The influence of the insertion technique on the pullout force of pedicle screws: An experimental study

Panagiotis E. Chatzistergos, George Sapkas, Stavros K. Kourkoulis (Lead / Corresponding author)

Research output: Contribution to journalArticlepeer-review

43 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)E332-E337
Number of pages6
JournalSpine
Volume35
Issue number9
DOIs
Publication statusPublished - Apr 2010

Keywords

  • Insertion technique
  • Pedicle screw
  • Pullout force
  • Self tapping

ASJC Scopus subject areas

  • Orthopedics and Sports Medicine
  • Clinical Neurology

Fingerprint

Dive into the research topics of 'The influence of the insertion technique on the pullout force of pedicle screws: An experimental study'. Together they form a unique fingerprint.

Cite this