Defining Normal Vertebral Angulation at the Thoracolumbar Junction

The purpose of this cross-sectional study is to define the normal range of endplate angulation at T12 and L1 and, by doing so, to validate the angle measurement tools that are readily available on nearly all PACS. Two hundred consecutive lateral scout CT scans were examined in patients who were either 25 (n = 100) or 35 (n = 100) years old. The endplate angles for T12 and L1 were measured using a "Cobb angle" tool on a standard PACS workstation. Twenty-two cadaveric vertebrae were also imaged, and measurements obtained from the lateral scout CT image using electronic calipers were compared with measurements obtained with a goniometer. The mean endplate angle at T12 measures 4.34 degrees (2 SD, 4.5 degrees) and at L1, 4.48 degrees (4.26 degrees). The normal range of endplate angulation is therefore -0.16 degrees to 8.84 degrees at T12 and 0.22-8.74 degrees at L1. No statistically significant difference was seen in the endplate angulation when men were compared with women or 25- and 35-year-old age groups were compared. A strong correlation exists between direct and CT-derived endplate angle measurements. Vertebral endplate angulation can be reliably measured using widely available PACS workstation tools. The mean endplate angle for T12 and L1 is approximately 4.5 degrees, with an approximate range extending from 0 degrees to 9 degrees. For practical purposes, an endplate angle of 10 degrees or more can be considered outside the normal range.