How many cases to proficiency? A systematic review of the learning curve in endoscopic lumbar interbody fusion

Endoscopic lumbar interbody fusion (Endo-LIF) is increasingly used as a minimally invasive alternative to conventional MIS-TLIF. While recent systematic reviews have shown comparable clinical and radiographic outcomes, the learning curve for Endo-LIF has not been systematically synthesised. We aimed to evaluate the learning curve of Endo-LIF, determine how many cases are required to achieve proficiency, and assess the impact of surgeon experience on perioperative outcomes.

A systematic review was conducted according to PRISMA 2020. PubMed, Embase, Scopus, and Web of Science were searched for studies reporting learning-curve analyses of endoscopic lumbar fusion, including Endo-TLIF, ULIF, and UBE-TLIF. Learning-curve methods included cumulative sum (CUSUM), risk-adjusted CUSUM (RA-CUSUM), and chronological grouping. Outcomes included operative time, complications, radiation exposure, fusion, and defined proficiency thresholds.

Six retrospective cohort studies involving 653 patients were included. Proficiency thresholds ranged from approximately 19 to over 40 cases, with higher thresholds consistently identified when safety-adjusted (RA-CUSUM) rather than time-based methods were used. Operative time and radiation exposure decreased with experience, and learning-sensitive complications clustered early. Fusion rates and patient-reported outcomes were generally stable throughout the learning curve.

Endo-LIF demonstrates a clinically meaningful learning curve. Operative efficiency improves early, but safety stabilises later, particularly when risk-adjusted methods are applied. Training and credentialing should therefore be guided by safety-based performance metrics rather than operative time alone.