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Research article
Traditional and Cortical Trajectory Screws of Static and Dynamic Lumbar Fixation- A Finite Element Study
Shang-Chih Lin
National Taiwan University of Science and Technology
Corresponding Author
ORCiD: https://orcid.org/0000-0002-9135-5469
License:
This work is licensed under a CC BY 4.0 License. Read Full License
View the published version at BMC Musculoskeletal Disorders.
Background: Two types of screw trajectories are commonly used in lumbar surgery. Both traditional trajectory (TT) and cortical bone trajectory (CBT) were shown to provide equivalent pull-out strengths of a screw. CBT utilizing a laterally-directed trajectory engaging only cortical bone in the pedicle is widely used in minimal invasive spine posterior fusion surgery. It has been demonstrated that CBT exerts a lower likelihood of violating the facet joint, and superior pull-out strength than the TT screws, especially in osteoporotic vertebral body. No design yet to apply this trajectory to dynamic fixation. To evaluate kinetic and kinematic behavior in both static and dynamic CBT fixation a finite element study was designed. This study aimed to simulate the biomechanics of CBT-based dynamic system for an evaluation of CBT dynamization.
Methods: A validated nonlinearly lumbosacral finite-element model was used to simulate four variations of screw fixation. Responses of both implant (screw stress) and tissues (disc motion, disc stress, and facet force) at the upper adjacent (L3-L4) and fixed (L4-L5) segments were used as the evaluation indices. Flexion, extension, bending, and rotation of both TT and CBT screws were simulated in this study for comparison.
Results: The results showed that the TT static was the most effective stabilizer to the L4-L5 segment, followed by CBT static, TT dynamic, and the CBT dynamic, which was the least effective. Dynamization of the TT and CBT fixators decreased stability of the fixed segment and alleviate adjacent segment stress compensation. The 3.5-mm diameter CBT screw deteriorated stress distribution and rendered it vulnerable to bone-screw loosening and fatigue cracking.
Conclusions: Modeling the effects of TT and CBT fixation in a full lumbosacral model suggest that dynamic TT provide slightly superior stability compared with dynamic CBT especially in bending and rotation. In dynamic CBT design, large diameter screws might avoid issues with loosening and cracking.
Keywords
pedicle, cortical bone trajectory, lumbar instability, adjacent segment degeneration, finite-element analysis
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CURRENT STATUS: Published
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Posted 12 Jun, 2020
Published
On 14 Jul, 2020
No community comments so far
Editor assigned
On 08 Jun, 2020
Submission checks complete
On 07 Jun, 2020
Editor invited
On 07 Jun, 2020
No comments provided
Editorial decision: Minor revision
On 04 Jun, 2020
Editor assigned
On 19 May, 2020
Submission checks complete
On 18 May, 2020
Editor invited
On 18 May, 2020
No comments provided
Editorial decision: Major revision
On 14 May, 2020
Review #2 received
Received 30 Apr, 2020
Reviewer #2 agreed
On 22 Apr, 2020
Reviewer #1 agreed
On 12 Mar, 2020
Review #1 received
Received 12 Mar, 2020
Reviewers invited
Invitations sent on 05 Mar, 2020
Editor assigned
On 23 Feb, 2020
Submission checks complete
On 22 Feb, 2020
Editor invited
On 22 Feb, 2020
No comments provided
Review #4 received
Received 01 Feb, 2020
Review #3 received
Received 01 Feb, 2020
Review #2 received
Received 01 Feb, 2020
Editorial decision: Major revision
On 01 Feb, 2020
Reviewer #5 agreed
On 12 Jan, 2020
Reviewer #4 agreed
On 22 Nov, 2019
Reviewer #3 agreed
On 19 Nov, 2019
Review #1 received
Received 19 Nov, 2019
Reviewer #1 agreed
On 18 Nov, 2019
Reviewer #2 agreed
On 18 Nov, 2019
Reviewers invited
Invitations sent on 17 Nov, 2019
Editor assigned
On 05 Nov, 2019
First submitted
On 04 Nov, 2019
Submission checks complete
On 04 Nov, 2019
Editor invited
On 04 Nov, 2019
Metrics
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PDF Downloads: ...
HTML Views: ...
Subject Areas
Orthopedic Surgery
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This preprint is under consideration at BMC Musculoskeletal Disorders. A preprint is a preliminary version of a manuscript that has not completed peer review at a journal. Research Square does not conduct peer review prior to posting preprints. The posting of a preprint on this server should not be interpreted as an endorsement of its validity or suitability for dissemination as established information or for guiding clinical practice.
Learn more about In Review
Research article
Traditional and Cortical Trajectory Screws of Static and Dynamic Lumbar Fixation- A Finite Element Study
Shang-Chih Lin
National Taiwan University of Science and Technology
Corresponding Author
ORCiD: https://orcid.org/0000-0002-9135-5469
Badges
Prescreen
This manuscript passed our Prescreen assessment
Complete author information
Appropriate declaration statements
Potential risks to human health
Prescreen
Peer Review Timeline
CURRENT STATUS: Published
Version 4
Posted 12 Jun, 2020
Published
On 14 Jul, 2020
No community comments so far
Editor assigned
On 08 Jun, 2020
Submission checks complete
On 07 Jun, 2020
Editor invited
On 07 Jun, 2020
No comments provided
Editorial decision: Minor revision
On 04 Jun, 2020
Editor assigned
On 19 May, 2020
Submission checks complete
On 18 May, 2020
Editor invited
On 18 May, 2020
No comments provided
Editorial decision: Major revision
On 14 May, 2020
Review #2 received
Received 30 Apr, 2020
Reviewer #2 agreed
On 22 Apr, 2020
Reviewer #1 agreed
On 12 Mar, 2020
Review #1 received
Received 12 Mar, 2020
Reviewers invited
Invitations sent on 05 Mar, 2020
Editor assigned
On 23 Feb, 2020
Submission checks complete
On 22 Feb, 2020
Editor invited
On 22 Feb, 2020
No comments provided
Review #4 received
Received 01 Feb, 2020
Review #3 received
Received 01 Feb, 2020
Review #2 received
Received 01 Feb, 2020
Editorial decision: Major revision
On 01 Feb, 2020
Reviewer #5 agreed
On 12 Jan, 2020
Reviewer #4 agreed
On 22 Nov, 2019
Reviewer #3 agreed
On 19 Nov, 2019
Review #1 received
Received 19 Nov, 2019
Reviewer #1 agreed
On 18 Nov, 2019
Reviewer #2 agreed
On 18 Nov, 2019
Reviewers invited
Invitations sent on 17 Nov, 2019
Editor assigned
On 05 Nov, 2019
First submitted
On 04 Nov, 2019
Submission checks complete
On 04 Nov, 2019
Editor invited
On 04 Nov, 2019
Metrics
Comments: 0
PDF Downloads: ...
HTML Views: ...
Subject Areas
Orthopedic Surgery
License:
This work is licensed under a CC BY 4.0 License. Read Full License
View the published version at BMC Musculoskeletal Disorders.
Background: Two types of screw trajectories are commonly used in lumbar surgery. Both traditional trajectory (TT) and cortical bone trajectory (CBT) were shown to provide equivalent pull-out strengths of a screw. CBT utilizing a laterally-directed trajectory engaging only cortical bone in the pedicle is widely used in minimal invasive spine posterior fusion surgery. It has been demonstrated that CBT exerts a lower likelihood of violating the facet joint, and superior pull-out strength than the TT screws, especially in osteoporotic vertebral body. No design yet to apply this trajectory to dynamic fixation. To evaluate kinetic and kinematic behavior in both static and dynamic CBT fixation a finite element study was designed. This study aimed to simulate the biomechanics of CBT-based dynamic system for an evaluation of CBT dynamization.
Methods: A validated nonlinearly lumbosacral finite-element model was used to simulate four variations of screw fixation. Responses of both implant (screw stress) and tissues (disc motion, disc stress, and facet force) at the upper adjacent (L3-L4) and fixed (L4-L5) segments were used as the evaluation indices. Flexion, extension, bending, and rotation of both TT and CBT screws were simulated in this study for comparison.
Results: The results showed that the TT static was the most effective stabilizer to the L4-L5 segment, followed by CBT static, TT dynamic, and the CBT dynamic, which was the least effective. Dynamization of the TT and CBT fixators decreased stability of the fixed segment and alleviate adjacent segment stress compensation. The 3.5-mm diameter CBT screw deteriorated stress distribution and rendered it vulnerable to bone-screw loosening and fatigue cracking.
Conclusions: Modeling the effects of TT and CBT fixation in a full lumbosacral model suggest that dynamic TT provide slightly superior stability compared with dynamic CBT especially in bending and rotation. In dynamic CBT design, large diameter screws might avoid issues with loosening and cracking.
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8