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Related Health Info / Articles Total Disc Replacement

A new approach to surgical treatment of degenerative disc disease of the lumbar spine has recently been approved on a limited basis in the United States. Just as we now are able to replace worn-out hip and knee joints with metallic and plastic artificial joint products, the new lumbar spine technique allows for replacement of damaged, painful or inadequate intervertebral discs with a titanium/polyethylene prosthesis designed to restore normal disc function. Individual disks in the lumbar spine can be replaced by the artificial disc unit, thereby restoring normal functional capacity for rotation, side bending, flexion and extension. Further, the height of the degenerative discs that may have been lost can be restored to some small degree by the traction and placement of the disc in the intervertebral disc space. It is hoped that this procedure will replace the current approach to painful intervertebral lumbar discs, which involves fusing the vertebral bodies and removing the disc material.

Although fusion is often a successful treatment for this disease process, it contains significant drawbacks. In some cases, there are multiple damaged discs, so fusing any of them confers more stress on the remaining ones. Frequently, this leads to a breakdown of an intervertebral disc above or below the level of fusion, which itself becomes painful after a number of years, necessitating further surgery or becoming an ongoing source of chronic pain. An advantage of the artificial disc is that by restoring and maintaining mechanical motion at an intervertebral disc level, the adjacent disc segments are not overloaded with additional movement and do not experience an acceleration in any degenerative process. Further drawback to the fusion procedure is that it often requires four to nine months for the bone material to fully integrate into the vertebral bodies above and below the level of the fusion and become solid. Conversely, recovery for an artificial disc procedure is often only a few weeks. Another advantage of artificial disc procedures is that they can be performed by endoscopic approaches, minimizing the need for extensive hospitalization and anesthesia.

Two artificial disc products have been approved to varying degrees for use in the United States. The first to be approved in the United States was the Charite lumbar disc, which had been developed in Germany and was released in the United States approximately two years ago. Though there had been extensive use of the disc in Europe, there were problems that developed soon after its release, including separation of the plastic polyethylene components. Therefore, it is not being used frequently. The most popular disc being used today, and the second to be approved, is the ProDisc. This had been developed in the early 1990’s by a French orthopaedic surgeon, Dr. Marnay. The ProDisc had a longer period of evaluation in Europe with up to eleven years of follow-up. Studies were repeated in the United States with follow-up times of two to three years. In general, follow up using the ProDisc design has shown excellent results.

The ProDisc discs use titanium plates on the superior and inferior attachments to the vertebral bodies, with a plastic material allowing for gliding motion and rotation between the metal plates. No strong adhesives are used on these discs, as the titanium surfaces are coated with a semi-porous material that allows for bone growth from the superior and inferior vertebral bodies that firmly secures the artificial discs in place.

The most recent artificial discs are the FlexiCore and the Maverick. They are the first artificial discs entirely made of metal. They have no polyethylene component and work with a ball-and-socket combination that allows for full rotation, side bending, flexion and extension, without any gliding motion as is often the case with the polyethylene-containing artificial discs. The discs have not yet been approved for use by the FDA.

Currently, the ProDisc and Charite are released for use at single lumbar disc levels, with occasional permission for use at a second level. Ongoing clinical trials are taking place with continued follow-up on all the artificial disc products. Studies in the United States and Europe would indicate that it is possible to replace three to four levels with artificial discs in the lumbar spine. The potential for this type of technology to be used at the cervical and/or thoracic spine also exists. Clinical trials are currently underway for the use of similar artificial disc products in the cervical spine. These are in the midst of clinical trials and are not yet available.

The application of artificial disc technology to the spine is an exciting new development, as the goal is to restore the functional capacity of the individual segments of the spine to their normal motion capabilities. It signals a new approach being undertaken in spinal surgery that reverses the trend toward fusion and resulting limitation of motion.

Authors: Jerel H. Glassman, D.O., St. Mary’s Spine Center, San Francisco, CA