Optimizing Fixation in Osteoporosis: A Finite Element Analysis of Six Pedicle Screw Augmentation Techniques for Axial Pullout Strength.

Abstract

This finite element analysis (FEA) systematically compared the axial pullout resistance of six pedicle screw augmentation techniques in osteoporotic lumbar vertebrae to inform clinical decision-making. Seven patient-specific L3 vertebral models were reconstructed from osteoporotic male patients (68 ± 5 years). Seven screw configurations were tested: unaugmented control (A), increased diameter (B), globally reduced pitch (C), locally reduced pitch at cortical zone (D), cement augmentation (E), bicortical purchase (F), and cortical bone trajectory (CBT, G). A total of 49 FE models were subjected to axial pullout at 0.01 mm/s. Maximum pullout force and von Mises stress in cortical/cancellous bone were recorded. Groups E (2349 ± 219 N), F (2307 ± 321 N), and G (2425 ± 460 N) showed substantially higher pullout resistance than control (1238 ± 36 N), with improvements of 88%, 92%, and 96%, respectively; the three performed comparably. Group B showed moderate improvement (26%). Group G recorded the highest cortical bone stress (265 ± 12 MPa), while Group E had the lowest cancellous bone stress (2.6 ± 0.2 MPa). Cement augmentation, bicortical fixation, and CBT significantly enhance axial pullout resistance in osteoporotic bone by reinforcing load-bearing capacity or optimizing cortical engagement. Modifications limited to diameter or pitch provide only marginal benefits. Augmentation strategy should be individualized based on bone quality, anatomy, and operative requirements.