Investigation of toggling effect on pullout performance of pedicle screws

Abstract

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.

Technical Note: Pedicle Cement Augmentation with Proximal Screw Toggle and Loosening

“…Standalone comparison of expandable pedicle screws with standard pedicle screws demonstrated the former has a greater peak pullout force. Aycan et al suggested due to toggling and the brittleness of PMMA, expandable pedicle screws with PEEK shell might be a better alternative in dynamic loading. Nevertheless, major complications such as the one reported here will further question the safety and efficacy of this technique.…”

How to improve the safety of bicortical pedicle screw insertion in the thoracolumbar vertebrae: analysis base on three-dimensional CT reconstruction of patients in the prone position

“…Clinicians wisely use bone cement augmentation, cortical bone channels, expandable pedicle and novel screw fixation. These new techniques have achieved satisfactory clinical results for the osteoporosis patient [ 8 , 15 – 18 ]. But for patients with non-severe osteoporosis, especially those in the middle-aged and elderly with a certain amount of bone loss, surgical techniques that increase the strength of internal fixation may be a better option, particularly in increasing the diameter of the pedicle screw, the depth necessary for insertion, and the insertion angle show an advantage [ 19 , 20 ].…”

Pullout Strength Predictor: A Machine Learning Approach

“…Finite element analysis, cadaver experiments and testing on novel surrogate bone models can be incorporated into the database [29]. Additional failure mechanism such as cyclic loading and toggling can be investigated to represent the in vivo condition [30].…”