Comparative Finite Element Analysis of Denosumab and Bazedoxifene on Pedicle Screw Stability in Osteoporotic Spines

Pedicle screw fixation in osteoporotic spines remains challenging. Bazedoxifene (BZA) and denosumab (Dmab) are widely used agents for osteoporosis, but their comparative effects on spinal instrumentation are not well understood. This study aimed to evaluate the effects of BZA and Dmab on biomechanical parameters of spinal instrumentation using finite element analysis (FEA).

In this prospective, open-label study, postmenopausal women with primary osteoporosis were assigned to receive either BZA (daily oral, 20 mg) or Dmab (subcutaneous, 60 mg every 6 months) for 12 months. FEA models of the L4 vertebra were generated from CT scans using a calibration phantom (Mindways, Austin, TX, USA). Vertebral compression force was evaluated to represent overall vertebral strength. Pedicle screw fixation strength was assessed under axial (pullout strength) and non-axial directional forces (cranial, caudal, lateral, medial). Inverse probability of treatment weighting (IPTW) and multivariable regression were used to balance baseline differences and compare biomechanical outcomes between groups.

Thirty patients were enrolled (15 per group); the final analysis included 12 in the BZA group and 13 in the Dmab group. Compared to BZA, Dmab significantly improved compression strength (adjusted mean difference: 8.1% [95% CI, 0.9-15.3], p = 0.030) and pullout strength (15.8% [95% CI, 6.2-25.4], p = 0.003). Directional FEA revealed greater resistance to cranial (17.4% [95% CI, 4.9-30.0], p = 0.009) and lateral (10.8% [95% CI, 0.9-20.8], p = 0.035) loading with Dmab, while no significant difference was observed in caudal- and medial-directed force.

Finite element modeling suggested that Dmab enhanced pedicle screw fixation more effectively than BZA, particularly against axial and cranial/lateral-directed forces. These biomechanical differences underscore the potential advantage of Dmab in preoperative osteoporosis management to improve pedicle screw stability.