Predictors of Cage Subsidence After Oblique Lumbar Interbody Fusion

Background/Objective: Oblique lumbar interbody fusion (OLIF) achieves indirect decompression through restoration of disc height. Because maintenance of the restored disc space is essential for sustained neural decompression, solid fusion without cage subsidence is a key determinant of successful surgical outcomes. This study aimed to evaluate preoperative and intraoperative predictors of cage subsidence and radiographic fusion after OLIF. Methods: Seventy patients (119 levels) who underwent OLIF using a polyether–ether–ketone cage and posterior screw fixation between 2015 and 2023 were retrospectively reviewed. Preoperative bone quality was assessed using the computed tomography-based Hounsfield unit (HU) and magnetic resonance imaging-based vertebral bone quality (VBQ) score on T1-weighted images. Radiographic parameters of anterior and posterior disc height (ADH, PDH), segmental and lumbar lordotic angle (SLA, LLA), foraminal height (FH), and cage position were measured preoperatively at one-year follow-up. Results: Cage subsidence occurred in 21.0% of spinal levels (25/119 levels). Multivariate analysis identified these measures as independent predictors: HU (OR 1.017; p = 0.012), VBQ score (OR 2.716; p = 0.016), and PDH distraction (OR 1.418; p = 0.019). ROC analysis identified cutoff values of HU < 145.86 (AUC = 0.654), VBQ score > 3.30 (AUC = 0.723), and PDH distraction > 4.79 mm (AUC = 0.672). None of the evaluated factors were significantly associated with one-year radiographic fusion. Conclusions: Lower HU, higher VBQ score, and excessive PDH distraction are independent risk factors for cage subsidence after OLIF, although these factors do not appear to affect short-term fusion outcomes.