The intervertebral disc of the cervical spine is critical for normal motion and function of the neck. Degenerative changes of the disc may cause a desiccated piece of the disc to extrude through a tear in the back of the disc and compress a nerve root. Also, a focal bone spur formed through the degenerative process may compress a nerve. If non-operative treatment does not result in relief of neck and arm pain from the compressed nerve, surgical decompression is indicated.
Standard Surgical Procedure
The standard surgical procedure approaches the cervical disc from the front with removal of the entire worn-out disc and elimination of the compression on the nerve. A fusion is usually then performed to stabilize the motion segment. A bone graft is placed between the vertebral bodies where the degenerated disc was removed.
This is a highly successful operation, however, limitations exist because of the fusion procedure. An increased incidence of degeneration of the disc above and below the fusion occurs due to the increased forces on the adjacent motion segment. Bone graft is required either from the patient's own iliac crest, or from cadaver bone. And finally, immobilization is required postoperatively with a cervical collar, an internal plate and screws, or both.
Cervical Artificial Disc Replacement
A cervical artificial disc replacement is a device that is placed into the intervertebral disc space instead of a bone graft after the disc is removed with the goal of retaining as much normal motion as possible while keeping the motion segment stable. The theoretical advantages are to reduce the incidence of adjacent segment degeneration while maintaining normal neck motion, the elimination of bone graft donor site complications and possible disease transmission from donor bone graft, and early neck motion without bracing requirements.
There are presently two artificial cervical disc replacement devices that are undergoing FDA approval study in the United States: the Bryan disc and the PRESTIGE® Cervical Disc.
Figure 1. The Bryan disc is a metal-on-plastic design (titanium and polyurethane).
The PRESTIGE® Cervical Disc is a metal-on-metal design (stainless steel) that has undergone a long history of evolution. The original stainless steel artificial cervical disc was the United Kingdom (UK)Cummins design implanted in the early 1990's. This was a ball and socket articulation. The Bristol disc evolved from this design with a ball and trough articulation in order to allow physiologic translation of the motion segment.
Figure 2. The PRESTIGE® Cervical Disc is a metal-on-metal design (stainless steel).
The Bristol disc has undergone extensive testing in the UK with positive two-year follow-up showing continued satisfactory motion on flexion-extension x-rays (Figures 3 and 4):
PRESTIGE® Cervical Disc
The PRESTIGE® Cervical Disc is a minor modification of the Bristol metal-on-metal design with a sleeker profile and instrumentation that allows easier and more reliable implantation. The United States Food and Drug Administration (FDA) prospective, randomized trial will be getting underway very soon. Patients with a herniated cervical disc causing a radiculopathy that does not improve with nonoperative treatment will be randomized to either the PRESTIGE® Cervical Disc or the standard fusion procedure with allograft bone and an anterior cervical plate. The results of this trial will be used by the FDA to determine if widespread release is allowed. This will likely take one to two years.
Update: The PRESTIGE® Cervical Disc was approved by the U.S. Food and Drug Administration July 16, 2007.