L5-S1 Disc Access

Chapter 18 L5-S1 Disc Access



Thomas S. Lee, William A. Ante, Michael B. Furman


Accessing the L5-S1 disc is frequently more challenging than accessing the other lumbar levels. The posterior iliac crest often obstructs direct access to the desired disc’s geometric center when the otherwise optimal fluoroscopic trajectory is used. As a result of these unique characteristics, access to this level is described separately here.


This chapter will describe an extradural, oblique, and tilted technique to efficiently and safely access the disc. The transdural approach (i.e., through the L5-S1 interlaminar space and dura) is not recommended or reviewed. A single- or double-needle technique can be used, but a double needle will be likely necessary for some of the described L5-S1 intervertebral disc access “tricks.” The recommended needle gauge is 22 or more for intradiscal entry. If a double-needle technique is used, the introducer spinal needle gauge should be 18 (for an 18 g/22 g combination) or 20 (for a 20 g/25 g combination).


Initially we present a direct trajectory that is similar to that described in the previous chapter. For those patients with high iliac crests or other technical limitations, additional options are presented. The “tricks” described here optimize L5-S1 disc access, including the “over-tilt” and curved-needle techniques. If only one “trick” is to be used, often the “over-tilt” will be sufficient.


We will also demonstrate the fluoroscopic axial view; this is an imaging technique that is unique to the L5-S1 disc.1


As we have for other lumbar disc levels, we recommend that the needle entry be contralateral to the patient’s more symptomatic side to avoid the confusion of needle-entry site pain with the patient’s typical pain.


Note: Please see page ii for a list of anatomical terms/abbreviations used in this book.



1 Direct Trajectory Technique


This technique will result in an initial trajectory that is identical to that seen with standard disc access (see Chapter 17), as long as the iliac crest can be cleared. This technique is used if the iliac crest does not obscure access to the L5-S1 disc.



image Trajectory View




image Trajectory View Safety Considerations




image Avoid the L5 spinal nerve.


image Remain immediately lateral to the junction of the S1 SEP and the inferior base of the S1 SAP, i.e., “low in the hole.”


image Superior or lateral migration can contact the spinal nerve.


image Avoid the dura.


image 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.



image Notes on Positioning in the Trajectory View




image The posterior iliac crest often obstructs the optimal trajectory visualization of the target needle entry site, despite other trajectory view optimization techniques.


image To visualize the entry site, a less ipsilateral oblique positioning of the intensifier may be required; this may complicate the positioning of the superior articular process bisecting the diameter of the superior endplate.


image 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.


Confirm the level (with the anteroposterior view).


Tilt the fluoroscope’s image intensifier cephalad.



image Optimize the L5-S1 disc visualization by adjusting the degree of tilt and lining up the S1 superior endplate (SEP), the L5 inferior endplate (IEP), or both.


image Typically greater cephalad tilt is required as 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.


image An optional pillow can be placed under patient’s abdomen with greater posterior rotation on the ipsilateral side of needle entry to reduce lumbar lordosis and to obtain 5 to 10 degrees of additional rotation.


image Have patients with protuberant abdomens lie slightly obliquely so the needle entry side is slightly elevated; their abdomen may otherwise theoretically push the retroperitoneum into the needle’s trajectory.


Oblique the fluoroscope’s image intensifier ipsilateral to needle insertion (Figure 18–1).



image 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.


image The target needle destination is immediately anterior to the junction of the SAP and the S1 SEP.


image If you cannot clear the iliac crest with this technique, use one of the other ones described later in this chapter (i.e., “the cheat” or the curved-needle technique).


image image

Figure 18–1 A, Fluoroscopic image of the trajectory view for the L5-S1 disc. B, Radiopaque and radiolucent structures. The 3 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 access to the L5-S1 disc then no other “trick” is necessary. Simply access the disc as described in Chapter 17.



2. The “Over-Tilt”




image Safety Considerations


Avoid the common iliac vessels.



image Do not advance too ventrally.


Avoid the spinal canal.



image Do not only advance the needle tip medially if this view shows that the needle is dorsal to the disc.


The “over-tilt” is a technique that will result in an initial trajectory with a cephalad tilt that is not entirely parallel to the L5-S1 disc to “cheat” above the iliac crest.



a 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 (Figure 18–2, A and B).

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Dec 23, 2015 | Posted by in INTERVENTIONAL RADIOLOGY | Comments Off on L5-S1 Disc Access

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