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Hydrogels to stem cells: Researchers, surgeons revisit disc nucleus replacement
It may prove more appropriate than TDR for patients who undergo lumbar discectomies.
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Nearly a dozen companies in the fast-growing area of disc nucleus replacement seek to be first in the country to introduce a viable nucleus replacement product, with half of them beginning or about to begin clinical trials.
After earlier attempts at disc nucleus replacement (DNR), many put their research and development programs into high gear a few years ago, selecting promising prosthesis designs, geometry, materials and surgical techniques. Others emphasized the clinical side, starting European trials.
Their goal: Safely replace the nucleus pulposus in patients with herniated lumbar or cervical discs post-discectomy or with early degenerative disc disease (DDD).
From metal implants used in the 1950s to the Prosthetic Disc Nucleus (Raymedica) product developed more than a decade ago, modern DNR has been mostly unsuccessful. Today’s designs must address adverse reactions, extrusions and endplate stresses, while effectively restoring disc height and biomechanics.
“There are a couple of things in favor of nucleus replacements,” said Gunnar B. Andersson, MD, PhD, an Orthopedics Today editorial board member. “At the stage when you replace the nucleus typically you don’t have severe degenerative changes in other parts of the spine, such as the facet joints, so you’re at an earlier stage in the degenerative process. … And you get to replace the disc. Here you could potentially do some good.”
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Image: Yue J | Image: Disc Dynamics |
New trials begin
In June and July, Disc Dynamics, Pioneer Surgical Technology and Raymedica received FDA approval for investigational device exemption (IDE) studies of lumbar nucleus arthroplasty devices.
Nuvasive also got the go-ahead for its cervical DNR trial.
“Having learned a lot of lessons from TDR, it’s enabled us to re-look at nucleus replacement,” said Jeffrey Wang, MD, chief of the orthopedic spine service at the University of California-Los Angeles.
For many patients who undergo discectomies, TDR might be overkill. DNR might be more appropriate, Wang told Orthopedics Today because it is less invasive and does not cause damage that might preclude a future procedure. “I think it’s kind of gone full circle.”
New trials abound. In August Matthew Songer, MD, implanted the first patients with Pioneer Surgical Technology’s Nubac device, a two-part PEEK-on-PEEK device for DDD, according to a press release.
“I have been waiting for advances in non-fusion technology for many years, as fusion often leads to further spinal degeneration at adjacent levels,” principal investigator Kenneth A. Davenport, MD, said in the release. He is chief of staff at Marquette (Mich.) General Hospital, the IDE site where Songer did the surgeries.
Officials at Biomet Spine and Replication Medical told Orthopedics Today they expect IDE trials to start in the third or fourth quarter.
Biomet Spine’s one-piece Regain DNR device is made of a biocompatible pyrocarbon used for heart valves. Studied in European clinical trials since 2004, Regain’s IDE trial was set to begin this summer at limited sites, officials said.
“This is just a simple device. It’s a very scientifically contoured pebble with a geometry that keeps it from kicking out,” Wang said. It can be placed using an anterior or lateral approach. “There’s a lot of room for error, meaning that you don’t have to have things very precise and it’ll center itself within the disc space.”
The device does not continually stress the area or the interfaces but moves with normal motions so pressures shift accordingly. Studies showed patient selection with Regain arthroplasty — those with normally-shaped endplates that are not too flat — is as critical as identifying the disc that is the source of the discogenic pain, Wang said.
Dascor “balloon” trials
Disc Dynamics’ Dascor balloon nucleus prosthesis is on track after successful use in Europe, where it is CE marked.
In the OR, the surgeon inserts a polyurethane balloon into the nucleus space via a 5-mm hole in the annulus fibrosus and fills it with a curable polymer to achieve a custom fit, said Disc Dynamics medical director John E. Sherman, MD. The Dascor device has been implanted at L3 to L5 in about 70 patients in Belgium, France and Germany, all with 5-mm disc height, minimum. Investigators reported one infection.
Enrollment for another 100-patient European study should begin this year, Sherman said. The Dascor U.S. pilot study will involve four or five sites and expand to about 20.
“We, as surgeons, do need to appreciate that this is a disc arthroplasty in terms of removing the nucleus safely without damaging the annulus,” he said.
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Image: Nuvasive | Image: Biomet Spine |
A word of caution
As active as the DNR segment of the spine market is, some experts wonder whether this treatment is yet another orthopedic technology in search of an indication. Alexis P. Shelokov, MD, a spine surgeon who consults on disc replacement patents, is concerned about introducing such new technology without having clear-cut indications. “We are lacking, I believe, a comprehensive diagnostic classification or an agreed upon diagnostic method to help isolate the part of the disc that’s in trouble,” Shelokov said.
Whether considering TDR or DNR, the first step should be appropriate and careful identification of the pain generator. Without that, Shelokov worries about the consequences of this “technology explosion” and possible results of DNR done for DDD. For this to work, clinicians need to use methods like discograms to definitively isolate the part of the disc or exact disc causing the trouble.
Other unknowns in the new DNR equation include novel materials and techniques, like injecting materials or stem cells that re-hydrate to fill the nucleus space or heal damaged discs, an approach popularized with chemonucleolysis.
Replication Medical’s capsule-shaped NeuDisc prosthesis, an anisiotropic synthetic hydrogel embedded in layered Dacron, is proposed to treat one-level DDD at L3-S1.
It is being studied in about 25 patients in two European trials, according to James Yue, MD, at Yale University School of Medicine. He is principal investigator for the U.S. IDE trial set to begin this fall.
Surgeons implant the 6-mm diameter NeuDisc through a small anulotomy. “When it expands it becomes six times the size of itself … so it cannot come back out the small hole,” he said.
In the works now: A surgical technique for tricky L5-S1 implantations, where the anulus is weaker.
With lumbar discectomies, “you have a 20% failure rate roughly for reherniation or subsequent surgery for fusion or disc replacements. So 1 out of 5 patients ends up getting another surgery after discectomy. That’s a pretty high number. I think that’s where the real import will be for this type of device. Maybe we can take 1 out of 5 and make it 1 out of 20,” Yue said.
Lumbar spine is not the only area seeing DNR progress. Nuvasive received FDA approval for an IDE pivotal trial of its NeoDisc cervical device. Officials told Orthopedics Today they expect to soon begin enrolling the 500 patients randomized to get the implant at one-level C3-7 or plated fusion. A small U.K. trial showed good results based on radiographic and Visual Analog Scale outcomes at 12 months postop. The NeoDisc implant replaces a cervical disc nucleus, part of its anulus and the anterior longitudinal ligament via a silicone elastomer nucleus in an embroidered jacket.
For more information:
- McLeod A, Reah C, Jackowski A. Neodisc: Design and pre-clinical testing of a textile/elastomeric partial cervical disc replacement. Presented at the Spine Arthroplasty Society 2006 Meeting. May 9-13, 2006. Montreal.
- Yue, J. Neudisc anisotropic synthetic hydrogel for nucleus replacement. #21 Presented at the 19th International Intradiscal Therapy Society Meeting. April 5-9, 2006. Phoenix.
- Dr. Andersson owns stock in Pioneer Surgical Technology. Dr. Wang is a consultant for Biomet but does not have a financial interest in any of the products mentioned. Orthopedics Today was unable to determine whether Dr. Yue has a direct financial interest in the products discussed in this article or if he is a paid consultant for any companies mentioned.