Disc Replacement Rivals Spinal Fusion
Two surgical options yield similar results for degenerative disc disease.
People with degenerative disc disease in the lumbar (lower) spine who undergo disc replacement fare better in the short term – and at least as well overall – compared with those who have fusion surgery, according to a review of seven studies published online in ANZ Journal of Surgery. This analysis builds on existing evidence.
Degenerative disc disease, a common cause of low back pain, occurs when one or more discs – gel-filled cushions between the bones of the spine (vertebrae) – rupture or deteriorate. Unlike other “degenerative” conditions, symptoms from the disc problems often improve in a few weeks with minimal treatment. However, a small proportion of people have persistent symptoms that may require surgery.
For decades, the gold standard has been lumbar fusion, which removes the damaged disc(s) and fuses adjacent vertebrae to prevent motion-related pain. But only 60 to 80 percent of patients who undergo lumbar fusion have satisfactory pain relief, according to Jeffrey S. Fischgrund, MD, a professor of orthopaedic surgery at Oakland University William Beaumont School of Medicine in Rochester, Mich. “And fusing one level in the spine may lead to accelerated [disc] degeneration – and a new source of pain – in the adjacent levels," he says. Plus, it reduces mobility.
Artificial disc replacement (ADR) – sometimes called artificial intervertebral disc replacement (AIDR) – is a surgical alternative to fusion procedures. The damaged disc is removed and replaced with an artificial implant – in this case, a sliding polyethylene core between two metal endplates. The aim is to maintain the spine's normal motion and biomechanics.
"ADR preserves motion, theoretically resulting in less adjacent segment issues," Dr. Fischgrund says. "But the adoption of this procedure has been relatively low, as the results have not lived up to initial expectations."
Because ADR is controversial, investigators at the Royal Australasian College of Surgeons in North Adelaide, Australia, decided to find out just how safe and effective the procedure really is.
Between 2005 and 2012, they searched electronic databases for clinical studies comparing lumbar fusion and ADR, eventually finding six randomized controlled trials (comprising nine studies) and one nonrandomized comparative study that met their criteria. The studies used four types of artificial discs and three different fusion procedures. The largest study included 688 patients and the smallest 67 patients. Most were followed for two to five years after surgery.
To evaluate safety, researchers looked at the number of adverse events such as infection and nerve or blood vessel injury that occurred after both ADR and fusion. Overall, they found little difference, although two studies reported significantly more life-threatening complications after fusion.
The effectiveness of each procedure was gauged using pain scores, post-surgical use of opioid painkillers, patient satisfaction and Oswestry Disability Index (ODI) scores, which measure how back pain affects function.
After two years, most studies showed significant improvements in pain and function, less opioid use and fewer problems in adjacent segments of the spine in ADR patients. The ADR group was also far more satisfied with their procedure overall. But by five years after surgery, researchers found no significant differences in outcomes between the ADR and fusion groups.
Vijay K. Goel, PhD, professor of orthopaedic bioengineering at the University of Toledo, in Ohio, notes that the study does not provide a complete analysis.
"The authors have not discussed the efficacy in preserving motion following ADR and fusion surgery,” says Goel, who was not involved with this study. “Besides pain mitigation, ADRs are expected to preserve motion. [If they don't], then the whole justification for their use may be questioned somewhat, irrespective of the clinical outcome."
Goel also notes that at least one brand of artificial disc has undergone a redesign, and that second- and third-generation artificial discs “are showing better promise” than older designs – but the study results lump older and newer artificial discs together. “The authors need to identify the version used in each study cited in the review."
Another missing piece of the puzzle, according to one expert in spinal biomechanics, is long-term follow-up. Anton E. Bowden, PhD, assistant professor of mechanical engineering at Brigham Young University in Provo, Utah, says most spine studies don't follow patients long enough. "What happens with adjacent-level degeneration will only be seen over the longer term," he explains.
Bowden, who helped design a new type of artificial disc intended to facilitate normal spine motion, strongly favors ADR over fusion. "By every metric we know, fusion is not a great surgery," he says. "Disc replacement is a tremendous step biomechanically toward a better solution.”
But he acknowledges it is still a newer procedure with its own challenges. “We're at the same evolutionary point we were when we stopped fusing hips and started doing hip replacement,” he says. “Fusion makes the spine too tight; artificial discs can be too loose. In both cases, you can get problems in adjacent segments of the spine.”
As a parting thought, Dr. Fischgrund stresses that any spine surgery is always a last resort.
"Patients with chronic low back pain should consider surgical intervention only after all other treatment modalities have failed, and the pain significantly interferes with the normal activities of daily living," he says.
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