Throughout this book, suggestions for optimal positioning of the patient and alignment of the C-arm are illustrated for each type of block (Fig. 1-1). The patient’s position is chosen with three factors in mind: safety, access for the block, and patient comfort, in this order of priority. Safety is first and requires a clear understanding of the anatomy, thus the description of each block begins with a discussion of the relevant regional anatomy. Avoiding critical structures is best accomplished at the outset in planning the approach for neural blockade. A good example is found in the celiac plexus block. Although the rib margins and the vertebral column are easily visualized under fluoroscopy, the position of the abdominal aorta, diaphragm and pleural reflections, and adjacent liver, kidney, and spleen must be inferred to perform this block safely and successfully. As you review the regional anatomy for each block, it will be apparent that the same target can be approached from many different angles. In most cases, only a single technique is illustrated. The illustrated techniques have been chosen with an eye toward minimizing the risks of the procedure. Although some approaches are actually simpler to perform (e.g., cervical medial branch blocks from a lateral approach), they are best reserved for experienced practitioners because of the inherent dangers in getting confused by the complex radiographic anatomy of the cervical spine. Finally, when all else is equal, position can be chosen to promote patient comfort. Indeed, most patients are more comfortable in the supine position than in the prone position, particularly for cervical injections. Once you understand the anatomy of the target for any given block and the critical structures between the skin’s surface and the needle’s final destination, you may choose to vary both patient position and alignment of the C-arm to suit your own preferences.

Alignment of the C-arm is illustrated for each block, and the approximate angle of the C-arm is also described within the text. The accepted convention is to describe the position and angle of the C-arm according to the direction the x-rays travel from the x-ray source, through the patient, to the image intensifier. To minimize radiation exposure, the x-ray source is typically kept under the x-ray table (see Fig. 2-6). Thus, when the patient is placed prone without angulation of the C-arm, an anterior-posterior radiograph is obtained, and when he or she is placed supine, a posterior-anterior radiograph results. Lateral movement of the C-arm from the sagittal plane is termed oblique angulation. When the x-ray path is angled away from the axial plane toward the head, this is termed cranial angulation and when toward the foot is termed caudal angulation.

Image guidance can improve the accuracy and comfort of many injections while minimizing the time required to perform them when a coaxial technique for needle placement is used. The term “coaxial” emphasizes that the advancing needle and the x-ray path share a common axis. In this way, the needle tip is advanced from the skin’s surface to the final target at a depth with only small changes in the needle’s direction. The needle tip and the target are seen at all times. Compare this with the more traditional means of using surface landmarks to determine the initial site of needle entry through the skin, followed by advancing the needle until it contacts a bony surface. Subsequent adjustments require that the needle is withdrawn its entire length before redirection. In the past, radiographic guidance was used infrequently and then only to confirm the needle’s final position.

To illustrate the coaxial technique, an intra-articular lumbar facet injection is shown in Figure 1-1. The patient is positioned prone. The lumbar facet joint to be injected is brought into clear view by moving the C-arm to align the x-ray path with the axis of the joint (see Fig. 1-1A). Using computed tomography (CT) and three-dimensional reconstruction, an image rotated to the same axis illustrates the bony anatomy (see Fig. 1-1B). Once the facet joint is seen clearly, a radiopaque marker is placed on the skin’s surface until it overlies the target joint (see Fig. 1-1C). In this way, the area of skin directly overlying the target along the x-ray axis is identified. The skin and subcutaneous tissues are then anesthetized directly under the tip of the surface marker using a small amount of local anesthetic. The needle is inserted a short distance until it is seated in the subcutaneous tissues overlying the target. The angle of the needle is adjusted until it is roughly parallel to the x-ray axis. This initial adjustment is performed without taking any radiographs—a glance at the axis of the C-arm image intensifier in comparison to the axis of the needle is all that is needed to bring them into rough alignment during initial needle placement. The needle should remain quite superficial until it is well aligned with the x-ray beam (see Fig. 1-1D). The needle is perfectly aligned with the x-ray beam when the hub of the needle is superimposed on the tip and appears as a radiolucent circle. Only after it is well aligned should the needle be advanced any deeper. Some examples of common difficulties with initial needle placement are shown: Figure 1-1E illustrates poor needle alignment, and Figure 1-1F