Prediction of Angle Loss after L4/5 Oblique Lumbar Interbody Fusion : Development of a Risk Stratification Model.

Abstract

Objective: To evaluate the influence of preoperative disc morphology and cage-related variables on disc angle change following single-level L4/5 oblique lumbar interbody fusion (OLIF), and to identify predictors of postoperative angle loss and angular subsidence.

Methods: This retrospective study analyzed 80 patients who underwent L4/5 OLIF with posterior percutaneous screw fixation and 1-year radiographic follow-up. Radiographic parameters included preoperative disc angle (DAPRE), sacral slope (SS), and cage position along the anteroposterior axis (Cage_Y). Postoperative disc angle loss was defined as a decrease in disc angle immediately after surgery. Angular subsidence was defined as a decrease in disc angle at follow-up compared to the postoperative period multivariate logistic regression was used to identify independent predictors of these outcomes. Threshold values were determined by receiver operating characteristic curve analysis.

Results: DAPRE >6.0°, SS <32.0°, and posterior cage placement (Cage_Y <1.9 mm) were independently associated with immediate angle loss. Among them, DAPRE showed the strongest predictive power (odds ratio, 7.9). Additionally, a greater initial angular gain was associated with a higher risk of angular subsidence. Based on these three parameters, a risk score (0-3 points) was generated, which showed a stepwise increase in the incidence of angle loss (0% to 81.3%) and subsidence over follow-up.

Conclusion: DAPRE, SS, and Cage_Y are key predictors of disc angle outcomes after OLIF. This model provides a simple, clinically applicable tool to predict alignment maintenance and optimize surgical planning in degenerative lumbar conditions.