Cutting Flute and Thread Design on Self-Tapping Pedicle Screws Influence the Insertion Torque and Pullout Strength

Abstract

Self-tapping screws are commonly used in trauma and maxillofacial surgery and are increasingly used for pedicle screw insertions. In order to evaluate how the quantity and length of cutting flutes on self-tapping pedicle screws affect the insertion torque and pullout strength, eight different self-tapping pedicle screw designs were evaluated. All screws had a threaded length of 35 mm and featured variations in the number of leads, as well as the length and quantity of cutting flutes. Five samples of each design were inserted into pre-drilled, untapped holes (ø2.7 mm, length 35 mm) in sawbone blocks of density 20 PCF. The insertion torque and pullout strength were measured according to ASTM F543. The results showed that screws with a longer cutting flute of 9.5 mm had a lower mean maximum insertion torque than screws with shorter 2.9 mm cutting flutes. Pedicle screws with a double-lead thread design had a greater insertion torque than their single-lead counterparts, and the use of three cutting flutes produced a lower torque than two cutting flutes. The results demonstrated a greater pullout strength in screws with a single-lead thread rather than a double-lead, three cutting flutes instead of two, and a longer length for the cutting flute. In conclusion, to provide immediate stability and reduce the surgical insertion time, a single-lead, self-tapping pedicle screw incorporating three long cutting flutes is recommended because of the significantly greater pullout strength. This design could also reduce the risk of implant loosening in comparison to double-lead, self-tapping pedicle screw designs.

Pullout Strength of Pedicle Screws Inserted Using Three Different Techniques: A Biomechanical Study on Polyurethane Foam Block

“…Compared to strategy C, strategy B resulted in a greater decrease in pullout strength for all screw types without cyclic loading, with the DLT screw showing the greatest reduction. Pullout strength is an important factor affecting the screw holding captivity and is typically evaluated using ASTM F543 [ 9 , 10 , 11 , 12 , 13 ]. The results showed that the MSLT screw had greatest pullout strength among the three screw types for all insertion methods, while the difference between the SLT and DLT groups was not significant when using the same insertion method.…”

“…Thus, altering the depth or purchase of the original screw after insertion can have a demonstrable negative effect on the pullout strength. Pullout strength test using synthetic bone is a common parameter for assessing the stability of pedicle screws during preclinical testing [ 9 , 13 ]. However, to date, no studies have compared the pullout strength of pedicle screws with different thread designs when the screw height is adjusted after implantation.…”

A Passive Wireless Smart Washer for Locking Force Monitoring on the Orthopedic Pedicle Screw

“…Unfortunately, there is some probability of the orthopedics screws to become loose, which may make orthopedic treatment failure and bone-screw-related complications, including infection and inflammation [1][2][3][4]. To reduce risk of orthopedic screws loosen, improving orthopedic screws fixation [5][6][7][8] and monitoring orthopedic screws loosen status [9,10] are desired.…”