Orthopedic surgeons at the University of California San Francisco (UCSF) Medical Center are investigating the effectiveness of an implant that may replace damaged lower back discs. European patients who have received the stainless steel and plastic assembly in place of degenerated discs have reported significant improvement in back and leg pain after a minimum of seven years of follow-up, according to investigators.
“In European clinical trials, the implant alleviated disc-related lower back pain while maintaining spine mobility – and eliminated the need for fusion of the lower spine,” said
David S. Bradford, MD, UCSF professor of orthopedic surgery and lead investigator of the UCSF study.
UCSF Medical Center is one of 13 centers currently evaluating Prosdisc®, which replaces discs damaged by degeneration, bulging, herniation, or thinning. The objective of the randomized clinical trial, which will enroll approximately 510 patients over four years, is to compare the safety and effectiveness of the Prodisc® implant to spinal fusion surgery. In fusion, the mainstay of surgical treatment for low back pain caused by degenerative disc disease (DDD), surgeons use rods and screws attached to the bones of the spine to hold them until the bones heal together.
While fusion of the lumbar spine has increased at the highest rate of any spinal procedure in the last ten years, advisability for patients, techniques and results remain controversial and unclear, according to Bradford. The ability of the bone to heal or fuse varies. In addition, spinal fusion at one or more levels can cause stiffness and decreased motion in the spine and more stress to be transferred to adjacent levels of the spine. Consequently, not all patients have a successful outcome, he said.
“Most important, fusion is not targeted toward restoration of normal structure and function,” said Bradford. “This prospective, randomized study will tell us is if the Prodisc® can eliminate back pain by preserving or restoring motion in the spine, restoring the structure and height of damaged vertebrae, and restoring the normal bio-mechanics of the lumbar spine.”
The artificial disc device, developed in France in the late 1980s, has two porous cobalt-chrome plates, with stabilizing keels that integrate into adjacent vertebrae, and a polyethylene ball-bearing core. The core functions on a ball-and-socket principle to fulfill the role of healthy discs — which permit limited motion and flexibility, while maintaining stability in specific segments of the spine and absorbing and distributing load.
The Prodisc® implants are suited for patients with degenerative disc disease at one or two levels of the spine. Patients should be between the ages of 18 and 60 and are eligible if they have failed at least six months of conservative therapy. Some patients will receive the Prodisc®, while others will receive the currently accepted treatment, spinal fusion.
Back pain is the most common ailment of the working-age adult, affecting over four million individuals each year in the United States. It is estimated that treatment of lower back pain in the United States costs more than $100 billion a year. While most acute episodes of low back pain respond well to non-operative treatment, the management of chronic low back pain remains a difficult challenge, according to Bradford.
The rate of back surgeries, including fusion of the spine, has increased by more than 600 percent between 1979 and 1990. In addition to spinal fusion, current treatments also include disc excision (discectomy) and the use of injections, electrothermal therapies, and implanted neural stimulators and medication dispensers. In addition to artificial disc replacement, researchers in the spinal disorders division at UCSF Medical Center are also investigating disc regeneration using techniques of cellular and molecular biology and intervertebral disc arthroplasty (artificial joint creation). This may include replacing only the center of the disc, the nucleus, according to the UCSF researchers.
The Prodisc® prosthesis, manufactured by Spine Solutions, Inc. of New York, is one of two similar devices being investigated. A separate study is analyzing the effectiveness of the SB Charite III Dynamic Disc Spacer, manufactured by the Link Spine Group in Branford Connecticut. This device was developed in the mid-1980s at the Berlin Charite Clinic in Germany.