Comparison and prediction of pullout strength of conical and cylindrical pedicle screws within synthetic bone

Abstract

Background: This study was designed to derive the theoretical formulae to predict the pullout strength of pedicle screws with an inconstant outer and/or inner diameter distribution (conical screws). For the transpedicular fixation, one of the failure modes is the screw loosening from the vertebral bone. Hence, various kinds of pedicle screws have been evaluated to measure the pullout strength using synthetic and cadaveric bone as specimens. In the literature, the Chapman's formula has been widely proposed to predict the pullout strength of screws with constant outer and inner diameters (cylindrical screws).

Pullout characteristics of percutaneous pedicle screws with different cement augmentation methods in elderly spines: An in vitro biomechanical study

“…The instrumentation technique itself, using different screw insertion torques and screw insertion angles, play a role for pullout resistance [13,16,17]. Screw design parameters, such as screw diameter, length, conical or cylindrical shape and the thread, may also influence the pullout resistance [18,19]. In elderly specimens, these technical variables seem to have less influence compared to normal bone, especially if a cement augmentation method is used [5].…”

Analysis of Primary Stability of Dental Implants Inserted in Different Substrates Using the Pullout Test and Insertion Torque

“…Due to the difficulty in obtaining of human bone models with a homogeneous sample, the American Society for Testing Materials [25] has shown that polyurethane blocks have mechanical properties that mimic the human bone and this is considered the standard material for mechanical testing with orthopedic implants [16–19]. Some authors have used polyurethane blocks for analyzing primary stability of dental implants [8, 22] using methods such as resonance frequency analysis and insertion torque.…”

“…Some authors have used polyurethane blocks for analyzing primary stability of dental implants [8, 22] using methods such as resonance frequency analysis and insertion torque. Thus, the selection of polyurethane materials used in this study derived from the analysis of similar studies [13, 16, 17] to assess the insertion torque and pullout or tensile strength of dental implants since they showed similar results when compared with the human cadaver bone [18, 19]. …”

The Effects of Geometrical Parameters of the Pedicle Screw on Its Pullout Strength: In-Vitro Animal Tests

“…While using artificial discs to recover some of conical pedicle screws (12). They found that the pullout strength of the pedicle screws is a function of bone strength, screw design, and pilot hole (12). Previously, Chapman et al, used an analytical formula to predict the pullout strength of cancellous/cortical screws inserted into the synthetic bone (13).…”

“…There are certain diseases, such as disc degeneration, which can alter the shape of the intervertebral discs (IVDs) leading to a change in the vertebra's load distribution pattern. While using artificial discs to recover some of conical pedicle screws (12). They found that the pullout strength of the pedicle screws is a function of bone strength, screw design, and pilot hole (12).…”