Article Figures & Data
Figures
- Figure 1
Illustration of the fenestrated screw designs and cement types used in the different experimental groups for the study. All the titanium alloy Everest screws are designed such that their inner diameters measure 1.8 mm, with each fenestration measuring 1.6 mm. The 2 Teknimed polymethylmethacrylate cements vary in their viscosity. There are 6 possible combinations of fenestration design and cement viscosity.
- Figure 2
Illustrative example of specimen preparation for experimental testing of relationship between fenestrated pedicle screw design and cement plume geometry on pullout forces, conducted in (A) foam blocks and (B) vertebral specimens. Foam blocks with the density of cancellous bone were encased in plastic, prior to being instrumented with 1 of 3 fenestrated pedicle screw designs from Everest. Cadaveric vertebra were bilaterally instrumented with the same screw type; one side was augmented with cement, while the other side was left uncemented and used as a control. Test screws within the foam and vertebral specimens were augmented with Teknimed polymethylmethacrylate cements of medium and high viscosity.
- Figure 3
Experimental setup for pullout testing of different fenestrated pedicle screw designs from instrumented foam blocks and vertebral specimens. (A) The foam blocks and potted vertebra were fixed to the base of an Instron E10000 universal testing machine, with a vice yielding 3° of rotational freedom, which permitted coaxial alignment of the screw axis with the axis of the pullout force. (B) A Jacobs chuck was used to grip the screw head. The chuck was fixed to the Instron loadcell via 2 universal joints to limit motion artifact. The loadcell was connected to the Instron linear actuator. All screws were pulled out at a displacement rate of 5 mm/min. (C and C2) Illustrative example of an instrumented vertebral specimen undergoing pullout testing.
- Figure 4
Effect of polymethylmethacrylate (PMMA) cement augmentation on pullout loads of fenestrated pedicle screws when tested in foam blocks. Tests were conducted with 3 different screw designs manufactured by Everest with varying fenestration distribution and Teknimed PMMA cements of medium and high viscosity.
- Figure 5
Scatterplot demonstrating a significant correlation between lateral plume diameter and pullout strength when tested within foam blocks (coefficient = 0.386, P = 0.02).
- Figure 6
Vertebral body testing: Effect of cement augmentation with Teknimed F20 or hV on 3 different fenestrated screw designs when tested within lumbar vertebra. In all but the XP1152-15 (design 3) with F20 group, cementation resulted in a statistically significant increase in pullout forces when compared with a matched control. The mean difference between test and control is represented with 95% CI. (*P < 0.05).
- Figure 7
Vertebral testing: Correlation scatterplots of variables in pedicle screw instrumentation of 3 different screw designs, anterior-posterior (A/P) plume diameter, screw insertion angle, and vertebral body width were found to significantly correlate with pullout strength. (A) A/P plume diameter and pullout strength (coefficient = −0.420, P = 0.011); (B) screw insertion angle and pullout strength (coefficient = 0.381, P = 0.022); and (C) body width and pullout strength (coefficient = 0.395, P = 0.017).
- Figure 8
Illustrative examples of computed tomography-guided dimensional analysis of cement plume geometry formed with 3 different Everest fenestrated screw designs and 2 viscosities of Teknimed polymethylmethacrylate cement. Medium-viscosity (F20) plumes are represented in the top row (A–C); high-viscosity plumes (hV) are shown in the bottom row (D–F). Only design 2 demonstrated a consistently confined cement plume, with purchase toward the cortical bone of the vertebra, without anterograde or retrograde leak. Cement viscosity was not found to influence the plume distribution.
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