Objective: Although several studies have documented indirect decompression after oblique lateral interbody fusion (OLIF), limited research exists that directly quantifies the degree of decompression. This study seeks to quantify the degree of indirect decompression achieved by OLIF using magnetic resonance imaging (MRI).

Methods: This is a retrospective study of consecutive adult patients at a single institution who underwent multistage lumbar interbody fusion via antepsoas (OLIF) retroperitoneal approach for spinal stenosis with radiculopathy. Pre and Postoperative MRI were used to measure the following radiologic parameters: anterior and posterior disc heights, bilateral foraminal height, bilateral foraminal area, bilateral subarticular recess width, and thecal sac area. Paired sample t-tests were performed to evaluate pre and postoperative changes in MRI measurements.

Results: A total of 24 patients (age 66.4 ± 5.98, BMI 29.3 ± 4.73) with a total of 63 operative levels were reviewed: L1-L2 (3), L2-L3 (17), L3-L4 (22), L4-L5 (22). Anterior disc height, posterior disc height, bilateral foraminal height, bilateral foraminal area, bilateral subarticular lateral recess, and thecal sac area all demonstrated a statistically significant improvement (p < 0.05) for all levels except L1-L2.

Conclusions: OLIF provides a significant amount of indirect decompression from L2-L5 including increased anterior and posterior disc height, bilateral foraminal height, bilateral foraminal area, bilateral subarticular recess, and thecal sac area. The proximal adjacent level above an interbody level also shows increased foraminal height and area.