Artificial Disc Replacement

While hip and knee joint replacement surgery or arthroplasty has grown increasingly common since its advent in the early 1960s with a high degree of patient satisfaction, spine arthroplasty (or artificial disc replacement) has not been a viable option in the United States until recently.

The challenge has been to develop a suitable replacement for the intervertebral discs. The replacement must not only be safe to implant, reliable and long lasting, it also must have the ability to mimic the complex range of movement required of a disc. Efforts to find a solution to these challenges have been ongoing for more than 40 years.

Several artificial disc replacements for both the neck (cervical) and back (lumbar) spine are currently being offered to appropriate candidates at select U.S. centers.

An Alternative to Traditional Spinal Fusion

Age, genetics and everyday wear-and-tear of routine activities eventually can contribute to damage and degeneration of the discs that cushion the bones of the spine (the vertebrae). To treat degenerative disc disease, doctors usually begin with conservative (nonsurgical) medical treatment. When conservative therapy fails, other approaches, possibly including surgery, may be recommended. Currently, the gold standard for surgical treatment of problematic degenerative disc disease is spinal fusion. This procedure attempts to permanently lock two or more spinal vertebrae together so they cannot move except as a single unit. This may alleviate pain in a motion segment.

Spinal fusion, however, has well known potential disadvantages, including:

• Loss of motion and flexibility
• Permanently altered motion characteristics and biomechanics
• Potential for accelerated degeneration of the discs above and below the fused level that can lead to more pain and the need for more surgery

Artificial disc replacement offers a reversible, viable alternative to fusion that possibly avoids the accepted shortcomings of fusion. By inserting an artificial disc instead of performing spinal fusion, there is the possibility of reducing damage to nearby discs and joints. This is because artificial disc replacement allows for motion preservation, near normal distribution of stress along the spine and restoration of pre-degenerative disc height.

How a Disc Is Replaced

Spine surgeons at the Cedars-Sinai Spine Center are at the forefront of development and evaluation of a safe and effective artificial disc. The evolution for hip and knee replacement has taken more than 40 years to reach its current stage of technology in materials, design and technique. Although the idea of an artificial disc is not new, artificial disc replacement technology has just in the recent decade become mature enough to be used clinically in extensive testing in Europe. The unique biomechanical challenges of artificial disc replacement have presented a challenge of both design and material.

Although revolutionary in material and design, the technique to install an artificial disc (whether in the neck or low back) is routine and safe. In both traditional disc surgery and artificial disc replacement the procedure begins by removing the gelatinous disc between the vertebrae.

Once the disc is removed, two metal plates are pressed into the bony endplates above and below the space now vacated by the disc. Metal spikes hold these plates in place on the bone. Eventually bone will grow over and around the metal plates. A plastic spacer made of a polyethylene core is put between the plates. The patient's own body weight compresses the spacer after the surgery is complete. The device allows for six degrees of freedom.

Recovery from artificial disc replacement and care afterwards are much like that for other anterior approaches to lumbar spine surgery. In some cases, recovery is faster than for a traditional fusion surgery. There is less pain from the procedure and fewer complications in general. The materials used in artificial disc replacements are similar the materials used in routine hip and knee replacement surgery. The materials are designed not to cause sensitivities once in the body