Lumbar Disc Prosthesis Study         Spine surgeons in Texas in March 2000 performed the first surgical implantation in the United States of an intervertebral disc prosthesis.     This marked the beginning of the United States Food and Drug Administration (FDA) approved trial of the disc prosthesis device, which was manufactured in Hamburg, Germany. The study will be continued at ten United States investigational sites. The criteria for inclusion in the study is degenerative disc disease (wear and tear changes) with back pain rather than leg pain as a major complaint and be 18 to 60 years old.     This intervertebral dynamic disc spacer device has been used outside the United States for at least ten years.     The artificial disc consists of a polyethylene core that slides between two metal end plates. Reduction of pain and improvement in the lumbar spine's function are the goals of the study. The three part prosthesis is not available outside the study, which is only being conducted at the investigational sites. Approval by the Food and Drug Administration (FDA) could take up to four years.     One of the surgeons at the Texas Back Institute commented that every ten to fifteen years there is a revolutionary step in spine surgery and the artificial disc replacement may be that next step. Obviously it is far too early to tell.     The device is named the S. B. Charit'e Implant. The idea of the implant is to replace the disc and work as well as a patient's own once healthy intervertebral disc. The implant tries to keep the movement between the back bones (vertebral bodies) going and prevent them from collapsing by holding them distracted.     The ten year results using the intervertebral disc prosthesis outside the United States have indicated that it is most effective when used in younger patients approximately 20 to 50 years of age. Presently the S. B. Charit'e intervertebral disc prosthesis is available in 11 countries, which does not include the United States. It is projected that, if the prosthesis is approved by the FDA, it could be commercially available in the United States by 2004. It will continue to be investigated at the 10 investigational sites in the United States until that time.     The doctors who developed the artificial disc have not found that it was necessary to brace or immobilize the back after surgery. Walking is allowed soon after surgery. The patients are typically discharged from the hospital in three or four days.     The best results have been found to be in patients who do not have arthritis or too much degenerative change in the back. The condition of the bone overall needs to be quite good, therefore it would not be useful in someone with osteoporosis. Back ache should be the predominant symptom because if the patient has primarily leg ache, this is due to a nerve root irritation and perhaps would not lessen after surgery as back pain is expected to with this procedure.     The implant comes in different sizes to accommodate a wide variety of patient sizes. While the implant is usually used at one level, it is occasionally implanted at two adjacent levels during the same operation.     Disc Prosthesis in place in anatomical model spine. Left. Assembled disc prosthesis. Right. Components of the prostheiss two metal plates and polyethylene central core.