Analysis of the learning curve of unilateral biportal spinal endoscopic surgery for lumbar disc herniation

English Keywords:Lumbar disc herniation  Unilateral biportal endoscopy  Learning curve  Minimally invasive spinal surgery

English Abstract:

  【Abstract】 Objectives: To analyze the learning curve characteristics of surgery for single-segment lumbar disc herniation(LDH) under unilateral biportal endoscopy(UBE), and to quantify the number of cases required to achieve procedural proficiency, therefore providing objective evidence for the standardized training of UBE techniques. Methods: A retrospective analysis was performed on 60 consecutive patients with single-segment LDH who underwent UBE surgery performed by a single surgeon at our institution between July 2024 and January 2025. The cohort comprised 36 males and 24 females, with ages ranging from 23 to 77 years(52.8±13.9 years). Cumulative summation(CUSUM) analysis was applied to analyze operative time. When the CUSUM curve exhibited a distinct inflection point(cumulative deviation peak) and followed by a systematic shift in trend, then this point was defined as the staging threshold to delineate the phases of the learning curve. Operative time, number of fluoroscopic exposures, postoperative length of stay(PLOS), complication rate, preoperative and 4-week postoperative Oswestry disability index(ODI), and MacNab clinical outcomes were compared across the phases. Wright′s learning curve model was used to establish a mathematical curve function for statistical analysis of operative time, and the number of cases required to reach the competence improvement phase was calculated. Results: CUSUM analysis identified two cumulative deviation peaks of 1513.92 and 1593.8, corresponding to the 16th and 40th cases, respectively. Based on these findings, the learning curve was divided into three phases(groups): the learning phase(cases 1-15), the competence improvement phase(cases 16-39), and the proficient and stable phase(cases≥40). No significant differences were found between the three groups in terms of gender, age, body mass index(BMI), or surgical segments(P>0.05). The operative time was 193.13±54.68min in the learning phase, 90.08±22.25min in the competence improvement phase, and 72.76±11.03min in the proficient and stable phase. PLOS decreased from 6.4±1.5d in the learning phase to 4.57±0.93d in the proficient and stable phase. No significant differences were observed between the three groups in postoperative complication rates or MacNab outcomes at discharge(P>0.05), whereas the difference in operative time was statistically significant(P<0.05). The complication rate was 20%(3/15) in the learning phase, 4.2%(1/24) in the competence improvement phase, and no complications occurred in the proficient and stable phase(0/21). Compared with the proficient and stable phase, the operative time and complication rate in the learning phase were significantly reduced(P<0.05). 15 cases were required to reach the competence improvement phase and 39 cases to achieve the proficient and stable phase calculated by the mathematical curve function based on Wright′s learning curve model. Conclusions: UBE surgery for single-segment LDH is safe and effective. The learning curve demonstrates distinct phased characteristics, and can be divided into three phases of learning phase, competence improvement phase, and proficient and stable phase. Surgical efficiency improves steadily with accumulated experience, and approximately 40 cases are required for a surgeon to achieve proficient and stable performance.