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 a number of Cervical Disc Replacement devices that have shaped the scene we have currently. The Bryan Disc made significant advances into understanding cervical motion preservation surgery. It is however somewhat obsolete now and is not being utilised as commonly (see figures 1,2 and 3).
Also there is amongst others, the Nuvasive PCM (see Figures 4, 5 and 6.), the Synthes Prodisc C (see Figures 7, 8, and 9) and perhaps the most stringently tested of them all, the SpinalKinetics M6-C (Figures 10,11 and 12)
Click here for a full range of current cervical disc replacements
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Figure 2. Bryan disc in neck flexion
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Figure 3. Bryan disc in neck extension
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The Nuvasive PCM® Cervical Disc stands for Porous Coated Motion. It 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. 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.
Currently the PCM cervical artificial disc is in the clinical trial investigational stage in the U.S. but has been used for over 10 years successfully in Europe.
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Figure 4. PCM Disc Replacement
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The PCM disc has undergone modifications and extensive testing in Europe and the USA with positive two-year follow-up showing continued satisfactory motion on flexion-extension x-rays (Figures 5 and 6):
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Figure 5. PCM disc replacement in neck flexion
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Figure 6. PCM disc replacement in neck extension
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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. The endplates are sprayed with a titanium layer to promote bony in-growth, which helps the device stay firmly in place. The Prodisc-C is currently in clinical trials in the U.S.
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Figure 7 Prodisc-C 
Figure 8
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Figure 10. Spinal Kinetics M6-C
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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 will be 3-4 years before they are widely available in the general US population. The current consensus in Australasia is still one of uncertainty. Currently no restrictions apply and to date many cervical disc replacements have been performed. The Royal Australasian College of Surgeons is currently awaiting the results of various clinical trials for different prostheses and these will guide the relevant committees as to the effectiveness of these devices over other techniques. Government subsidy as in Medicare Benefits will follow suit in due course if they are proven as at least equivalent or superior to established surgical techniques. |
Dr Pope is trained extensively to implant all of the above mentioned devices including others to the strictest of regulatory standards and is approved by the respective companies as an accredited trained surgeon to safely implant their devices.
