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Published on: May 31, 2017
Investigation of pullout strength in different designs of pedicle screws for osteoporotic bone quality using finite
Shih-Chieh Yang1, Pao-Hsin Liu2, Yuan-Kun Tu1
1Department of Orthopedic Surgery, E-Da Hospital, I-Shou University, Kaohsiung City, Taiwan.
Purpose:
The purpose of this study was to investigate pullout strength of three types of pedicle screws with and without cement augmentation in osteoporotic bone using finite element analysis.
Methods:
Twelve 3D finite element models were created to investigate the effect of pullout strength when comparing between pedicle screw types and bone cement clouds. The bottom side of bone block model was constrained and U-shape head was applied 1 mm in direction of longitudinal axis of pedicle screw to perform pullout resistance. The material properties of the FEA was set as linear elastic, homogenous, isotropic condition. The element sensitivity of convergence testing has been performed and variation of the sequential analytical results was less than 3%.
Results:
The results showed that the maximum total reaction force (133.8 N) was detected in the model of cannulated pedicle screw combined with a central pin with 4 ml cement augmentation, but, in contrast, the minimum total reaction force (106.8 N) was discovered in the model of cannulated pedicle screw without cement. A strong relationship (r = 0.9626) is found in comparison with the biomechanical results between pullout strength of sawbone testing and reaction forces of the FEA.
Conclusions:
The study concludes that the cannulated pedicle screw can not only provide an inner guider for cement flow and increase bending resistance (deflection effect) when a central pin is selected, but also can improve the pullout strength in the osteoporotic bone to add cement augmentation. The design of the cannulated pedicle screw is suggested for poor bone quality to change pullout failure.
