Learning curve of biportal endoscopic spinal surgery: a retrospective two-center study

Biportal endoscopic spinal surgery (BESS) technique is a novel, useful, and minimally invasive therapeutic strategy for lumbar degenerative diseases, which has advantages over other surgical techniques. However, the degree of technical difficulty in learning BESS is controversial and not well established. This study aims to determine the learning curve of BESS technique through cumulative sum (CUSUM) analysis.