Wednesday, 09 June 2010 21:13

Artificial disc replacement

Artificial Disc Replacement

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Overview

Lost days of work, high cost of healthcare and one of the most common reasons for visiting the doctor: these are just some of the effects on the nations of the world from pain felt along the length of our spinal column, otherwise known as the vertebral column. Invariably, at one time or another during our adult lives, a huge number of us will suffer from back pain, often severe enough to be quite debilitating. In fact, statistics reveal that back pain will affect as many as 80% of us during our adult lives. The figure is revealed as 50% of adults for people suffering similar levels of debilitation as the result of neck pain. Back and neck pain both need to be taken seriously as each, in their own area of the vertebral column can give rise to serious disability, depending on the cause of the actual pain experienced.

Prior to the introduction of an acceptable design for the artificial disc replacement prosthesis in the USA during October 2004 and in Europe from 1993, more than 200,000 back pain sufferers every year underwent spinal fusion surgery. While not ideal, this was all that was available until artificial disc replacement became a viable alternative. Operations involving the artificial disc replacement prosthesis are highly successful, enabling patients to resume most of their previous activities with considerably reduced pain on movement.

Causes of Pain in the Vertebral Column

There are many, and various, conditions that can cause pain in different regions of the back, some of which are not even directly related to the spine itself. However, this would best be dealt with in more detail as a separate issue. Suffice to say, for the purposes of artificial disc replacement surgery, much of the pain experienced can be quite excruciating and severe enough to cause major and on-going disability, often as the result of the process of degeneration of the bones that make up the spine and, most likely actual degeneration of the inter-vertebral discs, those cushions that are interspersed between each vertebral bone. The diagram to the left shows healthy vertebrae, interspersed with healthy discs.

Discs Can Rupture due to Degeneration

A ruptured disc is sometimes called a herniated disc. However, despite the two different names, they both mean the same thing and the names are inter-changeable. In terms of spinal conditions, bulging discs are remarkably common although that is not to say that a bulging disc will inevitably go on to become herniated. Each of our vertebral discs is surrounded by a ligament and, if the center of the disc is pushed outwards towards the ligament, this results in a bulging disc. Quite often you can have a bulging disc and not know about it, only finding out about it if you need to have MRI investigation for another reason. However, if the disc bulges into the space reserved for the spinal canal this becomes cause for concern.

 

Structure of the Spine and Discs

Our spine is, quite literally, the backbone of our bodies, giving us structure and shape and providing the necessary support for all the other muscles, bones, tendons and ligaments to attach to. The spine is made up of a series of individual bones, each one interspersed with discs to prevent friction and act as shock absorbers, as well as enable greater flexibility and movement of the spinal bones when working in conjunction with each other. Facet joints are especially important for this to occur efficiently.

Discs consist of two distinct parts. The annulus fibrosus, or outer portion, as the name suggests, consists of a tough fibrous layer that encases the inner jelly. This outer layer of disc is in direct contact with nerve fibers, as well as pain receptors known as nocioceptors. The nucleus pulposus, otherwise known as the inner part, consists of jelly-like material made up of water and various proteins. During the normal aging process, as the discs degenerate, they begin to lose some of that water which can cause them to flatten out slightly. The fibrous layer can become slightly more brittle and give rise to cracks or tears, allowing the inner substance to leak out. The cracks and tears themselves can cause pain but, mostly these degenerative discs only cause pain if the leaking inner material presses up against the nocioceptors. This kind of back pain is known as discogenic low back pain.

Eventually, as degeneration continues, more water is lost, reducing their cushioning abilities, eventually causing more tears on the fibrous casing, finally resulting in the disc collapsing completely and causing the space between the vertebra to narrow, causing a shift of the facet joints that are the actual joints holding each separate bone together. This resultant change of position puts additional pressure on each facet joint causing additional problems to occur. If no treatment is provided osteophytes, also known as 'boney spurs' can develop around the facet joints and around the disc space.

Symptoms and Diagnosis

People usually experience quite severe pain in the back, often radiating to the buttocks and upper thighs. When the neck is involved the pain tends to radiate across the shoulders and over the shoulder blades, often into one or other of the arms. However, since there are so many conditions that can result in pain in the back or pain in the neck, your doctor will need to take a full history and complete some extensive examinations and tests. This will include a range of diagnostic tests, including X-rays and an MRI scan.

These will show up physiological changes such as bone spurs, altered position of vertebrae, or enlargement of the facet joint, also referred to as facet hypertrophy. Diagnostic tests also reveal instability on movement. An MRI scan is particularly useful to show where a disc might have lost water, where facet joint hypertrophy could exist, whether there is any stenosis or if one of the discs has herniated.

When would an Individual Consider Artificial Disc Replacement?

Most people who suffer with back pain respond well to non-surgical methods of treatment, what doctors refer to as 'conservative' treatment. However, if the back pain begins to interfere with daily activities that are affecting your quality of life and conservative efforts to treat you are not having much effect, then it may be necessary to consider surgery. Overall, and certainly until recently, surgery involved spinal fusion. This has been found to be successful in between 75% – 80% of patients but, quite often, these surgical interventions that involved fusion of the spine failed to heal sufficiently to completely eradicate back and neck pain as well as leaving patients with limited movement in the spine.

They have developed the most successful model based on two metal plates, each with teeth to implant it between the bones and a polyethylene core to enable cushioning and reduce friction. The design is completed with a metal ring that surrounds the whole prosthesis, enabling it to be picked up by X-ray. This artificial disc is known as the LINK SB Charite III.

The diagram above shows the Charite Artificial Disc that has been approved by the FDA for use in just one area of the lumbar spine, between bones L4 – S1, and only for patients who are suffering from degenerative disc disease that has not responded to conservative treatment after a minimum treatment over a period of 6 months. The Charite Artificial Disc is manufactured in Raynham, Massachussetts, USA by DePuy Spine Inc.

Artificial Disc Replacement is not Suitable for all Candidates

Candidates considered suitable for this kind of surgery are very carefully vetted and not all are found to be suitable for artificial disc replacement. As mentioned above, the FDA has approved one specific prosthesis for use between the 4th lumbar vertebrae and the 1st sacral vertebrae – and then only for patients whose condition hasn't responded to treatment after at least six months' continuous, non-invasive treatment. Furthermore, some patients may not be considered suitable due to their bones not being considered strong enough to support the prosthesis, perhaps due to the aging process.

Once inserted the artificial disc replacement tends to move and settle into position, making it unsuitable for patients who already have a vertebral slippage, otherwise known as spondylolisthesis, in excess of 3mm. At present, following clinical consultations, the most suitable candidates for artificial disc replacement fall into two categories:

Those with degenerative disc disease
Those with post-discectomy syndrome

Discectomy syndrome refers to pervasive and persistent pain that patients continue to suffer following surgery to remove a disc that has ruptured.

What are the Different Kinds of Artificial Disc Replacements Used?

The FDA in the US approves this artificial disc replacement for use. It was developed by Professor Karin Buttner-Janz and Professor Kurt Schellnack, specialists in spinal surgery, in Berlin, Germany during the 1980s. This was the very first artificial disc replacement prosthesis. Although the original design was made by Waldemar Link GmbH in Europe, the design was purchased by the DePuy Group in 2003 and further modified before being acknowledged by the FDA as suitable for use in patients following extensive consultation and trials.

Worldwide, more than 15,000 patients have been treated successfully using the Charite artificial disc replacement, having been used in Europe for surgery for more than 17 years. The FDA approved the Charite for used in a certain sector of patients in October 2004, since then thousands of patients have been successfully treated with an artificial disc replacement.

Pre-Surgery Preparation

You will be evaluated as being suitable for surgery by the surgeon performing your operation. It is particularly important to advise your surgeon about your medication if you are a diabetic so that your condition can be monitored during surgery. The stress of the surgery on your body is likely to destabilize you, even if your diabetes is usually well under control so, continue to monitor your glucose levels more frequently for a few weeks following surgery, as well as prior to your operation. An anesthesiologist will also evaluate you to ensure that you are suitable for general anesthetic. To ensure there is as little risk as possible to you during and immediately after your operation you will be advised to consider making some small alterations to your lifestyle. This will minimize any risk factors and help your body to recover from the stress of surgery.

What Happens on the Day of the Surgery?

You will be asked to arrive at the hospital very early in the morning on the day of your operation, having had nothing to eat from midnight the night before. If you are going to be included in the morning operating list some surgeons prefer that you have nothing to eat or drink from 10pm the previous night.

You will be taken down to the operating room and administered a general anesthetic before being wheeled into the operating room. The only real difference between artificial disc replacement in the cervical vertebrae and those in the lumbar vertebrae is that the operation for the lumbar ADR is an anterior presentation. In other words, you will be lying on your back in the operating room and your operation will take place through your abdomen.

For this surgery there will be two surgeons present, a vascular surgeon and a general surgeon. The artificial disc replacement is placed in position through an incision in your tummy. The surgeon will move your internal organs to one side to gain access to the spine. This operation is much more straightforward done from the front as the surgeons can see better what is damaged and how much of your spine needs to be removed. The surgeon, wearing a surgical microscope, then spreads the vertebral bones widely apart to gain access to the damaged disc, making sure to remove as much damaged tissue as possible, taking special care to remove any tissue pressing against any of the nerves. Any osteophytes the surgeon comes across will also be removed. A special surgical device then separates the two adjacent bones – a bit like jacking up a car! The surgeon then uses a fluoroscope, which is a kind of X-ray, to place the artificial prosthesis in the correct space that has been prepared to take the new artificial disc replacement. Still relying on the view from the fluoroscope the surgeon then moves the vertebrae attached to the artificial devise to ensure that the ADR has been inserted correctly and all the pressure has been removed from the surrounding nerves.

The final step is to take an X-ray just to ensure everything is in the correct position, after which the surgery is completed with stitching up the various layers with different layered stitching, then stitching or clamping the skin together so that it gets to heal with the minimum of scar tissue.

What Happens After Surgery

Immediately post-operatively you will have intravenous lines in place and usually a urinary catheter. Both of these are usually removed by the second day. You will usually find that you are given IV antibiotics for the first 24 hours in order to prevent any immediate post-operative infection developing. The IV line is also used to provide you with adequate pain relief during the first couple of days: intravenous pain relief acts much faster than medication by any other route, as well as acting much faster, providing you with the most effective form of pain relief at a time when you need it most. Achieving the most appropriate level of comfort immediately post-operatively is an important part of your rehabilitation process so, if you do experience an unacceptable level of pain, contact the nursing staff and let them know. Only you can know how much pain is acceptable to you and how much pain you are prepared to cope with!

Rehabilitation

For most people their stay in hospital, following surgery, lasts for around 3 – 4 days and is usually accompanied with an increasing awareness that their previously painful symptoms are improving. This gradual improvement continues over the subsequent weeks, with most people gradually being able to completely tail-off all their medication eventually. Some people find they may need an extra couple of days in hospital, depending on the degree of pain. The hospital staff is aware that everybody recovers at a different rate and experience different levels of pain, so there is no pressure on you to leave hospital before you feel ready. Many people find they are able to get up and walk around within hours of their operation.

If you are able to do so this is much better for you as it will reduce the possibility of complications such as DVT or embolism developing. As long as you are careful how you move gentle exercise is encouraged and, on your return home you should be able to carry out your normal activities quite soon. One of the advantages of ADR is that you are unlikely to need any back support during the healing period and can get back to driving a car or cycling quite quickly although you are advised not to lift more than about 10lbs for up to a month or so after surgery. It is important, however, that you let your body heal at its own rate and don't attempt to do too much too soon.

During your post-operative period you will continue to be followed up by your surgeon, with subsequent X-rays to check everything is healing properly. You need to follow your surgeon's advice about how soon you can return to work although this is largely dependent on the kind of work you do. In general, however, you will usually be advised that you should be fit enough to return to sporting activities by about the 13th week following surgery.

Risks Associated with Artificial Disc Replacement

There are risks associated with any surgery, but with good management and co-operation on your part prior to surgery, these can be minimized considerably. The most obvious risks associated with ADR, apart from the usual surgical risks are:

The metal plate breaking
The implant dislocating out of the joint
Infection surrounding the prosthesis

Aside from that, there is the usual risk of developing DVT and, those in the higher risk category will be offered daily injections of Lovenox or, orally, Coumadin can be prescribed. The other problem that can occur is a dural tear, although this is usually noted during surgery and repaired. If it develops later it can cause quite severe headaches and infection but usually the leaking dura will close itself off through your body's own healing process. The worst case scenario, if it doesn't heal on its own accord, is a second operation to heal the breach in the dura.
Overall, most patients who undergo surgery for ADR resume their normal daily occupations quite quickly and, while nobody likes the prospect of surgery, the operation to fit an artificial disc in place of damaged tissue is usually a very safe procedure that offers excellent results to thousands of people who would, otherwise be severely debilitated. While still regarded as a new procedure, the insertion of artificial disc prosthesis is a vast improvement on the only other option which was spinal fusion; nowhere near as effective or successful as ADR is promising to be.

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