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Impact of augmentation strategies on the failure of pedicle screws beneath cranio-caudal cyclic loading.

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Impact of augmentation strategies on the failure of pedicle screws beneath cranio-caudal cyclic loading.

Eur Backbone J. 2017 Jan;26(1):181-188

Authors: Bostelmann R, Keiler A, Steiger HJ, Scholz A, Cornelius JF, Schmoelz W

Summary
PURPOSE: Augmentation of pedicle screws is really useful in chosen indications (as an illustration: osteoporosis). Usually, there are two strategies for pedicle screw augmentation: inserting the screw within the non cured cement and in situ-augmentation with cannulated fenestrated screws, which may be utilized percutaneously. A lot of the printed research used an axial pull out take a look at for analysis of the pedicle screw anchorage. Nonetheless, the loading and the failure mode of pullout checks don’t simulate the cranio-caudal in vivo loading and failure mechanism of pedicle screws. The aim of the current research was to evaluate the fixation results of various augmentation strategies (together with percutaneous cement utility) and to research pedicle screw loosening beneath physiological cyclic cranio-caudal loading.
METHODS: Every of the 2 take a look at teams consisted of 15 vertebral our bodies (L1-L5, three of every stage per group). Imply age was 84.three years (SD 7.eight) for group 1 and 77.zero years (SD 7.00) for group 2. Imply bone mineral density was 53.three mg/cm3 (SD 14.1) for group 1 and 53.2 mg/cm3 (SD four.three) for group 2. 1.5 ml excessive viscosity PMMA bone cement was used for all augmentation strategies. For take a look at group 1, pedicles on the proper facet of the vertebrae have been instrumented with strong pedicle screws in normal vogue with out augmentation and served as management group. Left pedicles have been instrumented with cannulated screws (Viper cannulated, DePuy Backbone) and augmented. For take a look at group 2 pedicles on the left facet of the vertebrae have been instrumented with cannulated fenestrated screws and in situ augmented. On the proper facet strong pedicle screws have been augmented with cement first approach. Every screw was subjected to a cranio-caudal cyclic load beginning at 20-50 N with growing higher load magnitude of zero.1 N per cycle (1 Hz) for a most of 5000 cycles or till complete failure. Stress X-rays have been taken after cyclic loading to guage screw loosening.
RESULTS: Take a look at group 1 confirmed a major increased variety of load cycles till failure for augmented screws in comparison with the management (4030 cycles, SD 827.eight vs. 1893.three cycles, SD 1032.1; p < zero.001). Stress X-rays revealed vital much less screw toggling for the augmented screws (5.2°, SD 5.four vs. 16.1°, SD 5.9; p < zero.001). Take a look at group 2 confirmed 3653.three (SD 934) and 3723.three (SD 560.6) load cycles till failure for in situ and cement first augmentation. Stress X-rays revealed a screw toggling of 5.1 (SD 1.9) and 6.6 (SD four.6) levels for in situ and cement first augmentation strategies (p > zero.05).
CONCLUSION: Augmentation of pedicle screws typically considerably elevated the variety of load cycles and failure load evaluating to the nonaugmented management group. For the augmentation approach (cement first, in situ augmented, percutaneously utility) no impact might be exhibited on the failure of the pedicle screws. By the cranio-caudal cyclic loading failure of the pedicle screws occurred by screw lower by way of the superior endplate and the attribute “windshield-wiper impact”, usually noticed in scientific apply, might be reproduced.

PMID: 25813011 [PubMed – indexed for MEDLINE]

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