Can Disc Replacements in the Cervical Spine Prevent Further Disc Disease?Surgeons from the Spine Institute of Louisiana who wrote this article received the 2010 Outstanding Paper award for Surgical Science. The award was based on their study of adjacent segment degeneration (ASD) following artificial disc replacements (ADRs) in the cervical spine (neck).
There have been many reports that after a spinal fusion for disc degenerative disease, the disc at the next level (usually the one above the fused segment) is the next to degenerate. The loss of motion and adjacent segment disease were two reasons why scientists developed the artificial disc replacement (ADR).
At first, disc replacements were only available for the lumbar spine. But now, artificial disc replacements (ADRs) have been designed for the neck as well. Many studies have shown that disc replacements do indeed preserve joint motion, so the first problem has been solved. Naturally, surgeons (and patients) want to know if the artificial disc replacement also takes care of the problem of adjacent disc degeneration.
In this study, 93 patients with disc disease in the neck failed a minimum of six months of conservative (nonoperative) care and ended up with surgery. Conservative care included medications, physical therapy, chiropractic care, and steroid injections.
Half the group had the fusion procedure. The other half had an artificial disc replacement. The fusion technique used is called anterior cervical discectomy and fusion (ACDF). The name ACDF describes the approach (anterior is from the front), the location (cervical spine), and the actual procedure (discectomy removes the disc and fusion uses bone graft to fill in the hole where the disc once was).
The patients were randomly assigned to one or the other surgical treatment. Random assignment means a computer generated names for each group. The patients didn't even know what type of surgery they had until after the fact.
In the group of patients who had a disc replacement, 43 patients had a one-level procedure and 16 had two-levels replaced at the same time. Three different types of FDA-approved disc replacements were used. In the fusion group, 28 patients had a fusion at one level and six patients had a two-level fusion. Data on bone density and the presence of lumbar disc degeneration was collected and compared for both groups.
Success of each procedure was determined by measuring before and after changes in pain (or other symptoms) and improvements in function (as measured by the Neck Disability Index).
X-rays were compared before surgery and at regular intervals after surgery for up to four years. Any sign of adjacent segmental disease was noted. Lack of improvement, new (or worsening) neurologic symptoms, and the need for more surgery affecting the operated area(s) were used as measures of failure.
The mid-term results (after a median of three years) showed no difference between disc replacement and fusion. Both groups experienced an equal number of cases of adjacent segment degeneration (ASD). Between 15 and 18 per cent of all patients were affected by ASD. The period of time free from this problem was about three years for both groups.
There did not appear to be any link between age, sex (male versus female), tobacco use, or number of levels of surgery with the final outcomes. One key finding in this study was the fact that patients who had lumbar disc degeneration were more likely to experience segmental disc degeneration in the cervical spine.
In summary, motion preservation technology has led to the development of artificial disc replacements for the cervical spine (neck). This was the first study to examine patients receiving cervical spine disc replacement(s) for adjacent disc disease. Artificial disc replacements are safe and effective in reducing pain and neurologic symptoms. It does not appear that this new technology preserves the disc segment above and below any better than fusion surgery does.
The patients will continue to be followed in order to see what happens over a longer period of time. The surgeons will also keep track of patients who experience implant failure for any reason and report on that in future publications. The finding that disc degeneration in the lumbar spine predicts adjacent segmental disease in the cervical spine following disc replacement will also be studied more closely.
Ajay Jawahar, MD, MS, et al. Total Disc Arthroplasty Does Not Affect the Incidence of Adjacent Segment Degeneration in Cervical Spine: Results of 93 Patients in Three Prospective Randomized Clinical Trials. In The Spine Journal. Vol. 10. No. 12. Pp. 1043-1048.
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