Study Design. A retrospective study (level of evidence: level 4). Objective. To evaluate the radiographic outcomes after extreme lateral lumbar interbody fusion (XLIF) and oblique lateral lumbar interbody fusion (OLIF) procedures especially the effect of indirect decompression to the ligamentum flavum and to evaluate the effect of facet degeneration to the radiographic outcomes of these procedures. Summary of Background Data. Indirect decompression via lateral lumbar interbody fusion provides spinal canal area expansion. However, the effect to the ligamentum flavum area and thickness at the operated spinal level is unclear. Methods. Thirty-five patients (57 lumbar levels) underwent XLIF or OLIF with percutaneous pedicle screw fixation (PPS) without direct posterior decompression were retrospectively studied. Radiographic parameters including ligamentum flavum area (LFA), ligamentum flavum thickness (LFT), cross-sectional area (CSA) of thecal sac, posterior disc height, foraminal height, cage alignment, and facet degeneration were measured on magnetic resonance image (MRI). Cage position was assessed with plain radiography. Results. All of the radiographic parameters were significantly improved. Comparing pre- and postoperative value, mean LFA decreased from 78.9 ± 24.9 mm 2 to 66.9 ± 26.8 mm 2 (–14.2%; P -value < 0.00625). Mean right LFT decreased from 2.9 ± 0.9 mm to 2.3 ± 0.7 (–17.0%; P -value < 0.00625). Mean left LFT decreased from 3.3 ± 1.6 mm to 2.6 ± 0.9 mm (–17.6%; P -value < 0.00625). Mean CSA of thecal sac increased from 93.1 ± 43.0 mm 2 to 127.3 ± 52.5 mm 2 (50.8%; P -value < 0.00625). All radiographic outcomes were not significant difference between lumbar levels that have grade 0–1 and grade 2–3 or between grade 2 and grade 3 facet degeneration. Conclusion. Ligamentum flavum area and thickness were significantly reduced after lateral lumbar interbody fusion through both XLIF and OLIF. Unbuckling of the ligamentum flavum played an important role for improvement of spinal canal area after t...