Decompression and fusion, first described 50 years ago, has been the surgical procedure of choice for all these years. All the advances in cervical surgery have been towards increasing fusion rate, with lessening of morbidity and complications. Fusion with grafts/anterior fusion cages with of without plating, foster lordosis, maintain intervertebral body spacing and address and /or potentially avoid axial pain and pseudoarthrosis.

Although a fusion rate in excess of 90% has been achieved by modern fusion, there is mounting evidence that cervical fusion (arthrodesis) increases the stress on the non operated discs and therefore adversely impacts the rate of adjacent disc degeneration.

We know that fusion increases motion at adjacent levels as shown by Brumley et al (1)

Hilibrand et al showed in a study of 374 patients followed up for 21 years found adjacent segment disease occurred at a constant rate of 2,9% per year during the decade after fusion. (2) Although a portion of these patients had progression of their disease resulting from the natural history of spondilosis, Goffin et al showed (3) that the rate of radiographic adjacent segment disease was identical whether a fusion was performed for trauma or degeneration.

Progression of adjacent level degeneration has been shown to be worse if it is already present at the time of index level fusion. It has also been shown and is experienced by all spine surgeons that if degeneration is present at an adjacent level at the time of fusion the patient does not have the same good results as a patient without adjacent level disease at the time of fusion. (4) Clement and O’Leary.

Williams et al (5) showed in his study that fusion leads to an increase of adjacent disc herniation up to 16%.

The benefits of a anterior (front) approach to the cervical spine are well appreciated. Although posterior (back) and anterior lateral partial discectomy approaches may be alternatives to an anterior approach as means to avoid the biomechanical consequences of fusion, the long term progressive degenerative process is left unattended.

The abovementioned conclusions as well as the fact that fusion was and is done in the cervical spine in most instances without any radiological evidence of instability led to the design and production of many total disc replacements.

Hypothetically, the concept of a fully functional disc prosthesis , which re-establishes more nearly normal bio-mechanics to the disc level , if introduced early enough in the symptomatic degenerative disc disease, should return the biomechanical natural history of the adjacent level from that of a disease to that of an individual’s normal aging process.

In light of this evidence, a major role of cervical disc replacement will be adjacent to already established cervical fusions, when degeneration becomes symptomatic.

Many functional cervical disc replacements was tested and produced until now.

Prestige LP (low profile Cervical Disc) Clinical history of more than 15 years

The Bryans total disc replacement was introduced in 2001and has a follow up of 4 years. It was the first disc included in a USA FDA trial.

	Another cervical disc replacement on the market at this stage is the PCM
	Another cervical disc replacement on the market at this stage is the the Pro disc C
	Another cervical disc replacement on the market at this stage is the Mobi C
	The Centurion is an South- African designed product, and is produced and marketed in the USA as the Kineflex where FDA trials is underway.

Although some of the discs has a central core of poly urethane ( Bryans) and Polyethylene (Mobi C and PCM) , there is a tendency in the USA to prefer metal cores.(Prestige and Kineflex ).

Indications are generally the same as for cervical discectomy and fusion. Degenerative disc disease requiring surgical treatment at one or two levels, for symptoms or signs of cervical radiculopathy with ,or without axial neck pain.

Although myelopathy was included as an indication initially, the surgeons that are most experienced exclude myelopathy. ( Jan Goffin, Luiz Pimenta).Although this may be included later, it is safer to exclude patients with myelopathy , until a longer follow up is seen. In our own series patients with congenital narrow canals are also excluded.

The exclusion criteria are: Metabolic or neoplastic bone disease; instability more than 3,5 mm, active infection, age over 65 ( an age limit is difficult to decide on, and the limit of 60 to 65 was used as the older patients were more prone to have more paravertebral joint degeneration with non optimal bone quality).

It must be noted that although lumbar disc replacement was approved in the USA after extensive trials with the La Charite, most of the cervical replacements is still under trial.

In South – Africa, we have had extensive experience of up to 4 years. A 12 % fusion rate was seen, with most patients doing good to excellent. This experience was with the Bryans disc.

International studies were published of one and two year follow and even 3 year follow up with results as good as fusion. This is expected as adjacent level degeneration will be experienced at a later stage. (6), (7), (8).

Further longer term studies are needed to see the future role of cervical disc replacement.

References:

1.Brumley J, Komistek R, Jones A, Hajner M. Handout at the OAAOS Conference Orlando, Florida.

2.HilibrandAS, Carlson GD et al. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthodesis. J Bone Joint Surg (Am) 1999;81:519-28.

3.Goffin J, Van Loon J, Van Calenburgh et al. Long-term results after anterior cervical fusion and osteosynthetic stabilization for fractures and/or dislocations of the cervical spine. J Spinal Disord 1995;8:500-8.

4.Clement and O’Leary. Spine 1990; 15:1023-5

5.Williams et al: J Bone Joint Surg 46A: 1779-1964.

6. Goffen J, Casey A, Kehr P, Liebig K et al. Preliminary Clinical Experience with the Bryan Cervical Disc Prosthesis. Neurosurgery 51: 840-847,2002

7.Goffin J, Van Calenburgh et al. Intermediary Follow-up After Treatment of DDD with The Bryan Cervical Disc Prosthesis. Spine 2003;Vol 28, No 24:2673-2678.

8.Pamenta L, McAfee P, Cappucino Aet al. Clinical experience with the new artificial cervical PCM disc. The Spine Journal 4(2004)315s-321s.

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