PEEK rods are not inferior to titanium rods in short-segment lumbar fusion: a retrospective cohort study of screw loosening and clinical outcomes

Aim Polyetheretherketone (PEEK) rods are a semirigid alternative to titanium rods in lumbar fusion, but their effect on screw loosening remains uncertain. This study compared PEEK and rigid titanium rods in short-segment lumbar fusion. Material and methods This retrospective two-center cohort included 498 adults with at least 6 months of follow-up who underwent short-segment posterior lumbar fusion for lumbar spinal stenosis at two institutions by the same surgeon with seven years of spinal surgery experience. Patients received PEEK (n = 212) or rigid titanium rods (n = 286). The primary outcome was computed tomography–detected screw loosening. Logistic regression adjusted for age, sex, instrumented segments, cement augmentation, comorbidity, smoking, center, operative period, and follow-up duration. Sensitivity analyses used 9- and 12-month thresholds and excluded connector or postoperative infection cases. Results Screw loosening was less frequent with PEEK than with rigid titanium rods (20.3% vs 44.8%, p < 0.001). Lower- and upper-level loosening and reoperation were also less frequent with PEEK, while complication rates were similar. PEEK remained associated with lower loosening odds in the primary model (adjusted OR 0.58, 95% CI 0.36–0.94; p = 0.027) and expanded model (adjusted OR 0.60, 95% CI 0.37–0.98; p = 0.041). Findings remained directionally consistent after excluding connector or infection cases. In the ≥9- and ≥12-month analyses, adjusted estimates favored PEEK but were not significant. Conclusion PEEK rods were associated with lower screw-loosening odds in the primary and additional analyses. However, the nonrandomized design and nonsignificant longer-follow-up analyses preclude conclusions of definitive mechanical superiority.