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The Influence of the Insertion Technique on the Pullout Force of Pedicle Screws

CHATZISTERGOS, Panagiotis, SAPKAS, GEORGIOS and KOURKOULIS, STAVROS (2010) The Influence of the Insertion Technique on the Pullout Force of Pedicle Screws. Spine, 35 (9). E332-E337. ISSN 0362-2436

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Abstract or description

Study Design: The pullout strength of a typical pedicle screw was evaluated experimentally for different screw insertion techniques.

Objective: To conclude whether the self-tapping insertion technique is indeed the optimum one for self-tapping screws, with respect to the pullout strength.

Summary of Background Data. It is reported in the literature that the size of the pilot-hole significantly influences the pullout strength of a self-tapping screw. In addition it is accepted that an optimum value of the diameter of the pilot-hole exists. For non self-tapping screw insertion it is reported that undertapping of the pilot-hole can increase its pullout strength. Finally it is known that in some cases orthopedic surgeons open the threaded holes, using another screw instead of a tap.

Methods: A typical commercial self-tapping pedicle screw was inserted into blocks of Solid Rigid Polyurethane Foam (simulating osteoporotic cancellous bone), following different insertion techniques. The pullout force was measured according to the ASTM-F543–02 standard. The screw was inserted into previously prepared holes of different sizes, either threaded or cylindrical, to conclude whether an optimum size of the pilot-hole exists and whether tapping can increase the pullout strength. The case where the tapping is performed using another screw was also studied.

Results: For screw insertion with tapping, decreasing the outer radius of the threaded hole from 1.00 to 0.87 of
the screw’s outer radius increased the pullout force 9%. For insertion without tapping, decreasing the pilot-hole’s diameter from 0.87 to 0.47 of the screw’s outer diameter increased its pullout force 75%. Finally, tapping using another screw instead of a tap, gave results similar to those of conventional tapping.

Conclusion: Undertapping of a pilot-hole either using a tap or another screw can increase the pullout strength
of self-tapping pedicle screws.

Item Type: Article
Uncontrolled Keywords: pedicle screw, pullout force, insertion technique, self tapping.
Faculty: Previous Faculty of Health Sciences > Nursing and Midwifery
Depositing User: Panagiotis CHATZISTERGOS
Date Deposited: 11 Feb 2013 15:54
Last Modified: 24 Feb 2023 13:36
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