Prestige Cervical Disc System Biology Essay

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The PRESTIGE® Cervical Disc System is a device that was developed by the Medtronic Sofamor Danek Company. The Premarket Approval Application was approved by the Centre for Devices and Radiological Health (CDRH) of the FDA in July 2007. It consists of two stainless steel parts which articulate via a ball and trough mechanism, and have screws to secure them to adjacent spinal neck vertebrae (C3-C6). When a spinal disc has been damaged or has herniated towards the thecal sac and the spinal cord, the distance between the flanking vertebrae is reduced, thereby causing spinal nerve damage - myelopathy. Sometimes, lateral movements of the vertebrae tend to damage the Spinal Nerve root (radix), and the condition is called radiculopathy. Previous procedures involved the removal of the damaged disc, and introducing an allograft between the vertebrae - spinal fusion surgery (anterior interbody fusion procedure with allograft and plate stabilization), thus maintaining an adequate gap between the vertebrae, but the movement of the neck is slightly restricted than before. However, the PRESTIGE® Cervical Disc System has a ball and trough mechanism which helps retain the original degree of movement of the neck. This device can be used only in the C3-C6 vertebral region, and not anywhere else on the backbone.

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The clinical trials involved the study of this device on 276 patients, and this was compared with the single level anterior interbody fusion (AIF) procedure on 265 patients. Although both classes of patients showed side effects during and after the surgery, the patients with the Prestige device showed better results (lesser complications) than the patients who underwent the AIF procedure. Also, the degree of neck movement retained was higher in the patients with the Prestige device than in the patients who underwent the fusion procedure. The device should not be used in patients with a current infection, or those who are allergic to stainless steel. Most of the patients with spinal disc problems tend to recover just by taking bed rest or physiotherapy, and only a small minority of the cases are referred to spinal surgeons for such procedures.

The Medtronic Company was started in 1959 by Earl Bakken and Palmer Hermundslie, and was originally a repair shop for medical devices. It has grown rapidly over the years into a multibillion dollar company. Medtronic developed the ATLANTIS® Cervical Plate System for treating patients with degenerative spinal disc disease. But it was clearly understood that the motion was restricted than before due to fusion of two of the vertebrae. This led to the development of the PRESTIGE® Cervical Disc System.

The Spinal Disc or Intervertebral disc is present between adjacent vertebrae of the backbone, except for the first cervical segment - the atlas. It acts as a shock absorber between the vertebrae, and also as a ligament in binding holding the vertebrae together. It has an outer ring - annulus fibrosus and an inner jelly like matrix - the nucleus pulposus. The fibres of the annulus fibrosus are tough, and disperse pressure uniformly across the disc. The nucleus pulposus acts as a shock absorber, and helps maintain the gap between the vertebrae.

A tear in the annulus fibrosus can cause the slipping out of the nucleus pulposus. This condition is called spinal disc herniation. The tear in the disc may be caused due to loss of water content because of disease or age. This causes a loss in height of the disc, bringing the vertebrae closer. This is a consequence of the loss of shock absorption properties of the disc, and it also results in the narrowing of the openings for the spinal nerves. This also aides the formation of bone spurs, which push against the spinal cord or nerves. When the spinal nerves are under pressure, it is called nerve root compression (Radiculopathy). This causes intense pain in the neck and arms. If the disc herniates towards the spinal cord or towards the nerve root, it can cause neurologic compromise or serious paralysis of both the upper and lower extremities, though this is extremely rare. Osteophyte formation is another complication in which bony projections grow on the vertebrae and squeeze the nerves coming out of the spinal cord. Osteophyte formation is a consequential change in bone formation due to damage and wear from inflammation.

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PRESTIGE® Cervical Disc System is a two-piece articulating metal device that is inserted into the intervertebral disc space at a single cervical level using an open anterior approach. The device is manufactured form wrought type 316 stainless steel (ASTM F-138) and consists of two metal plates which interact via a ball and trough mechanism. The superior component of the implant contains the ball portion of the mechanism, and the inferior component incorporates the trough portion. The flat portion of each component, which contains the vertebral end plate, is aluminum oxide grit blasted. Each component is affixed to the vertebral body by two bone screws through an anterior flange. The bone screws are held in place by a lock screw mechanism. In the implanted disc, the bone screws are divergent in the cephalic/caudal direction and convergent in the medial/lateral direction. The device assembly was designed to allow the following motions ex-vivo: a minimum of 100 motion off the neutral position in flexion/extension and lateral bending, unconstrained axial rotation, and 2mm of anterior/posterior translation. The device was initially produced in three size configurations - 6mm x 12 mm, 7mm x 12 mm and 8mm x 14mm, to suit the needs of the public.

A device modification was performed, and six new sizes were added after the completion of the clinical trials based on surgeon feedback (Table 1). Moreover, the anterior cut angle on the superior component was modified from 100 to 30, thus strengthening the anterior flange. Ths change was made in devices of all sizes. The FDA determined that the new sizes were adequately characterized by preclinical bench testing and that, given the modifications made, collection of additional clinical data on the new devices was not necessary.

The biomechanical properties of the device were studied by Bench tests. Static compression, Compression fatigue, subluxation, subsidence, push-out, pull-out and wear testing were done on the device. The size configuration of the device chosen for these tests was the worst case configuration - the 6mm x 16mm device (chosen after testing by the sponsor). The results of all these tests were better than the acceptance criteria of the FDA. The wear testing showed that the device lost weight in the order of 10-4g during flexion and extension tests. The particulate matter lost from the device during the test was taken and characterized under a scanning electron microscope at magnifications as high as 20,000X. Animal study was done to check for toxicity of the particles using a rabbit model. The results showed no signs of particle or device induced toxicity till 6 months of evaluation period.

The 6mm x 16mm device could withstand a compression fatigue of 225N, which was far higher than the required 74N (load of the cervical spine as reported by White and Panjabi). The worst case design for the subsidence test was the 8mm x 12mm device because it had the smallest footprint. Again, it could withstand a subsidence force of 718 +/- 62N, which was far higher than the required 74N. The Subluxation tests - push out and pull out, all showed very good results, far exceeding the required criteria.

Patent / FDA Approval

Overall success, i.e., an improvement in the pain and disability outcome scale, neurological success, maintenance of disc height, as well as no implant related serious adverse event or second surgical procedure was the basis for demonstrating the effectiveness of the device. The overall success rate, with and without the disc height criteria, for the PRESTIGE® group was found to be statistically non-inferior to fusion with bone graft and plate stabilization for the treatment of cervical degenerative disc disease from C3 to C7. The primary efficacy endpoint was met at the time of interim analysis.

The safety profile demonstrated that the PRESTIGE® Cervical Disc was as safe as the control, in regards to adverse events and the need for second surgeries. The results of the clinical study provide a reasonable assurance that the PRESTIGE®M Cervical Disc is safe and effective for the indicated population.

The results from the pre-clinical studies (mechanical and animal) support the use of the device in vivo. Thus, CDRH has determined that there is a reasonable assurance of safety and effectiveness of the PRESTIGE® Cervical Disc based on the results of the preclinical testing and the results of the clinical study.

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At an advisory meeting held on September 19, 2006, the Orthopedic and Rehabilitation Devices Panel recommended that Medtronic Sofamor Danek's PMA for the PRESTIGE® Cervical Disc be approved, subject to submission to, and approval by, the Center for Devices and Radiological Health (CDRH) of the following:

* The indications should be altered to read: "Device is indicated for reconstruction of the disc following single-level anterior discectomy for decompression of intractable radiculopathy and/or myelopathy."

* The PMA approval should be limited to all claims of non-inferiority only.

* The sponsor should conduct a post-approval animal study to address particulate migration and the device/bone interface.

* The sponsor should conduct a post-approval study of the device that looks at the long term safety and function of the device.

* The sponsor should have no educational material that suggests that preserving motion at one segment preserves the adjacent segment from having disease.

The CDRH concurred with the Panel recommendation of September 19, 2006 that there is a reasonable assurance of safety and effectiveness of the PRESTIGE® Cervical Disc based on the results of the preclinical testing and the results of the clinical study. Accordingly, CDRH issued a letter to Medtronic Sofamor Danek on March 13, 2007, advising that its PMA was approvable subject to Medtronic Sofamor Danek addressing issues related to the post approval conditions. Medtronic Sofamor Danek submitted a response on March 26, 2007.

Below is a discussion of FDA action on each of the Panel's recommendations:

The indications should be altered to read: "Device is indicated for reconstruction of the disc following single-level anterior discectomy for decompression of intractable radiculopathy and/or myelopathy."

The sponsor agreed to alter the device indications to read, "The PRESTIGE® Cervical Disc is indicated in skeletally mature patients for reconstruction of the disc from C3-C7 following single-level discectomy for intractable radiculopathy and/or myelopathy. The PRESTIGE® device is implanted via an open anterior approach. Intractable radiculopathy and/or myelopathy must present with at least one of the following items producing symptomatic nerve root and/or spinal cord compression which is documented by patient history (e.g., pain [neck and/or arm pain], functional deficit, and/or neurological deficit), and radiographic studies (e.g., CT, MRI, x-rays, etc.): 1) herniated disc, and/or 2) osteophyte formation. "This change has been reflected in the package labeling and all promotional materials.

The PMA approval should be limited to all claims of non-inferiority only. FDA permitted the sponsor to report the findings of their superiority analysis that was prespecified at the time of IDE. Statistical superiority was demonstrated in the PRESTIGE® group for overall success (with and without the FSU height component) and the neurological component. Statistical superiority was not demonstrated in the PRESTIGE® group for the NDI (primary effectiveness variable that addresses pain and function) and FSU height components. Claims derived from these findings should take into account the fact that the superiority finding for overall success was driven primarily by superiority in the neurological component. Proportions for the NDI variable were nearly identical between the two groups.

The sponsor should conduct a post-approval animal study to address particulate migration and the device/bone interface. At the September 19, 2006 Advisory Panel Meeting, the panel requested a post-approval study to look at both the particulate migration and the device/bone interface. The panel noted that the injected particles could not be readily located in the animals at sacrifice. In addition, the panel wanted to look more closely at the long term fixation of the device. Hence, one of the conditions of approval from the panel for this PMA was a post-approval animal study to address particle migration and the longer term fixation of the device. Given the long history of use of this stainless steel material in the spine and literature 2 showing similar results to the sponsor's study, FDA determined that another post-approval animal particulate study would not add value to this data set. In addition, an animal study of one or two years will not yield long term information on the device fixation. Because there were no incidences of device loosening that required re-operation among the cohort of implanted PRESTIGE® patients, FDA did not require an additional post-approval animal study.

The sponsor should conduct a post-approval study of the device that looks at the long term safety and function of the device. FDA agreed. See final conditions of approval below.

The sponsor should have no educational material that suggests that preserving motion at one segment preserves the adjacent segment from having disease. The sponsor agreed to remove any statement from their labeling or promotional materials that states or implies that motion retention preserves adjacent segments from having disease.

As part of the development of the final conditions of approval for this PMA, FDA considered not only the Panel input, but also the available data, issues that should be further evaluated, and our experience with post-approval studies for spinal implants.

Clinical Studies

In the largest clinical trial of its kind, the PRESTIGE® Cervical Disc proved to be a safe, effective alternative to fusion for patients with degenerative disc disease in the cervical spine.

The PRESTIGE® Cervical Disc, used in a procedure called cervical disc arthroplasty, or cervical artificial disc replacement, has been studied in the most rigorous manner possible. Its safety and effectiveness as an alternative to anterior cervical discectomy with fusion (ACDF) for the treatment of radiculopathy and/or myelopathy related to degenerative disc disease in the neck or cervical spine has been evaluated in a Level 1, multi-center prospective randomized controlled study that involved 541 patients - the most extensive clinical study of its kind ever conducted and completed for the cervical spine.

The goal of the PRESTIGE® Cervical Disc clinical trial was to compare the outcomes associated with cervical artificial disc replacement with the PRESTIGE® Cervical Disc and ACDF. It was conducted at 32 study sites across the United States and treatment took place between October 2002 and August 2004. Patients in the study, who had to be at least 18 years of age with symptomatic cervical degenerative disc disease with associated neurologic involvement that had not responded to non-surgical treatment for at least 6 weeks, were randomly assigned to the PRESTIGE® Cervical Disc or ACDF investigational groups.

276 patients in the PRESTIGE® Cervical Disc study group received an anterior cervical discectomy and decompression followed by placement of the PRESTIGE® Cervical Disc.

265 patients in the fusion control group received an anterior cervical discectomy and decompression with the placement of an interbody ring allograft and the ATLANTIS® Cervical Plate System (also by Medtronic).

Patients in both groups underwent tightly-controlled radiographic and clinical examinations pre-operatively, and at routine follow-up periods post-operatively.

According to the study, patients who underwent cervical artificial disc replacement with the PRESTIGE® Cervical Disc achieved equivalence to all treatment outcome parameters and superiority in neurologic success and overall success at 24 months, compared to the outcomes of patients in the ACDF treatment group.

Some key findings of the PRESTIGE® Cervical Disc clinical trial include:

At the 12 and 24 months follow-up points, the PRESTIGE® Cervical Disc patient group reported more improvement in their neck pain and a greater ability to go about their daily activities than the fusion control group.

Patients receiving the PRESTIGE® Cervical Disc maintained sagittal (front and back) angular motion averaging more than 7 degrees in the normal physiologic range of motion. Pre-operatively, the PRESTIGE® Cervical Disc group had a mean angular motion of 7.55 degrees, which increased to an average of 7.59 degrees at 12 and 24 months post-operatively.

On average, patients receiving the PRESTIGE® Cervical Disc had a median return to work that was 16 days faster than those in the ACDF treatment group.

Patients in the PRESTIGE® Cervical Disc group experienced no implant failures or migrations.Clinical research artificial discClinical research artificial disc

Fewer patients in the PRESTIGE® Cervical Disc group required secondary surgical procedures than those in the ACDF investigational group.

The PRESTIGE® Cervical Disc is the first artificial disc to be approved by the U.S. Food and Drug Administration for use in the cervical spine, and the first of a family of spinal artificial discs under development by Medtronic. Constructed of two pieces of stainless steel in a ball-and-trough configuration, the device is designed to be inserted into the remaining intervertebral disc space after a diseased or damaged disc has been removed.

There are some risks associated with the use of the PRESTIGE® Cervical Disc including, but not limited to, early or late loosening of the components, component sizing issues, and anatomical or technical difficulties. Patients may also experience possible tissue reaction; formation of bone that may reduce spinal motion or result in a fusion, either at the treated level or adjacent levels; and the development of new radiculopathy, myelopathy, or pain. For more information, please click here for links to important safety information or the patient information brochure which contains the complete list of indications, warnings, precautions, adverse events, clinical results, and other important medical information.

Traditionally considered the "gold standard" for the treatment of degenerative disc disease in the cervical spine, ACDF involves removing the affected disc material then fusing, or creating a bond between, the vertebrae on either side of the disc space. The procedure has been successful in many patients; however, a potential disadvantage associated with spinal fusion is the loss of motion and flexibility in the treated vertebral segment.