Role of iliac crest tangent in correct numbering of lumbosacral transitional vertebrae

Abstract

Background/aim: The iliac crest tangent (ICT) has recently emerged as a reliable landmark to correctly number the lumbosacraltransitional vertebrae (LSTV). We retrospectively evaluated the reproducibility and accuracy of the ICT as a landmark in subjectswithout disc degeneration.Materials and methods: Fifty-eight patients with LSTV [19 female, 41 (26–52) years] and 55 controls without LSTV [23 female, 40(26–55) years] who had undergone spinal computed tomography were included. The ICT was drawn on the coronal images, with thecursor in the sagittal view set to the posterior ⅓ of the vertebral body located one level above the LSTV. When more than 1.25 vertebralbody was counted below the ICT, the LSTV was considered as S1, otherwise it was considered as L5. The gold standard was countingthe vertebrae craniocaudally.Results: The interobserver agreement was good for determining ICT level (Cohen’s kappa = 0.78, P < 0.001). The rate of correctnumbering by ICT in the LSTV group was significantly less than in the controls (43.1% vs. 96.4%, respectively, P < 0.001). Patients withsacralization had a significantly lower correct numbering rate than patients with lumbarization (33.3% vs. 63.2%, respectively, P = 0.03).Conclusion: ICT does not seem to be a reliable landmark for correct numbering of LSTV in patients with no intervertebral discdegeneration.