The surgical technique used for OLIF has been previously described at our institute [13 (link),14 (link),20 (link)]. The patients were briefly placed in the right lateral decubitus position for the left-sided retroperitoneal approach. The surgical level of the disc was marked on the skin in true lateral view under C-arm fluoroscopy. An oblique skin incision was made 3–5 cm ventral to the anterior margin of the intervertebral disc. After dissecting the 3 layers of the abdominal wall muscles, the peritoneal fat was identified. The disc annulus was exposed through an open corridor between the psoas muscle and peritoneum. At the anterior border of the psoas muscle, the plane between the disc annulus and the psoas muscle was bluntly dissected using a peanut gauze ball to not injure the psoas muscle bundle. A slight dorsal retraction of the psoas muscle was applied during tubular retractor fixation. The entire surgery was performed using a Medtronic OLIF system (Medtronic, Memphis, TN, USA) with a minimally invasive tubular retractor, fusion material (Grafton, Medtronic), and a percutaneous pedicle screw fixation system (either Sextant or Longitude system, Medtronic) (Fig. 1). Posterior decompression was not performed on any of the patients included in this study.