Cervical Artificial Disc Replacement Technologies

A number of disc arthroplasties are currently in various phases of development and clinical testing in the United States. These devices use a variety of materials and design concepts. At the time of the compilation of this manuscript, all cervical disc replacements in the US are available for investigational use only. As of August 2006, the FDA has approved two artificial discs for use in the general patient population for lumbar artificial disc replacement: the Charite disc (made by DePuy) and the ProDisc-L (made by Synthes). Presumably, artificial cervical discs will be approved by the FDA for use in the general patient population in the US in the near future.

Bryan cervical artificial disc

The Bryan cervical disc (made by Medtronic Sofamor Danek) is composed of a plastic (polyurethane) center with titanium endplates. It is designed as a one piece device that allows unconstrained motion. The Bryan cervical artificial disc is unique in that there is a flexible membrane that surrounds the nucleus (the inner portion of the disc) that is filled with a lubricant. This membrane is designed for two purposes: to contain any wear debris that forms and to prevent any soft tissue in-growth. This disc is designed to allow a normal range of motion of the neck. See Figure 1.

The Bryan cervical disc has been implanted in patients in Europe and two year results have been obtained. 73 patients underwent disc replacement with the Bryan cervical disc, and 52 patients reported an excellent to good outcome. Currently the Bryan disc is under clinical investigation in the U.S.

Prestige ST cervical artificial disc

The Prestige cervical disc (made by Medtronic Sofamor Danek) is a derivation of the original Bristol disc. It is made of a cobalt-chrome alloy that allows full range of coupled motion. It is designed as a metal on metal joint that essentially has a ball and groove articulation. This type of design allows all range of motion about the center of motion of the ball component. The prosthesis is attached to the spine via locking screws that attach to the vertebral bodies above and below the disc. The endplates of the Prestige disc are grit blasted to allow for bony in-growth, which helps keep the artificial disc securely in place. See Figure 2.

Robertson et al. reported on 27 patients who had the Prestige II disc implanted (the precursor to the Prestige ST) for single level disease. At the two-year mark, the 27 patients had improved pain and function as compared to the fusion group.⁴

Cervitech PCM Disc

The PCM, which stands for Porous Coated Motion (made by Cervitech) consists of a cobalt-chrome alloy with UHMWPE (Ultra High molecular weight polyethylene) This represents a metal on polyethylene articulation. The outside coating of the disc consists of a titanium/calcium phosphate double coating attached to a serratus surface. This design allows for a press-fit fixation as well as the ability for bone in-growth, which helps keep the disc securely in place.5 The PCM cervical artificial disc is designed to match the natural contour of the uncovertebral joint. It allows for minimal limitations of range of motion and minimal constraint. See Figure 3.

Currently the PCM cervical artificial disc is in the clinical trial investigational stage in the U.S.

Prodisc-C artificial cervical disc

The Prodisc-C (made by Synthes Spine) is similar to the lumbar version of the Prodisc. It consists of two metal plates each made of cobalt chrome. Extending from the upper and lower part of each plate is a metallic fin. The two plates ride on a UHMWPE insert that is fixed to the lower plate. The Prodisc – C allows for a range of motion within a specific range as allowed by the prosthesis.6 The endplates are sprayed with a titanium layer to promote bony in-growth, which helps the device stay firmly in place. See Figure 4.

The Prodisc-C is currently in clinical trials in the U.S.

Cervicore artificial cervical disc

The Cervicore (made by Stryker Inc) is a metal on metal cervical disc made of cobalt chrome. It has a saddle shaped design to match the contour of the cervical vertebral body. The base plates have a titanium spray that allows for bony in-growth as well as three spikes for fixation. After the Cervicore device is inserted, screws are placed through anterior flanges to promote primary fixation of the artificial disc to the bone. See Figure 5.

Implantation of the Cervicore prosthesis in the United States has begun as of late 2005 under an FDA clinical investigation.

Mobi-C artificial cervical disc

The Mobi-C (LDR Spine) represents a metal on polyethylene device. It consists of two metal baseplates with a UHMWPE insert. The Mobi-C represents the first second-generation cervical disc replacement. The insert is considered to have a mobile bearing technology that allows it to have more range of motion. There are two lateral stops on the inferior endplate that limit the movement of the insert. See Figure 6.

The Mobi-C artificial disc has received approval from the FDA to undergo an IDE trial in the United States. Over 100 such devices have been implanted in patients in Europe.

SECURE-C artificial cervical disc

The SECURE-C (Globus Medical) consists of two metal endplates that are secured to the top and bottom surfaces of vertebrae and have a plastic core that fits between the two plates. The design of the Secure-C disc aims to simplify the insertion technique in artificial discs in the cervical region. In July 2006 Globus Medical received FDA approval to conduct a US-based trial under an IDE at up to 20 sites in the US.

Kineflex-C artificial cervical disc

The Kineflex-C (SpinalMotion) is a 3-piece modular design consisting of two cobalt chrome molybdenum (CCM) end-plates and a CCM core. The theory behind the metal-on-metal design is that it should last longer than other materials. Movement of the disc is allowed within limits, as dined by a retention ring. The current US study began in January 2005 and is expected to be completed in January 2009 with 400 participants.

All of the above cervical artificial disc devices are still in various stages of development and testing and are not yet available for use in the general patient population in the US. It is expected that at least one or a few types of cervical artificial disc replacement technologies should be available for general use by mid-2007, or possibly sooner.

Jeffrey A. Goldstein, MD contributed to this article.

References

1. Reitz H, Joubert MJ. Intractable headache and cervio-brachialgia treated by complete replacement of cervical intervertebral discs with a metal prosthesis. S Afr Med J 1964;881–4.
2. Gore DR, Sepic SB, Gardner GM. Neck pain: a long-term follow-up of 205 patients. Spine 1987;12:1–5.
3. Hilibrand AS, Carlson GD, Palumbo MA, et al. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am 1999;81:519–28.
4. Robertson J, Porchet F, Brotchi J et al. A multicenter trial of an artificial cervical joint for primary disc surgery. Society for Spinal Arthroplasty. Montpellier, France, May 2002.
5. Link HD. The Spine Journal 4 (2004) 294S-302S
6. Bertagnoli R. Prodisc-C, a new player in total disc arthroplasty. Lecture at Swiss Spine Institute. Zurich, 2003.