Factors Other Than Fusion or Disc Replacement Determine Risk of Adjacent DiseaseEver since disc replacement became available for the cervical spine (neck), research has been ongoing to compare fusion surgery to disc replacement. One of the key questions has been whether or not disc replacement reduces the risk of adjacent-level disease. This study from the Spine Institute of Louisiana and Texas Spine and Joint Institute provides some additional information on this topic.
The assumption is that a fusion procedure stops motion thus increasing stress and load on the disc at the next spinal level (above or below the fusion). Disc replacement preserves motion so, in theory, should result in less adjacent-level deterioration.
Studies done so far show that patients obtain the desired pain relief with both procedures (fusion and disc replacement). The disc replacements are newer and appear to be safe and effective. Long-term studies of adjacent-level disease following disc replacement are not available just yet. Studies like this one offer short to mid-term results (two to four years follow-up).
The patient group in this study was made up of 170 adults with symptomatic cervical degenerative disc disease. Everyone in the group had failed to receive benefit needed from six months of active conservative management. They were randomly divided into the two treatment groups and followed at regular intervals over the next 32 to 54 months.
Imaging studies (MRIs, CT scans) were used to look for any evidence of degenerative changes at the nonoperated levels next to the surgical segment. They found no significant difference between the two groups in the number of patients who developed adjacent-level disc degeneration during that period of time. About 14 to 16 per cent of the 170 patients developed problems at the next spinal level.
Only a small number (four per cent) had severe enough disease to need further surgery. Most of the patients were treated conservatively without surgery. Nonoperative care included the use of antiinflammatory medications or pain relievers, physical therapy, and epidural steroid injection.
They did examine a number of other factors as potential risk factors. These included patient age, sex (male or female), smoking habits, bone density, and previous history of back problems. Only two of these factors showed any statistical significance as factors that could predict adjacent segmental disease. Those two factors were osteopenia (decreased bone density) and current history of lumbar spine degenerative disc disease.
The authors point out that it will take time for the fairly new research on artificial disc replacement to catch up with the 10 years (or more) of outcome studies on fusion for the cervical spine. Two years is not enough to predict long-term effects on adjacent spinal segments.
The results of this mid-term study indicate there isn't a significant difference in rates of adjacent-level disease between cervical fusion and cervical disc replacement. Other factors (besides the type of surgery performed) may have a greater impact (e.g., bone mineral density and presence of disc degeneration in the lumbar spine). The authors intend to continue following this group of patients and report again later on long-term results.
Pierce D. Nunley, MD, et al. Factors Affecting the Incidence of Symptomatic Adjacent-Level Disease in Cervical Spine After Total Disc Arthroplasty. In Spine. March 15, 2012. Vol. 37. No. 6. Pp. 445-451.
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