Abstract: Objective　To investigate the accuracy of the cage placement in the extreme lateral interbody fusion (XLIF) approach with reference to the lateral boundary of the anterior longitudinal ligament in lumbar spine.　Methods　Sixty-six patients admitted to the Department of Spine Surgery, the Third Affiliated Hospital of Guangzhou Medical University from January 2019 to February 2021 were prospectively collected. All the patients were undergone the XLIF surgery in the lumbar spine. Thirty-three cases were randomly assigned into a regular decision group, and the placement of cage was determined by the intraoperative C-arm images. Another thirty-three cases were into the improved decision group, and the placement of cage was also determined by the intraoperative C-arm images. Meanwhile, the cage should be placed closely against the lateral boundary of the anterior longitudinal ligament. The basic clinical characteristics and the location of cage in each lumbar segment were compared between the two groups, and the occurrence of perioperative complications in both groups were also recorded.　Results　A total of 114 lumbar segments were treated by XLIF approach, and there were no significant differences in the baseline characteristic between the two groups (P>0.05). The cages in the improved decision group were significantly more centrally located than that in the regular decision group (P<0.00). Although the perioperative complications, including weakness of iliopsoas muscle and anterolateral thigh numbness, were recorded in both groups, no other neurological complications, no major vascular injuries, and nobowel perforations occurred in either group. There was only one case required a second surgical neural decompression due to the backward position of the cage in the regular decision group.　Conclusions　The junction between the lateral part of the anterior longitudinal ligament and lumbar annulus can be determined as the anterior boundary of the cage placement, which can improve the accuracy of the cage placement and effectively prevent the cage placement from deviating to the anterior or posterior, which has important guiding significance in the clinical application of XLIF. 

Key words: Extreme lateral interbody fusion（XLIF）, 　Anterior longitudinal ligament, 　Cage placement