Static versus Expandable Interbody Fusion Devices: A Comparison of 1-Year Clinical and Radiographic Outcomes in Minimally Invasive Transforaminal Lumbar Interbody Fusion

STUDY DESIGN: Retrospective cohort study. PURPOSE: To compare the radiographic and clinical outcomes of static versus expandable interbody cages in transforaminal lumbar interbody fusion using minimally invasive surgery (MIS-TLIF). OVERVIEW OF LITERATURE: Expandable interbody cages may potentially improve radiographic and clinical outcomes following MIS-TLIF compared to static pages, but at a potentially higher cost and increased rates of subsidence. METHODS: A retrospective chart review of 1- and 2-level MIS-TLIFs performed from 2014 to 2020 was reviewed. Radiographic measurements were obtained preoperatively, 6 weeks postoperatively, and at final follow-up. Patient-reported outcome measures (PROMs) including the Oswestry Disability Index, Visual Analog Scale (VAS) back, and VAS leg were evaluated. Multivariate linear regression analysis determined the effect of cage type on the change in PROMs, controlling for demographic characteristics. Alpha was set at 0.05. RESULTS: A total of 221 patients underwent MIS-TLIF including 136 static and 85 expandable cages. Expandable cages had significantly greater anterior (static: 11.41 mm vs. expandable: 13.11 mm, p<0.001) and posterior disk heights (static: 7.22 mm vs. expandable: 8.11 mm, p<0.001) at 1-year follow-up. Expandable cages offered similar improvements in segmental lordosis at 6 weeks (static: 1.69° vs. expandable: 2.81°, p=0.243), but segmental lordosis was better maintained with expandable cages leading to significant differences at 1-year follow-up (static: 0.86° vs. expandable: 2.45°, p=0.001). No significant differences were noted in total complication (static: 12.5% vs. expandable: 16.5%, p=0.191) or cage subsidence rates (static: 19.7% vs. expandable: 22.4%, p=0.502) groups at 1-year follow-up. CONCLUSIONS: Expandable devices provide greater improvements in radiographic measurements including anterior disk height, posterior disk height, and segmental lordosis, but this did not lead to significant improvements in PROMs, complication rates, subsidence rates, or subsidence distance.