Fig 7.

Needle depth classification. A, The lateral junction of the neural foramen (dotted line) is defined by a line segment connecting the anterolateral margin of the vertebral body with the most lateral margin of the facet joint. A needle tip in a zone within 2 mm medial or lateral to this segment (solid lines) is classified as within the junctional zone (J). A needle tip >2 mm lateral is classified as within the extraforaminal zone (E), and a needle tip >2 mm medial is classified as within the foraminal zone (F). Examples of extraforaminal (B), junctional (C), and foraminal (D) needle tip positions.