CUSUM and RA-CUSUM Analysis of the First-Year Learning Curve for UBE in a Neurosurgeon with Endoscopic Skull Base Experience.

Background and objectives: 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 CUSUM(RA-CUSUM) analyses.

Methods: Between May 2024 and May 2025, a total of 108 patients who underwent UBE were retrospectively analyzed. Procedures included lumbar discectomy(UBE-LD, n=89) and unilateral laminotomy for bilateral decompression(UBE-ULBD, 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% CI:28-37), and at the 17th case in patients with LDH(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 LDH subgroup(95% CI:31-42).

Conclusions: This study provides a detailed assessment of the learning curve for unilateral biportal endoscopic 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.