CHAPTER 295 Nucleoplasty and Posterior Dynamic Stabilization Systems
Nucleoplasty
Lumbar disk disease is a pervasive problem throughout industrialized countries. Both radiculopathy and diskogenic lumbago can be attributed to tears within the annulus fibrosus. Although herniation of the nucleus pulposus has been a known surgical entity since Mixter and Barr’s original work,1 the cause and treatment of diskogenic pain is less well understood. For more than 50 years, open discectomy has been the “gold standard” for disk decompression in the treatment of sciatica.2,3 More recently, radical discectomy with fusion has become an aggressive form of surgical treatment for diskogenic pain. Despite the success of discectomy, complications from the open procedure include: reherniation in up to 10% of patients, epidural fibrosis, loss of height, instability, and residual back pain.4–7 Alternatively, an array of minimally invasive disk-based techniques has arisen in parallel to discectomy, such as chemonucleolysis, automated percutaneous discectomy, laser discectomy, intradiscal electrothermal therapy (IDT), and coblation nucleoplasty. Advantages of these treatments include minimal scarring, avoidance of canal structures, and short hospital times. This section will briefly discuss some of these methods, with an emphasis on nucleoplasty, which perhaps has the greatest promise. The following section will address the concept of dynamic stabilization, a related but separate topic in the treatment of motion preservation lumbar spine surgery.
As the trends within surgery have shifted to minimally invasive, reductionist methods, the concept of definitive percutaneous treatment of disk disease has become increasingly attractive. In general terms, nucleoplasty is a technique in which intervertebral disk material is typically removed, rather than inserted, via a percutaneous route. The lumbar levels below the conus medullaris are the primary targets, in particular, L4-5 and L5-S1, and rarely L3-4.8 Additionally, the cervical spine can be treated.9 More specifically, nucleoplasty refers to the structural modification and treatment of the nucleus pulposus. The coblation form of nucleoplasty was introduced in July 2000 with the PercDLE SpineWand (ArthroCare, Austin, TX). Technically this method differs from other methods such as IDET annuloplasty and percutaneous discectomy. However, an understanding of all of these treatment options is relevant to the field.
Nucleoplasty is ideally used for small, contained disk herniations. Historically, there has been limited data examining disk size and annular characteristics in relation to discectomy outcome; for example, the large SPORT trial’s requirements for disk herniation were “protrusion, extrusion, or sequestered fragment.”10 However, several studies have suggested that treatment for smaller, contained disk herniations is particularly challenging. Patients with contained fragments and less than 6-mm herniation have been shown to respond poorly to diskectomy.11–15 One prospective study of 187 patients examined postlumbar discectomy outcomes based on annular competence and presence of a fragment.13 Notably, 38% of patients with no discrete fragment or annular tear were likely to experience residual sciatica, compared with only 1% of patients with a fragment and small annular tear. The small, contained herniation group had milder but more protracted symptoms and a smaller herniation size on magnetic resonance imaging (MRI). The authors stated that this group of patients with sciatica more closely resembled patients with chronic back pain, with symptoms disproportionate to anatomic findings. Thus, the contained disk herniation with radicular and/or diskogenic symptoms remains a difficult clinical entity to treat with standard discectomy.
Chemothermal Ablation: Chemonucleolysis and intradiscal electrothermal therapy
Chemonucleolysis
Chemonucleolysis is one of the oldest, least invasive methods available to treat lumbar disk disease. The technique uses chymopapain for enzymatic lysis of the nucleus and was first described by Lyman Smith in 1964.16 It was largely abandoned in North America with the rise of microdiscectomy and reports of anaphylactic complications. Chymopapain is no longer commercially available in the United States. However, the technique is still used in Europe and Asia. Multiple recent studies have reported success rates of 85% or greater in a carefully selected population.17,18 The best prognostic criteria are similar to microdiscectomy: leg pain greater than back pain, positive straight leg raise, and soft, noncalcified disk herniation on imaging.17 Discography determines the symptomatic level in the case of multiple disk herniations. Immediate epidural extravasation of contrast is a contraindication. However, delayed extravasation is acceptable. In a typical protocol, 4000 U of chymopapain dissolved in 1 to 2 mL of saline is injected into the center of the symptomatic disk (Fig. 295-1, A). The enzyme may potentially dissolve annular structures; there is no additional aspiration of lysate. Complications include back stiffness (up to 50%) and pain that can last for weeks. Anaphylactic reactions to the protein occur in less than 0.5% of patients.19 Test dosing of the skin should be done before the procedure.
Intradiscal Electrothermal Therapy
IDET annuloplasty involves the fluoroscopic insertion of a thermal resistance probe into the disk space via a cannula from a contralateral approach to the symptomatic side (Fig. 295-2). The treatment consists of radiofrequency ablation of the annulus fibrosus in a controlled manner. The probe is heated to a temperature required for coagulation of nerve endings and contraction of collagen. IDET is typically used for diskogenic back pain as opposed to radiculopathy from contained disk herniation. It may be used in place of interbody fusion in the treatment of diskogenic pain.8,20 In this regard, IDET does not afford a decompressive benefit to the same degree as percutaneous diskectomy or nucleoplasty (see later discussion). Multiple outcome trials and series have shown modest benefit of IDET in select patients with discography-concordant chronic low back pain.20–23 Two randomized controlled trials reported conflicting findings when IDET was compared with a placebo.24,25 Repeat IDET has been reported as successful but the literature is scant.26
Minimally Invasive Disk Decompression
The principle of central disk decompression governs most of the techniques that remove nuclear material from the disk space. If the space is even partially decompressed, radiculopathy can improve from a reduction in volume, which may not be radiographically evident.27 A small reduction in volume can create a disproportionately large reduction in pressure based on hydrostatic forces.28,29 The partial vacuum created by nucleus aspiration causes a retraction of the disk and regeneration of annular fibers to contain nuclear material that may be protruding into the canal. Thus the process is effective only in select patients who still have an intact annulus fibrosus without large or free fragments. Broad, circumscribed disk protrusions on MRI are typical radiographic findings. Discography can be helpful in distinguishing annular fissures from intact external fibers and true extrusions (see Fig. 295-1). Relief of intradiscal pressure may also decrease leaching of inflammatory mediators, thereby alleviating both chemical and mechanical causes of diskogenic pain.30,31
Typical inclusion criteria for percutaneous discectomy (and nucleoplasty) are: relatively young age (<50 years), failure of conservative measures including physical therapy (>6 weeks), radiculopathy and/or lumbago, absence of significant motor deficit, and concordance of a provocative discogram (although not essential in cases of clear radiculopathy). In general, exclusion criteria include greater than 50% loss of disk height, sequestered disk herniation, greater than one third canal occupation, spinal instability or fracture, morbid obesity, infection, or spinal stenosis from osteophytic disease.32 Relative contraindications include motor weakness, previous open surgery, spinal stenosis, or compressive facet arthropathy. Typically patients will have a 6-month or greater history of symptoms, with exacerbations under loading conditions that increase the pressure and diameter of the disk.33 Ideal candidates have a diffuse disk protrusion and radicular pain greater than back pain.8 However, the procedure may be performed for diskogenic pain as well. Decompression and subsequent scar formation may reinforce the annulus with a fibrous scar, facilitate closure of radial tears, and contribute to stabilization.34
Automated Percutaneous Lumbar Discectomy
First described by Onik in 1985, automated percutaneous lumbar discectomy (APLD) is the most widely performed percutaneous decompressive technique, preceding nucleoplasty by 15 years. It has been performed with modest success over the past 2 decades. The technique involves insertion of a mechanical (automated) probe to perform a nucleotomy via a “suction and cutting” mechanism (see Fig. 295-1, C). A 2.8-mm outer cannula is inserted fluoroscopically via the posterolateral approach on the predominantly painful ipsilateral side and positioned against the annulus. Then, a rounded-tip aspiration probe with a side port is passed into the disk space. Disk material is sheared off by the pneumatically driven guillotine effect of the sharp inner cannula (see Fig. 295-1, C). Suction aspiration of nuclear material is stopped when there is blood return or decreased flow. Approximately 1 to 3 g are removed.35 Aspiration times average less than 20 minutes. Afterward, a steroid or topical anesthetic may be injected along the same tract. Iatrogenic fragment herniation is a rare complication (<1%), which may occur from annular weakening or direct pressure of the probe.34,36
Unfortunately, randomized trials of APLD have shown limited to no benefit.35,37,38 Proponents of APLD have criticized these studies for small sample sizes, poor patient selection, and the authors’ learning curve of the technique.34 A large prospective trial with a 1-year follow-up found a 75% successful treatment rate.39 Proper patient selection is critical; sequestered or free fragments and canal compromise greater than 50% are predictors of poor outcome. Overall, several hundred thousand patients have undergone APLD. In general, however, the success rates of APLD for radiculopathy seem lower than standard microdiscectomy.40
Laser Discectomy
Intradiscal laser discectomy is another method that works via reduction of intradiscal pressures. Between 1100 to 1200 J of energy from the laser vaporizes a portion of the nucleus pulposus (see Fig. 295-1, D). Various lasers have been used, including Nd:YAG and KTP.532 Despite the technical limitations of thermal spread, several large series have reported improvement in approximately 70% of patients, including those with diskogenic pain.41–44 However, no randomized controlled trials (RCTs) have been performed. Laser-induced steam can be seen in the disk space afterward if it is not removed via the cannula, but this has not resulted in complications.
Nucleoplasty
Radiofrequency (RF) nucleoplasty (coblation nucleoplasty or plasma disk decompression) is a method of decompressive nucleotomy that uses current to dissolve portions of the nucleus pulposus (see Fig. 295-4).
Unlike IDET and laser discectomy, in which thermal complications or limitations are potential drawbacks,45 coblation does not in itself generate heat; rather, the RF current isolates and dissociates components of surrounding tissues, resulting in their dissolution. The catheter creates a low thermal plasma field in which there is minimal thermal injury to adjacent tissue.46 Histologically, the coblation channels create clean coagulation borders of the nucleus pulposus. Chen and coworkers found that the annulus, end plates, and neural elements were histologically normal at the level of the procedure in a cadaver study.46 Surgically, coblation technology has gained prominence in the otorhinolaryngology field for tonsillectomy and turbinoplasty procedures for its sparing of vital neighboring structures.47,48
Method
Under general anesthesia or conscious sedation, the patient is placed in a prone or lateral decubitus position. Conscious sedation must be used in discography. Under fluoroscopic guidance, a 17-gauge, 6-inch spinal access cannula is inserted into the disk space via a posterolateral extrapedicular approach (Fig. 295-3).49 The cannula is placed at the annular-nuclear junction. The Perc-DLE SpineWand (ArthroCare, Sunnyvale, CA.) is advanced down the access cannula until the probe tip is 5 mm beyond the cannula edge, ensuring that the active probe is within the nucleus pulposus and past the inner layer of annulus fibrosus.
The wand is a 1-mm diameter, bipolar instrument. In ablation mode, the wand generates approximately 120 V of energy, with resultant temperatures of 50° to 70° C at the wand tip.50 An ionized plasma field is created. The decompression is performed by advancing the wand in ablation mode to create a channel from the posterolateral annulus to the anteromedial annulus (Fig. 295-4, A). When the wand is withdrawn, it is switched to coagulation mode, which allows for widening of the channel to approximately 1 mm by denaturing type II collagen and proteoglycans, with resultant shrinkage of the surrounding collagen (Fig. 295-4, B). Six channels are created at the 2, 4, 6, 8, 10, and 12 o’clock positions, forming a cone-shaped area of nucleotomy (Fig. 295-4, C). The entire radiofrequency ablation process requires 2 to 3 minutes and results in disk volume reduction of 10% to 20%.51 Approximately 1 mL of tissue volume is removed with the six channels. A bilateral approach may be used for maximal nucleus pulposus removal or for centrally herniated disks.
