Assessment of Ureters at Dangerous Locations in Lateral Lumbar Interbody Fusion

INTRODUCTION: This study aimed to investigate the ureteral running position from the viewpoint of the spine, and to identify the spinal level and left-right difference in the ureter at a dangerous location of ureteral injury during surgery. METHODS: This retrospective study included 100 consecutive patients (39 males and 61 females; average age, 70.4 years). Preoperative contrast-enhanced computerized tomography (CT) scans obtained in the supine position for patients who underwent lateral lumbar interbody fusion (LLIF) were analyzed. The ureter location was divided into four regions on the axial CT images based on the lumbar disk levels as follows: A (ventral-medial), B (ventral-lateral), C (dorsal-medial), and D (dorsal-lateral). The C region surrounded by the vertebral body and the psoas muscle was assumed to have the highest probability of ureteral injury. We examined the characteristics of the ureteral position at each disc level. RESULTS: In the upper lumbar spine, the ureter was outside the lateral dorsoventral axis from the contact point of the psoas muscle, while in the lower lumbar spine, it was inside the axis. The ureters located in the C region increased significantly in the lower lumbar disk levels (L1-L2 and L2-L3: 0%; L3-L4: 5.5%; L4-L5: 14.8%; L5-S: 31.5%). Comparing the left and right sides, especially at L4-L5, the ureter in the C region was observed in 21% of all ureters on the left side and in 9% on the right side. With respect to gender differences, the ureters present in the C region were significantly more common in women at lumbar disk levels L3-L4, L4-L5, and L5-S. CONCLUSIONS: The ureters in the C region were common on the left side and at lower lumbar disk levels. To avoid ureteral injury, it is necessary to confirm the location of the ureter by using preoperative images and performing LLIF carefully.