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

Background and aim: Iliac crest tangent (ICT) has recently emerged as a reliable landmark to correctly number the lumbosacral transitional vertebrae (LSTV). We retrospectively evaluated the reproducibility and accuracy of ICT as a landmark in subjects without 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 the cursor in the sagittal view set to the posterior one third of the vertebral body located one level above the LSTV. When more than 1.25 vertebral body was counted below the ICT, the LSTV was considered as S1, otherwise as L5. The gold standard was counting the vertebrae craniocaudally. Results: The inter-observer agreement was good for determining ICT level (Cohen’s kappa=0.78, p<0.001). The rate of correct numbering by ICT in LSTV group was significantly lesser than controls (43.1% vs 96.4%, respectively, p<0.001). Patients with sacralization had significantly less correct numbering rate than 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 disc degeneration. Key words: computed tomography, iliac crest tangent, lumbosacral transitional vertebra