Canal Injections

Fig. 17.1

Sacral hiatus (arrow) with the sacral cornu (∗). (Reproduced with permission from Dr. Danilo Jankovic)

../images/457420_1_En_17_Chapter/457420_1_En_17_Fig2_HTML.jpg — Fig. 17.2

Sacral hiatus covered by sacrococcygeal ligament. (Reproduced with permission from Dr. Danilo Jankovic)

The sacral hiatus contains lower sacral and coccygeal nerve roots (passing through the sacral hiatus), filum terminale externa, and fibro-fatty tissue (Fig. 17.3). The coccygeal plexus is formed as an anastomosis between S4, S5, and coccygeal nerve. Depending on age, the termination of the thecal sac varies between the lower border of the S1 foramen in adults and the S3 foramen in children. In 1–5% of patients, the dural sac terminates at S3 or below, an important fact to remember when placing the epidural needle to avoid dural puncture. Variations in the anatomy of the sacrococcygeal area (up to 10%) or even total absence of the posterior wall of the sacral canal can make the identification of anatomy in this region challenging.

../images/457420_1_En_17_Chapter/457420_1_En_17_Fig3_HTML.jpg — Fig. 17.3

Filum terminale and dura in sacral canal. (Reproduced with permission from Dr. Danilo Jankovic)

Patient Selection

Chronic low back pain with radicular pain secondary to disc herniation or radiculitis not responding to conservative treatment can be considered for caudal canal injection. It is especially useful when there is difficult anatomy in the lumbar spine, such as previous lumbar surgery or degenerative changes, limiting transforaminal or interlaminar access to the epidural space.

Ultrasound Scan

Position: Prone or Kraske position with the buttocks separated.
Probe: Linear probe is generally used. A convex probe rarely is needed, except in some cases of obese patients.

../images/457420_1_En_17_Chapter/457420_1_En_17_Fig4_HTML.jpg — Fig. 17.4

Short-axis (upper panel) and long-axis (lower panel) scan of the caudal canal. (Reprinted with permission from Philip Peng Educational Series)

Scan 1

Figure 17.4 Upper panel. A transverse scan is performed first and the structures need to be identified are the sacral cornua (SC), the apex of the sacral hiatus (indicated with bold arrows), and the sacrococcygeal ligament (line arrows). The caudal epidural space (∗∗∗) is the hypoechoic area in between the surface of the sacrum and the sacrococcygeal ligament.

Scan 2

Figure 17.4 Lower panel. The transducer is turned 90 degrees to have long-axis view of the sacral canal. The sacral canal (∗∗∗) and the entrance (bold arrows) covered by the thick sacrococcygeal ligament (line arrows) are well appreciated.

Procedure

Needles: 17G Tuohy epidural needle (when catheter insertion is planned); or a 3.5-inch 22G spinal needle
Drugs: Volume 10–20 mL with diluted local anesthetic and 40 mg Depo-Medrol (volume depending on using catheter or not)

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