Objective:

(1) To investigate if implant-related factors such as cage size and cage position are associated with radiological improvement after indirect decompression with oblique lateral interbody fusion (OLIF). (2) To investigate the risk factors associated with indirect decompression failure (IDF) at the surgical levels after OLIF.

Methods:

From February 2015 to December 2019, 92 consecutive patients (188 levels) with lumbar spinal stenosis who underwent indirect decompression via OLIF with or without posterior instrumentation were retrospectively studied. Radiographic variables were measured pre- and postoperatively. The radiographic results were compared for cages with different heights and positions. Indirect decompression failure (IDF) was defined as revision surgeries within 6 months or persistent compressive symptoms 6 months after the surgery.

Results:

Postoperative improvements were observed in all measured radiographic parameters except for segmental lordosis. Taller cages were associated with more shrinkage of the bulging disc and greater increase in dural sac diameter. Surgical levels treated with cages placed in posterior positions showed larger postoperative subarticular diameters. 12 patients (16 levels) had IDF. Multivariate logistic regression showed that after adjusting for age, sex, and BMI, smaller preoperative dural sac cross-sectional area (CSA) and anterior positioning of cages were both independent risk factors for IDF.

Conclusions:

OLIF is an effective procedure for indirect decompression. To avoid reoperation for lumbar spinal stenosis, surgeons should aim to place the center of the cage at the posterior half of the lower endplate. Surgical levels with a preoperative dural sac CSA <44 mm² may not be suitable for indirect decompression.