UCSF spine surgeons test artificial disc for the neck

By Kimberly Wong

UCSF Spine Center surgeons are conducting a clinical trial to investigate the safety and effectiveness of an implant that replaces damaged discs in the neck.

The trial will compare the implant to fusion surgery. Fusion of neck vertebrae has been the treatment of choice for nerve compression caused by disc herniation and has been shown to have excellent early and intermediate outcomes, said Bobby Tay, MD, UCSF assistant professor of orthopedic surgery and primary UCSF investigator on the study.

However, neck fusion can cause stiffness and less ability for the fused vertebrae to absorb shock. This means that stress is transferred to the areas above and/or below the fusion site, and over time can cause these areas to wear out, he said.

“This clinical trial will tell us if the device can eliminate disc problems in the neck that lead to nerve compression, while preserving or restoring motion to the diseased cervical spine, restoring the alignment and height of damaged vertebrae and recreating near-normal cervical spine bio-mechanics,” he said.

Since the study of the implant began in 2002-03, patients in Germany, France and the United States who have received the artificial disc in place of damaged discs have reported anecdotally of significant improvement in both nerve pain and overall function, said Tay.

UCSF Medical Center is one of eight centers in the United States currently evaluating the cervical implant. The trial will enroll approximately 160 patients at the various centers over two years.

In fusion, surgeons remove the damaged disc and then stabilize the spine with a segment of bone placed between the affected vertebrae and a titanium plate to hold the bones in place until they heal together. The bone segment can be taken from the patient’s pelvis or from donated bone. With the implantation of the artificial disc, no additional surgery to remove bone from the patient’s pelvis is necessary and recovery time is quicker, according to Tay.

The artificial disc, developed in France and Germany, has two porous cobalt-chrome plates, with stabilizing keels that integrate into adjacent vertebrae, and a polyethylene 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 cervical implant is suited for patients with spinal cord compression and radiating arm pain caused by disc damage at a single level of the cervical spine, Tay said.  Patients should be between the ages of 18 and 60 and are eligible if they have failed six months of conservative therapy. Patients in the study will receive either the artificial disc or single level fusion.

The implant, named Prodisc-c, is manufactured by Synthes/Spine Solutions, Inc., which is funding the clinical trial. The company is based in Paoli, Penn.

According to Tay, more than half of people over the age of 40 have cervical disc disease. Symptoms include pain radiating down the arm and numbness, in addition to neck pain. Healthy discs, located in between the seven vertebrae in the neck and along the rest of the spine, act as cushions and shock absorbers between each bone. Damage to discs can be caused by degenerative disease, injury or heavy lifting. Once a disc is compromised or pushed out of position, it can press on spinal nerves, he explained.

UCSF surgeons also are testing a device similar to the cervical implant for use in the lower back. This clinical trial began in 2002. In addition, researchers in the spinal disorders division at UCSF Medical Center are investigating disc regeneration using techniques of cellular and molecular biology and intervertebral disc arthroplasty (artificial joint creation). According to UCSF researchers, this may include replacing only the center of the disc, the nucleus.

Additional participating surgeons on the UCSF cervical implant clinical trial are Christopher Ames, MD, UCSF assistant professor of neurosurgery; Sigurd H. Berven, MD, UCSF assistant professor of orthopedic surgery; David Bradford, MD, UCSF professor of orthopedic surgery; Vedat Deviren, MD, UCSF assistant professor of orthopedic surgery; Serena Hu, MD, UCSF associate professor of orthopedic surgery; and Philip Weinstein, MD, UCSF professor of neurosurgery.

For more information about this UCSF clinical trial, contact research coordinator Vivian Tan at 415-502-5333.