Expandable versus Static Cages in Minimally Invasive Lumbar Interbody Fusion: A Systematic Review and Meta-analysis.

STUDY DESIGN 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 A systematic search was performed in accordance with the PRISMA guidelines identifying studies reporting outcomes among patients who underwent MIS-LIF. RESULTS Fourteen articles with 1,129 patients met inclusion criteria. Compared to MIS-LIFs performed with static cages, those with expandable cages had a significantly lower incidence of graft subsidence (expandable: incidence 0.03, I2 22.50%; static: incidence 0.27, I2 51.03%, p interaction <0.001), length of hospital stay (expandable: MD 3.55 days, I2 97%; static: MD 7.1 days, I2 97%, p-interaction <0.01) and a greater increase in disc height (expandable: MD -4.41 mm, I2 99.56%; static: MD -0.79 mm, I2 99.17%, p interaction =0.02). There was no statistically significant difference among Oswestry Disability Index (expandable: MD -22.75, I2 98.17%; static: MD -17.11, I2 95.26%, p interaction =0.15), fusion rate (expandable: incidence 0.94, I2 0%; static incidence 0.92, I2 0%, p interaction =0.44), overall change in lumbar lordosis (expandable: MD 3.48 degrees, I2 59.29%; static: MD 3.67 degrees, I2 0.00%, p interaction 0.88), blood loss (expandable: MD 228.9 ml, I2 100%; static: MD 261.1 ml, I2 94%, p interaction =0.69) and operative time (expandable: MD 184 minutes, I2 95.32%; static: MD 150.4 minutes, I2 91%, p interaction =0.56). CONCLUSION Expandable interbody cages in MIS-LIF were associated with a decrease in subsidence rate, operative time and greater in increase in disc height.