During surgery for herniated discs, the affected vertebrae are often fused to reduce the pressure on the nerves and spinal cord. However, this limits the flexibility of the spine. Artificial intervertebral discs are used to maintain the flexibility and mobility of the spine after a herniated disc. The prosthesis replaces the entire disc, relieving pain and reducing the pressure on the spinal cord and nerves. Artificial intervertebral discs are therefore a viable alternative to vertebral fusion in the cervical or lumbar spine.
The advantage of an intervertebral disc prosthesis is that it guarantees and maintains the mobility of the affected section of the spine. By using the artificial intervertebral disc, the strain on the adjacent vertebral bodies can be reduced.
There are two different types of intervertebral disc prosthesis: the cervical prosthesis and the lumbar prosthesis. The cervical prosthesis is used in the cervical spine and the lumbar in the lumbar spine.
The artificial intervertebral discs can be tailored to the body measurements of the individual patient. To do this, the surgeon has access to a range of metal plates and sliding cores of different heights. To adjust the curvature, there are intervertebral disc prostheses available in which the angle of inclination can be adjusted.
Cervical disc prostheses are the smaller of the two types of prosthesis. Their special shape means they are adapted to the functionality of the cervical vertebrae. The artificial lumbar intervertebral discs not only differ in size, but also in strength, which means they can absorb the high degree of pressure in the lumbar spine.
The artificial disc consists of two metal plates, which are made either from titanium or a mixture of cobalt and chrome-molybdenum. The plates are coated with a titanium alloy. The rough surface allows the prosthesis to grow together with the adjacent vertebral bodies. Between the metal plates, there is a core made from polyethylene or metal. The core is like two half-spheres that sit between the plates. This shape ensures the mobility of the intervertebral disc prosthesis.
Anchored between the metal plates, this simulates the inner core of the intervertebral disc. It is made from a plastic polymer and its structure allows it to be compressed, making it just as flexible as the original core of the intervertebral disc.
Intervertebral discs are surrounded by a ring of fibres. In the prosthesis, this is simulated by the artificial ring. This ring comprises several layers of fibres made from ultra-high molecular weight polyethylene (UHMWPE).
The shell is made from a viscoelastic plastic polymer. Because it forms a sheath around the middle part of the artificial ring, it prevents natural tissue from growing into the prosthesis.
Titanium end plates are attached to the top and bottom of the artificial ring. These are coated with a titanium alloy. This rough surface allows the adjacent vertebral bodies to grow onto the prosthesis.
The anchoring is cement-free. Anchoring spikes are used to secure the artificial intervertebral disc to the adjacent vertebral bodies. The rough surface (as mentioned above) of the coating on the metal plates ensures that the implant quickly fuses with the vertebral bodies. The advantage of an ingrowing prosthesis is that ingrowth guarantees a secure fit, which in turn ensures good durability of the prosthesis.
An artificial disc is always inserted from the front. The procedure takes up to two hours, depending on the location and stage of degeneration of the affected intervertebral disc.
The patient should completely avoid sitting for long periods (more than an hour), as well as heavy lifting and carrying, for six weeks after the operation.