Unilateral biportal endoscopic TLIF with large-footprint cage: step-specific learning curve analysis

To analyze the learning curve of unilateral biportal endoscopic transforaminal lumbar interbody fusion (UBE-TLIF) using a large-footprint cage and identify operative components associated with improvements in operative efficiency during the learning process. In this retrospective cohort study, we reviewed 62 consecutive patients who underwent single-level UBE-TLIF. Total endoscopic operative time (endoscope-in to endoscope-out) was analyzed using cumulative sum (CUSUM) analysis to determine the learning-curve transition point. Operative time was subdivided into decompression and endplate preparation with cage insertion. Step-specific durations were compared across learning phases using one-way and two-way mixed analysis of variance, and correlations with total operative time were evaluated via Pearson analysis. CUSUM analysis identified a transition point at case 30, defining early ( n = 30) and late ( n = 32) phases. Operative time decreased from 124.1 ± 19.2 to 91.0 ± 3.9 min ( p < 0.001). Endplate preparation with the cage insertion step showed a greater reduction (64.8 ± 16.0 to 41.4 ± 3.0 min) than decompression (57.9 ± 6.7 to 49.7 ± 2.6 min), with a significant Step × Phase interaction ( p < 0.001). Endplate preparation with cage insertion showed the strongest association with total operative time (r = 0.95). The learning curve for UBE-TLIF with a large-footprint cage stabilized at approximately 30 cases. Among operative steps, endplate preparation with cage insertion demonstrated the greatest improvement in operative efficiency during the learning process. These findings suggest that focused training in this technical component may be beneficial during early implementation of the technique.