Fig. 3. Plain film image illustrating the correct prearthrographic needle positioning of the 22-gauge spinal needle in the poster-oinferior quarter of the sacroiliac joint.
ments are quite strong, and once transversed, an abrupt decrease in resistance to forward motion is appreciated (Fig. 3). At this time lateral imaging is performed to confirm that the needle tip has not transversed the anterior ligamentous structures and passed into the presacral region, an unusual but not impossible event. Further, 0.5 to 1.0 cc of nonionic contrast (180 mg/dL iohexol [Omni-paque]; Nycomed, Princeton, NJ) may be injected to document appropriate needle placement.
Pharmaceutical therapy of the sacroiliac joint routinely involves the utilization of both an anesthetic agent and a steroid agent. If septic arthritis is suspected, steroids should never be instilled. Analysis of joint effusion aspiration samples or sterile nonbacteriostatic saline lavage samples may be necessary to exclude an infected joint (15). The anesthetic agent and steroid are generally drawn into a single syringe for simultaneous intraarticular injection. Just such a steroid-anesthetic mixture might include 40 mg of methylprednisolone acetate (0.5 mL of Depo-Medrol) with 2-3 cc of 0.5% bupivacane hydrocloride (Marcaine) for each separate joint injected.
Various local anesthetic agents that have been utilized for joint space injection include 5-25 mg of Xylocaine (lidocaine), 10-50 mg of Carbocaine (mepivacaine), 2.512.5 mg of Sensorcane (bupivacaine), and 2.5-12.5 mg of Marcaine (bupivicaine). Various long-acting steriod agents that have been utilized for joint space injection include 1.5-3 mg of Celestone suspension (betametha-sone sodium phosphate and beta-methasone sodium ace tate), 2-6 mg of an Aristospan suspension (triamcinolone hexacetonide), and 4-10 mg of Hydeltranol (prednisolone tebutate). Care must be made to ensure com-binations of agents are compatible to be admixed to avoid such potential incompatibilities leading to precipitation or floc-culation (16).
If CT-guided injection is being utilized, the patient is placed on the CT table in a prone position. Contiguous axial views can be obtained through the sacroiliac joint to visualize the mid- and lower joint spaces. The proposed site of skin puncture can be marked utilizing an opaque or metallic marker, such as a paper clip. Once a proposed site is chosen, the skin can be marked with an indelible marker and thereafter prepped and draped in a similar fashion as described in the preceding. A procedure and instruments similar to those described in the preceding for fluoro-scopic guidance can be used with CT as the guidance modality. Prior reports suggest that although CT may provide additional clinical information in up to 10% of patients, it is not advocated for routine use (17). Rather, it is reserved for morbidly obese patients or for those patients who have otherwise failed sacroiliac joint injection localization or intubation attempts performed under fluoroscopy.
As the sciatic nerve rests anterior to the piriformis muscle, aggressive injection of local anesthetic or improper position of the needle tip may cause a transient lower extremity weakness. Recent reports of magnetic resonance imaging (MRI) guidance for sacroiliac joint injection may help to minimize this potential complication (18).
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