Degenerative Disc Disease
Disc degeneration occurs during the natural aging process of a person. While everyone experiences disc degeneration as they age, not all are symptomatic. The pain generators for degenerative disc disease are most likely multi-factorial. The outer fibril portion of the disc, or annulus fibrosus, acts as a support structure and a “tire” to contain and protect the inner, gel-like portion of the disc, the nucleus pulposus. The outer third of the annulus is innervated and if damaged, may result in pain. The nucleus pulposus contains a number of inflammatory molecules. If the inflammogens come in contact with the pain fibers in the sensitized nerve endings of the outer annulus (or if nerves grow into the nucleus), back pain may result. If they come in contact with the posterior nerve root, leg or radicular pain may result. Patients classified as having degenerative disc disease typically present with axial (back) pain greater than radicular pain.

Spinal discs have very little blood supply and therefore cannot heal themselves as effectively as those tissues with adequate blood supply. However, over time the pain from chronic degenerative disc disease decreases as the inflammatory molecules dissipate. Patients needing treatment typically undergo a fusion procedure, which is major back surgery. In the past 5 years, however, less invasive treatment options have been introduced, such as annuloplasty.

Disc Herniation
Another injury of the spinal disc that can cause pain is a disc herniation. A disc herniation happens when a portion of the disc protrudes into the spinal canal, compressing the nerve root and/or causing an inflammatory response. A large portion of disc herniations occur in the lower spine (L4/L5, L5/S1) because those vertebral levels bear the greatest load.

There are different types of disc herniations; one is a contained herniation with no nuclear penetration of the annulus. Another is an extruded herniation that protrudes beyond the annulus. The last is a sequestered herniation with a free fragment of nucleus pulposus. Disc herniations are typically seen in the posterolateral (near and far) or directly posterior in the disc. The symptoms typically present with a disc herniation are both back and leg pain.

Treatment Options
Whether the disc will heal by itself will typically be determined in the first 6 weeks. During this period a patient may undergo conservative therapy to treat symptoms; which may include physical therapy, medications, and/or injections. If the patient does not improve with conservative therapy, more aggressive procedures may be considered.

For degenerative disc disease, annuloplasty or fusion may be considered. For disc herniation, the treatment depends on the nature of the herniation: if the herniation is contained, a percutaneous discectomy may be performed; if the herniation is not contained, open discectomy is typically recommended.

See Figure 1 for the typical treatment progression of a patient with leg/back pain.

Figure 1: Typical treatment progression of a patient with leg/back pain.

Treatment options for degenerative disc disease refractory to conservative care include annuloplasty and fusion. Fusions have been performed for over 30 years for structural and degenerative conditions. In 1998, a new procedure was introduced to treat degenerative disc disease, called IDET (Intradiscal ElectroThermalTM Therapy) or annuloplasty. Fusion remains the gold standard for treating degenerative disc disease, but IDET may be a good treatment option for a very select group of patients.

IDET is a minimally invasive treatment for degenerative disc disease, especially with young patients who may experience accelerated degeneration from the added stress on adjacent segments from fusion¹. It is an outpatient procedure that requires only local anesthesia and mild sedation. Using a posterolateral approach similar to discography, a needle is placed in the nucleus of the spinal disc. A catheter is then inserted through the needle into the disc and positioned along the posterior wall of the annulus. The thermal catheter is then heated using a specific algorithm, theoretically denaturing the chemically-sensitized nociceptors penetrating the nucleus of the disc, thereby eliminating the pain they cause and/or contracting the collagen within the annulus that has been weakened through the degenerative process, thus strengthening the annular wall. The patient typically goes home that day with a small bandage on the entry site.

A double-blind, prospective, randomised, placebo controlled study was published on IDET in 2004. Outcomes from this study showed that 40% of patients fitting very strict inclusion criteria achieved greater than 50% pain relief, while approximately 50% of patients realized no significant benefit². So while IDET may provide an additional option for very carefully selected patients with discogenic pain, it is not a procedure for broad use.

The posterolateral lumbar fusion was first used to treat patients with degenerative disc disease in 1971. There are many ways to fuse two vertebrae together to reduce painful motion between segments, but they all have one thing in common: bone grafts. Hardware such as plates, screws, or cages may be used as an adjunct to the procedure to facilitate bone graft healing. Regardless of the method used, the ultimate goal is to eliminate motion between the two vertebral bodies that cause the pain. One literature review indicated that the studies available for fusion (47, no randomised studies) show 68% of patients had a satisfactory outcome (range 16-95%)³.

Disc Herniation
Treatment options for disc herniations that do not respond to conservative care include percutaneous discectomy, open discectomy, and fusion. Fusion options are discussed above, so this section describes discectomy procedures.

Similar to the progression of treatments for degenerative disc disease, open discectomy was introduced over 60 years ago, with a percutaneous approach following 20 years later to provide less invasive treatment options. Each technique has evolved over time to the most common procedures today, microdiscectomy (an open procedure) and DISC Nucleoplasty® (a percutaneous procedure).

Open Discectomy
Microdiscectomy is performed under general anesthesia and the patient typically stays overnight following the procedure. While the patient lies on their stomach, a one-inch incision is made in the back. Material is removed from the symptomatic disc and retractors are used to keep the skin and muscle out of the surgeons working field. Usually bone and ligaments must be removed to give the surgeon access to the herniated disc. Tools and a microscope (or in some cases, an endoscope) are then used to remove disc nucleus tissue and any disc fragments to decompress the nerve root. Once the nerve is decompressed, sutures are used to close the surgical site and the patient is taken to recovery.

Percutaneous Discectomy
Percutaneous discectomy is an outpatient procedure performed under fluoroscopic guidance. With the most common method, the patient lies on their stomach and a needle is inserted into the back and navigated into the disc under fluoroscopic guidance using a typical posterolateral discography approach. The patient is awake during the procedure for careful monitoring, using local anesthesia and a mild sedative to keep the patient comfortable. Once the needle is positioned within the disc a device is inserted through the needle to remove nucleus tissue. Once the disc is sufficiently decompressed, the needle and device is removed and the patient goes home that day with a small bandage over the entry site.

Since the introduction of a percutaneous approach to disc decompression approximately 40 years ago, many technologies have been introduced to more effectively decompress the disc. Chemonucleolysis was first used in the 1960s, involving the chemical dissolution of the nucleus by injection of an enzyme through the needle into the disc nucleus. By removing some of the disc tissue, chemonucleolysis decompressed the disc and relieved symptoms. Success rates approached almost 80% at 6-month follow up in a double-blind study⁴, but some serious complications reduced its use and it is no longer used in many parts of the world.

APLD and laser discectomy were the next techniques introduced. The APLD procedure uses a blunt-tipped, reciprocating, suction-cutting probe to remove nuclear tissue. One study of APLD showed a success rate of 77.5%⁵. Laser discectomy used a YAG laser to remove tissue and saw success rates above 75%⁶. Research of laser techniques showed that removing tissue at the centre of the disc decompresses a herniation at the periphery proving the mechanism of action of percutaneous discectomy⁷. Extensive set-up and the requirement of a large annular incision decreased the use of these techniques.

DISC Nucleoplasty™ is the most widely used method of percutaneous disc decompression today. Based on the knowledge learned from previous methods, DISC Nucleoplasty was launched in 2000. DISC Nucleoplasty requires entry to the disc through a 17-gauge needle, limiting annular damage with the smallest access available. DISC Nucleoplasty removes tissue in the disc nucleus using patented Coblation® technology, low temperature plasma excision. Studies have shown that DISC Nucleoplasty effectively removes nuclear tissue without damage to collateral tissue. An additional study showed that DISC Nucleoplasty significantly reduces intradiscal pressure when disc material is removed, which is the same premise for disc decompression as APLD and laser discectomy. Over 40,000 DISC Nucleoplasty procedures have been performed to-date with significant numeric pain scores reduction in 75-80%^8,9 of patients, and sustained VAS (Visual Analog Score) pain score reduction¹⁰. A recent study also shows a promising biochemical healing response in the spinal disc when treated with Coblation technology. This data provides the first glimmer of hope in slowing down the degenerative process of the spine.

The Dekompressor™ is the newest instrument on the market for percutaneous discectomy, introduced in 2002. The Dekompressor uses an Archimedes pump principle: it utilises an auger to withdraw nucleus up the access cannula into a collection chamber. There is currently no reliable data available for this technique. Studies are needed to demonstrate safety and efficacy of the device.

References

1. Pauza et al, A Randomized, Placebo controlled Trial of Intradiscal Electrothermal Therapy for the Treatment of Discogenic Low Back Pain. The Spine Journal 2004; 4:27-35
2. Turner et al, Patient Outcomes after Lumbar Spinal Fusion. JAMA 1992; 268(7):907-11
3. Fraser RD, Chymopapain for the Treatment of Intervertebral Disc Herniation-A Preliminary Report of a Double Blind Study. SPINE 1982; 7:608-612
4. Davis GW et al, Automated Percutaneous Lumbar Diskectomy: A Prospective Study of 518 Cases with 1 Year Follow-up. SPINE 21
5. Choy DS, Percutaneous Laser Disc Decompression (PLDD): Twelve Years Experience with 752 procedures in 518 patients. J Clin Laser Med Surgery 1988, 16(6):325-331
6. Choy DS, Percutaneous Laser Disc Decompression (PLDD): Twelve Years Experience with 752 procedures in 518 patients. J Clin Laser Med Surgery 1988, 16(6):325-331
7. Singh V. Piryani C. Liao K. Nieschulz S. Percutaneous Disc Decompression using Coblation (Nucleoplasty) in the Treatment of Chronic Discogenic Pain. Pain Physician. 2002; 5: 250-259
8. Singh V. Piryani C. Liao K. Evaluation of Percutaneous Disc Decompression using Coblation in Chronic Back Pain with or without Leg Pain. Pain Physician. 2003; 6: 273-280
9. Sharps L. Percutaneous Disc Decompression using Nucleoplasty. Presented at 6th International Congress of Spinal Surgery; Ankara, Turkey, September 2002
10. O’Neill C. et al. Percutaneous Plasma Decompression Alters Cytokine Expression in Porcine Intervertebral Discs. The Spine Journal 2004; 4:88-98

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