Reliability of the L3 Transverse Process as a Landmark for Lumbar Spine Enumeration Across Different Vertebral Segmentation Patterns: A Retrospective CT Study

Background/Objectives: Vertebral numbering on limited lumbosacral imaging is difficult when the thoracic or lumbar count varies. The L3 transverse process has been proposed as a landmark because it is often the longest, but this has not been tested across segmentation patterns. This study assessed whether L3 as the level bearing the longest transverse process is independent of thoracic and lumbar vertebral count on whole-spine CT.

Methods

Of 499 trauma CT examinations with confirmed numbering, all 49 non-standard thoracolumbar formulas were included, together with 17 C7T12L5 spines that remained after exclusion of transitional and numerical anomalies at every level (n = 66). Bilateral lumbar transverse-process lengths were measured on multiplanar reconstructions. The longest level was identified by morphological and presacral numbering. Associations with thoracic patterns (C7T11, n = 10; C7T12, n = 43; C7T13, n = 13) were tested with the Fisher-Freeman-Halton exact test and Monte Carlo simulation. Nine primary analyses were adjusted with the Holm procedure. Inter-observer agreement was assessed with an intraclass correlation coefficient.