Artificial Disc Preserves Range of Motion, Restores Disc Height
Karla Harby Feb. 25, 2005 (Washington)
Disc replacement with a prosthesis ( Charité) was superior to interbody BAK spinal fusion in a randomized controlled study designed according to specifications of the U.S. Food and Drug Administration (FDA). This study led to FDA approval of the device in October 2004.
Compared with the 99 patients who were randomized to receive fusion, the 205 patients who received disc replacement experienced an 82.5% increase in flexion and range of motion at two years of follow-up. (All BAK fusion patients lost all range of motion, which is the intent of the procedure.)
The prosthesis was significantly more effective than fusion in restoring the height of the collapsed disk space P < .001). The initial disk space height at the L5-S1 vertebrae operative level started at 5.2 (1.44) mm and increased to 13.5 (1.18) mm for patients who received the prosthesis. By contrast, the BAK patients at L5-S1 started at an initial disk space height of 5.9 (1.74) mm, and increased to an immediate postoperative disk space height of 11.9 (2.07) mm.
Those who received the prosthesis also suffered fewer complications and gained better flexibility, said lead author Paul C. McAfee, MD, chief of spinal reconstructive surgery at St. Joseph Medical Center in Towson, Maryland. "Even the receptionist can tell which patients got the disc replacements and which ones got the fusions," he said.
The U.S. version of the device consists of a sliding plastic core sandwiched between two cobalt chromium alloy plates. The outside surfaces of the plates are equipped with protrusions that help the plates become secured to adjacent vertebrae.
The patients enrolled were all disabled for at least six months owing to degenerative spinal disorders. In this series, the prosthesis patients achieved motion of more than seven degrees. "We're starting with a very abnormal disc, so we can't get it back to normal function, which is 15 degrees. But many patients ended up with 10 to 15 degrees," Dr. McAfee said.
In the U.S. trial, five patients experienced migration of the prosthesis more than 2 mm as a complication, and one of those required revision surgery, Dr. McAfee said. Overall, the fusion group has gone on to a 10% incidence of complications, whereas the disc replacement complication rate has been 4% to date.
Motion preservation is thought to help preserve adjacent vertebrae by reducing the stresses on them that are caused by spinal fusion, said Courtney W. Brown, MD, assistant clinical professor of orthopaedic surgery at the University of Colorado at Golden. He served as one of the surgeon-investigators in the multicenter trial.
Patient acceptance of the technique has also been assessed. At a minimum of two years of follow-up, with more than 90% of patients reporting, 82% of the prosthesis patients said they would "definitely" or "probably" choose the procedure if they had to do it over again.
Dr. McAfee stressed that orthopaedic surgeons need expert ssistance with the early stages of surgery on the lower spine because the prosthesis is implanted from the front. "Most neurosurgeons and orthopaedic surgeons do their own approach on the cervical spine, but we enlist the help of a well-trained vascular surgeon to go through the retroperitoneum," he said. "There is potentially a higher risk in the lumbar vein because of large blood vessels."
Dr. Brown praised Dr. McAfee for the fact that surgeons have not seen any catastrophic complications. "Because Paul McAfee is in charge, everybody who puts these discs in has had to go back for training. Paul has made a strong effort to make sure this is a safe procedure," he said.
Dr. Brown noted, however, that the prosthesis is not the same as a natural disc. Although the prosthesis offers a more natural result, "the reality is that we have not replaced the disc," he told Medscape.
Dr. McAfee receives research and miscellaneous funding from DePuy Spine, Inc. Dr. Brown participated in the trial as an investigator. AAOS 72nd Annual Meeting: Abstract 189. Presented Feb. 24, 2005. Reviewed by Gary D. Vogin, MD
