Importance of Surgical Order for Minimizing Vascular Injury During the L5-S1 Approach in Multilevel Oblique Lateral Interbody Fusion Surgery.

Objective: In oblique lateral interbody fusion (OLIF) surgery at the L5-S1 level (OLIF51), anatomical complexity and the possibility of vascular injury during retraction of the common iliac vein (CIV) make the surgery challenging. We radiologically evaluated patients who underwent OLIF surgery to determine approaches that can make OLIF51 surgery easier during multilevel OLIF. Methods: We retrospectively analyzed 275 consecutive patients who underwent OLIF surgery between September 2014 and December 2019. The distance between the left and right CIVs (dCIV) was measured using an axial image at the L5 lower endplate level, and the height of the iliocaval junction (hCIV) was measured from the L5 lower endplate to the iliocaval junction in the sagittal image. The sum of anterior disc height of each level (sADH) was calculated. Results: Eighty-two patients (33 males and 49 females) were enrolled. The number of three- (L2-3-4-5), two- (L3-4-5), and one-level (L4-5) fusions was 13, 21, and 48, respectively. Changes between the pre- and postoperative sADH, dCIV, and hCIV values were 17.1±4.7, 7.7±3.5, and 13.1±4.7 mm in three-level fusion; 10.6±4.1, 5.6±3.7, and 7.0±3.1 in two-level fusion; and 4.3±2.5, 3.3±2.7, and 3.0±2.0 mm in one-level fusion, respectively. As the number of surgical levels increased, the changes in sADH, dCIV, and hCIV significantly increased. Conclusions: The dCIV and hCIV values increased when the upper segment underwent surgery before OLIF51 during multilevel OLIF.