Abstract
This chapter describes strategies to enter the L5-S1 disc, which requires a modified technique, and delineates the “tricks” to approach the L5-S1 disc when the posterior iliac crest makes access more challenging. Initially, we present a direct trajectory that is similar to that described in Chapter 17A . For patients with high iliac crests or other technical limitations, additional options are presented. The “tricks” described here optimize the L5-S1 disc access, including the “over-tilt” and curved needle techniques. If only one “trick” is to be used, the “over-tilt” will often be sufficient.
Keywords
discogram, discography, fluoroscopy, L5-S1, lumbar, lumbar disc, lumbosacral, manometer, provocation
Note: Please see pages ii , iii for a list of anatomic terms/abbreviations used throughout this book.
This chapter describes strategies to enter the L5-S1 disc, which requires a modified technique, and delineates the “tricks” to approach the L5-S1 disc when the posterior iliac crest makes access more challenging. Initially, we present a direct trajectory that is similar to that described in Chapter 17A . For patients with high iliac crests or other technical limitations, additional options are presented. The “tricks” described here optimize the L5-S1 disc access, including the “over-tilt” and curved needle techniques. If only one “trick” is to be used, the “over-tilt” will often be sufficient.
We will also demonstrate the fluoroscopic axial view; this is an imaging technique that is unique to the L5-S1 disc because of the lumbosacral lordosis.
Direct Trajectory Technique
This technique is used if the iliac crest does not obscure access to the L5-S1 disc space. The technique will result in an initial trajectory that is identical to that seen with standard disc access (see Chapter 17A ), as long as the iliac crest can be cleared.
Trajectory View
Confirm the level (with the anteroposterior view).
Tilt the fluoroscope’s image intensifier cephalad.
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Optimize visualization of the L5-S1 disc by adjusting the degree of tilt and lining up the S1 superior end plate (SEP), L5 inferior end plate (IEP), or both.
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Typically, greater cephalad tilt is required compared with the other disc levels to position the posterior iliac crest away from the point of disc entry. Therefore, preferentially lining up the S1 SEP (instead of the L5 IEP) will improve the likelihood of clearing the iliac crest as a result of the S1 SEP’s more cephalad orientation.
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Optional: Place an abdominal pillow lateralized ipsilateral to the needle entry side to reduce lumbar lordosis and to obtain 5 to 10 degrees of additional obliquity.
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Lay patients with protuberant abdomens slightly oblique, so the needle entry side is elevated; their abdomen may otherwise theoretically push the retroperitoneum into the needle’s trajectory.
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Oblique the fluoroscope’s image intensifier ipsilateral to needle insertion ( Fig. 17B.1 ).
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Attempt to position the fluoroscope such that the superior tip of the S1 superior articular process (SAP) is bisecting or nearly bisecting the diameter of the S1 SEP.
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The target needle destination is immediately anterior to the junction of the SAP and the S1 SEP.
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If you cannot clear the iliac crest with this technique, use one of the alternate techniques described later in this chapter (i.e., the “over-tilt” or curved needle technique).
Fig. 17B.1
A, Fluoroscopic image of the trajectory view of the L5-S1 disc. B, Radiopaque and radiolucent structures. The three needles shown in the picture are already placed in the three cephalic discs. The green “X” identifies the trajectory. If the iliac crest does not block the access to the L5-S1 disc then no other “trick” is necessary. Simply access the disc as described in Chapter 17 .
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Notes on Positioning in the Trajectory View - ▪
The posterior iliac crest often obstructs the visualization of the optimal trajectory of the target needle entry site, despite other trajectory view optimization techniques.
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To visualize the entry site, less ipsilateral oblique of the intensifier may be required; this may complicate the positioning of the SAP bisecting the diameter of the SEP.
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Solving this visualization challenge while getting a reasonable trajectory may require one or both of the “tricks” described in this chapter; however, often the “over-tilt” will be all that is needed.
Trajectory View Safety Considerations - ▪
Avoid the L5 spinal nerve (SN). Superior or lateral migration of the needle tip can contact the SN.
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Remain immediately anterior to the junction of the S1 SEP and the inferior base of the S1 SAP, i.e., “low in the hole.”
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Avoid the dura. While advancing the needle toward the disc, do not drive too far medial until entering the disc. A medial straying needle can enter the dura.
The “Over-Tilt”
The “over-tilt cheat” is a technique that utilizes an initial cephalad tilt trajectory that is not entirely parallel to the L5-S1 disc to pass the needle above the iliac crest.
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Visualize the midpoint of the target L5-S1 disc with the appropriate ipsilateral oblique rotation. The S1 SAP should bisect the diameter of the S1 SEP, but the iliac crest will still overlap the target point ( Fig. 17B.2, A and B ).
Fig. 17B.2
A, L5-S1 discogram fluoroscopy setup with the S1 SAP bisecting the diameter of the S1 SEP. However, the iliac crest is overlapping the target point (red “x”) . B, Radiopaque structures that correspond to Fig. 17B.2, A . C, L5-S1 discogram fluoroscopy setup with the needle placed. The iliac crest is no longer overlapping the target point. Because of the “over-tilted” angle, the disc end plates are no longer lined up. D, Radiopaque and radiolucent structures that correspond with Fig. 17B.2, C . As always, stay “low in the hole” to avoid hitting the exiting L5 spinal nerve (SN). The small green “x” corresponds to the needle placement for direct L5-S1 entry. E, L5-S1 discogram with the introducer needle in place and with the L5 IEP and S1 SEP now lined up. Because the disc end plates are lined up, the needle is not parallel to the beam; hence, this is not a “true” trajectory view. F, Radiopaque and radiolucent structures that correspond with part E of this figure. L5-S1 discogram with the introducer needle in place and with the L5 IEP and S1 SEP now lined up. Because the disc end plates are lined up, the needle is not parallel to the beam; hence, this is not a “true” trajectory view. G, L5-S1 discogram, lateral view, with the needle just entering the intervertebral disc. Note that because the needle trajectory used the “over-tilt,” the needle is not parallel to the end plates. H, Radiopaque structures that correspond with part G of this figure. L5-S1 discogram, lateral view, with the needle just entering the intervertebral disc. Note that because the needle trajectory used the “over-tilt,” the needle is not parallel to the end plates. I, L5-S1 discogram, anteroposterior view, with the needle just entering the intervertebral disc. The end plates are lined up, but the needle is entering with the angle used for the “over-tilt” to clear the iliac crest. J, Radiopaque structures that correspond with part I of this figure. L5-S1 discogram, anteroposterior view, with the needle just entering the intervertebral disc. The end plates are lined up, but the needle is entering with the angle used for the “over-tilt” to clear the iliac crest. K, L5-S1 discogram, lateral view, with the needle approaching the geometric center; this is the “final position” of the intervertebral disc. Note that because the “over-tilt” was used, the needle trajectory is not parallel to either end plate and that it is actually aimed toward the S1 SEP. The needle tip will need to be adjusted superiorly. L, Radiolucent structures that correspond with part K of this figure. L5-S1 discogram, lateral view, with the needle approaching the geometric center; this is the “final position” of the intervertebral disc. M, L5-S1 discogram, anteroposterior view, with the needle in the geometric center; this is the “final position” of the intervertebral disc. N, Radiopaque structures that correspond with part M of this figure. L5-S1 discogram, anteroposterior view, with the needle in the geometric center; this is the “final position” of the intervertebral disc.Related posts:
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