A Possible Solution to the Problem of Metal Plates in Neck Fusion
Bioabsorbable plates are fairly new to the spinal fusion scene. For a long time now, surgeons have used an approach called the anterior cervical discectomy and fusion (ACDF). Anterior refers to the location of the incision and the way surgeon enters the spine (front of the neck). Anterior fusion is performed through the front of the spine to avoid the spinal cord and spinal nerves. Cervical refers to the neck and discectomy is the removal of the disc from between two vertebrae.
Most surgeons use bone graft material to fill in the space left by removal of the disc and a metal plate to hold the spine in place while the bone graft material fills in. The use of a metal plate and screws to hold it in place is called instrumentation. Stiffness is the desired outcome of fusion in order to provide stability. Fusion rates have improved greatly with this surgical technique.
But even as successful as this approach has been, there can still be problems. Sometimes the screws back out and/or the plate shifts its position. Because the plate is along the front of the spine, swallowing can be impaired. Too much stiffness is a potential problem when using a metal plate system but there is general agreement that fusion without instrumentation is less effective than with instrumentation. And X-rays can't penetrate the metal plate, so it's difficult to assess the fusion site.
That's why bioabsorbable plates that eventually break down and become absorbed into the fusion have been developed. The plate and screws hold up well for the first six months, providing full strength. But then they start to break down bit by bit. The body absorbs the by-product as it dissolves. By the end of the first year, the plate is only at 32 per cent of its full strength. And by the end of 18 months, it is completely resorbed. The plate is translucent so that X-rays taken anytime during the postoperative period pass through the plate and show the status of the fusion site.
But even with all of the technical advances with this procedure, there can still be problems. In this study of 30 patients with cervical fusion at one level (between C3 and C7 using these new plates), the fusion rate was good (92.3 per cent), but the rate of subsidence was still high for the bone graft used in the procedure. Subsidence means the extra bone used to fill in sinks down into the vertebra, leaving it less stable than a solid fusion. Neck deformity called kyphosis (too much forward curve in the spine) occurs when subsidence develops.
Major complications (e.g., infection, bleeding) were about the same for the bioabsorbable plates as with the standard metal instrumentation. Some patients still reported neck and arm pain. Loss of function or failure to resume normal everyday activities accounted for a 41 per cent rating of poor-to-good (rather than excellent). Slightly more than half (59 per cent) of the patients had excellent results.
The authors of this study suggests that bioabsorbable plates stabilize the spine better than having no plate but there are enough problems that further study and improvements in this technique are required before it can be recommended instead of metal instrumentation for ACDF procedures. Long-term study is also needed to see how patients (and the graft site) fare years down the road. Unlike permanent plates, with the dissolving kind, there won't be any plate-related complications years later as there have been with metal instrumentation.
Sometimes when there's bone or disc degeneration in the cervical spine (neck), fusion is needed to stabilize the area. Over the years, one procedure in particular has gained popularity because of its effectiveness: the anterior cervical discectomy and fusion (ACDF).
Andre Tomasino, MD, et al. Bioabsorbable Instrumentation for Single-Level Cervical Degenerative Disc Disease: A Radiological and Clinical Outcome Study. In Journal of Neurosurgery: Spine. November 2009. Vol. 11. No. 5. Pp. 529-537.
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