Indications and Technique

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IDET is indicated in the treatment of chronic, activity-limiting disco-genic low back pain that has been refractory to conservative measures and is generally characterized by:

1. Function-limiting low back pain of at least 6 months' duration

2. Back pain greater than leg pain with no true radicular symptoms

3. Failure to improve significantly with a comprehensive nonoperative back care program including

Progressive exercise (physical therapy) At least one fluoroscopic epidural injection A course of anti-inflammatory medication Activity modification

4. No extruded disc fragments and no neural impingement revealed by magnetic resonance imaging

5. Pain-provocative discogram with concordant pain reproduction on low-pressure injection at one or more disc levels

Images should be carefully reviewed to detect any annular tears and to exclude any free or extraligamentous herniation of nuclear material. The critical aspect of diagnosis and patient selection relies on a concordant pain response elicited on discography by an experienced discographer. Contraindications include nerve root compression (radicular pain distribution or motor findings on exam), extruded disc fragment, active infection and/or discitis, and bleeding disorder. Severe degenerative disc disease with greater than 50% decrease in disc height is a relative contraindication, since disc narrowing may preclude catheter navigation or placement of the catheter within the disc.

The procedure is generally performed in a fluoroscopy suite,21 using an intravenous conscious sedation protocol, typically with mi-dazolam and fentanyl. The sedation level should be such that the patient is comfortable and sleepy but can be roused easily for questioning about radicular symptoms during needle placement and catheter heating. As with all spinal procedures, the indications for the procedure, risks, and appropriate expectations should be discussed with the patient prior to beginning, and informed consent should be obtained. If performed carefully by a skilled operator, IDET is very safe, and complications are very rare (<2% in our experience).20 The risks are generally those associated with any needle puncture, plus the additional potential risks of traversing nerve damage on disc access, disc herniation from catheter manipulation, and localized nerve damage from the application of thermal energy.

Having given informed consent, the patient is placed prone on a flu-oroscopy table and midazolam sedation is initiated, while the low back is prepared and sterile drapes arranged. The prep area should be roughly equivalent to that used for discography. The disc to be treated is visualized fluoroscopically, and the fluoroscope is angled parallel to the disc, such that the endplates above and below are seen en face (Figure 7.4). The imaging orientation is typically craniocaudal angulation for L4-5 and L5-S1 and caudocranial for L1-2 and L2-3 (Figure 7.5). Then, to permit visualization and selection of the appropriate site for disc entry, the fluoroscope is obliqued laterally without changing the craniocaudal angulation. The site of entry is nearly the same as that used for discography and is chosen to allow access to the anterior aspect of the disc nucleus while minimizing the chance of encountering the traversing nerve root from the level above. From the level above the disc to be treated, the lumbar nerve root descends obliquely across the lateral aspect of the disc. Appropriate obliquity is generally achieved when the superior articular facet has traversed between one third and one half of the disc (Figure 7.6). In this projection, there is a triangular access window bordered medially by the superior articular process, inferiorly by the superior endplate, and superiorly and laterally by the traversing root (Figure 7.7).

Local anesthesia is achieved in the skin overlying the triangular access window and is carried down to the peridiscal soft tissues with a 22-or 25-gauge spinal needle. The spinal needle is advanced slowly, and if any radicular symptoms are provoked on needle advancement, the position of the traversing nerve is noted and the spinal needle is withdrawn and reoriented to approach the disc medial to and below the position of the nerve root as close as possible to the superior articular process.

After local anesthesia, a skin dermatotomy is made with a scalpel blade and the 17-gauge introducer needle is then advanced along the

Vertebrae Not Aligned
Figure 7.4. AP radiograph angled in craniocaudal fashion, parallel to the L4-5 intervertebral disc; the superior endplate of L5 and the inferior endplate of L4 are seen en face.

trajectory of the spinal needle and into the disc (Figure 7.8). The needle is advanced slowly to avoid encountering the traversing root, and if radicular symptoms are elicited, the needle is withdrawn and reoriented to avoid the root. A tactile resistance and gritty crunching is encountered when the needle first enters the annulus, and the fluoro-scope is then repositioned in a posteroanterior (PA) projection. Care should be taken not to advance the needle beyond the disc margins, and if there is any confusion about the position of the needle tip during advancement, the position should be checked fluoroscopically in two orthogonal planes. The patient may report transient localized back pain as the needle penetrates the annulus. Radicular symptoms are not expected and may indicate needle position too close to the descending root. The needle position is checked in the PA projection confirming the tip position just inside the annulus. Under lateral fluoroscopy, the introducer needle is then advanced minimally to achieve positioning of the tip in the nucleus pulposus just in the anterior half of the disc. Optimal positioning is with the tip between a 12 and a 3 o'clock position (Figures 7.9 and 7.10). The needle is rotated to ensure that the opening in the needle tip points medially to facilitate catheter navigation. The stylet is removed from the introducer needle, and the catheter

Figure 7.5. Lateral diagram showing angulation (arrows) necessary for parallel approach to the lumbar discs. Cau-docranial angulation is required for accessing the upper lumbar discs, and craniocaudal angulation is necessary for accessing the lower discs.

Figure 7.6. Oblique lateral radiograph demonstrating projection for safe disc access at discography or annuloplasty. An-gulation is chosen parallel to the disc to be accessed, and obliquity is chosen to optimize access to the central disc and avoid the traversing nerve root. Optimum access is typically obtained when the superior articular process of the level below the disc has traversed between one third and one half of the disc under fluoroscopy.

Fluoroscopic DiscographyTraversing Nerve Root

Figure 7.7. Oblique lateral diagram depicting the access window for safe disc entry. In the oblique projection, the access window to the disc is defined by a roughly triangular window delineated by the superior articular process medially, the superior endplate below, and the traversing nerve root laterally and above. Staying close to the superior articular process keeps the needle as far as possible from the traversing nerve root.

is advanced slowly into the needle until the distal marker on the catheter enters the needle hub, indicating that the catheter tip is about to exit the tip of the needle. The catheter must be aligned such that the curve in the catheter tip points medially to allow the curve in the catheter tip to deflect off the inner margin of the disc annulus. Under lateral fluoroscopy, the catheter is slowly advanced into the disc. A

Vertebral Curve Catheter
Figure 7.8. Oblique lateral radiograph demonstrating disc access with the introducer cannula. The needle enters the annulus in the access window parallel to the angulation of the disc.

Figure 7.9. Axial diagram depicting optimum positioning of the introducer needle in the disc. For IDET, optimum catheter positioning is just in the anterior half of the nucleus between 12 and 3 on the clock face. This approach facilitates guiding the catheter along the inner aspect of the anterior annulus.

Vertebral Curve Catheter

small amount of resistance is expected when the catheter first enters the disc, but to avoid binding the catheter tip on annular tears, care should be taken to ensure that the catheter tip always advances when the proximal end is advanced. If significant resistance is met, positioning should be checked fluoroscopically to ensure that the catheter is not damaged, and the catheter should be removed and reoriented. The curve in the catheter is utilized to steer the catheter around the inner margin of the annulus. Lateral fluoroscopic monitoring allows the operator to visualize the catheter curving off the anterior and poste-

Figure 7.10. AP radiograph demonstrating the introducer cannula in the disc. The cannula is oriented parallel to the disc and positioned between 12 and 3 o'clock in the anterior half of the nucleus.
Vertebral Curve Catheter

rior margins of the annulus and to ensure that the catheter does not breach the anterior or posterior margins of the disc and enter either the retroperitoneum or the spinal canal (Figure 17.11). The catheter should be visualized gently curving off the anterior and posterior margins of the disc without extending significantly beyond the margins of the vertebral bodies above or below (Figure 7.12). Once the posterior curve has been visualized and the catheter tip is no longer pointing directly posterior, the fluoroscope is reoriented in the PA projection. If the catheter becomes inadvertently kinked during navigation, and is difficult to withdraw, the introducer needle should be partially withdrawn a few centimeters, whereupon further attempts at removing the catheter can be made. If the catheter is not easily removed from the introducer and becomes bound to the needle tip, the catheter and needle should be gripped firmly together and withdrawn as a unit to avoid shearing the catheter. To avoid damage to the catheter and the possibility of shearing, the catheter should never be advanced or withdrawn forcefully when resistance is encountered. A damaged catheter should never be heated and should be replaced.

Catheter navigation is generally not painful for the patient but may, rarely, provoke some minor back pain. If severe discomfort or radicular symptoms are encountered, manipulation should be stopped and positioning should be carefully checked fluoroscopically to confirm catheter location within the disc.

Lateral Vertebral Shearing

Figure 7.11. The course of the catheter along the inner aspect of the annulus and optimal positioning for treatment of the posterior annulus. (A) Axial cross section demonstrates a smooth curving course of the catheter along the inner annulus to terminate with the heating element (between the radiopaque markers) positioned along the posterior an-nulus. (B) Lateral projection is typically used for advancing the catheter under fluoroscopy. Lateral projection allows the operator to view the catheter making smooth curves along the anterior and posterior aspects of the annulus to avoid perforation into the retroperitoneum and spinal canal. (C) AP projection demonstrates optimal final positioning of the catheter with the heating element draped across the posterior annulus pedicle to pedicle.

Figure 7.12. Lateral radiograph demonstrating smooth curves of the catheter along the anterior and posterior margins of the annulus with no perforation of the disc.

Figure 7.12. Lateral radiograph demonstrating smooth curves of the catheter along the anterior and posterior margins of the annulus with no perforation of the disc.

Vertebral Annular Fissures PicsPosterior Annular Fissure

The catheter is slowly advanced to achieve positioning with the heating element (distal 2 in. of catheter from tip to radiopaque 2 in. marker) draped across the entire posterior annulus of the disc (pedicle to pedicle on the PA projection). The catheter position is examined and photographed in two projections (Figure 7.13), documenting the position of the heating element across the posterior annulus and not contacting the introducer needle.

In extremely degenerated or desiccated discs, it may not be possible to navigate the entire posterior annulus without binding in annular fissures. Every attempt at optimum positioning should be made, maneuvering the curved catheter tip and introducer as just described. If the catheter tip cannot be advanced beyond the midline of the posterior annulus, an initial treatment is carried out at the best achievable position and the procedure repeated from the contralateral approach so that the entire posterior annulus is heated.

Once appropriate catheter positioning has been achieved, the catheter is attached to the generator box and the resistive element is heated. Resistance display on the generator box should be noted, since an excessively high reading (>250-300 ohms) may indicate that the catheter has been damaged, hence should not be used. Heating

Overlaps Heating

Figure 7.13. Radiographs demonstrating final positioning of the catheter for treatment. (A) AP projection demonstrates the heating element positioned across the annulus pedicle to pedicle. Although the catheter overlaps the introducer on this projection, the heating element is not in contact with the needle at any point. (B) Lateral projection demonstrates the catheter to be contained entirely within the disc, with the heating element positioned along the posterior annulus.

Figure 7.13. Radiographs demonstrating final positioning of the catheter for treatment. (A) AP projection demonstrates the heating element positioned across the annulus pedicle to pedicle. Although the catheter overlaps the introducer on this projection, the heating element is not in contact with the needle at any point. (B) Lateral projection demonstrates the catheter to be contained entirely within the disc, with the heating element positioned along the posterior annulus.

Overlaps Heating
b

a protocols vary but are generally selected to maximize safe heat application to the annulus and minimize discomfort to the patient. A typical protocol uses gradual increase in temperature to achieve catheter heating of 90°C for 4 to 6 minutes. The patient may report provocation of typical back pain and some typical referred pain with energy delivery. This can be controlled with intravenous analgesics at the discretion of the treating physician. True radicular symptoms, however, are not expected, and if pain radiating to the leg is reported, energy delivery should be halted at once and the catheter repositioned.

After treatment, the catheter is withdrawn with a steady pull, taking care to avoid snagging the catheter on the introducer needle. Intradiscal antibiotics may be injected at the discretion of the treating physician as a prophylaxis against potential disc infection. The needle tract is anesthetized with local anesthetic as the introducer needle is withdrawn. If the catheter position was suboptimal and a second treatment from the contralateral approach is required, no antibiotics should be injected until the second treatment is complete.

Hemostasis is achieved with a few minutes of manual compression, and the entry site is dressed with a sterile bandage.

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