| Parameter | Imaging Modality Sequence | Level where measured | Description |
|---|---|---|---|
| Interfacet distance | MRI | Axial T2W | Distance on a line connecting the Lower intermedial joint space of facet joints vertebral (post-op) (Fig. 1 B-x') or inner disc flaval surfaces along the same line (pre-op)18 (Fig. 1 A-x) |
| Effective AP distance | MRI Sag T2W | Mid-body | Distance between a vertical line connecting the annulus of adjacent discs and the upper spino-laminar junction (pre-op) (Fig. 1 G) or the dorsal dural margin (post-op) (Fig. 1 H) |
| Lateral recess depth | MRI Axial T2W | Lower intervertebral disc | Distance between the posterior surface of disc and anteromedial portion of superior articular process (post-op) (Fig. 1 B - y' & z') or its attached ligamentum flavum (pre-op) (Fig. 1 A - y & z)19 |
| Lateral recess angle | MRI Axial T2W | Lower intervertebral disc | Angle between the floor (posterior disc margin) and roof (anterome-dial edge of superior articular process [post-op] (Fig. 1 D) or its attached ligamentum flavum [pre-op] (Fig. 1 C)) of the lateral recess20* |
| Cross-sectional area of the spinal canal | MRI Axial T2W | Lower intervertebral disc | (Fig. 1 E & F) |
| Cobb's angle | AP standing radiograph | Angle between the superior end-plates of the uppermost and lowermost split laminar levels |
↵* modified to be used in MRI to include the effect of posterior annular bulge and hypertrophied ligamentum flavum on lateral recess angle. MRI – Magnetic resonance Imaging; AP – Antero-posterior; T1W – T1-weighted sequence; T2W – T2 weighted sequence.