Injection therapies are interventional techniques used to treat pain conditions that have failed to respond to other, more conservative therapies. It is important, among other items, to inquire as to the allergy history of the patient prior to proceeding with any invasive injection of the sacroiliac joint. Specifically, providone iodine based skin preparation agents, iodine-based arthrography contrast agents, local anesthetic agents, steroids, and agents used for preserving various pharmaceuticals may all be present for utilization during portions of this procedure. Specific inves-tigation as to whether there is a history of latex allergy should be made, as some arthrogram kits come complete with latex gloves or other latex-containing devices, such as syringes, included. Many liquid pharmaceuticals are secured in the bottle by rubber-containing stoppers, which must be removed and not transversed with the injection needle for such patients, for example. Alternatives exist for most of these agents and utilization of substances to which the patient may be allergic is contra-indicated, especially as they can lead to such life-threatening reactions as anaphylaxis in certain individuals.

Sacroiliac joint injection can be safely performed in the outpatient setting in the fluoroscopy suite. No premedication is otherwise indicated in the absence of an allergy to the materials being utilized. Few side effects are reported

Fig. 2. Axial CT image of the sacroiliac joint (arrows).

from the local injection of anesthetics or steroids (14). Sacroiliac joint injection can be performed under the radiologic guidance of fluoroscopy or computed axial tomography (CT). Fluoroscopy is the preferred modality as the procedure can be performed more quickly, with greater ease of physician movement and patient access, and can be more cost effective than utilizing the more bulky and technologist-intensive CT scanner.

The patient is placed in the prone position on the fluoro-scopy table. To view the sacroiliac joint in the tangential plane, the patient may be positioned in an oblique position, or if the fluoroscopic equipment permits, the image intensifier can be rotated to the appropriate obliquity, as determined under fluoroscopic imaging. Recall that the sacroiliac joints are angled between 10 and 30° posteriorly relative to the coronal plane, and 10-20° medially relative to the sagittal plane (9). In the prone position, the medial-most appearing portion of the joint is the most posterior joint plane, with the more lateral appearing portion being the anterior joint plane. Angling the fluoroscopy tube 20-25° in a cephalic direction will help to displace the posteroinferior portion of the sacroiliac joint in a caudal direction, allowing it to be clearly differentiated from the inaccessible anterior portion of the joint, which will be translated more cephalad on the image intensifier. To minimize irradiation to the physician's hands and other anatomy, a metallic localization probe can be used as a pointing device, and, under fluoro-scopy, the desired location for needle placement can be found on the patient's skin, thereafter being marked with an indelible skin marking pen.

The skin under and around the marked site is prepared and draped in standard, sterile fashion, utilizing a providone iodine based skin prep when possible, and an isopropyl alcohol based prep for patients with an iodine allergy. At least three sterile washes are made on and about the area to be injected and instrumented. Following air drying of the skin preparation agent, the sterile drapes are placed into position. Using a small (3- or 5-cc) syringe and a small 25-gauge injection needle, a skin wheal is made using 1% or 2% lidocaine, through which slightly deeper anesthesia may be given, depending on the body habitus of the patient. (Skin anesthesia is not always used, with some authors reporting that the direct transdermal puncture of the joint may be less painful than the puncture necessary for cuta-neous anesthesia) (15). The 25-gauge needle is left in place in the skin, to confirm the desirability of the chosen site of injection. It is important that the site of intubation of the sacroiliac joint by the needle be the inferior aspect as this is the diar-throdial, synovial portion, which is under investigation or being treated by this technique. As defined in the preceding, the upper portion of the sacroiliac joint is fibrous. The preferred skin puncture site is therefore located approx 1 cm caudal to the inferior margin of the joint space, allowing the needle to approach the joint with a posteroanterior and mild caudocephalad trajectory (15).The 25-gauge anesthetizing needle is replaced with a 22-gauge spinal needle (3 1/2- or 5-in, depending on patient body habitus). In obese patients a longer needle may be utilized; however, a 22-gauge needle remains the routine choice for needle size. The 22-gauge needle is placed through the anesthetized skin, from a slightly medial position to the desired joint space intubation site, allowing for the needle and its tip to be angled slightly laterally, following the normal angle and obliquity of the sacroiliac joint itself.

It is usual that the needle tip, when advanced, will articulate with the iliac bone, and when so, the tip can be immediately moved slightly more medial to be positioned within the joint space. The posterior longitudinal liga

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