Accuracy of the lateral cage placement under intraoperative C-arm fluoroscopy in oblique lateral interbody fusion

Background: In oblique lateral interbody fusion (OLIF), the lateral cage enters into the disc space obliquely, and is then turned to the true lateral direction to achieve a lateral lumbar interbody fusion. The OLIF cage is sometimes placed asymmetrically although it seemed to be placed accurately on intraoperative C-arm images. The present study aimed to investigate the accuracy of cage placement and its effect on the radiological outcome in OLIF. Methods: This study involved a retrospective radiological analysis of 127 lateral cages in 75 consecutive OLIF patients. The cage deviations from the midline and cage obliquity were evaluated using three sets of images: (1) intraoperative C-arm fluoroscopy, (2) postoperative standing radiographs, and (3) postoperative computed tomography (CT). Results: The mean cage deviation from the midline was measured as 2.5 +/- 2.7 mm on intraoperative C-arm images, but was found to be more deviated on postoperative radiographs and CT (5.4 +/- 3.8 mm and 3.8 +/- 3.7 mm; P = 0.000 and 0.005, respectively). The cage obliquity on the intraoperative lateral C-arm was minimal in 26 (20.5%) cases, mild in 69 (54.3%), and moderate in 32 (25.2%), but was found to be more obliquely on postoperative radiographs as minimal in 9 (7.1%), mild in 55 (43.3%), and moderate in 63 (49.6%) (P < 0.001). Anterior/posterior disc heights, disc lordotic angle, fusion rate, and cage subsidence rate were not different according to cage obliquity (all P> 0.05). Conclusions: Cage deviation from the midline and obliquity is underestimated on intraoperative C-arm images in OLIF. Although minimal cage deviation and obliquity did not affect the radiological outcome, great care should be made for the orthogonal cage insertion. (C) 2018 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.