Cumulative Sum and Risk-Adjusted Cumulative Sum Analysis of the First-Year Learning Curve for Unilateral Biportal Endoscopy in a Neurosurgeon with Endoscopic Skull Base Experience

Objective: Unilateral biportal endoscopy (UBE) has emerged as a minimally invasive alternative for lumbar spine surgery; however, its learning curve still presents certain challenges. This study aimed to evaluate the learning curve of UBE during its first year of adoption by a neurosurgeon with extensive endoscopic skull base surgery experience, using both cumulative sum (CUSUM) and risk-adjusted cumulative sum (RA-CUSUM) analyses. Methods: Between May 2024 and May 2025, a total of 108 patients who underwent UBE were retrospectively analyzed. Procedures included UBE lumbar discectomy (n = 89) and unilateral laminotomy for bilateral decompression (n = 19). CUSUM and RA-CUSUM analyses were applied to identify learning curve inflection points. Results: The mean operative time was 69.49 ± 30.23 minutes. Perioperative or postoperative complications occurred in 10 patients (9.3%). CUSUM analysis demonstrated a significant cut-off point at the 26th case in the overall cohort (95% confidence interval [CI]: 28–37) and at the 17th case in patients with lumbar disc herniation (95% CI: 15–20). RA-CUSUM analysis revealed that complication rates stabilized after the 49th case in the overall series (95% CI: 45–55) and after the 35th case in the lumbar disc herniation subgroup (95% CI: 31–42). Conclusions: This study provides a detailed assessment of the learning curve for UBE spinal surgery from the perspective of a neurosurgeon with prior endoscopic skull base experience. Using both CUSUM and RA-CUSUM analyses, the transition points to technical and clinical proficiency were objectively defined. These results emphasize the role of previous endoscopic experience in facilitating a shorter learning process and underscore the value of individualized, risk-adjusted analyses for accurately evaluating surgical performance.