Total Disc Arthroplasty: The Next Big Thing?

In June, DePuy Spine, Inc., went before the FDA seeking approval for the Charité Lumbar Disc Replacement, and received preliminary approval contingent on development of an appropriate training program. Over the next two years, other companies are expected to seek FDA approval for at least three other lumbar discs and three cervical discs based on trials under way.

The era of disc replacement surgery has clearly arrived. But what does this mean? Why do we need disc replacements? Who is a candidate for this surgery? What are the results? What are the risks?

Though we don’t yet know all of the answers, our patients are already asking the questions.Many physicians will find that their patients know more about disc replacement than they do. A Google search using the phrase “lumbar disc replacement” at the time this article was written yielded 28,300 hits, and that number surely has risen.

This article is an introduction to total disc arthroplasty, the goal of which is to reduce pain and disability while preserving motion.

Alternative to fusion?
Fusion has long been regarded as a treatment for pain associated with joint degeneration. Hip and knee fusion, while not common, was effective and the only surgical treatment until the advent of joint replacement. Currently, standard surgical treatment for refractory chronic low back pain is fusion. It is effective in carefully selected patients with success rates of 60-80 percent. The cost of this success, however, is the risk of accelerated degenerative change at adjacent segments. The idea of disc replacement as an alternative to fusion is not new. Fernstrom is credited with the first clinical description of a prosthesis in 1964.(1) Although his steel ball placed into the disc space was not a clinical success, it did encourage others to continue their work.

The European experience with disc implants is approaching 20 years; the North American experience is much shorter. The first successful disc arthroplasty was developed by Buddner-Janz at Charité Hospital in Berlin. The initial design was problematic, and the current implant is in its third generation (Charité SB III).

Early reported trial results indicate disc replacement is probably as effective at reducing pain and disability as is fusion. Disc replacement also seems to preserve motion.(2-4 Longer-term European studies have not yet shown a clear benefit in terms of adjacent segment degeneration, but these trials involve only seven to 10-year results.(5-7) The FDA will base its approval on current trials that will include two-year results. Two other lumbar implants with twoyear data will come up for approval in the next year (ProDisc II, Spinal Solutions, and Maverick,Medtronic Sofamor Danek).

The good news is that each of these FDA trials is a randomized, controlled trial with fusion as the control group. The bad news is that the purported benefits of disc replacement are changes in long-term outcome, well beyond two years. The trials will have only provided a partial answer when the implants are approved.

Indications, contraindications It is clear that disc replacement will not be a panacea for low back pain and that not all patients who are surgical candidates will be candidates for disc arthroplasty. The main indication will be refractory mechanical low back pain of discogenic origin. Another relative indication will be treatment of adjacent segment degeneration above an existing fusion. Patients requiring decompressive laminectomies for spinal stenotic symptoms will not be candidates due to the loss of the stabilizing influence of the posterior tension band. Patients with scoliosis or spondylolisthesis also are not candidates, since disc replacement is not likely to positively affect the deformity. Osteoporosis is a relative contraindication due to the risk of implant subsidence. In early studies, patients with significant facet joint degeneration did not do as well.(5)

Technically challenging
Disc replacement is technically challenging and for many surgeons will involve a major change in their usual operative practice. All current discs are placed through the anterior approach, which is unfamiliar to many spine surgeons. Most spine surgeons will require an access surgeon, such as a general or vascular surgeon, to expose the spine. Those surgeons familiar with the anterior lumbar approach for anterior lumbar interbody fusions will have an initial advantage over those who have previously done only posterior lumbar procedures.

All other arthroplasties have demonstrated a finite lifespan. For hip and knee replacement, this is typically 15 years. Most hip and knee replacement patients are in their 60s or older, so a 15-year implant life is sufficient. Revision knee and hip arthroplasty, although challenging, is relatively routine. Patients undergoing disc arthroplasty will be much younger (30s to 50s) and revision anterior surgery at the lower lumbar level is very difficult. Therefore, the question of implant longevity is of vital importance.

The greatest potential benefit of disc replacement is likely to be in the decreased risk of adjacent segment degeneration. Conversely, the greatest surgery-related problem is likely to be late implant failure due to wear or loosening.

Spinal Column, Fall 2004. Cleveland Clinic Spine Institute (CCSI).
Copyright @2004. The Cleveland Clinic Foundation. All Rights Reserved.
http://cms.clevelandclinic.org/spine/documents/Publications/Spinal%20Column%20Fall%202004%20FINAL.pdf

SpineUniverse Editorial Comment:
Dr. Orr's article was published prior to the Food and Drug Administration's approval of the Charité Artificial Disc (DePuy Spine) in October, 2004.

References
1. Fernstrom U. Arthroplasty with intercorporal endoprothesis in herniated disc and in painful disc. Acta Chir Scand (Suppl). 1966;357:154-159.

2. Zigler JE, Vialle EN, Burd TA, et al. Lumbar spine arthroplasty: Early results using the ProDisc II: A prospective randomized trial of arthroplasty versus fusion. J Spinal Disord Tech. 2003 Aug;16(4):352-61.

3. Tropiano P, Huang RC, Girardi FP, et al. Lumbar disc replacements: Preliminary results with ProDisc II after a minimum follow-up period of one year. J Spinal Disord Tech. 2003 Aug;16(4):362-68.

4. McAfee PC, Fedder IL, Saiedy S, et al. SB Charité disc replacement: Report of 60 prospective randomized cases in a United States center. J Spinal Disord Tech. 2003 Aug;16(4):424-33.

5. Lemaire JP, Skalli W, Lavaste F, et al. Intervertebral disc prosthesis: Results and prospects for the year 2000. Clin Orthop. 1997 Apr;337:64-76.

6. Cinotti G, David T, Postacchini F. Results of disc prosthesis after a minimum follow- up period of two years. Spine. 1996 Apr 15;21(8):995-1000.

7. Griffith SL, Shelokov AP, Buttner-Janz K. A multicenter retrospective study of the clinical results of the LINK SB Charité intervertebral prosthesis: The initial European experience. Spine. 1994 Aug 15;19(16):1842-9.