Two lumbar disk replacement systems have been approved by the FDA, but payors are backing a noncoverage decision from CMS

Low back pain affects as many as 80 percent of all people at some time in their lives; during any single month, approximately 40 percent of Ameri-cans complain of low back pain. As a result, back pain is one of the primary reasons that patients see orthopaedists.

Most low back pain is idiopathic and has an excellent prognosis. Evidence-based medicine points to time, education, non-narcotic medications, elimination of risk factors such as obesity and tobacco use, good body biomechanics, and a regular exercise program as the most effective treatments. Although few randomized, prospective studies are available to guide the choice of treatment in conservative care, the relative costs and risks of injury to the patient are low and the prognosis with time is usually excellent.

However, chronic, severe low back pain with disability does develop in some patients. The treatment options in these cases are more controversial. The management of this diagnosis is further confounded by a variety of social, behavioral, and economic issues, including drug-seeking behavior and abuse of workers’ compensation benefits or personal injury awards.

Spinal fusion
For the small group of patients who has truly disabling structural pain resulting from some type of segmental instability or intrinsic irreparable disk injury, spinal fusion may be an effective alternative to prolonged conservative treatment. Dynamic radiographs, bone scans, and magnetic resonance images provide clinical diagnostic support to help identify the painful disk(s). Discography, although not fully accepted as a diagnostic test, may give the surgeon confidence in pinpointing the source of the pain and may help to avoid an intervention in a patient who has nonconcordant pain or contradictory test results.

Surgery has become increasingly reliable in achieving fusion. In fact, with pedicle screw instrumentation, circumferential fusions, and biologics, the tools are available to achieve close to a 100 percent fusion rate. Unfortunately, patient satisfaction—even among patients with “successful” fusion—has not reached the same rates.

After a well-indicated, one-level fusion, only about two thirds of patients will report that they are satisfied with the results of the surgery. Problems such as stiffness, persistent low back pain, and muscle fatigue may result from extensive muscle stripping, epidural scarring, inadequate restoration of sagittal balance, and kinematic changes that may result in degenerative changes to adjacent levels.

Alternative technologies
As a result, motion-preserving, non-fusion technologies may be appealing alternatives. Several developing technologies have the potential to improve clinical outcomes for patients, particularly for those with diagnoses that have low satisfaction levels. Among these developing technologies are total disk replacement (TDR), pedicle screw-based motion devices, facet replacing devices, interspinous spacers, nuclear replacements, and annular repair devices.

The U.S. Food and Drug Administration (FDA) has given two TDR systems premarket approval for clinical use—the Charité Artificial Disc, marketed by DePuy Spine, and the ProDisc™-L Total Disc Replacement, marketed by Synthes. Other devices are in differing stages of premarket approval.

The two TDR devices are pictured in Figure 1. The Charité is a third-generation device with two cobalt chromium alloy endplates and a non-constrained ultra-high molecular weight polyethylene (UHMWPE) sliding core. The Charité interference to the vertebral bodies consists of small fixation pegs on a smooth surface. The ProDisc-L is a second-generation device with two cobalt chromium alloy endplates and a semi-constrained spherical joint. The UHMWPE insert is convex and fixed to the lower plate. The endplates are fixed to the vertebrae with a keel and a porous ingrowth coating.

Both devices are approved for use in skeletally mature patients with degenerative disk disease at one level from L4-S1 (Charité) or L3-S1 (ProDisc-L). They are recommended for patients who have no more than 3 mm of spondylolisthesis at the involved level and for whom at least 6 months of conservative treatment has been unsuccessful. Contra-indications include stenosis and osteoporosis. The anterior approach requires mobilization of the great vessels. This exposure may be tech-nically challenging and potentially risky for the patient if revision is required.

IDE studies weren’t enough
The prospective, randomized investigational device exemption (IDE) studies conducted for these devices were not blinded, nor did they show the superiority of the TDR devices to other treatment options (Table 1). In fact, the studies were not designed to show superiority, only to prove that the results of the disk replacement were as good as the compared fusion technique (the BAK cage was used as control in the Charité study; circumferential fusion was used as the control in the ProDisc-L study). The problem, however, is that a non-superiority study is not sufficient to show the true value and real risks of a treatment.

In August 2005, Richard A. Deyo, MD, MPH, co-director of the University of Washington Center for Cost and Outcomes Research, requested a National Coverage Determination on the Charité-Lumbar Artificial Disk Replacement (LADR) from the Centers for Medicare and Medicaid Services (CMS). At the time of the request, the Charité system was the only LADR product that was FDA approved and available for evaluation.

Following a national coverage analysis and meetings with the manufacturers, CMS determined that LADR with the Charité disk is not reasonable and necessary treatment for the Medicare population older than 60 years of age, and CMS, therefore, would not cover the procedure or device. CMS did not issue a national coverage determination for Medicare beneficiaries 60 years of age or younger, leaving the matter to be determined on a local basis. (The full decision memo is available at www.cms.hhs.gov.)

The final memo did include a provision to reopen the determination if another LADR product became available. With the FDA’s approval of the ProDisc-L, CMS initiated the first reconsideration of the national coverage determination and has issued a proposed decision memo (available at www.cms.hhs.gov). The proposed decision mirrors the initial determination of noncoverage, and a final decision on the first reconsideration will be issued on August 23, 2007 (after this issue of AAOS Now went to press).

Timing was an issue
The noncoverage decision on LADR with the Charité disk was issued 2 months before CMS launched its Coverage with Evidence Development (CED) program. The program is applicable “when a particular medical intervention has yet to conclusively demonstrate an improvement in health outcomes, but existing information clearly suggests the intervention may provide an important benefit.”

Had the timing been different, the CED program might have provided an excellent opportunity to gather additional evidence on the performance of total disk replacement devices while providing a treatment alternative to the older Medicare population.

This was a precedent-setting case in orthopaedics for noncoverage of devices that have FDA premarket approval. Private insurers have followed the CMS position, declining coverage for the procedure and product. For example, the Aetna Clinical Policy Bulletins consider implantation of artificial prosthetic intervertebral disks for replacement of degenerative intervertebral disks to be experimental and investigational.

To avoid a recurrence of this situation, manufacturers should include representatives from payors as well as from the FDA in designing the IDE studies. A comparison showing that a new device is not inferior to an already accepted treatment is insufficient for CMS to make “reasonable and necessary” determinations. The studies must be designed to show the superiority of the new treatment or device.

Manufacturers are encouraged to include representatives from CMS in their initial meetings with the FDA. The burden is on the manufacturer to take this step, because CMS cannot attend these meetings without express invitation from the manufacturer.

What’s the future for disk replacement?
Approximately 20,000 TDR procedures have been performed worldwide during the past two decades; more than 3,000 have been performed in the United States. Clinical experience shows that patients who receive TDR recover more quickly than those who undergo fusion procedures. Wear studies for the metal-on-polyethylene devices indicate that wear rates are 5 percent to 10 percent of the wear rates in total hip and total knee arthroplasty, suggesting that devices implanted in young, active individuals may be expected to last a lifetime.

TDR also maintains motion when the disk is properly positioned and mobilized. This could result in a lower rate of degeneration at adjacent levels. Facet pain remains a question, especially in the less constrained devices, which may also lead to increasing facet degeneration and pain.

Accurate placement of the TDR requires great skill. Computer-aided orthopaedic tools may further enhance the accurate placement of these devices and help to minimize the possibility of an outlier.

In addition, payors express concern about the complications that could result from TDR. Removal of an infected or dislocated TDR is a life-threatening procedure, and several deaths have already occurred in the United States. Any reoperation places the great vessels at risk.

The Charité and ProDisc-L are the first devices available for TDR in the United States. As with any new technology, we can expect continued improvement in performance and outcomes over time, as well as advances in the materials used, including the development of metal-on-metal and ceramic devices. Although the anterior approach remains a concern, systems incorporating a posterior approach are being developed.

When evaluating the safety, efficacy, and performance of TDR, orthopaedic surgeons should remember the significant improvements that have been made in the evolution of total hip and total knee prostheses. Today, no operations improve the quality of life more than these two orthopaedic procedures, and the procedures themselves are far superior to the initial efforts. In the future, TDR may similarly improve, even though chronic low back pain is a more complicated condition than osteoarthritis of the hip or knee.

References

1. Blumenthal S, McAfee PC, Guyer RD, et al: A prospective, randomized, multi-center Food and Drug Administration investigational device exemptions study of lumbar total disc replacement with the CHARITE artificial disc versus lumbar fusion: Part I. Evaluation of clinical outcomes. Spine 30;2005:1565-1575.
2. Zigler J, Delamarter R, Spivak JM, et al: Results of prospective, randomized, multi-center Food and Drug Administration investigational device exemption study of the ProDisc-L total disc replacement versus circumferential fusion for the treatment of 1-level degenerative disc disease, Spine 32;2007:1155-1163.

Vijay K. Goel, PhD, is the Endowed Chair and McMaster-Gardner Professor of Orthopaedic Bioengineering Co-Director, Engineering Center for Orthopaedic Research Excellence in the departments of bioengineering and orthopaedic surgery in the colleges of engineering and medicine at the University of Toledo. Dennis P. McGowan, MSc, MD, is a member of the Biomedical Engineering Committee and may be reached at dmcgowan49@hotmail.com.