Figure 7.

Measurement of the paramedian sagittal diameter based on CT scans. Spinal canal transverse diameter is calculated at the maximally stenosed level (AB). A vertical line extending through the endpoints of the transverse diameter (C and F) determines the boundary of spinal canal (AC and BF). The anteroposterior spinal canal diameter is measured at three sites: the midline of the canal (point E), the boundary of the canal (point C), and midpoint between the midline and boundary (point D). The normal anteroposterior canal diameter is calculated as the average diameter of the adjacent non‐stenosed segments.