When a disc degenerates with age, trauma, or smoking, weight is transferred to the outer lining (annulus) causing painful tears in the disc and causes the facet joint surfaces to jam closely together producing arthritis of the facet joints. Also, if a large portion of the disc herniates or too much of the central disc is removed during discectomy, the same weight transfer and disc space narrowing occurs. Gradual decreases in the openings for nerves exiting the spine (neuroforamina) occur causing pain in the extremity. Surgical fusion of the vertebrae has been an answer to these problems for many years, however after fusion, there is no motion in the fused vertebrae, eventually causing the disc above and below to degenerate and become painful. Artificial discs have been used in Europe and Australia for over a decade. Currently, there are two discs in clinical trials in the US (SB3 and Prodisc). Other discs not yet in US clinical trials include the PDN surgically implanted disc (used in Sweden and Germany), and the Biodisc, an injectable disc.
While there is palpable enthusiasm for these devices, it should be noted the potential for any artificial implant to fail and require removal. Enthusiasm in the medical world was similarly noted for fusion surgery ten years ago, but this has been tempered by a significant number of patients who receive no relief or were worse after fusion surgery. Thus far, the greatest experience is with the SB3 Charite disc which has shown good results in Europe for many years, and is now in clinical trials in the US. However, all three discs require open surgery. A newly developed injectable nucleus (shown below) may change the way we treat disc disease. It uses cow albumen cross linked with gluteraldehyde. Each of the two linked syringes contains one of these components. During injection, the components travel through a mixing chamber then through the needle, then into the disc. It hardens to the consistency of the annulus within 9 seconds and has shown long term stability to repeated pressure and torsion. It is expected clinical trials will begin on this disc in the year 2002. An identical product has already received a partial FDA approval for use in treating torn blood vessels.
Another method of disc replacement involves extraction of part of the cartilage endplate of a normal disc and culturing the cells outside the disc. These cells multiply, then are injected back into a degenerative disc. Early trials are underway now for this method of disc repair.