Abstract
ABSTRACT Objective: To evaluate the insertion torque and the pulling force of each screw with different diameters and tap. Methods: Polyurethane blocks with a pilot hole of 2.7 mm were used in the study. An experimental group with 5 blocks was formed, the insertion torque was evaluated with a torque meter, and the pullout strength of each Globus screw of 5.5 mm and 6.5 mm was assessed. Results: The comparison of the insertion torque on the 5.5 mm screws with pilot hole without tapping and with a smaller diameter than that of the screw (4.5 mm) and a different thread, and with the tapping with the same diameter as that of the screw (5.5 mm) and equal or different thread presented a statistical difference with a higher value of the insertion torque in the group in which the tapping was not performed. As for the pulling force of the 5.5 mm screw, the non-tapping of the pilot hole resulted in statistical difference with the same diameter of the screw (5.5 mm) and with a different thread of the screw. The pullout force on the 6.5 mm screw was higher in the group where the pilot hole was not tapped according to the non-parametric Kruskal-Wallis test, with significance level of p <0.05 in the comparison of the groups. Conclusions: Pilot hole tapping reduced insertion torque and pullout resistance of the pedicle screw influencing the fixation with tapping with the same screw diameter and different thread design.
Highlights
Spinal fixation systems that use the vertebral pedicle as the implant anchor point have been used extensively in the spinal surgery environment.[1]
The insertion torque and the pullout strength of pedicle screws is influenced by different factors, such as bone mineral density, screw geometry, and pilot hole preparation.[2,3,4]
The insertion torque and pullout strength values of the 5.5 mm and 6.5 mm screws are shown in Table 1 and in Figures 3 and 6
Summary
Spinal fixation systems that use the vertebral pedicle as the implant anchor point have been used extensively in the spinal surgery environment.[1]. Tapping consists of using a tool to cut the inner surface of the pilot hole for the adaptation of the screw thread. This technical step for the placement of screws in the bones originated from osteosynthesis of the long bones and was adapted for spine surgery. Another variable that has been evaluated is tap thread design and it has been observed that the use of a tap with thread design different from the screw thread design, even though of smaller diameter in relation to the outer diameter of the screw, causes a reduction in the pullout strength of the implants
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