Difference in vertical mid-vertical angle (lumbar spine)
The difference in vertical mid-vertical angle is the difference in the vertical mid-vertebral angle (VMVA) between the caudal segment angle and the adjacent cephalad segment angle of the three most caudal segments of the lumbar spine as measured on a mid-sagittal MRI or a lateral radiograph.
A line drawn through the midpoint of the horizontal lines through the upper and the lower endplates of the vertebral is the vertical mid-vertical line. The angle formed by two adjacent vertical mid-vertical lines is called the vertical mid-vertebral angle.
The VMVA is greatest at the most caudal mobile segment of a lumbar vertebra in a normal individual and decreases progressively across the more cephalad adjacent segments 1.
In cases of lumbosacral transitional vertebra, the cephalad adjacent segment angle is similar or larger than the transitional caudal segment angle 1.
The difference in VMVA is the most reliable method of identifying a high-grade lumbosacral transitional vertebrae 1.
In cases of a solid bone bridge (i.e. Castellvi type 3 and 4), the difference in VMVA of ≤+10° has a sensitivity/specificity of 100/89% (mid-sagittal MRI) and 94/74% (lateral radiograph respectively 1.
- Type IIa/b: 16°
- Type IIIa/b: - 9°
- Type IV: -5°