For OLIF L2–L5, similar to XLIF, the patient should be positioned in a right lateral decubitus position on a radiolucent table to expose the spine from the left side, as the working passage between the psoas muscle and the IVC is narrower on the right side [85,86]. Once positioned, the legs are slightly flexed. A line is drawn across the desired disc level from the anterior to the posterior. This determines the incision, which is typically made approximately 3–5 cm anterior to the midpoint of the line (Figure 2a). The fascia of the external oblique muscle is first encountered and incised using electrocautery, followed by gentle finger dissection of the external oblique, the internal oblique, and the transversalis muscles (Figure 2c–e). While working on the transversalis fascia, the finger’s force is directed obliquely and posteriorly to prevent entry into the peritoneal cavity. Once the retroperitoneal fat plane is reached, the space should be developed both cephalad and caudal to the desired disc level (Figure 2f), followed by anterior retraction of the peritoneal sac and posterior retraction of the anterior belly of psoas muscle to establish the working corridor (Figure 2g). After retraction of the psoas muscle, the disc space is visualized and a guide wire is inserted, followed by a series of dilations to create space pushing aside the surrounding tissues (Figure 2h,i). Subsequently, a retractor is positioned over the dilators and can be anchored to the vertebral body using a pin. The retractor blades are oriented such that it allows for an orthogonal maneuver (rotating the instruments in a manner that they are obliquely inserted but become direct lateral as they go deeper) during disc removal, sequential trialling, and final placement of the interbody cage. Annulotomy and discectomy is performed under X-ray guidance (Figure 2j,k). After completing the disc preparation, a contralateral annular release is performed using a blunt-tipped shaver or cobb elevator, as carried out during XLIF (Figure 2l). Sequential trials distract the disc space and allow indirect decompression. Finally, a wide-bodied interbody cage is placed within the disc space (Figure 2m). The procedure may be accompanied by lateral or posterior stabilization, contingent upon the indication, the requirement for direct decompression, and the surgeon’s preference [87,88].

Surface marking is carried out with the help of X-ray guidance. A line is drawn across the L5-S1 disc level from the posterior to anterior and is extended onto the abdominal area. Subsequently, a second line is drawn from the center of the L5-S1 disc, projecting perpendicular to the floor onto the abdomen’s surface. Finally, approximately two finger-breadths anterior to the anterior superior iliac spine (ASIS), a third line is drawn connecting the first and second lines where the incision is made. The anatomical advantages of positioning the patient laterally enable abdominal contents to naturally fall away from the spine, resulting in a reduction in the need for peritoneal retraction. Dissection is performed as described for OLIF L2–L5. The common iliac artery pulse can be felt on the anterior border of the psoas, and the common iliac vein is medial to the artery. The adventitial layer containing the superior hypogastric plexus and sympathetic chain within is to be released by blunt dissection. After successfully releasing the adventitial layer, the left common iliac vein can be gently retracted laterally if needed.

3.3. Advantages of OLIF over XLIF