Motion Preservation - An Overview
As spinal fusion aims at immobilizing unstable vertebrae in order to stop pain generated from unstable segment, a wave of new technologies initiated in Europe trying to accomplish the same goal without the sacrifice of a segment motion. Spinal fusion is an old and time revered operation, initially created for treatment of life threatening conditions such as tuberculosis and severe scoliosis, which has been applied during the midst of the 20th Century to more common and localized conditions such as arthritis and degenerative disc diseases, conditions that were not treated surgically at all before.
Spinal fusion is still throughout the world the "Gold Standard" for patients who fail conservative treatment. It is a valid solution to incapacitating conditions, but the drawbacks are numerous and have not been completely elucidated. The fusion procedure, welding, at the affected level of the two vertebrae, eliminates the source of pain, but at the same time, a fusion of one or more segments changes the biomechanics of the spine and obviously affects the lumbar spine mobility. Actually the greatest problem might very well be the limitation of the patient ability to adjust his/her spine position according to different activity of every day life, switching from the sitting to standing position. This adaptation has to take place in the adjacent discs. This could be one of the reasons why fusions seem to lead to adjacent disc degeneration and further surgery. Recent data (Wang et al.) revealed that as many as 37% of fusion patients require further surgery within 10 years. Others argue that part of it is simply due to the natural progression of the disease. This debate will be solved when patients from the Prospective FDA study will be followed up to 10 years.
Motion Preservation Surgery represents a new approach to spinal degenerative disease. The goal is to insure pain relief while preserving function and to avoid the drawbacks of spinal fusion. Addressing different types of patients and different stages of the disease, various techniques have been developed over the years, mostly in Europe. None of these technologies are currently FDA approved and widely available in this country at the time of writing (07 / 2004), although the FDA panel gave a favorable opinion on June 2nd 2004 for the Charite Artificial Disc (Depuy). Other products are under FDA investigation and numerous others are being developed in the US and elsewhere. Doubtlessly considerable revenues are being anticipated for companies, spawning humongous commercial interest in these products. Real scientific data will soon be very difficult to separate from mere advertising recommendation. Surgeons and patients will have a hard time weaving their way through the maze of information that will very soon invade the media.
Three main categories of products are currently being tested in the U.S. Their indications and claimed advantages are different from one another and might very well in the future be complementary and be used in combination. However at this stage they are tested individually within strict FDA prospective studies.
1- Artificial Discs. The main trials concern for the lumbar Spine: the SB Charite (Depuy), the Prodisc (Synthes), the Maverick (Medtronic). They replace the degenerative disc with an artificial device made of various materials (alloys, PolyEthylen) in various combinations. For the cervical spine several products are already being tested.
2- Dynamic Stabilization (Dynesis). With this device the spine is stabilized but maintains some flexibility. It acts as an "Artificial Ligament". The exact indications are not quite elucidated but early experience in Europe seems promising and an FDA trial is on going in the US.
3- Nucleus Replacements aim at replacing the disc at an earlier stage than disc replacement patients, when the outer layer of the disc is still healthy. The expected advantage over total disc replacement is to be less invasive.
It is our recommendation that patients and physicians rely on three main sources of information:
- The FDA data when available (usually close before the final approval)
- The previous publications from Europe, mostly. Although in most cases their methodology is not perfect by US standards, they usually are from honorable surgeons and give the public a good perspective on the products.
- The investigator surgeons. The list is frequently posted in the company's website. They always have the most current information, beyond rumors and gossips.