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 lumbosacral transitional vertebrae (LSTV). We retrospectively evaluated the reproducibility and accuracy of the 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 ⅓ 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 it was considered as L5. The gold standard was counting the vertebrae craniocaudally.

Results: The interobserver agreement was good for determining ICT level (Cohen’s kappa = 0.78, P < 0.001). The rate of correct numbering by ICT in the LSTV group was significantly less than in the controls (43.1% vs. 96.4%, respectively, P < 0.001). Patients with sacralization 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 disc degeneration.

Keywords: Computed tomography; iliac crest tangent; lumbosacral transitional vertebra.

Figure 1

A) Sagittal CT of spine, yellow line crossing the posterior half of the vertebra (white arrow) located one level above LSTV (blue arrow). B) The corresponding coronal CT demonstrating the ICT passing through the uppermost points of the iliac crests. Note the less than 1.25 vertebra, indicating presence of sacralization.

Figure 2

A) Sagittal CT of spine, yellow line crossing the posterior half of the vertebra (white arrow) located one level above LSTV (blue arrow). B) The corresponding coronal CT demonstrating the ICT passing through the uppermost points of the iliac crests. Note the more than 1.25 vertebra, indicating presence of lumbarization.