Objective of this study is to assess the pullout performance of various pedicle screws in different test materials after toggling tests comparatively. Solid core, cannulated (cemented), novel expandable and solid-core (cemented) pedicle screws were instrumented to the polyurethane foams (Grade 10 and Grade 40) produced in laboratory and bovine vertebra. ASTM F543 standard was used for preparation process of samples. Toggling tests were carried out. After toggling test procedures, pullout tests were performed. Load versus displacement graph was recorded, and the ultimate pullout force was defined as the maximum load (pullout strength) sustained before failure of screw. Anteriosuperior and oblique radiographs were taken from each sample after instrumentation in order to examine screw placement and cement distribution. The pullout strength of pedicle screws decreased after toggling tests with respect to the initial condition. While the cemented solid-core pedicle screws had the highest pullout strength in all test materials, they had the highest strength differences. The cemented solid-core pedicle screws had decrement rates of 27% and 16% in Grade 10 and Grade 40, respectively. There are almost same decrement rate (between 5.5% and 6.5%) for all types of pedicle screws instrumented to the samples of bovine vertebra. The pullout strengths of novel expandable pedicle screws in both of early period and after toggling conditions were almost similar, in other words, the decrement rates of it were lower than other types. According to the data collected from this study, polymethylmethacrylate augmentation significantly decreases pullout strength following the toggling loads. Higher brittleness of cured polymethylmethacrylate has adverse effect on the pullout strength. Although augmentation is an important process for enhancing pullout strength in early period, it has some disadvantages for preserving stabilization in a long time. Expandable pedicle screw with polyetheretherketone shell may be good alternative to polymethylmethacrylate augmentation on both primer stabilization and long-term loading application with toggling.
Isolated 9th and 10th cranial nerve palsies following OCF are very rare. To our knowledge, we report the first case of an early onset of 9th and 10th cranial nerve palsies with an early full recovery in short period of time and discuss the probable mechanism of isolated nerve palsy in the light of the relevant literature.
Pedicle screws are the main fixation devices for certain surgeries. Pedicle screw loosening is a common problem especially for osteoporotic incidents. Cannulated screws with cement augmentation are widely used for that kind of cases. Dual lead dual cored pedicle screw has already given promising pullout values without augmentation. This study concentrates on the usage of dual lead dual core with cement augmentation as an alternative to cannulated and standard pedicle screws with cement augmentation. Five groups (dual lead dual core, normal pedicle screw and cannulated pedicle screw with augmentation, normal pedicle screw, dual lead dual cored pedicle screw) were designed for this study. Healthy bovine vertebrae and synthetic polyurethane foams (grade 20) were used as embedding test medium. Test samples were prepared in accordance with surgical guidelines and ASTM F543 standard testing protocols. Pullout tests were conducted with Instron 3300 testing frame. Load versus displacement values were recorded and maximum pullout loads were stated. The dual lead dual cored pedicle screw with poly-methyl methacrylate augmentation exhibited the highest pullout values, while dual lead dual cored pedicle screw demonstrated similar pullout strength as cannulated pedicle screw and normal pedicle screw with poly-methyl methacrylate augmentation. The dual lead dual cored pedicle screw with poly-methyl methacrylate augmentation can be used for osteoporotic and/or severe osteoporotic patients according to its promising results on animal cadaver and synthetic foams.
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