Factors affecting indirect dural expansion in lateral interbody fusion for degenerative lumbar spondylolisthesis.

Purpose: To investigate the factors affecting indirect dural sac expansion on MRI in single-level Lateral Lumbar Interbody Fusion (LLIF) for degenerative lumbar spondylolisthesis. The focus was on identifying preoperatively selectable and intraoperatively modifiable factors that contribute to or detract from successful indirect decompression, as evidenced by dural sac expansion.

Methods: A retrospective review of 88 consecutive patients who underwent single-level LLIF surgery for degenerative lumbar spondylolisthesis at a single academic institute from January 2013 to December 2022 was conducted. Parameters measured included preoperative and postoperative slip distance, disc height (DH), cage position, and the canal cross-sectional area (CSA) of the dural sac using MRI. Multivariable regression analysis was conducted to identify factors affecting the change in CSA and segmental disc angle (SDA).

Results: The study included patients with an average age of 68.1, primarily undergoing L4-5 LLIF. Significant improvements were noted postoperatively in CSA and disc heights. Multivariable regression showed that smaller preoperative posterior DH and more posterior cage positions significantly increased CSA, whereas smaller anterior DH and more anterior cage positions increased SDA. There was no significant correlation between the change in slip distance and CSA.

Conclusions: Factors contributing to indirect decompression following LLIF for lumbar degenerative spondylolisthesis are primarily associated with an increase in posterior intervertebral height. However, an excessive increase due to posterior placement of the interbody cage may negatively impact the local lordotic angle. The study also suggests that a focus on slip correction may not significantly influence the efficacy of indirect decompression.