Intradiscal Pressure Study of Percutaneous Disc Decompression With Nucleoplasty in Human Cadavers

Intradiscal Pressure Study of Percutaneous Disc Decompression With Nucleoplasty in Human Cadavers SPINE Volume 28, Number 7, pp 661 665 2003, Lippincott Williams & Wilkins, Inc. Yung C. Chen, MD,* Sang-heon Lee, MD, PhD, and Darwin Chen Study Design. Intradiscal pressure was measured after percutaneous disc decompression by nucleoplasty in human cadavers with different degrees of disc degeneration. Objectives. To assess intradiscal pressure change after disc decompression, and to analyze the influence of degeneration on the intradiscal pressure change. Summary of Background Data. Partial removal of the nucleus has been shown to decompress herniated discs, relieving pressure on nerve roots and, in some cases, offering relief from disc pain. Nucleoplasty, a new minimally invasive procedure using patented Coblation technology, combines coagulation and ablation for partial removal of the nucleus. Coblated channels remove the tissue volume and may decrease the disc pressure. Methods. Three fresh human cadaver spinal specimens (T8 L5; age, 54 84 years; mean age, 70.7 years) were used in this investigation. The intradiscal pressure was measured at three points: before treatment, after each channel was created, and after treatment using a 25-guage 6-inch needle connected to a Merit Medical Systems Intellisystem Inflation Monitor. The needles were calibrated initially to approximately 30 pounds per square inch. For the control, the change in disc pressure was recorded by the same procedure without using Coblation energy. To evaluate the effectiveness of nucleoplasty, disc pressure changes were compared between treatment with and without Coblation energy. Results. Intradiscal pressure was markedly reduced in the younger, healthy disc cadaver. In the older, degenerative disc cadavers, the change in intradiscal pressure after nucleoplasty was very small. There was an inverse correlation between the degree of disc degeneration and the change in intradiscal pressure. Conclusions. Pressure reduction through nucleoplasty is highly dependent on the degree of spine degeneration. Nucleoplasty markedly reduced intradiscal pressure in nondegenerative discs, but had a negligible effect on highly degenerative [Key words: disc degeneration, From the *Spinal Diagnostic and Treatment Center, Daly City, California, the Spinal Diagnostics and Treatment Center, Daly City, California, and the College of Physicians and Surgeons: Medicine, Columbia University School of Medicine, New York, New York. Acknowledgment date: November 29, 2001. First revision date: May 30, 2002. Acceptance date: August 30, 2002. Device status/drug statement: The device(s)/drug(s) is/are FDAapproved or approved by corresponding national agency for this indication. Conflict of interest: Corporate/Industry funds were received to support this work. Although one or more of the author(s) or family members has/have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this manuscript, benefits will be directed solely to a research fund, foundation, educational institution, or other nonprofit organization which the author(s) has/have been associated. Address reprint requests to Yung C. Chen, MD, Spinal Diagnostic and Treatment Center, 901 Campus Drive, Suite 310, Daly City, CA 94015. disc herniation, intradiscal pressure, nucleoplasty] Spine 2003;28:661 665 Discogenic lower back pain (LBP) is a major health concern in the United States, affecting more than 10 million people and costing more than $20 billion in treatment. 1 Surgical techniques such as interbody fusion have not always been effective at treating LBP 2 4 and can involve many complications. Nonoperative techniques also have been ineffective at reducing pain and restoring function. 5 In recent years, minimally invasive techniques have been developed by using percutaneous access to the outer posterior anulus. Chemonucleolysis, percutaneous nucleotomy, percutaneous discectomy, and laser treatments incorporate this approach, and all have been shown to reduce intradiscal pressure. 6 10 However, each treatment has its limitations, and success rates vary considerably. 11 14 Partial removal of the nucleus pulposus in contained disc has been shown to decompress herniated discs, relieve pressure on nerve roots, and in some cases, alleviate disc pain. 15,16 Nucleoplasty, a new minimally invasive procedure, uses radiofrequency (RF) energy to remove nucleus material and create small channels within the disc. With Coblation technology, RF energy is applied to a conductive medium, causing a highly focused plasma field to form around the energized electrodes. The plasma field is composed of highly ionized particles. These ionized particles have sufficient energy to break organic molecular bonds within tissue and form a channel. The by-products of this non heat-driven process are elementary molecules and low-molecular-weight inert gases, which are removed from the disc via the needle. On withdrawal of the Perc-D Spine Wand (ArthroCare, Sunnyvale, CA), the newly created channel is thermally treated, producing a zone of thermal coagulation. Thus, nucleoplasty combines coagulation and tissue ablation (patented Coblation technology) to form channels in the nucleus and decompress the herniated disc. The purpose of this study was to assess the intradiscal pressure change after disc decompression with nucleoplasty, and to analyze the influence of disc degeneration on the intradiscal pressure change. Current minimally invasive techniques have been shown to reduce pressure, but no experimental study of this nature has been reported for nucleoplasty. Subsequent studies will examine the safety, efficacy, and histologic effects of nucleoplasty. Methods In this study, three human cadaver spines were used. These spines were 81, 77, and 54 years of age, and of unknown weight. They were removed from the cadavers for facilitated 661

662 Spine Volume 28 Number 7 2003 Figure 1. The intradiscal pressures were measured before nucleoplasty, after each channel was created, and after nucleoplasty. A, Human cadaver spine (anterior aspect), nucleoplasty ArthroCare Perc-D Spine Wand, left, with intradiscal 25-gauge pressure needle. B, Arthrocare nucleoplasty channel monitor. C, Merit Medical Systems Intellisystem Inflation Monitor. access to the For the 81-year-old cadaver, discs T8 L4 were used. For the 77-year-old cadaver, discs L1 L5 and T9 T10 were used. For the 54-year-old cadaver, discs T9 L4 were used. To evaluate for disc degeneration, cadaver spines were analyzed by anteroposterior, lateral, and oblique radiographs. The degree of spine degeneration was scored on a 4-point scale: Grade 1 (normal), Grade 2 (mild: slight disc space narrowing or mild osteophyte formation), Grade 3 (moderate: moderate disc space narrowing or sclerosis with moderate osteophyte formation), Grade 4 (severe: marked disc space narrowing, less than 50%, or marked osteophyte formation). The 54-year-old cadaver spine was rated as Grade 2 (mild degeneration), but the other two cadaver spines (81 and 77 years old, respectively) were classified as Grade 4 (severe degeneration). The specimens were differentiated into groups and compared: Grade 2 (healthy discs) with Grade 4 (severe degenerative discs). Each spine was treated with both the control procedure and nucleoplasty. To calibrate pressure readings and make pressure changes more evident, a small amount of saline was injected into the nucleus using a 25-gauge 6-inch needle connected to a Intellisystem Inflation Monitor (Merit Medical Systems, Inc., South Jordan, UT). Intradiscal pressure was increased by injecting saline to approximately 30 psi to represent mechanically sensitive discs 1 (Figure 1). The control treatment was established by advancing an ArthroCare Perc-D Spine Wand into the discs six times through a 17-gauge introducer needle without Coblation energy (Figure 1). Pressure was recorded before treatment, after each of the six needle advances, and 1 and 2 minutes after treatment. Correction of the Spine Wand and pressure sensor positions in the nucleus was confirmed via fluoroscopic anteroposterior and lateral views. For the Nucleoplasty treatment, six channels were created within each disc by advancing the Spine Wand (ablation) and retracting it (coagulation) with Coblation energy. Before treatment and after each channel was created, the pressure was recorded. The pressure then was recorded at 1 and 2 minutes after the six channels were created. This procedure was repeated within the same disc at three different directions, recalibrating the pressure at each direction using the saline injection. Results Intradiscal pressure was markedly reduced in the younger, healthy disc cadaver with nucleoplasty, as compared with the control condition (P 0.001). In the degenerative discs of the elderly cadavers, the intradiscal pressure reduction after nucleoplasty was statistically significant, as compared with the control condition (P 0.05). However, this reduction was very small (less than 2 psi on the average) and had little clinical impact on the overall disc pressure. The healthy discs in Cadaver 3 (age, 54 years) experienced a 100% drop in intradiscal pressure, whereas the degenerative discs in Cadavers 1 and 2 (ages, 81 and 77 years) dropped only 5.8% and 3.66%, respectively ( Figure 2). Table 1 shows the actual nucleoplasty pressure changes in comparison with the control condition for both degenerative and healthy disc cadavers. Figure 2. The pressure change was dramatic in the cadaver spine with healthy discs, but very slight in the spines with degenerative

Intradiscal Pressure Study Chen et al 663 Table 1. Nucleoplasty and control treatments for healthy and severe degenerative discs Cadavers 1 and 2 (average) Severe Degenerative Discs Cadaver 3 Healthy Discs Pressure (psi) Control Nucleoplasty Control Nucleoplasty Pre-treatment Channel No 32.69 / 1.44 30.14 / 4.72 27.29 / 11.57 25.33 / 10.77 1 32.44 / 1.24 29.79 / 4.66 27.29 / 11.57 7.69 / 14.99 2 32.56 / 1.24 29.5 / 4.35 27.43 / 11.65 0.60 / 1.32 3 32.44 / 1.12 29.54 / 4.44 27.43 / 11.65 0.43 / 1.13 4 32.44 / 1.12 29.61 / 4.55 27.43 / 11.65 0.00 / 0 5 32.44 / 1.12 29.61 / 4.55 27.43 / 11.65 0.00 / 0 6 32.44 / 1.12 29.61 / 4.55 27.43 / 11.65 0.00 / 0 Post-treatment 1 min. 31.90 / 1.02 29.38 / 2.20 27.36 / 11.66 0.00 / 0 2 min. 31.70 / 1.30 28.88 / 2.36 27.00 / 11.52 0.00 / 0 In Figure 3, the healthy discs of Cadaver 3 show a rapid pressure decline after two channels were created with nucleoplasty. The degenerative discs of Cadavers 1 and 2 remained close to their initial pressure values with nucleoplasty. The dramatic pressure decrease in healthy discs is significantly different (P 0.005) from the decrease in degenerative Discussion Nucleoplasty is a new minimally invasive treatment for herniated discs that uses radiofrequency (RF) energy for partial removal of the nucleus pulposus. The RF energy is used to create a plasma field of highly ionized particles that have adequate energy to disintegrate nucleus proteins. The temperature is kept below 70 C to minimize tissue damage. The products of the non heat-driven process are elementary particles and low-molecular-weight gases, which are removed quickly from the surgical site. The purpose of this study was to determine whether nucleoplasty produces a change in intradiscal pressure. In the experiments, nucleoplasty was highly effective at reducing intradiscal pressure in healthy cadaver Pressure measurements dropped dramatically with the creation of two or three Coblation channels. In degenerative discs, however, nucleoplasty reduced intradiscal pressure only slightly. In both degenerative disc cadavers, the pressure dropped approximately 5% for all the Many factors can explain the ineffectiveness of nucleoplasty for degenerative First, aging of the lumbar spine causes the elastic nucleus pulposus to become dehydrated and fibrotic. 17 Second, healthier discs contain a soft and hydrated central region that distributes stress, whereas degenerated discs have only a small hydrostatic region that exhibits high stress. 18 Thus, it is possible that the dehydrated, fibrotic nature of the degenerated discs prevents them from decompression once Coblation channels have been created. That is, although nucleus material has been removed and channels have been created, the disc still does not Figure 3. The pressure decreased rapidly in the cadaver with healthy discs, but remained close to initial levels in the cadavers with degenerative

664 Spine Volume 28 Number 7 2003 decompress to reduce intradiscal pressure. The current authors suggest that the disc decompression effect of nucleoplasty is ineffective for severely degenerated Other minimally invasive intradiscal techniques such as chemonucleolysis, percutaneous nucleotomy, percutaneous discectomy, and laser treatments have been shown to reduce intradiscal pressure, 6,7,9,10 but have their limitations. Chemonucleolysis involves a higher risk of severe complications, especially with inexperienced physicians. 12 Chemonucleolysis with chymopapain can lead to fatal anaphylaxis, 19 cartilaginous endplate damage, and hemorrhage. 20 Postacchini 12 suggested that percutaneous automated nucleotomy may not be truly effective, and that successful outcomes could be caused by the spontaneous resolution of symptoms. The therapeutic efficacy of manual percutaneous discectomy also remains to be shown. 12 Laser discectomy yields results comparable to those of manual or automated percutaneous discectomy, 11 but is considerably more expensive. Percutaneous laser nucleolysis can damage endplates from excess thermal energy, 9 and also has been shown to be significantly less effective than chemonucleolysis. 21 Nucleoplasty has certain advantages over these minimally invasive techniques. Because the temperature is kept low during ablation, charring or burning of surrounding tissues is minimized. The procedure is under the physician s complete control, unlike chemonucleolysis, which is dosage dependent. 10 In addition, pressure changes are immediate, whereas chemonucleolysis with chondroitinase ABC may require as long as 7 days for completion. 22 In fact, Figure 2 shows that disc pressure drops with the creation of two or three Coblation channels, far fewer than the six channels recommended by ArthroCare. The creation of fewer channels during treatment may reduce the chances of future disc degeneration because less disc material is removed. Nucleoplasty also can be performed from either side of the affected disc, not just from the ipsilateral symptomatic side. Thus, treatment approaches are not limited to one site only. Because of these advantages, nucleoplasty has the potential to be a safe and effective treatment for herniated The limitation of this study was that pressure measurements were performed on cadavers and not in vivo. Cadaver models cannot account for intradiscal pressure changes that occur during live muscle contraction and different positions (sitting, standing and the like), which may affect results. Another possible limitation was the method of pressure measurement. Because a small amount of saline was injected into the discs to calibrate the pressure, it is possible that nucleoplasty may have removed saline along with the nucleus tissue. Future research should focus on nucleoplasty pressure changes in vivo, and while the patient is in different positions. This study has demonstrated that nucleoplasty markedly reduces intradiscal pressure in nondegenerate Nucleoplasty s intradiscal pressure-reducing effects are highly dependent on the degree of spine degeneration, and the treatment is ineffective for severely degenerated Key Points Nucleoplasty treatment for herniated discs immediately (within two channels) and dramatically reduced intradiscal pressure in healthy, nondegenerative Nucleoplasty was ineffective at reducing pressure for degenerative Nucleoplasty has the potential to be a viable, effective, and safe treatment for lower back pain resulting from disc disease. 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