Lumbar Artificial Discs - artificial disc replacement
We have known for some time that discs can be a source of pain. Up until recently, lumbar fusion has been the standard surgical approach for this.
If the disc can be proven as the source of the pain, why not cut it out and replace it with bone graft? This was the best that could be done. In many cases it worked well, in others rather less so.
The artificial disc - a new approach
If the disc is damaged and painful, why not replace it?
Spinal fusion stiffens the vertebrae each side of the abnormal disc and this may give problems with other disc levels. The artificial lumbar intervertebral disc is designed to restore and maintain the normal motion at the joint level concerned.
Only recently has disc replacement broken through as a mainstream option for low back pain. It is the next big thing in spinal surgery, although long term results are not yet convincingly better than spinal fusion, but they are comparable. This means they are not worse.
The use of an artificial disc to replace a painful and damaged spinal disc was developed in Europe over some years with the Charité designed in the Berlin Charite Clinic, Germany. There are several other designs being developed and approved.
Artificial discs may offer a chance of successful treatment for low back pain. A published study from the Charite trial showed improved pain and functional scores in patients with artificial discs. They went back to work earlier and had better spinal motion compared to patients with the usual fusion operation.
Spinal fusion surgery is still the main treatment of choice for people with chronic back pain who have not been helped through conservative treatment (physical therapy, exercise, medication, manipulation). Fusion can return people to work, increase their activities of daily living, and allow them to enjoy a relatively pain-free day-to-day life.
200,000 spinal fusions are performed every year in the US. The technique has been refined but is not entirely predictable in outcome.
In a large review of over 4000 patients, authors Bono and Lee found fusions to take in 85% of cases. The average success rate in terms of relief from pain was 75%. You can see that leaves 25% of people in the unchanged or potentially worse category. They found it took an average 15 months for healing and recovery. Fusion also throws abnormal stresses onto joint levels close by, causing unwelcome effects in some cases
Increased likelihood of degeneration at neighbouring levels of the spine (also called transition syndrome) makes it difficult for spinal surgeons to advise relatively young people to consider lumbar fusion surgery. If other levels are affected in time, they may have further pain and disability with no real chance of operative treatment.
Advantages of the artificial disc
The artificial disc has theoretical benefits over spinal fusion for chronic back pain. There may be increased success rates, in this cases better pain reduction. Maintaining normal spinal movement may also avoid early degeneration of the discs which remain nearby.
The ChariteTM Artificial Disc
This total disc replacement uses two metal alloy end plates and a sliding, ball-like core. The metal end plates are made from high quality cobalt chromium alloy. This is well tolerated inside the body and the same material which makes up total knee replacements.
The end plates have metal teeth sticking out from the top and bottom which help lock them in to the vertebral bones above and below.
The central sliding core is made of polyethylene and this design is very like hip and knee replacements in that the same principal materials are used to achieve very low friction and easy movement.
The central sliding core is designed to allow core to shift about within the disc space during spinal motion, moving backwards with bending forwards and frontwards in bending back. This mimics the normal movements of the spinal joints and may reduce the likelihood of the facet joints hitting together in more extreme movements. However this has not actually been shown to be the case yet.
The aims of the artificial disc
The Charité Artificial Disc was designed to restore the original height of the disc spaces (before the discs lost water and height), to restore movement to the spinal joint, to prevent the onset of disc degeneration at neighbouring segments, to reduce or eliminate pain from movement or from nerve compression, and to improve the patient’s functional activities.
It was designed to be compatible with bodily tissues and to last a long time. The life span is claimed to be 85 million cycles, which means we can bend back and forwards this number of times before the disc would be expected to fail. That’s a lot of bending and arching. 40 years is a time estimate for this prosthesis to last.
The replacement is designed to imitate the segmental motion of a normal spine. It allows the low back to sit in normal lordosis (the natural slight arch of the lumbar spine), and to allow normal use of the facet joints.
Overall this type of disc has been implanted 10,000 times, since 1987.
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