The patient is placed in prone position. The C-arm is placed initially in neutral position. The target point is the inferior, posterior aspect of the joint, approximately 1–2 cm cephalad of the most inferior end [22]. In this view, both anterior and posterior joint lines are seen and the posterior joint line is usually the more medial one (Fig. 48.4). The C-arm is rotated and adjusted until the medial cortical line of the medial silhouette is maximally crisp, which coincides with the beam directed into the posterior opening of the inferior joint space (Fig. 48.5). Usually, this view is obtained with 5–20° of contralateral rotation. A 22- or 25-gauge spinal needle is used and directed toward initially to the sacrum first to appreciate the depth required. Once the bone is contacted, the needle is redirected toward the joint line. The operator should note the depth of the initial contact so that the needle should not penetrate a few more millimeters deeper than this depth (Fig. 48.6). Once the needle has entered the joint space, 0.3–0.5 mL of contrast is injected. In posteroanterior view, the contrast material should be seen traveling rostral along the joint (Fig. 48.7). A lateral X-ray should be used to confirm the needle position (Fig. 48.8). The joint volume in asymptomatic individual is approximately 1.6 mL but is about 1.08 mL in patients requiring SIJ injection. Thus, the injectate is usually 1 mL.