Approximately 45% of back pain can be attributed to discogenic source.1,2 Lumbar discogenic pain is typically caused by pathophysiological changes that occur within the intervertebral disc. A loss of hydration in the nucleus pulposus from aging, chronic abnormal posturing, or injury can lead to both, delamination and fissuring in the annulus fibrosus (Figure 36-1A, B). This structural damage is a part of unclear degenerative process, where in addition to described changes, there is an in-growth of the nerve endings (nociceptors) that are normally restricted to the outer third of the annulus, extending now to the nucleus of the affected disc. Inflammatory cytokines such as tumor necrosis factor, nitric oxide and metalloproteinases, are also released, causing pain through several possible mechanisms. These changes transform the disc into a primary nociceptive structure. In addition, structural changes intrinsic to the intervertebral disc can lead to reduced mechanical load-bearing capacity resulting in altered spinal biomechanics, which can contribute to future back pain.
Comparison between intact and fairly degenerated lumbar disc. Preparation was fixed in 10% neutral buffered formalin for 1 week. Individual lumbar segments were prepared, taking care to preserve the posterior elements. (A) Mostly intact annulus with minor lamellar disorganization in a minimally degenerated disc with the absence of fissuring. (B) Lamellar disorganization in a degenerated lumbar disc with presence of radiating tear extending to the outer 1/3 of the annulus.
Intradiscal biacuplasty (Figure 36-2) is the latest minimally invasive, posterior annulus heating procedure (annuloplasty) for treatment of discogenic pain. This technique employs two bipolar electrodes, between which bipolar radiofrequency lesioning is conducted. The use of internally cooling electrodes provides for stable and relatively even heating over a large portion of the posterior annulus. Throughout the entire procedure, the patient is awake and able to communicate with the physician. This allows feedback from the patient, and reassurance from the physician, as the probes are positioned and radiofrequency heating conducted. With the patient laying prone, 2 TransDiscal electrodes are inserted bilaterally via introducers using fluoroscopic guidance. Once positioned in the posterior annulus, and confirmed by fluoroscopic imaging, RF generator delivers controlled energy to the tissue. The temperature change is measured via strategically positioned thermocouples near the tip of the probe. Over a period of approximately 10 minutes, the heat delivered should increase temperature of the internal thermo sensor incrementally to 50°C, and then maintained for an additional 5 minutes. The procedure has been shown to lead to significant pain relief at 3, 6, and 12 months, as well as the improvements in functional capacity and patient satisfaction. While still a recently described technique, it appears to be the most promising of all annuloplasty methods. Randomized controlled studies are ongoing, and further evaluation is needed.