Impact of Expandable versus Static Interbody Cages on Subsidence and Outcomes in Minimally Invasive Transforaminal...

Study DesignSystematic review and meta-analysis.ObjectiveTo compare expandable and static interbody cages in MIS-TLIF with respect to subsidence, radiographic outcomes, fusion rates, and patient-reported outcomes.MethodsFollowing PRISMA 2020 guidelines and a preregistered PROSPERO protocol, we searched PubMed/MEDLINE, Embase, Scopus, Web of Science, the Cochrane Library, and OVID through December 2025. Studies reporting clinical or radiographic outcomes of MIS-TLIF using expandable or static cages were included. Random-effects meta-analyses were performed, and risk of bias was assessed using Joanna Briggs Institute tools.ResultsTwenty-three studies encompassing 1838 patients and 2074 fused levels met inclusion criteria. Expandable cages demonstrated a lower pooled subsidence rate than static cages (12.8% vs 25.7%), representing roughly a 50% relative reduction. When subsidence occurred, its magnitude was similar between groups (5.33 mm vs 4.54 mm). Improvements in VAS back pain (4.27 vs 4.29), VAS leg pain (3.80 vs 4.28), and ODI (20.16 vs 28.29) were comparable. Sensitivity analyses limited to low-risk studies showed consistent trends, although Egger's regression suggested possible small-study effects for subsidence.ConclusionsIn MIS-TLIF, expandable cages are associated with lower subsidence rates while achieving radiographic and clinical outcomes similar to static cages. However, only three studies directly compared the two cage types; the synthesis largely relies on indirect comparisons is susceptible to confounding. These findings should not be regarded as evidence of a causal effect of cage design.