Clinical Outcomes of PMMA Spacers in the Induced Membrane Technique: A Systematic Review and Meta-Analysis

The induced membrane technique (IMT) is widely used for segmental bone defect reconstruction, with polymethyl methacrylate (PMMA) spacers playing a central role. However, evidence supporting specific PMMA spacer strategies remains uncertain. This systematic review and meta-analysis was conducted according to PRISMA 2020 and prospectively registered in PROSPERO (CRD420261349603). Clinical studies reporting outcomes of the induced membrane technique (IMT) using PMMA spacers were included. Random-effects meta-analyses were performed for bone union, time to union, infection recurrence, complications, and reinterventions. Risk of bias, certainty of evidence (GRADE), and evidence gaps were assessed. Fifty-five studies were included. The pooled bone union proportion was 91.6% (95% CI 87.5–95.1%; 55 studies; 1623 cases), and mean time to union was 7.65 months (95% CI 6.87–8.43; 31 studies; 976 cases). Infection recurrence was 4.94% (95% CI 1.60–9.42%), complications 20.0% (95% CI 15.4–25.4%), and reinterventions 16.1% (95% CI 11.6–22.0%). Evidence was predominantly non-comparative, with scarce direct comparisons between conventional and modified PMMA spacers. Evidence certainty was low to very low. In predominantly non-comparative studies, IMT using PMMA spacers was associated with a high bone union rate, although the evidence available for infection recurrence was more limited; complications and reinterventions remained clinically relevant. Evidence is insufficient to establish the superiority of modified over conventional PMMA spacers or to recommend a specific formulation.