Caudal

The prone position is preferred for caudal ESIs, but these can also be done in the lateral decubi-tus position with the hips flexed. Often, padding is placed under the pelvis to accentuate the

FIGURE 10 (A) Oblique spot image (10°) demonstrating the tunnel through which one can access the posterior epidural space from a paramedian approach. The L3/4 level has been selected, and the window resembles an upside-down horseshoe (arrow). (B) Similar spot image with spinal needle approaching the spinous process, which is to the left on this image. (C) Straight anteroposterior spot image demonstrates contrast within the posterior epidural space. The needle tip is directly in the midline when it enters the epidural space.

FIGURE 10 (A) Oblique spot image (10°) demonstrating the tunnel through which one can access the posterior epidural space from a paramedian approach. The L3/4 level has been selected, and the window resembles an upside-down horseshoe (arrow). (B) Similar spot image with spinal needle approaching the spinous process, which is to the left on this image. (C) Straight anteroposterior spot image demonstrates contrast within the posterior epidural space. The needle tip is directly in the midline when it enters the epidural space.

sacral hiatus. The sacral hiatus is palpated by running a finger down the middle of the sacrum, until the coccyx is identified. The paired cornua are just above this level, off midline, and often palpable. Once the hiatus is identified by palpation, it is verified with lateral fluoroscopy. After marking the hiatus, gauze padding is placed within the gluteal crease to block the spillage of sterilizing agent onto the perineum. Standard sterile preparation and drape are followed by anesthesia of the skin and sacral hiatus region, including periosteum, with 1% lidocaine buffered with sodium bicarbonate.

The choice of epidural needle size is based on individual preference, but patients complain of pain less with a 25-gauge spinal needle (3.5-inch) than a 22-gauge needle. A 20-gauge or larger may cause prolonged superficial sacral pain because of irritation caused by the needle scraping along the periosteum during its advancement. Also, larger needles may not be flexible enough to follow the hiatus contour and may penetrate through the sacrum into the perirectal region or dorsally out the sacral roof to the skin (Fig. 10). Creating a gentle curve at the end of the needle may help the needle to follow the slope of the sacrum.

With a 45° angle of entry and the bevel down, the needle is advanced through the sacrococcygeal ligament and stopped when the underlying bone is encountered. The needle is withdrawn slightly from the periosteum, and the entry through the hiatus is verified fluoro-scopically with AP and lateral views. After achieving satisfactory positioning, the bevel is turned up and the needle is laid almost horizontal, until the needle shaft is in the same plane as the sacral canal. The needle is slowly advanced through the canal, often requiring a gentle rotating motion allowing it to follow the curved contour of the canal. Intermittent AP and lateral views should confirm the midline position of the needle. Needle advancement is stopped at the S2/S3 junction or slightly lower (Fig. 11).

Following needle placement, the extradural location of the needle tip is verified, initially by having the patient Valsalva as well as aspirating with a 5 cc syringe, examining for cerebral spinal fluid and blood. Additionally, under fluoroscopy, 1 to 2 cc of nonionic contrast is injected. If the needle is extradural in location, the contrast distribution from the epidurogram resembles a Christmas tree and does not disperse rapidly (Fig. 12). If the contrast has a serpentine course and flows away from the midline, the needle tip is likely in an epidural vein. Often, only a minute adjustment to the tip is necessary to extricate it from the vessel. It may also help to direct the needle slightly dorsally because the epidural veins are more concentrated at the ventral aspect of the epidural space. If the contrast fills only one side of the epidural space, it may be due to a plica mediana dorsalis. Redirecting the needle or repuncture may be needed to ensure satisfactory medication delivery.

If the needle is in the subarachnoid space, the procedure is terminated. Readjusting of the needle is not recommended in this instance. The procedure should be rescheduled about seven days later.

After confirming the needle-tip position and documenting it with AP and lateral spot radiographs, the medication is injected. A typical injection consists of 2 cc of Kanalog-40 followed by 5 to 8 cc of preservative-free 0.5% lidocaine. Recommendations for volume of

FIGURE 11 Needle tip at the target, which is the midportion of S3.

FIGURE 12 (A) Typical "Christmas tree" pattern of epidural contrast in the sacral canal. (B) Lateral view confirms contrast within the canal.

injectate have varied widely. More recent reports (73,74) have shown that a volume of 10 mL consistently reaches the low-to-mid lumbar spine. A volume in this range will not overdilute the steroids.

There should not be any resistance during the injection and if any force is required, needle malposition should be considered. During the injection, patients may complain of pressure at the site of injection or dull or shooting pain down the legs. These symptoms subside with a decreased injection rate. After the medication is delivered, the needle is removed, the overlying puncture site is cleansed with alcohol, and an adhesive bandage is placed. The patient is assisted while rising slowly. The postprocedure routine is the same as for interlaminar injections.

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