Figure 1. Locations of 19 catheter tips (circled x) placed by a midline approach. The position of six catheter tips that did not lie at the longitudinal level of the intervertebral foramen and disc shown in the drawing are indicated in their correct position in the axial plane. In this and other images, anterior is at the top of the image, and anatomic left is at the right of the image. LF = ligamentum flavum; SAP = superior articular process.