Prosthetic Disc Nucleus Device Research Articles

The Combined Use of a Posterior Dynamic Transpedicular Stabilization System and a Prosthetic Disc Nucleus Device in Treating Lumbar Degenerative Disc Disease With Disc Herniations

Background Prosthetic replacement of spinal discs is emerging as a treatment option for degenerative disc disease. Posterior dynamic transpedicular stabilization (PDTS) and prosthetic disc nucleus (PDN) devices have been used sporadically in spinal surgery. Methods This was a prospective study of 13 patients averaging 40.9 years of age with degenerative disc disease who underwent posterior placement of a PDN with a PDTS. The Oswestry low-back pain disability questionnaire and visual analog scale (VAS) for pain were used to assess patient outcomes at the 3rd, 6th, and 12th postoperative months. Lumbar range of motion was evaluated using a bubble inclinometer preoperatively and at 12 months postoperatively. Radiological parameters including lumbar lordosis angle (LL), segmental lordosis angle (α), disc height at the operated level (DHo), and disc height of the adjacent level (DHu) were evaluated. A typical midline posterior approach for complete discectomy was followed by the simultaneous placement of the PDN with PDTS. Results Both the Oswestry and VAS scores showed significant improvement postoperatively ( P < .05). There were no significant differences in LL, α, DHo, and DHu parameters. We observed complications in 3 patients including 2 patients who had the PDN device embedded into the adjacent corpus; 1 had massive endplate degeneration, and the other experienced interbody space infection. In 1 patient, the PDN device migrated to one side in the vertebral space. Conclusion The use of a PDN in combination with posterior dynamic instrumentation can help to restore the physiologic motion of the anterior and posterior column and could help to establish posterior dynamic instrumentation as an important treatment of degenerative disc disease. Theoretically this concept is superior, but practically we need more advanced technology to replace disc material. Because this study examined the combination of the PDN and stabilization instrumention, the results cannot be compared with those reported in the literature for either PDN alone or dynamic screws alone. Level of Evidence Prospective cohort study with good follow-up (level 1b).

The combined use of a posterior dynamic transpedicular stabilization system and a prosthetic disc nucleus device in treating lumbar degenerative disc disease with disc herniations.

BackgroundProsthetic replacement of spinal discs is emerging as a treatment option for degenerative disc disease. Posterior dynamic transpedicular stabilization (PDTS) and prosthetic disc nucleus (PDN) devices have been used sporadically in spinal surgery.MethodsThis was a prospective study of 13 patients averaging 40.9 years of age with degenerative disc disease who underwent posterior placement of a PDN with a PDTS. The Oswestry low-back pain disability questionnaire and visual analog scale (VAS) for pain were used to assess patient outcomes at the 3rd, 6th, and 12th postoperative months.Lumbar range of motion was evaluated using a bubble inclinometer preoperatively and at 12 months postoperatively. Radiological parameters including lumbar lordosis angle (LL), segmental lordosis angle (α), disc height at the operated level (DHo), and disc height of the adjacent level (DHu) were evaluated. A typical midline posterior approach for complete discectomy was followed by the simultaneous placement of the PDN with PDTS.ResultsBoth the Oswestry and VAS scores showed significant improvement postoperatively (P < .05). There were no significant differences in LL, α, DHo, and DHu parameters. We observed complications in 3 patients including 2 patients who had the PDN device embedded into the adjacent corpus; 1 had massive endplate degeneration, and the other experienced interbody space infection. In 1 patient, the PDN device migrated to one side in the vertebral space.ConclusionThe use of a PDN in combination with posterior dynamic instrumentation can help to restore the physiologic motion of the anterior and posterior column and could help to establish posterior dynamic instrumentation as an important treatment of degenerative disc disease. Theoretically this concept is superior, but practically we need more advanced technology to replace disc material. Because this study examined the combination of the PDN and stabilization instrumention, the results cannot be compared with those reported in the literature for either PDN alone or dynamic screws alone.Level of EvidenceProspective cohort study with good follow-up (level 1b).

Prosthetic Disc Nucleus (PDN) Replacement for Lumbar Disc Herniation

A clinical follow-up study was performed to evaluate lumbar disc nucleus replacement clinically and functionally. The objective was to assess the clinical efficacy of the prosthetic disc nucleus (PDN) for treatment of lumbar disc herniation. The PDN was designed to treat patients suffering from disc herniation and/or degeneration. Clinical trials for PDN were first conducted in 1996, and the results showed that the PDN device was effective in most of the patients who were implanted. These studies had been carried out with patients who were implanted with a pair of the devices. The main complication was device migration. Therefore, a follow-up study based on a single PDN device implantation was designed to evaluate its clinical result. Forty-five patients with lumbar disc herniation were implanted with one PDN device from March 2002 to December 2002. Thirty (66.7%) patients came to the clinical, functional, and radiographic 6-month follow-up examinations. Independent analysis was performed by careful review of the charts, operative notes, preoperative and postoperative radiographs, magnetic resonance images, and follow-up records of all patients. After implantation, significant proportions of patients experienced pain relief. Improvements were noted in pain intensity, walking distance, lumbar mobility, neurologic weakness, Oswestry and Prolo scores, and intervertebral disc height. No difference in work status after PDN implantation could be detected. Compared with the preoperative height, the intervertebral disc had gained 19.7% (P < 0.001). Device migration, failure, and dislocation were not noticed in any patient. A few patients had minor complications such as transient low-grade fever. Clinically, a single PDN is preferred and can effectively increase the height of the intervertebral disc in patients with lumbar disc herniation. However, long-term follow-up of PDN implantation needs to be studied.

Partial Disc Replacement with the PDN Prosthetic Disc Nucleus Device

The aim of this study was to evaluate the efficacy of the PDN prosthetic disc nucleus device for the treatment of chronic discogenic back pain caused by degenerative disc disease. Among the 48 patients who underwent nucleus replacement surgery from January 2001 through May 2002, 46 patients were followed >6 months. The mean Oswestry Disability Index score was 58.9% preoperatively, and it improved to 18% at the 1-year follow-up. Visual Analogue Pain Scale scores improved from a preoperative mean of 8.5 to 3.1 after 1 year. The mean Prolo Scale score also improved from 5.2 preoperatively to 7.2 at 1 year. Major complications included four cases of device migration, requiring revision surgery, and infection in one patient. According to MacNab's criteria, results were excellent in 5 patients (10.9%), good in 31 (67.4%), fair in 3 (6.5%), and poor in 7 (15.1%). The overall clinical success rate was 78.3%. Nucleus replacement with the PDN device seemed to be effective in treating patients with chronic discogenic back pain caused by degenerative disc disease.

4:25 The Raymedica PDN prosthetic disc nucleus device in the baboon lumbar spine

Purpose of study: The purpose of this study was to monitor the course of events after placement of PDN prosthetic disc nucleus devices in the lumbar spine of the baboon and to assess the baboon as a model for future testing.Methods used: Three baboons underwent a lateral surgical approach to the lumbar spine. After discectomy, one animal had two custom-sized PDN implants tethered together and placed using the recommended surgical technique. Two additional animals were implanted but, because of limitations of instrumentation, had a single custom implant placed. Radiographs and computed tomography scans were obtained at 2, 4, 12 and 26 weeks to assess implant movement, disc height and end plate morphology. At 26 weeks, segments were harvested, processed undecalcified and evaluated.of findings: The two animals receiving a single device experienced migration of the implant from the disc in the first 2 weeks. Revision procedures using a technique that disrupted the end plate were performed, and smaller tethered PDN devices were placed. In these two animals, from 2 to 26 weeks after revision, there was progressive loss in disc height, end plate degeneration, implant subsidence, circumferential lucency and increasing sclerosis at adjacent vertebrae. Osteophytes bridged the disc space by 26 weeks. Histology revealed mild inflammation almost completely encapsulating the implants. The animal that received a PDN device pair at the initial surgery showed no signs of implant movement from 2 to 26 weeks, no changes in end plate morphology, no sclerosis, no increase in osteophytosis and only mild focal inflammation.Relationship between findings and existing knowledge: The two animals whose clinical outcome was unfavorable had a primary and revision procedure with focal disruption of the end plate, a possible initiator of osteophytosis. It is unknown whether the outcome would have been favorable at these levels if standard surgical techniques had been employed, but under these conditions, the degenerative changes of the disc and inflammatory response to the PDN devices were significant. In contrast, the animal that underwent only the primary procedure resulted in a favorable clinical outcome. Clinically, there have been reports indicating that the PDN device may be efficacious. There have also been reports on potential complications. The favorable response of one baboon to the implants is similar to reported favorable clinical outcomes. Migration of the PDN device from the disc space has been reported clinically; migration occurred in two baboons. Although there are no known clinical reports on histopathology associated with the PDN device, lucency, subsidence and sclerosis have been reported for interbody fusion devices and disc replacements.Overall significance of findings: These results indicate that the baboon may be an appropriate animal model for intervertebral disc research not only because the anatomy and morphology are similar to humans, but also because the potential complications and degenerative pathology are similar to those reported clinically.Disclosures: Device or drug: PDN prosthetic disc nucleus. Status: investigational.Conflict of interest: Eric Ledet, institutional research grant.

Understanding end plate changes associated with disc surgery

Purpose of study: As disc arthroplasty for the treatment of degenerative disc disease becomes more prevalent, questions are beginning to arise as to the possible effects that these devices may have on the vertebral end plates. The end plate changes seen on magnetic resonance imaging (MRI) films after disc surgery usually come in two forms: they can either appear as anatomical changes to the configuration to the cartilage/vertebral body, or the changes can manifest themselves through differential signal intensities on MRIs. These latter types of abnormalities, Modic changes, represent an alteration in the vascularity and fat content of the bone marrow. End plate remodeling and Modic changes are thought to occur in the response to a number of factors, including natural degeneration of the disc or bone, infection within or around the disc or adjustments of the vertebrae in response to changes in load pressures. Both end plate remodeling and Modic changes typically occur after most types of surgical procedures to the disc, such as decompression, discectomy and fusion. Although end plate remodeling and Modic changes are common, their long-term clinical significance is not well understood. The intent of this study is to document the short- and long-term effects of prosthetic nucleus devices on the vertebral end plates.Methods used: In this retrospective study we followed 60 patients implanted with PDN prosthetic disc-nucleus devices (Raymedica, Inc.) for a period of 12 months. Preoperative MRI films were compared with 6-week through 12-month follow-up images.of findings: Of the 60 patients examined, 67% showed some degree of postoperative end plate remodeling and/or Modic change. Early in the follow-up process, none of the changes could be correlated with any clinical symptoms, and MRI done at the 12-month follow-up showed that for the most patients the changes had stabilized. There were three cases where end plate remodeling continued to a degree that resulted in significant disc-height narrowing.Relationship between findings and existing knowledge: The presence of end plate remodeling and Modic changes in patients implanted with prosthetic nucleus devices is not unexpected given that this type of change is commonly seen after surgical procedures affecting the disc. The results are also in agreement with the concept that bone will remodel in response to changes in stress (Wolff's law).Overall significance of findings: Although vertebral body and end plate radiographic changes do occur in some patients implanted with PDN devices, these changes usually stabilize over time and rarely lead to clinical sequelae. Therefore, treatment decisions based on the presence of postoperative radiographic changes should not be made unless the changes can be correlated to clinical signs and symptoms.Disclosures: Device or drug: PDN prosthetic disc-nucleus device. Status: investigational.Conflict of interest: Rick Vazquez, employee of Raymedica Inc.; Mark Myers, consultant, Raymedica Inc.

Surgical and clinical results with the PDN prosthetic disc-nucleus device.

The PDN prosthetic disc-nucleus device has been in use for 6 years, both in clinical trials and through commercial sale. Surgical and clinical data for the device have been collected and analyzed to help determine the strengths and limitations of the implant. The shape of the device has been found to be an important element in predicting surgical success, with wedge and rectangular devices being the most stable. The patient's disc dimensions are also critically important. Data indicate that patients with a disc height of less than 5 mm should be excluded from surgery. Moreover, the anterior-posterior (AP) diameter of the disc endplates must be 37 mm or more in order to properly situate two devices within the disc--patients with a smaller AP diameter should receive only a single device. Body mass and overall patient weight are also good predictors of surgical success. If the patient's body mass index is 30 or greater, then the patient should not receive the implants. Complications related to the PDN implant have included migration of the device and endplate remodeling in some patients. This endplate remodeling has usually been mild, and has occurred in response to the change in load distribution. In a few cases there has been more pronounced remodeling with a loss of disc height. To minimize endplate remodeling, the PDN hydrogel has been reformulated to be softer, absorbing 80% of its weight in water. Subsequent to implementing changes in device design and patient selection, and with the introduction of the ALPA (Anterior-Lateral transPsoatic Approach) technique for implanting the devices, there has been an increase in surgical success with a concomitant reduction in the number of revision surgeries. The current surgical success rate for patients implanted from 1999 through 2001 is 88%. Clinical results are also very encouraging, with marked decreases in Oswestry and visual analog scale pain levels, and disc height also shows improvement and stabilization.

The PDN prosthetic disc-nucleus device.

The health of an intervertebral disc is based on a complicated interplay between physiology and biomechanics. The nucleus pulposus must remain well hydrated, and the surrounding anulus fibrosus must be competent in order for the disc to function properly. If either of these components fail, the disc will begin to degenerate, and clinically relevant symptoms may appear. Disc degeneration has traditionally been treated by either discectomy or immobilization of the affected vertebrae, and though these treatments can be effective, they also have their limitations. To help fill the therapy gap that exists for treating moderate degenerative disc disease, the PDN device has been developed. The device consists of a hydrogel core and a polyethylene jacket that are designed to assume the cushioning function of a healthy disc, while restoring/maintaining disc height and allowing normal range of motion. To receive the device, patients must have a preoperative disc height of at least 5 mm and the vertebral endplates must be free of significant defects such as Schmorl's nodules or fractures. Two approaches can be used for implanting PDN devices: a hemilaminotomy approach, where the disc is accessed through the back, or an Anterior-Lateral transPsoatic Approach (ALPA), where the disc is accessed from the side. In either case, the nucleus material is removed from the disc, and the devices are placed transversely within the nucleus cavity. The amount of research and development currently taking place in the field of disc arthroplasty gives hope that the treatment of degenerative disc disease will soon become multifaceted, with numerous choices being available to surgeons and their patients.

Artificial nucleus replacement: clinical experience.

The prosthetic disc nucleus is designed to help treat patients suffering from degenerative disc disease. The device consists of a hydrogel core that is encased in a polyethylene jacket and is intended to restore disc height while permitting normal range of motion. Clinical trials for the prosthetic disc nucleus were first conducted in 1996, and the device was found to be effective in most of the patients that were implanted. Additional trials in 1997-1998 were less successful, with 38% of patients requiring revision surgery because of device migration. Subsequent changes were made to device shapes and to the surgical protocol to facilitate implantation, thereby eliminating the high device migration rates. Following these modifications, the success rate for the device has improved significantly. Clinical data show excellent results with marked improvements in Oswestry and Prolo scores. Overall, disc height measurements have been well maintained within normal physiologic ranges. The prosthetic disc nucleus device is currently undergoing clinical trials in Canada, and an IDE application to the Food and Drug Administration was expected in the fall, 2001.