Expandable Versus Static Cages in Minimally Invasive Lumbar Interbody Fusion: A Systematic Review and Meta-Analysis

BACKGROUND: Expandable cages for interbody fusion allow for in situ expansion optimizing fit while mitigating endplate damage. Studies comparing outcomes after using expandable or static cages have been conflicting. METHODS: This was a meta-analysis A systematic search was performed in accordance with the Preferred Reporting Items for Systemic Reviews and Meta-Analyses (PRISMA) guidelines identifying studies reporting outcomes among patients who underwent minimally invasive lumbar interbody fusion (MIS-LIF). RESULTS: Fourteen articles with 1129 patients met inclusion criteria. Compared with MIS-LIFs performed with static cages, those with expandable cages had a significantly lower incidence of graft subsidence (expandable: incidence 0.03, I-2 22.50%; static: incidence 0.27, I-2 51.03%, P interaction <0.001), length of hospital stay (expandable: mean difference [MD] 3.55 days, I-2 97%; static: MD 7.1 days, I-2 97%, P interaction <0.01), and a greater increase in disc height (expandable: MD -4.41 mm, I-2 99.56%; static: MD -0.79 mm, I-2 99.17%, P interaction = 0.02). There was no statistically significant difference among Oswestry Disability Index (expandable: MD -22.75, I-2 98.17%; static: MD -17.11, I-2 95.26%, P interaction = 0.15), fusion rate (expandable: incidence 0.94, I-2 0%; static incidence 0.92, I-2 0%, P interaction = 0.44), overall change in lumbar lordosis (expandable: MD 3.48 degrees, I-2 59.29%; static: MD 3.67 degrees, I-2 0.00%, P interaction 0.88), blood loss (expandable: MD 228.9 mL, I-2 100%; static: MD 261.1 mL, I-2 94%, P interaction = 0.69) and operative time (expandable: MD 184 minutes, I-2 95.32%; static: MD 150.4 minutes, I-2 91%, P interaction = 0.56). CONCLUSIONS: Expandable interbody cages in MIS-LIF were associated with a decrease in subsidence rate, operative time and greater in increase in disc height.