Synonyms
Artificial disc, disc replacement, artificial disc replacement, disc arthroplasty, cervical disc prosthesis, lumbar disc prosthesis, disc prosthesis implantation
Definition
A disc prosthesis is an artificial disc replacement made of metal and plastic. An artificial disc is used to replace a worn (degenerated) natural disc. The aim is to eliminate the disc-induced (discogenic) back pain while maintaining the natural mobility of the spine.
As an alternative to this, stiffening of the spine (spondylodesis) in the affected spinal segment has been the surgical method of choice in recent decades. The figure shows a lateral x-ray of the cervical spine after successful implantation of a disc prosthesis. The reason for the operation was a disc herniation of the cervical spine that could not be treated sufficiently by conservative methods.
Not in all cases the disc prosthesis is the best therapeutic solution. Especially when wear-related changes in the spine, stiffening of the affected segment (medically called spondylodesis) is often the treatment of choice. During surgery for a disc prosthesis, the degenerated disc is completely removed and the disc prosthesis is instead placed between the vertebral bodies.
There it is anchored by metal projections according to the design of the prosthesis. Due to its special design, the disc prosthesis can follow the movements of the spine. Intervertebral disc prostheses are available for the cervical and lumbar spine. Both times the operation is performed from the front, not from the back.
Introduction
The possibility of installing a disc prosthesis represents a major step in spinal surgery. Disc prostheses have only been implanted in large numbers for a few years. Currently, about 11000 disc prostheses have been implanted worldwide, and the trend is clearly increasing.
In comparison, in Germany alone about 180,000 knee and hip prostheses are implanted annually. The experience with intervertebral disc prostheses is therefore still relatively young. Much about the long-term prognosis of a disc prosthesis is still unknown. Nevertheless, the first short to medium-term results after disc prosthesis implantation are very encouraging, which is why a significant increase in the number of implants is expected in the future.
Structure of a disc prosthesis
A disc prosthesis consists of two cobalt-chrome-molybdenum metal plates. The metal surface is coated with titanium or hydroxyapatite. The rough surface texture and the coating of the metal plates allows a good bony growth of the prosthesis to the adjacent vertebral bodies.
In order to ensure immediate stability after implantation, an intervertebral disc prosthesis has type-dependent metal extensions, which fix the disc prosthesis in the adjacent vertebral bodies (primary stability) and prevent it from shifting until the final bony growth. In order to be able to follow the movements of the spinal column, a disc prosthesis has a plastic (polyethylene) or metal core between the metal plates. During lateral inclination as well as forward and backward flexion, the spinal column movements occur along the axes of this disc core.
Before any surgical measure, unless it is an emergency, the entire spectrum of conservative therapy of the herniated disc should be used first. However, the optimal time for an intervertebral disc prosthesis implantation can also be missed if, due to disc degeneration (loss of height, water loss of the intervertebral disc), greater spinal instability has developed and subsequent degeneration of other vertebral body structures (e.g. the small vertebral joints). A distinction must be made between the indications for implanting a disc prosthesis in the cervical and lumbar spine.
The classic indication for the implantation of an intervertebral disc prosthesis is monosegmental back pain due to disc wear (discopathy). Monosegmental means that only one disc is diseased and needs to be replaced. Disc-induced means that the disc itself is the cause of the back pain and that there is no herniated disc or other wear-related spinal column changes are the cause.
Meanwhile, however, 2-3 disc segments are replaced simultaneously, even if adjacent discs are diseased and have their share in the back pain. In this regard, a good diagnosis is important, because not every disc wear is in need of treatment. Only those intervertebral discs are replaced that are worthy of treatment.
Also the postnucleotomy syndrome, in the sense of a persistent, disc-related back pain, after prior removal of a herniated disc, can be an indication for the implantation of a disc prosthesis. While the acute herniated disc in the lumbar spine is a contraindication for the implantation of a disc prosthesis and is removed by microsurgery (microdiscectomy) in the classical way, the herniated disc in the cervical spine is increasingly often treated with the disc prosthesis. Removal of the herniated disc alone is not possible in the area of the cervical spine, because removal of the herniated disc from the back, as is common in the lumbar spine, is technically very difficult and dangerous due to anatomical conditions. Up to now, herniated discs of the cervical spine have been operated on from the front, the affected intervertebral disc together with the herniated one removed and the adjacent vertebral bodies fused, i.e. the spinal column was stiffened in this section.
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