Mid-Term Outcomes of Screw Loosening in Lumbar Dynamic Stabilization with PEEK Rods versus Titanium Rods: A Minimum 4-Year Follow-Up.

Methods: Retrospective study.

Objective: This study aimed to retrospectively analyze screw loosening rates following dynamic fixation with PEEK rods and rigid fixation with titanium rods, assess mid-term outcomes of loosened screws.

Methods: A retrospective analysis included 203 patients who underwent lumbar pedicle screw fixation between March 2017 and June 2020 (57 with PEEK rods, 146 with titanium rods). Patients were followed for at least 48 months to evaluate screw loosening postoperatively and investigate outcomes of loosened screws. Multivariate logistic regression identified factors influencing screw re-stabilization.

Results: Both PEEK rod and titanium rod groups exhibited peak screw loosening rates approximately one year post-surgery, decreasing with longer follow-up. At 48 months, screw loosening rates were 5.3% and 15.8% for PEEK and titanium rods, respectively (P < 0.05). Among patients experiencing early loosening (within 12 months), the proportion of stabilized screws was significantly higher with PEEK rods (84% vs 34%, P < 0.001). Regression analysis revealed dynamic fixation (OR 4.579; 95% CI [1.611-12.519]), lowest fixed vertebra S1 (OR 3.151; 95% CI [1.352-9.233]), and L1-L4 average CT value (OR 1.132; 95% CI [1.015-1.263]) as independent risk factors for screw re-stabilization. The area under the ROC curve for L1-L4 average CT value predicting re-stabilization was 0.713 (P < 0.05), with an optimal threshold of 106 HU (sensitivity: 0.771; specificity: 0.803).

Conclusions: Following PEEK rod dynamic fixation surgery, a certain proportion of screw loosening may occur in the short term. With prolonged follow-up, screws gradually restabilize at the bone interface, with most loosened screws returning to a stable state.