Biomechanical comparison of sagittal-parallel versus non-parallel pedicle screw placement
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Date
2014-11
Publication Type
Journal Article
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yes
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Abstract
Background
While convergent placement of pedicle screws in the axial plane is known to be more advantageous biomechanically, surgeons intuitively aim toward a parallel placement of screws in the sagittal plane. It is however not clear whether parallel placement of screws in the sagittal plane is biomechanically superior to a non-parallel construct. The hypothesis of this study is that sagittal non-parallel pedicle screws do not have an inferior initial pull-out strength compared to parallel placed screws.
Methods
The established lumbar calf spine model was used for determination of pull-out strength in parallel and non-parallel intersegmental pedicle screw constructs. Each of six lumbar calf spines (L1-L6) was divided into three levels: L1/L2, L3/L4 and L5/L6. Each segment was randomly instrumented with pedicle screws (6/45 mm) with either the standard technique of sagittal parallel or non-parallel screw placement, respectively, under fluoroscopic control. CT was used to verify the intrapedicular positioning of all screws. The maximum pull-out forces and type of failure were registered and compared between the groups.
Results
The pull-out forces were 5,394 N (range 4,221 N to 8,342 N) for the sagittal non-parallel screws and 5,263 N (range 3,589 N to 7,554 N) for the sagittal-parallel screws (p = 0.838). Interlevel comparisons also showed no statistically significant differences between the groups with no relevant difference in failure mode.
Conclusion
Non-parallel pedicle screws in the sagittal plane have at least equal initial fixation strength compared to parallel pedicle screws in the setting of the here performed cadaveric calf spine experiments.
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Publication status
published
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Journal / series
Volume
156 (11)
Pages / Article No.
2147 - 2151
Publisher
Springer
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Edition / version
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Date collected
Date created
Subject
Biomechanical comparison; Sagittal non-parallel; Pedicle screw; Pull-out force
Organisational unit
03822 - Snedeker, Jess G. / Snedeker, Jess G.
Notes
It was possible to publish this article open access thanks to a Swiss National Licence with the publisher.