Predictive value of the superior endplate-cage angle for postoperative cage subsidence in stand-alone oblique lateral interbody fusion: a single-center retrospective study

Stand-alone oblique lateral interbody fusion (stand-alone OLIF) is a minimally invasive surgery for lumbar degenerative diseases, with cage subsidence as a common postoperative complication. This study aimed to investigate factors associated with cage subsidence following stand-alone OLIF, focusing on the clinical significance of the immediate postoperative superior endplate-cage angle (SEC angle). A total of 164 patients who underwent single-segment stand-alone OLIF at the Affiliated Hospital of Qingdao University between January 2020 and December 2024 were retrospectively enrolled. Based on computed tomography (CT) images at the 12-month postoperative follow-up, patients were divided into subsidence group ( n = 54) and non-subsidence group ( n = 110). Demographic, surgery-related, and radiological variables were collected. Potential factors were screened using univariate analyses and correlation heatmaps. Multivariable logistic regression analysis was then performed to identify factors associated with cage subsidence. Receiver operating characteristic (ROC) curve was utilized to further analyze the discriminatory performance of SEC angle. Cage subsidence occurred in 54 patients (32.9%). Univariate analysis showed significant differences between two groups in age, preoperative disc height (DH), endplate-cage angles, CT values of vertebral bodies and endplates, vertebral bone quality (VBQ) and its score, as well as endplate bone quality (EBQ) and its score ( P < 0.05). No significant between-group differences were observed in cage sagittal position and cage-endplate coverage-related parameters. Multivariable logistic regression confirmed the immediate postoperative SEC angle was associated with postoperative cage subsidence following stand-alone OLIF (odds ratio [OR] = 5.765, 95% confidence interval [CI]: 2.700–12.308, P < 0.001). ROC analysis showed that the cutoff value of SEC angle for discriminating cage subsidence was 2.85° (sensitivity = 0.667, specificity = 0.973, and area under the curve (AUC) = 0.877, 95% CI: 0.813–0.941, P < 0.001). Furthermore, the EBQ of the inferior endplate and EBQ score were also associated with cage subsidence, while preoperative DH was a protective factor (OR = 0.638, 95% CI: 0.436–0.931, P = 0.020). The immediate postoperative SEC angle was associated with cage subsidence after stand-alone OLIF and may serve as a useful radiographic marker for identifying patients at increased risk. Preoperative DH and EBQ score were also associated with subsidence. Therefore, careful preoperative endplate quality evaluation and meticulous intraoperative cage placement remain important for reducing cage subsidence.