Disc Replacement for the Neck: Does It Really DO Anything?Disc degeneration in the cervical spine (neck) can create pain, loss of motion, loss of function, and disability. Surgeons are now able to replace the damaged disc with an artificial unit. Artificial disc replacement is rapidly replacing spinal fusion. But the question has been raised: does it really do anything more than fusion?
The intended advantage of artificial discs is that they allow the spine to move normally. This concept is referred to as preservation of motion. Neck range of motion is saved at the diseased segment but also in the overall cervical spine. And, if each individual cervical segment is working well, the hope is that further adjacent disease (degeneration above or below the already damaged disc) can be prevented.
One way to see how well disc replacements are working is to measure neck range-of-motion before and after surgery. By looking at various patient and technical factors, surgeons can identify what might be needed to assure good motion after surgery.
In this study, surgeons from South Korea followed 39 patients who received an artificial disc replacement for one level in the cervical spine (neck). Everyone got the same unit (the Bryan Artificial Cervical Disc Prosthesis made by the Medtronic Company in the U.S.). One surgeon did all the procedures using the same methods and techniques for each patient.
Data collected and used to compare before and after results included patient age, sex (male or female), and neck range-of-motion. Technical data collected included amount of bone removed during the surgery, angle the disc was inserted into the disc space (after removing the damaged disc), and how far into the space the disc was inserted (depth).
What's your guess? Is it more likely that range-of-motion is affected by patient factors or technical factors? Let's see what they found. If you guessed "both", you would be right. Range-of-motion before surgery, age, and sex were all patient factors linked to improved motion during the follow-up period. Disc insertion angle was the technical factor most closely linked to post-operative results.
Men were more likely to have better motion than women. Patients of either sex who had the most motion before disc replacement had the best results after surgery. They found that by using this particular disc replacement system, bone resection wasn't a significant factor. A special machine makes all the cuts giving even, equal amounts of bone cut from each end.
The disc insertion depth didn't turn out to be statistically significant in relation to post-operative neck motion. But the authors still believe that it's a good idea to set the artificial disc in as far back as possible. That way, it restores the normal anatomy more closely, opens up the spinal canal, and takes more pressure off the spinal nerve root and spinal cord.
The authors concluded that if maintaining neck motion is the main goal of artificial disc replacements, then measuring motion before and after surgery should be a way to see how effective cervical disc replacement is. This study is unique in that it also looks at what might be affecting motion -- beyond just the fact that the damaged disc has been removed and a new unit installed.
By identifying which patients have the best results, surgeons can select patients more carefully for this procedure. Knowing which technical factors make a difference helps surgeons improve their operative technique for this particular procedure.
One final note: only one specific type of artificial disc replacement was used in this study. Each manufacturer has designed their units with specific stiffness, biomechanical factors, and other features. The results here represent important patient and technical factors affecting motion for just the Bryan prosthesis. Future studies are needed to make the same comparisons between different artificial devices.
Seok Woo Kim, MD, PhD, et al. Analysis of Factors That May Influence Range of Motion After Cervical Disc Arthroplasty. In The Spine Journal. August 2010. Vol. 10. No. 8. Pp. 683-688.
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