Minimally Invasive Spine Interventions
Discogenic-referred pain is now recognized in multiple retrospective and prevalence studies as the single most common etiology of chronic lower back pain (~40% of lower back pain generators).2-11 The application of lumbar discography in diagnosing internal disc disruption (IDD) has provided the spine specialist with crucial information in order to consider various nonsurgical as well as surgical treatment options. For an intervertebral disc to cause pain there needs to be an established innnervation pattern and mechanisms by which nociception can be precipitated. The pathophysiology of discogenic pain involves both biochemical (internal disc disruption: proteolytic/enzymatic denaturation of nuclear proteoglycans, decreased nuclear hydrophilicity) and biomechanical factors (annular disc disruption: chemical and mechanical sensitization, secondary inflammation). Painful degenerative discs have demonstrated biophysiological changes in the matrix including reduced total glycosaminogylcans, reduced water content, increased matrix metalloproteinases, increased vascularity, and deeper penetration of nociceptive fibers from the outer annulus. The nucleus pulposus contains inflammatory and nociceptive chemical mediators, and even the extent of annular wall tearing has been well correlated with concordant discogenic pain during diagnostic discographic stimulation.
Discogenic lumbar pain may present in a number of overlapping fashions: axial pain, axial pain with somatic-referred extremity pain, axial pain with radicular-referred pain, and axial pain with concurrent axial joint pain. Discogenic lumbar pain management options are available with more treatment opportunities than what were available 10-20 years ago. Over the last few years, these intradiscal therapeutic options have presented with such a flurry of newer technologies and techniques that, at times, they have outpaced the importance of reproducible, clinical outcome studies to verify their technical success and validity. Many pain management specialists are left with empirical and anecdotal experiences from personal and other colleague’s accounts. With this important thought in mind, I will mention a few of the more popular, common, and novel intradiscal lumbar therapeutic techniques available for lumbar spine pain management practitioners.
Intradiscal Electrothermal Annuloplasty
Intradiscal electrothermal annuloplasty (IDET™ or IDEA) using the SpineCATH® Intradiscal Catheter (created and trademarked in 1997 by ORATEC Interventions, Inc. and currently owned and operated by Smith & Nephew, Inc.) is a novel addition to the interventional physician’s armamentarium of treatments for patients with chronic, contained discogenic low back pain and concordant IDD and who have failed a program of aggressive, non-operative therapy.12-24 IDET provides a new outpatient treatment option for patients who are not recommended for, or who do not elect, other more invasive treatments, such as lumbar disc surgery (ie. discectomy or fusion). The SpineCATH intradiscal catheter has been approved by the Federal Drug Administration (FDA) for use in treating symptomatic patients with annular disruption of contained, lumbar herniated discs.12 This new technology has been developed to safely treat intervertebral discs in a minimally invasive manner and still provide physicians with a definitive approach to addressing internal disc disruption. The intradiscal catheter delivers controlled thermal energy directly to the annular wall and disc nucleus via a resistive heating coil in order to create temperature-controlled coagulation and shrinkage of intradiscal collagenous tissue. The SpineCATH system was specifically developed to thermocoagulate annular tissue, thermally modulate intradiscal collagen tissue, cauterize granulation tissue, and to minimally reduce intranuclear volume in small, contained disc herniations. The steerable catheter (which has undergone slight modifications in design since it’s inception) allows for precise intradiscal navigation for percutaneous spinal intervention. Performed under light sedation, the catheter is inserted through a 17-gauge introducer trochar needle and is easily positioned with fluoroscopic guidance. Since this procedure is significantly less invasive than operative disc surgery; the result is a percutaneous outpatient procedure that is no more invasive than a lumbar discogram. The initial success rate for the procedure, depending on patient selection, has been noted to be around 50-75%.14-24 A recent ongoing, randomized, double-blind, placebo-controlled 6-month outcome trial evaluating the efficacy of IDET for the treatment of chronic discogenic low back pain by Dr. Kevin Pauza and colleagues has verified the validity of statistically significant reduction in pain levels and physical limitations in treated vs. control subjects.24 This valuable ongoing study is something to be emulated by the other intradiscal pain management techniques in order to continue to verify the continual, reproducible successes of these newer technologies for the benefit of both insurance companies and patients alike.
Discogenic lumbar pain management options are available with more treatment opportunities than what were available 10-20 years ago.
The disc itself is a virtually avascular structure which allows heat to be held in the tissue with relatively little fluctuation during treatment. Adjacent structures are protected from thermal injury by the vascular circulation outside the disc which quickly dissipates any heat conducted beyond the disc. Temperature and power control give the IDET catheter the optimal ability to deliver focused energy at the point of contact. Heat is transferred by conduction from the catheter to the adjacent disc tissue. Temperature sensors deliver feedback to the generator which adjusts power levels as necessary to reach and maintain set target catheter temperatures. Optimum treatment temperatures are followed as previously documented in temperature mapping experiments done in the cadaveric and in vivo validation studies.12,14-16 These mapping studies indicated that optimal temperature levels for achieving collagen modulation (80-90º C) and for neurolysis of nociceptor destruction in the inner/outer annular wall (45-60º C) are achieved while maintaining low epidural temperature levels (maximum 40º C) and avoiding damage to myelinated nerves. These validation studies also documented an average total disc volume reduction, due to morphologic changes in the outer disc surface was 12.7% (range: 10-16.7%); and it was estimated that in the area of treated tissue alone (tissue reaching at least 60º C), there was an approximate 40% decrease in disc tissue volume, with type 1 collagen contraction.12-16