Biomechanical comparison of sagittal-parallel versus non-parallel pedicle screw placement.

Autor: Farshad, Mazda, Farshad-Amacker, Nadja, Bachmann, Elias, Snedeker, Jess, Schmid, Samuel
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Zdroj: Acta Neurochirurgica; Nov2014, Vol. 156 Issue 11, p2147-2151, 5p, 2 Color Photographs, 3 Black and White Photographs, 2 Charts
Abstrakt: 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. [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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