Figure 1

The illustration of the lines and angles in Method 1, Method 2 and Method 3. a Measurement of the angle from the inferior endplate of the vertebra above the degenerative disc to the superior endplate of the vertebra below on the flexion and extension films. b Measurement of the angle from the inferior endplate of the vertebra above the degenerative disc to that below the degenerative disc on the flexion and extension films. c Measurement of the angle from the posterior edge of vertebra above the degenerative disc to that below the degenerative disc on the flexion and extension films.