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Research Papers

Comparison of Pedicle Screw Loosening Mechanisms and the Effect on Fixation Strength

[+] Author and Article Information
Hedayeh Mehmanparast

Mechanical Engineering Department,
École de Technologie Superieure,
1100 Notre-Dame Street,
West Montreal, QC H3C 1K3, Canada;
Research Center,
Hôpital Sacré-Coeur de Montréal,
5400 Gouin Boulevard,
West Montreal, QC H4J 1C5, Canada
e-mail: hedayeh.mehmanparast-nodehi.1@ens.etsmtl.ca

Yvan Petit

Mechanical Engineering Department,
École de Technologie Superieure,
1100 Notre-Dame Street,
West Montreal, QC H3C 1K3, Canada;
Research Center,
Hôpital Sacré-Coeur de Montréal,
5400 Gouin Boulevard,
West Montreal, QC H4J 1C5, Canada
e-mail: yvan.petit@etsmtl.ca

Jean-Marc Mac-Thiong

Research Center,
Hôpital Sacré-Coeur de Montréal,
5400 Gouin Boulevard,
West Montreal, QC H4J 1C5, Canada;
Department of Surgery,
Université de Montréal,
2900 Éduard-Montpetit Boulevard,
Montreal, QC H3T 1C5, Canada
e-mail: macthiong@gmail.com

1Corresponding author.

Manuscript received April 2, 2015; final manuscript received October 12, 2015; published online October 27, 2015. Assoc. Editor: Tammy L. Haut Donahue.

J Biomech Eng 137(12), 121003 (Oct 27, 2015) (7 pages) Paper No: BIO-15-1144; doi: 10.1115/1.4031821 History: Received April 02, 2015; Revised October 12, 2015

Screw loosening is a common complication in spinal fixation using pedicle screws which may lead to loss of correction and revision surgery. The mechanisms of pedicle screw loosening are not well understood. The purpose of this study was to compare the pedicle screw pullout force and stiffness subsequent or not to multidirectional cyclic bending load (toggling). Pedicle screws inserted into porcine lumbar vertebrae underwent toggling in craniocaudal (CC), mediolateral (ML) directions, and no toggling (NT) before pullout. This study suggests that toggling and in particular CC toggling should be included in biomechanical evaluation of pedicle screw fixation strength.

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References

Figures

Grahic Jump Location
Fig. 1

Toggling test setup. Each specimen was secured in a custom fixture using polyester resin allowing change of orientation for (a) CC and (b) ML toggling.

Grahic Jump Location
Fig. 2

Pullout test setup. Each specimen was embedded in polyester resin and secured into custom fixture allowing alignment of pedicle screw head with the shackle gripped by the material testing system shaft for pullout.

Grahic Jump Location
Fig. 3

Pareto charts of the standardized effect of toggling mode and vertebral level on the pedicle screw: (a) pullout force and (b) stiffness. Vertical lines define the thresholds for significant effects (p < 0.05).

Grahic Jump Location
Fig. 4

Two-dimensional contour plot for (a) pullout force and (b) stiffness as a function of toggling modes and vertebral levels. The maximum pullout force was observed at L1 for NT mode whereas the minimum pullout force is shown at L3 for CC mode. The stiffness increased from L1 to L3 levels and from CC to NT modes.

Grahic Jump Location
Fig. 5

Comparison of pedicle screw: (a) pullout force and (b) stiffness between CC, ML, and NT toggling modes. Significant differences (P < 0.05) are shown by an asterisk (*). Error bars represent the standard deviations.

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