Beyond Interbody Fusion: Motion Preservation, Disc Arthroplasty and Nuclear Arthroplasty

Technologies for the treatment of spinal disc disease and trauma are being driven away from the relatively crude solution of fusing adjacent vertebrae to solutions that aspire to restore the dynamic structure and function of the spine.

Non-fusion products
Arguably one of the strongest underlying trends in the development of technologies for the treatment of degenerative disc disease is the trend toward dynamic stabilization, also referred to as motion-preservation. Both market leaders and small, innovative companies are focusing upon the challenges of stabilizing damaged or degenerated vertebrae without permanently freezing the joints via spinal fusion. Several non-fusion products are either on the market or in advanced clinical trials; as these devices come on to the market, non-fusion is expected to cannibalize the spinal fusion market, causing a slow-down in the fusion market as discussed above. However, both fusion and non-fusion markets will continue to be substantial markets, supported by the growing number of aging adults who wish to remain active in their later years. In addition, it will take several years for clinicians to convince themselves, through experience, that non-fusion is not only a viable option but one that gives satisfactory and long-term results to the patient. For example, surgeons are beginning to believe that dynamic stabilization needs to address the facet as well as the disc, in order to truly mimic the natural motion of the spine. Perhaps combination devices will achieve the desired physical mimicry in the future. Proof of safety and efficacy won’t emerge overnight, and in the meantime many clinicians are likely to continue to view, and utilize, spinal fusion as the gold standard for treatment of degenerative disc disease.

Disc arthroplasty (total disc replacement)
Cervical arthroplasty, or total disc replacement (TDR) is viewed as easier than lumbar arthroplasty (or TDR) because there is significantly more mechanical strain and a wider range of motion in the lumbar spine. Any device placed in the lumbar spine must meet a long list of requirements: it needs to be strong enough to support axial loading, preserve the proper intervertebral space, be very flexible so as to handle the rotation, flexion, extension and translation which occur in the lumbar spine, and should be relatively easy for the surgeon to customize to the individual patient. In addition, while cervical arthroplasty patients are usually in their 60s or older, lumbar arthroplasty patients tend to be on average about 35 years of age. Ideally, any lumbar artificial disc placed in a younger patient must be designed to last many more years than a cervical disc. Despite these technical challenges, both cervical and lumbar arthroplasty and artificial disc replacement markets will reap strong sales in the US as devices come out of clinical trials. As of this writing, there are three artificial cervical disc replacement devices approved in the United States: the Prestige® and the Bryan®. Both devices are by Medtronic Sofamor Danek (MSD), and both were approved for market by the FDA in July 2007. In December 2007, the FDA approved Synthes Inc.’s application to market its ProDisc-C total disc replacement product in the United States. The ProDisc-C is already approved and used in Europe and other areas outside the US. Therefore, for the time being, Medtronic Sofamor Danek holds 99.9% of the market in the US, while Synthes has just launched its product.

Companies developing total disc replacement include the following:

Advanced Prosthetic Technologies, Amedica, AxioMed Spine, B. Braun/Aesculap, Biomet Spine/EBI, Cervitech, DePuy Spine, Disc Motion Technologies, Globus Medical, Globus Medical, LDR Spine, Medtronic Sofamor Danek, Nexgen Spine, NuVasive, Orthofix International/ Blackstone Medical, Ranier Technology, Scient’x , SpinalMotion, Stryker Spine, Synthes Spine, Theken Disc, TranS1, U.S. Spine, Vertebron, Zimmer

Nuclear arthroplasty
Nuclear arthroplasty (also known as nucleus replacement), although not yet available in the US, is expected to expand the number of patients who will be treated, since the treatment falls in between conservative options and discectomy. Patients who previously would not have received any treatment, will increasingly be offered treatment with nucleus replacement. Spinal disc nucleus replacement is said to have several benefits, including the preservation of disc height, and maintenance of spinal mobility and flexibility. For some patients, TDR may be overkill; disc nucleus replacement may be sufficient. The fact that nucleus replacement acts and will act as an intermediate treatment step will increase the market size for nucleus arthroplasty. In addition, many patients will receive more than one nuclear arthroplasty, thus further increasing the size of the patient population. Late 2008 may see the first devices launched in the US for nucleus replacement.

Companies developing prosthetic disc nuclei include the following:

Arthro Kinetics, Biomet Spine/EBI, Corin, CryoLife, DePuy Spine, Disc Dynamics, Dynamic Spine, Gentis, NP Solutions, NuVasive, Pioneer Surgical Technology, Raymedica, Replication Medical, SeaSpine, Spine Wave, SpineMedica, Stryker Spine, Synthes Spine, TranS1, Vertebral Technologies, Zimmer Spine

Excerpt from “Spine Surgery Worldwide, 2008-2017: Products, Technologies, Markets and Opportunities” (March 2008). See link.

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