Lumbosacral

For a patient with normal spinal segmentation, identify the level in the anteroposterior (AP) view by counting cephalad from the sacrum; this is similar to the process of reading an MRI. In up to 15% of the population,¹ a transitional segment may occur. Transitional segments are typically described as involving the lumbarization of the first sacral segment or the sacralization of the fifth lumbar segment. Rarely patients will have six lumbar vertebrae, although some consider these to be lumbarized S1 segments, because an L6 spinal nerve is typically not described. In fact, one study showed that L6 segments do indeed behave like S1 segments; in patients with only four lumbar vertebrae, the inferior-most lumbar segment, L4, behaves like an L5.² This suggests that extra or missing ribs may add to counting confusion. Similarly, some patients may have aberrant segmentation of the cervicothoracic junction, the thoracolumbar junction, or both. Therefore, if a transitional segment is suspected, an MRI scout image is recommended for the purpose of counting caudad from C2 to the lumbosacral junction.³

Ultimately, it is most important to correlate the patient’s clinical symptoms with the pathoanatomy visualized on the imaging that is obtained. Subsequently, images obtained during the procedure need be correlated with the same visualized pathoanatomy. For example, if a patient has right L5 or S1 symptoms and if the MRI suggests the sacralization of L5, an extrusion at L5-S1, and foraminal narrowing at L5, the key concept is to correlate the fluoroscopic lateral image with the sagittal MRI so that the proper levels are injected (Figure 3–5). Often practitioners will focus unnecessarily on the lumbar numbering (i.e., counting caudad from T12 rather than counting cephalad from the sacrum) instead of simply correlating the available imaging (i.e., the sagittal MRI and the lateral fluoroscopic imaging). It is imperative that the presence of the transitional segment is well communicated and documented so that all treating physicians are using the same terminology.

Figure 3–5 A, Sagittal T2-weighted MRI of a sacralized L5. B, Intraprocedural fluoroscopic lateral image of the same patient, with needles being advanced toward the targeted bilateral L4 neural foramen. It is most important to correlate the fluoroscopic lateral view with the sagittal MRI to best treat the proper segment in a patient with a transitional segment. If a surgery has been performed or is being contemplated, it is also important to correlate your numbering with that of other treating physicians (e.g., surgeons, pain physicians, radiologists).

Thoracic

For a patient with normal spinal segmentation, identify the level in the AP view by counting caudally from the cervicothoracic junction or cephalad from T12. The ribs can be used as a guide, but caution must be taken, as some patients do not have 12 bony ribs.

Cervical

For a patient with normal spinal segmentation, identify the level by counting cephalad from the cervicothoracic junction in the AP view or down from C2 (dens) in the AP or lateral projection. For procedures that will be performed in the oblique projection (i.e., cervical transforaminal), identify the level by locating the most superior intervertebral foramen, which is the C2-C3 foramen where the C3 spinal nerve exits, and then count caudally (Figure 3–6).

Figure 3–6 Foraminal oblique view. Note that the most superior neural foramen is C3 (C2-C3) and that the needle is in the C6 (C5-C6) neural foramen. The arrow points to the C3 neural foramen.

Oblique the C-Arm to Optimize the “True” Anteroposterior View

The C-arm image intensifier is obliqued to obtain a “true” AP view relative to the patient, with the spinous process at the midline of the vertebral body and equidistant from each pedicle. The “true” AP view is not necessarily at 0 degrees of obliquity. If the patient has multiple levels to be treated, a “true” AP should ideally be obtained each time for the corresponding level (Figure 3–7).

Figure 3–7 A, Fluoroscopic image of a patient with scoliosis, with the L5 vertebral body slightly rotated and the L4 vertebral body in a “true” anteroposterior view. B, Fluoroscopic image of the same patient, with the C-arm slightly obliqued. Now the L5 vertebral body is in a “true” anteroposterior view, and the L4 vertebral body is slightly rotated. C, Fluoroscopic image of a left C6 transforaminal epidural steroid injection. The spinous processes of C7 and T1 are midline (the segment is in a “true” posteroanterior view), but the C6 spinous process is not midline. D, Fluoroscopic image of the same left C6 transforaminal epidural steroid injection, with the C-arm slightly obliqued. Now the spinous processes of C7 and T1 are not midline (the segments are not in a “true” posteroanterior view), but the C6 spinous process is midline (the segment is in a “true” posteroanterior view).

Tilt the C-Arm to Optimize the “True” Anteroposterior View

The vertebral body endplates, which are also known as the ring apophyses, cover both the superior and inferior horizontal surfaces of the vertebral body. The lining up of the vertebral body endplates is an important technique for obtaining a clear and direct view of the target region for many procedures. For example, when performing discography, the trajectory view requires direct parallel visualization of the endplates. This fluoroscopic view is obtained with the cephalad or caudad tilt of the C-arm image intensifier. This optimizes the superior endplate of the inferior vertebral body, which is visualized as a solid horizontal line rather than as an ellipse (Figure 3–8).

Figure 3–8 A, An image where the vertebrae are preferentially lined up. Note the more elliptical shape of the superior endplate of the L5 vertebral body. Although the L5 inferior endplate is preferentially lined up, the L5 superior endplate is not, because the two L5 endplates are not completely parallel to each other. The L4 endplates are clearly not lined up. B, Fluoroscopic image of the same left L5 procedure with the image intensifier tilted caudad to produce a fluoroscopic image of a “true” L4 anteroposterior view, with the L4 superior endplate preferentially lined up. Note the elliptic shape of the inferior endplate of the L4 vertebral body. Although the L4 superior endplate is preferentially lined up, the L4 inferior endplate is not, because the two L4 endplates are not completely parallel to each other. The L5 endplates are clearly not lined up.

Oblique the C-Arm to Optimize the “True” Lateral View

The C-arm should be obliqued 90 degrees from the angle at which the “true” AP view was obtained. The table may need to be laterally tilted to accommodate angles that cannot be obtained with the C-arm obliquity. When patients have multiple levels to be treated, the “true” lateral view should ideally be obtained for each respective level.

For the cervical spine, a “true” lateral view may be obtained by lining up the lateral masses. If the patient is prone or supine, this is accomplished with the use of the wig-wag, and it may require additional obliquing of the C-arm or the table. If the patient is in a side-lying position, this is accomplished by tilting and occasional additional obliquing. Sometimes each level must be lined up individually (Figure 3–9).

Figure 3–9 A, Fluoroscopic image of the C3-C4 zygapophysial joints not lined up. Note the apparent double joint line created by the impression of the bilateral zygapophysial joints. B, Fluoroscopic image of the C3-C4 zygapophysial joints lined up.

For the thoracic spine, a “true” lateral view may be obtained by lining up the ribs (Figure 3–10).

Figure 3–10 A, Lateral thoracic image not lined up. Note that the interlaminar line is vague and the bilateral ribs (arrows) are not superimposed. B, A true lateral thoracic image acquired by obliquing the C-arm to superimpose the ribs (arrows).

For a patient with scoliosis, the lateral view is obtained by obliquing the C-arm 90 degrees from the angle that was used to best visualize the AP view (Figure 3–11).

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Atlantoaxial Joint Intraarticular Injection Lumbar Zygapophysial Joint Nerve (Medial Branch) Radiofrequency Neurotomy, Posterior Approach Thoracic Zygapophysial Joint Intraarticular Injection, Posterior Approach Thoracic Zygapophysial Joint Nerve (Medial Branch) Radiofrequency Neurotomy, Posterior Approach Lumbar Interlaminar Epidural Steroid Injection, Paramedian Approach Cervical Interlaminar Epidural Steroid Injection, Paramedian Approach

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