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

BACKGROUND

This finite element analysis systematically compared the axial pullout resistance of 6 pedicle screw augmentation techniques in osteoporotic lumbar vertebrae to inform clinical decision-making.

METHODS

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 (G). A total of 49 finite element models were subjected to axial pullout at 0.01 mm/s. Maximum pullout force and von Mises stress in cortical/cancellous bone were recorded.

RESULTS

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 3 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).

CONCLUSIONS

Cement augmentation, bicortical fixation, and cortical bone trajectory 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.