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Researchers aim for U.S. approval of the next-generation Prosthetic Disc Nucleus
Raymedica’s PDN implant overcomes complications and expands to a larger patient population.
Disc nucleus replacement has evolved much since Charles D. Ray, MD, introduced the concept in 1988. Since then, Raymedica has updated its Prosthetic Disc Nucleus implant to meet the needs of surgeons and patients – and continues to do so today.
The Prosthetic Disc Nucleus (PDN) began as a bilateral two-device implant in 1990. In 2002, Raymedica introduced it as a single-device implant, the PDN-Solo.
Although the medical literature shows long-term patient satisfaction at 10-year follow-up, surgeons still experienced migration with the PDN and found that the implant was too robust for most patients, according to a company spokesperson.
To overcome complication risks and expand the PDN capabilities to a larger patient population with earlier disc degeneration, Raymedica introduced the HydraFlex implant. The implant is currently approved for use in Europe, and the FDA recently approved enrollment in an upcoming U.S. clinical trial with the HydraFlex.
Robert Schönmayr, MD, a neurosurgeon at the Horst-Schmidt-Kliniken in Wiesbaden, Germany, saw significant pain relief and patient satisfaction with the PDN over the long term.
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Images: Raymedica |
However, he stopped using the implant in 2004 because of what he considered a high migration risk: 10%. “Presently I use only total disc replacements … no nucleus replacement,” Schönmayr told Orthopedics Today.
Schönmayr performed a 10-year review of 11 patients with mild-to-moderate degenerative disc disease treated with disc nucleus replacement (DNR) using the PDN device in 1996.
Using a standard posterior discectomy approach, he replaced L4-L5 in three of the patients, L5-S1 in 6 patients and L5-6 in two patients.
At follow-up, Schönmayr found a mean Oswestry Disability Index score improvement from 45% at preop to 14% postoperatively. However, only eight patients remained satisfied with the surgery. Two patients experienced implant migration, one of which went on to revision surgery. Another patient with persistent lower back pain underwent implant removal and subsequent fusion at 4 months postop, according to a study abstract.
“Postoperatively increased disc height was not maintained in all patients due to endplate changes,” Schönmayr wrote in the abstract.
On the heels of these latest results and after consulting with a surgeon advisory board, Raymedica again updated its nucleus implant device. The HydraFlex is a softer, more anatomically shaped and faster-hydrating version of the PDN technology, a company spokesperson said.
In addition to these improvements, manufacturers reduced the insertion tab size to increase the footprint size, used more hydrogel and developed a completely new instrumentation set and surgical technique.
In April, Orthopaedics Today International Editorial Board member Rudolf Bertagnoli, MD, of Straubing, Germany, implanted the first HydraFlex implant. Since then, he has treated four additional patients with the device and found no complications.
“While the clinical results of the PDN-Solo were very good, this optimized system mitigates the risk of the complications by overcoming some of the factors that we feel contributed to … subsidence and device extrusion,” Bertagnoli told Orthopedics Today.
One significant change: The Hydra Flex is implanted with an anterolateral retroperitoneal approach, as opposed to a posterior approach.
“This approach allows … for a more total nucleoctomy, optimal device positioning and closure of the annulotomy — all considered factors in device movement,” Bertagnoli said. What is more, the HydraFlex reduces and even eliminates back pain, maintains range of motion and maintains weight between the two vertebral bodies, he added.
“Using the HydraFlex device … may significantly increase the number of subjects who return to their normal levels of activity,” Bertagnoli said.
Similar to the PDN-Solo, surgeons can view the HydraFlex on X-ray via two platinum-iridium markers on the lateral aspects. When complications occur, the HydraFlex is also easy to explant and clean out of the disc space, he said.
Raymedica’s next goal is to achieve FDA approval for the HydraFlex. The recent FDA-approved pilot study enrollment includes 20 patients, aged 20 to 70 years, with single-level degenerative disc disease from L2-S1. To qualify, patients must have failed conservative treatment for up to 6 months, according to Rick Delamarter, MD, an investigator on the U.S. clinical trial.
Delamarter, of Saint John’s Health Center in Santa Monica, Calif., and Reginald J. Davis, MD, FACS, of Baltimore Neurological Associates in Towson, Md., will each treat about 10 patients with the HydraFlex device at their respective locations. Full enrollment is expected by February or March 2007. Surgical technique will involve a minimally invasive anterolateral retroperitoneal approach, developed by Salvatore Brau, MD.
“He’s an anterior access surgeon [with] vast experience in these types of procedures, and … he has been part of the development team with the HydraFlex and the approach,” Delamarter told Orthopedics Today.
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Images: Raymedica |
“We’ll enter the disc space through [an annular] flap, which then can be reapproximated or closed, so we open the annulus just enough to get the disc out, get the implant in and then we close that flap again … [which is] a little bit different from the way we do the other operations,” Davis told Orthopedics Today. The annular flap is sutured in place after insertion. DNR and the implant devices will continue to evolve as surgeons discover the ideal patient indications and device features, like implant softness.
“At this point, honestly, we really don’t know the ideal softness of a nuclear implant. This will become clear over the next several years with the various studies going on,” Delamarter said. While Schönmayr currently does not perform DNR, he does see it as a “visionary concept” for early stages of disc degeneration in the future.
“As soon as it will be possible to replace degenerated and deformed vertebral facet joints, a nucleus replacement will have a much wider indication as supplement for restoration of the anterior load bearing surfaces,” he said. Schönmayr said that if the clinical trial reveals “promising results,” he plans to return to DNR, this time with the HydraFlex.
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- Dr. Delamarter has no direct financial interest in the products discussed in this article, nor is he a paid consultant for any companies mentioned.
- Orthopedics Today was unable to determine whether Drs. Schönmayr or Bertagnoli have a direct financial interest in the products discussed in this article or if he is a paid consultant for any companies mentioned.