Intradiscal Electrothermal Therapy

Updated: Nov 30, 2015
  • Author: Aathi R Thiyagarajah, MD; Chief Editor: Erik D Schraga, MD  more...
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Intradiscal electrothermal annuloplasty (IDEA) or intradiscal electrothermal therapy (IDET), as it is known commercially, is a new and minimally invasive technique for the treatment of discogenic low back pain. IDET involves the percutaneous threading of a flexible catheter into the disk under fluoroscopic guidance. The catheter, composed of thermal resistive coil, heats the posterior annulus of the disk, causing contraction of collagen fibers and destruction of afferent nociceptors. Although initial clinical studies suggest that IDET might be effective in approximately 70% of patients with chronic unremitting low back pain, its efficacy has not been assessed in randomized controlled clinical trials.

The objectives of this article are to review published reports and present a general overview of IDET. More than 75,000 IDET procedures have been performed in the United States since 1998. The average cost of IDET is 7-8 times less than the average hospital cost of lumbar fusion surgery.


Patient Selection

As with other interventional procedures, proper patient selection increases the chances of a favorable outcome. IDET should be considered in patients who have had discogenic low back pain for more than 6 months and whose condition has not responded to conservative treatment. [1]

Ideal candidates are patients with a single affected disk as determined by MRI and discography. Patients with the predominant complaint of axial pain with or without some non-radiating limp pain are selected. Patients with severe radicular symptoms due to a herniated disk or patients with severe spinal stenosis are not good candidates. A severely collapsed disk (>50% of disk height lost) might not respond well to IDET treatment because of technical difficulties in catheter placement and the procedure's questionable effect on high-grade disk injury. Similarly, severely disrupted disk morphology as revealed by discography may not respond well. Patients older than 55 years may have lower success rates because of poorer healing. Cigarette smoking may affect annular collagen tissue and hinder adequate recovery following the procedure.

Ideal candidates for IDET meet the following conditions:

  • Preserved disk height (>50%)
  • Contained disk herniation
  • Axial pain greater than leg pain for 3-6 months
  • Posterior annular deficit
  • Motivated patient with no major psychological issues
  • No facet disease
  • Patient younger than 55 years
  • Failure to improve after >6 wk of conservative treatment
  • Discogenic pain confirmed by provocation discography

Mechanism of Action

IDET is thought to decrease discogenic pain by 2 different mechanisms: thermal modification of collagen fibers and destruction of disk nociceptors. Breakage of heat-sensitive hydrogen bonds of the collagen fibers causes collagen contraction. With disk temperatures reaching 650°C, collagen may contract as much as 35% from its original size. The tightening of annular tissue may enhance the structural integrity of degenerated disk and repair the annular fissures. The process of disk restructuring (as shown by time courses of patients' pain relief) may take several months to reach its full extent. IDET might also cause destruction of sensitized nociceptors in the annular wall. Denervation by thermal energy is used widely for peripheral and central nervous system lesioning and might contribute to partial initial pain relief following the IDET procedure.


Technical Aspects

The technique for approaching the disk for IDET is similar to the technique used for discography.

After the skin is infiltrated with local anesthetic, a 17G introducer needle is inserted into the disk, guided by oblique fluoroscopic imaging.

Once the position of the needle in the nuclear cavity is established by anteroposterior and lateral fluoroscopic views, the thermal catheter is inserted through the needle. See the images below.

Anteroposterior fluoroscopy view shows the introdu Anteroposterior fluoroscopy view shows the introducer needle in the disk. A transpedicular approach was used to access the disk.
Lateral fluoroscopy view shows the introducer need Lateral fluoroscopy view shows the introducer needle in the disk.

The SpineCATH System thermal catheter is used (Oratec Interventions, Inc., Menlo Park, Calif). The catheter should be placed circumferentially around the inner surface of the posterior annulus. See the images below.

Anteroposterior fluoroscopy view shows the cathete Anteroposterior fluoroscopy view shows the catheter around the inner surface of the posterior annulus.
Lateral fluoroscopy view shows the catheter around Lateral fluoroscopy view shows the catheter around the inner surface of the posterior annulus.
Axial fluoroscopy view shows the catheter around t Axial fluoroscopy view shows the catheter around the inner surface of the posterior annulus.

Once the catheter is in satisfactory position, it is heated from 37°C to 65 °C. After the temperature has remained at 65° for 1 minute and the patient has not complained of excessive pain, the temperature is increased by 1°C every 30 seconds until it is between 80° and 90°C. The actual temperature of the annular tissue is as much as 15°C lower than the temperature of the catheter tip.

  • Comprehensive patient and cadaver temperature mapping studies have shown the safety of placing heating catheters within the disk tissue.
  • In these studies, the temperature of the epidural space reached a maximum of 39.30°C when the catheter tip was heated to 90°C. In the same studies, the disk tissue reached a maximum temperature of 72°C and the outer annulus 46°C with catheter tip temperatures of 90°C.

Postprocedure Care

The practitioner must realize, and point out to the patient, that recovery is gradual. During the first 7 days after the procedure, patients might experience a significant increase in pain. Significant pain relief may take 8-12 weeks. The healing process reaches its peak 4 months after the procedure. During that period, the patient must limit physical activity and follow a carefully structured rehabilitation program. In general, patients should not return to any kind of heavy physical work during the first 4 months following the procedure. A gradual increase in daily activities is recommended. The patient should do only minimal sitting or standing during the first few days after treatment, and a corset should be worn during the first 6 weeks. Athletic activities can be resumed gradually starting 6 months after the IDET procedure.

A sample rehabilitation program after IDET is as follows:

  • Week 1
    • Walking allowed
    • Wear lumbosacral corset during all activities
    • Sit for only 35-45 minutes at a time
    • No lifting, twisting, bending, or driving
    • No work
    • No physical therapy
  • Weeks 2-6
    • Wear lumbosacral corset during all activities
    • Increase sitting time as tolerated
    • Lift no more than 10 pounds
    • Driving allowed
    • No twisting or bending
    • Might return to light or sedentary work
    • No physical therapy
  • Weeks 6-12
    • Lift no more than 25 pounds
    • No twisting or bending
    • Might start physical therapy emphasizing lumbar stabilization program and biomechanics
  • Week 12 and beyond
    • Lift 25-50 pounds
    • Might return to full work
    • Continue physical therapy emphasizing home exercise program

Review of Published Studies

The first published report of IDET was by Saal and Saal. In that study, a cohort of 25 patients was shown to have improved clinical outcomes 6 months after they underwent IDET. [2]

Karasek and Bogduk, in a case-controlled study, compared the outcomes of 35 patients treated with IDET with those of 17 patients who were unable to undergo IDET because of lack of insurance coverage. [3]

  • The control group underwent a comprehensive, conservative regimen, which included physical therapy, strengthening, conditioning exercises, and education. This group was monitored for 3 months. The patients in the treatment group underwent IDET and were monitored for 1 year.
  • In the control group, only 1 patient had significant improvement 3 months after treatment, 3 had modest improvement, 4 had no improvement, and 9 had worsening of their condition; Visual Analog Scale (VAS) pain scores were not improved; only 1 of the 5 patients who were working prior to starting the study returned to work; analgesic use was not affected significantly.
  • In the IDET group, 32 of 36 patients had statistically significant ( P < .001) decreases in VAS scores 12 months after treatment; 60% of the treatment group had at least a 50% reduction in pain; 23% experienced complete pain relief; and all patients returned to work or continued to work. Of the 19 patients who had at least 50% pain relief, 11 discontinued opioid medication and 5 continued opioids at lower doses.

Saal and Saal completed a prospective case series of patients with 1 year of follow-up. [4] Sixty-two patients were selected for IDET from a pool of 1116 patients with low back pain who did not respond to at least 6 months of aggressive conservative care. Follow-up was at 1 year, and outcomes were analyzed by using preprocedural and postprocedural VAS, SF-36, and return-to-work status. Of the 62 patients treated, 44 improved their VAS by a mean of 3 points (P < .001). Physical function scores improved in 71% of the patients and showed a mean change of 20 (P < .001). Bodily pain scores improved in 74% of the patients, with a mean change of 17.4. Ninety-two percent of the patients returned to work.

Shadid et al studied 145 consecutive patients referred for IDET after having positive discography findings for discogenic back pain. [5] Of these, 120 were available for follow-up, with a mean duration of 18 months. The average duration of preprocedural symptoms was 39.8 months. Scores on a numerical rating scale and activity levels were monitored. Overall, approximately one third of patients improved, one third remained unchanged, and one third became worse. Fifty-five percent of the patients stated they would not repeat the procedure.

Pauza et al performed a randomized, placebo-controlled trial of IDET in which patients in the IDET group displayed greater mean improvements in pain, disability, and depression. [6]

Animal studies have been reported. In one such study, posterolateral anular lesions were experimentally induced and allowed to mature for 12 weeks in the intervertebral disks of sheep. [7] IDET was performed in an attempt to denervate and repair the annular lesion. The histologic and immunohistochemical effects of IDET were studied. Vascular granulation tissue and posterior anular neoinnervation were observed in the experimentally induced posterolateral anular lesions. IDET delivered at 90°C in the sheep consistently heated the posterior annulus and the nucleus to a temperature normally associated with coagulation of nociceptors and collagen contraction. IDET did not denervate the posterior annular lesion. Thermal necrosis was observed within the inner anulus and adjacent nucleus from 6 weeks after IDET. The reported benefits from IDET appear to be related to factors other than denervation and repair.

IDET-induced stress concentrations in disks obtained from cadavers have been analyzed. [8] These studies revealed that IDET has a significant but inconsistent effect on compressive stresses within intervertebral disks. This may provide a partial explanation for the variable success of IDET.

A prospective study was conducted to evaluate improvements in pain and disability in worker's compensation patients with discogenic low back pain who underwent treatment with the IDET procedure. [9] The study of 53 patients revealed that IDET can be a useful, safe, and cost-effective option in the management of carefully selected workers' compensation claimants who have discogenic chronic low back pain.

A single-arm, prospective clinical trial evaluated back pain severity, physical function, and quality of life outcomes in 56 highly selected patients with lumbar discogenic pain. [10] The patients were treated with IDET and monitored for an average of 20.5+/-4.4 months. Various outcomes were assessed, including back pain severity by VAS; sitting, standing, and walking tolerances; and health-related quality of life (measured with SF-36). Pain scores and functional tolerance improved, and 7 of 8 quality of life domains showed significant improvement over baseline evaluations. These results suggest that durable clinical improvements can be realized after IDET in highly selected patients who have mild disc degeneration, confirmatory imaging evidence of annular disruption, and concordant pain provocation by low pressure discography.

Past literature review has revealed that most patients have reported improvement in symptoms following both spinal fusion and the IDET procedure. The IDET procedure appears to offer symptom amelioration sufficiently similar to that afforded by spinal fusion without the attendant complications in early studies. [11] However, some authors consider IDET an antecedent rather than alternative to spinal fusion based on final outcome studies. [12]



Complications due to IDET are infrequent. In a retrospective study, the complications of 1675 IDETs performed at 5 different spine centers were reviewed. [13] In the same study, data related to 35,000 SpineCATH intradiscal catheters from the medical device reports (MDRs) of the United States Food and Drug Administration (FDA) were analyzed. A total of 6 nerve root injuries were reported. All but one of the nerve root injuries were reported as occurring at the time of disk puncture. Five of the six completely resolved and one case was resolving. No cases of diskitis were reported.

Six cases of post-IDET disk herniation were reported at the treated level 2-12 months after treatment. Four resolved with nonoperative care, and 2 required disk excision. Nineteen cases of catheter breakage were reported. All were associated with repeated catheter manipulation that resulted in kinking. In 16 of these, the catheters were left in the discs; none of these cases has been associated with any patient morbidity. Eight cases of superficial skin burn at the needle puncture site were reported. A case of post-IDET bladder dysfunction was reported.

A fatal case of an unintentional dose of intrathecal cefazolin, which had been diluted in the nonionic contrast agent that was used to confirm needle placement, was reported. [14] Cefazolin should not be mixed with the contrast agent used to document initial needle placement during discography.



IDET is an innovative tool for the treatment of discogenic back pain. Research suggests that IDET is effective in 60-70% of patients with chronic discogenic low back pain whose symptoms have not improved with a comprehensive nonoperative program. Physical function and quality of life outcomes in highly selected patients have improved. IDET is minimally invasive and has a low complication rate; therefore, it may offer advantages over surgery. [15, 16, 17] However, the outcomes of IDET have not been compared with those of fusion and chronic pain management. Validation of the initial reports of IDET in placebo-controlled randomized trials is needed. [18]

In practice, back pain and some leg pain of discogenic origin is a common presentation. The IDET procedure afforded improvements in leg pain that correlated well with improvements in back pain.