## Guided Mark-Up: Lumbar Spine Measurements

**George’s Deviation:** George’s line is the curve created by connection points chosen on the posterior sides of all vertebral bodies. According to some literature (based on the
“Harrison Spine Model”) suggests that in the ideal case these points lie on a smooth curve which is a section of an ellipse with certain major-to-minor axis ratio. Metron’s “George’s Deviation”
parameter is a sum of all the offsets from this perfect elliptical arc. A perfect value would be zero (0.0) meaning that all points lie on the ideal elliptical arc.The higher the value of this
parameter, the more deviation there is from a circular arc.

**Jackson’s Angle:** The angle between two constructed lines: one at the posterior of of L1, and the other at the posterior of the body of L5.

**Ulman’s Measure:** A perpendicular to the sacral base line is created at the sacral promontory. L5 should be at or behind this line. Ulman’s measure quantifies how far
anterior to this line L5 lies in terms of a percentage of the vertebral body’s size.

**Gravity Offset:** A vertical line is constructed from the centroid of the L3 body. Some literature suggests that this line should pass “near” the sacral promontory. The
‘Gravity Offset’ parameter measures this distance.

**L1-T12 Offset:** Construct a line from the inferior posterior corner of the L1 body vertically in the image, and then measure horizontal displacement of the inferior posterior
corner of the T12 body. Some literature suggests this value be “small”.

**Lumbar Lordosis:** The angle between two constructed lines: one along the inferior side of the T12 body, and the other along the sacral base line.

**L1-2 Angle:** The angular change in going from the L1 body to the L2 body - measured by comparing lines constructed along the posterior side of each vertebral body. Some
literature suggests the ideal value is 2.5 degrees.

**L2-3 Angle:** The angular change in going from the L2 body to the L3 body - measured by comparing lines constructed along the posterior side of each vertebral body. Some
literature suggests the ideal value is 6.3 degrees.

**L3-4 Angle:** The angular change in going from the L3 body to the L4 body – measured by comparing lines constructed along the posterior side of each vertebral body. Some
literature suggests the ideal value is 9.7 degrees.

**L4-5 Angle:** The angular change in going from the L4 body to the L5 body – measured by comparing lines constructed along the posterior side of each vertebral body. Some
literature suggests the ideal value is 15.9 degrees.