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Impact of augmentation methods on the failure of pedicle screws below cranio-caudal cyclic loading.

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Impact of augmentation methods on the failure of pedicle screws below 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 (for example: osteoporosis). Typically, there are two methods for pedicle screw augmentation: inserting the screw within the non cured cement and in situ-augmentation with cannulated fenestrated screws, which could be utilized percutaneously. Many of the printed research used an axial pull out check for analysis of the pedicle screw anchorage. Nevertheless, the loading and the failure mode of pullout exams don’t simulate the cranio-caudal in vivo loading and failure mechanism of pedicle screws. The aim of the current examine was to evaluate the fixation results of various augmentation methods (together with percutaneous cement software) and to research pedicle screw loosening below physiological cyclic cranio-caudal loading.
METHODS: Every of the 2 check teams consisted of 15 vertebral our bodies (L1-L5, three of every degree 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 methods. For check group 1, pedicles on the correct facet of the vertebrae had been instrumented with strong pedicle screws in commonplace style with out augmentation and served as management group. Left pedicles had been instrumented with cannulated screws (Viper cannulated, DePuy Backbone) and augmented. For check group 2 pedicles on the left facet of the vertebrae had been instrumented with cannulated fenestrated screws and in situ augmented. On the correct facet strong pedicle screws had 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 had been taken after cyclic loading to judge screw loosening.
RESULTS: Take a look at group 1 confirmed a big greater 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 important 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 methods (p > zero.05).
CONCLUSION: Augmentation of pedicle screws on the whole 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 software) no impact may very well be exhibited on the failure of the pedicle screws. By the cranio-caudal cyclic loading failure of the pedicle screws occurred by screw minimize via the superior endplate and the attribute “windshield-wiper impact”, usually noticed in medical apply, may very well be reproduced.

PMID: 25813011 [PubMed – indexed for MEDLINE]

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