Are pedicular screws and lateral hook screws more resistant against pullout than conventional spinal hooks and screws in terminal vertebral segment fixation?

Abstract

This study aims to biomechanically evaluate and compare four well-known types of terminal spinal constructs to a novel construct composed of a transpedicular screw with a lateral hook screw in terms of axial pullout strength in terminal vertebral segment fixation. Forty fresh-frozen lamb spines were divided into five groups with eight spines each. To stabilize the transverse process, a pedicular screw alone was used in group 1, a sublaminar hook alone was used in group 2, a sublaminar hook and a pedicular screw were used in group 3, claw hook alone was used in group 4, and a pedicular screw with a lateral hook screw was used in group 5. Biomechanical tests were performed using an axial compression testing machine and two noncontact camera systems. The mean pullout strength value was 927 N for group 1, 626 N for group 2, 988 N for group 3, 972 N for group 4, and 1194 N for group 5. Pullout strength values were statistically significantly higher in groups 3 and 4 compared to groups 1 and 2. There was no statistically significant difference between groups 3 and 4. Pullout strength value of group 5 was statistically significantly higher than the other groups. Pedicular screw with a lateral hook screw had the highest fixation value. Lateral hook screw may assist to prevent pullout in patients with pullout risk and hyperkyphosis and after hyperkyphosis surgery. Further prospective clinical studies are needed to show the benefit of such a construct in reducing the risk of distal instrumentation pullout.