Since first being described in 1955 by Robinson and Smith at Johns Hopkins Hospital, the anterior cervical discectomy and fusion (ACDF) has remained the gold standard for treatment of cervical disc disease with radiculopathy. Like most surgical treatments, however, there are problems that can occur as a result of surgery. Some of these, like loss of movement, are easily predicted and understandable. Others, like accelerated degeneration of adjacent levels leading to pain and additional surgery, are less predictable and may come as a surprise to our patients. Yet, when looking at large studies, there is an ongoing and increasing likelihood of problems over time (2.9%/year, 25.6% over 10 years with 6.8% re-operation rate)1 as a result at least in part of deterioration of discs and facet joints from the added stresses that are focused next to a fusion. Experimental studies have shown increased intradiscal pressures of 73-180% above those at unfused levels above the fusion and increases of up to 50% at adjacent levels below.2, 3 The increased propensity to develop additional degenerative changes in an individual who has already had problems at one or two levels leading to the first surgery only heightens our concern.
Therefore, efforts were undertaken to try to create a device that would function as a disc and would allow movement, rather than fuse a level in the spine. The earliest experience started in Europe in the late 1980’s. Lumbar disc replacements seem to work well but are difficult to access for future surgery since they need to be placed from an anterior approach with retraction of the abdominal aorta and left iliac/vena cava. The exposure for cervical disc replacements, which evolved a little later, is the same as for an ACDF and future surgery is similar to revision neck surgery, making them safer and more attractive.
The advantages of artificial disc replacement in theory are to restore a more normal feel to the neck, to maintain normal motion and to limit the potential for adjacent level degeneration as a result of stress transfer next to a fused level. They also allow for very rapid return to full activities because they do not require the 3-4 months of bony healing necessary for a fusion. The potential downsides are mechanical failure and persistent pain. Pain can originate from the movement of painful structures such as degenerative facet joints or recurrent or persistent irritation of nerve roots passing through narrow foramina.
Therefore the ideal candidate for an artificial disc is an individual with neck pain and arm pain from a herniated disc but with normal foraminal size and healthy facet joints. Indications may be stretched in a setting of multilevel stenosis or degenerative discs but with a greater risk of failure due to persistent pain. Occasionally neither anterior option is a good one and an isolated posterior foraminotomy is the best choice. Osteoporosis or the need for significant bone removal, foraminal stenosis and deformity would be contraindications for artificial cervical discs.
Many artificial cervical discs and fusions can be done as outpatient procedures making these an attractive alternative for individuals with acute or chronic cervical radiculopathy. As with most spinal procedures, exhaustion of conservative care and careful consideration of all factors is the best approach to achieve a favorable outcome.
References
1. Hillebrand et al. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J. Bone Joint Surg Am 1999; 81.
2. Pospiech J et al. Intradiscal pressure recordings in the cervical spine. Neurosurgery: 1999.
3. Eck JC et al. Biomechanical study on the effect of cervical spine fusion on adjacent-level intradiscal pressure and segmental motion. Spine 2002.
