. Then, using diameter parameters (screw diameter or screw fitness in the pedicle [%fill]), and length parameters (screw length or screw depth in the vertebral body [%length]), multiple regression analyses were performed in order to evaluate the factors affecting various fixations. Larger diameter and longer screws significantly increased the pullout strength and vertebral fixation strength; further, they decreased the equivalent stress around the screws. Multiple regression analyses showed that the actual screw diameter and %length were factors that had a stronger effect on the fixation strength than %fill and the actual screw length. Screw diameter had a greater effect on the resistance to screw pullout and flexion and extension loading (β =0.38-0.43, p
ISSN:1976-1902
1976-7846
DOI:10.31616/asj.2020.0353