Purpose
This study aimed to evaluate the predictive performance of preoperative computed tomography–based Hounsfield unit (HU) and magnetic resonance imaging-based vertebral bone quality score (VBQS) for cage subsidence after 1- to 2-level oblique lumbar interbody fusion (OLIF), and whether it differs by intraoperative cage placement position.
Methods
Ninety-one OLIF levels in 54 patients (2015–2022) were retrospectively reviewed in this single-center cohort. Subsidence was defined as ≥2 mm middle disc-height reduction or ≥2 mm cage protrusion at 1 year. Multivariable logistic regression with cluster-robust standard errors estimated adjusted odds ratios (OR); the pre-specified primary test was the lower-instrumented-vertebra HU×cage-position interaction.
Results
Subsidence occurred in 24 of 91 levels (26.4%). Each one-standard-deviation decrease in lower-instrumented-vertebra HU was independently associated with subsidence (adjusted OR, 0.40; 95% confidence interval, 0.20 to 0.81; p=0.011); VBQS was not. The subsidence group included more osteoporosis-range levels (<110 HU; 62.5% vs. 25.4%, p=0.003). The interaction was not significant (p=0.553), but the HU effect concentrated in middle-placed cages (adjusted OR, 0.345; p=0.012) and attenuated in anterior-placed cages (OR, 0.50; p=0.185).
Conclusion
Lower-instrumented-vertebra HU is an independent predictor of cage subsidence after 1- to 2-level OLIF, most evident in middle-placed cages.

Background
Oblique and anterior lumbar interbody fusion have been widely performed in the lumbar spinal disease but we cannot get a direct decompression effect with these procedure. Objective: The purpose of this study is to report clinical and imaging outcomes of microscope assisted direct decompression combined with oblique lumbar interbody fusion (OLIF) or anterior lumbar interbody fusion (ALIF).
Methods
Twelve patients who received microscope assisted direct decompression during OLIF or ALIF for lumbar spinal stenosis were enrolled. The OLIF was performed for the lesion upper than the L4-5 or in the case of multisegmental disease. The ALIF was performed for the lesion at the L5-S1. After anterior-approaching surgery, percutaneous fixation of pedicle screw was performed and we did not perform an additional decompression posteriorly in all cases. For the clinical outcomes, we evaluated short form 36 (SF-36), Oswestry disability index (ODI) score and visual analog scale (VAS) pain score. For the imaging outcomes, we obtained postoperative lumbar magnetic resonance imaging (MRI).
Results
The OLIF was performed for 9 patients and the ALIF was performed for 3 patients. In the clinical outcomes, SF-36 was improved from 25.40 to 69.83 and ODI score was also improved from 69.83 to 16.50. VAS pain score of back was improved from 4.3 to 1.6 and VAS pain score of leg was improved from 7.5 to 2.2. In the imaging outcomes, all patients had severe stenosis before surgery. After surgery the severity of the stenosis was reduced to mild state in 9 cases and moderate state in 3 cases postoperatively.
Conclusions
We could obtain the good clinical outcomes and effective decompression through microscope assisted direct decompression during OLIF or ALIF.

Objectives
We report the new minimally invasive technique and its clinical results of oblique lumbar interbody fusion (OLIF) combined with central decompression using biportal endoscopic spinal surgery (BESS). Summary of Literature Review: The OLIF procedure is one of the minimally invasive spine surgeries and is being frequently attempted recently to treat lumbar degenerative disease. It has been reported that it effectively decompresses foraminal stenotic lesions indirectly by inserting a large cage anteriorly, which reduces spondylolisthesis and widens the disc space. However, OLIF has limited effect for severe central canal stenosis, since it cannot achieve direct decompression. Therefore, authors report a new minimally invasive technique of OLIF combined with direct central decompression using BESS for severe central stenosis along with its clinical results as a pilot study.
Materials and Methods
For patients who were candidate for fusion surgery due to spondylolisthesis (more than one segment) or foraminal stenosis, authors performed OLIF and central decompression using BESS simultaneously, when the patients had concomitant severe central canal stenosis. From June to December, 2017, 8 patients (16 levels) were enrolled, the operative time, blood loss, complications and clinical results have been evaluated. The clinical results were analyzed by Visual analog scale (VAS) scores, Oswestry disability index (ODI) and Roland Morris Disability Questionnaire (RMDQ) of preoperative, 1month, 3month postoperative and final follow-up.
Results
Mean operative time and blood loss were 238.4 minutes and 173.3ml, respectively. In all cases, there were no operative complications, and mean follow-up period was 7.1 months. The mean back VAS, lower extremity VAS, ODI, and RMDQ at the final follow-up were improved from 5.4±2.4 to 2.0±0.9, 7.0±1.1 to 1.6±1.7, 64.2±11.8 to 44.2±10.6, and from 17.5±4.2 to 12.9±4.0.
Conclusion
A new combination technique of OLIF and BESS for direct decompression can be regarded as effective alternative procedure to treat the foraminal and central stenotic lesions of lumbar degenerative disease.