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Artificial Disc Replacement Surgery for Discogenic Low Back Pain

INTRODUCTION

 Disabling low back pain may be due to symptomatic degeneration of the intervertebral disc.  The most likely source of acute pain from the disc is tearing of its outer part (the annulus) and ingrowth of nerve fibres into the disc due to attempted repair process.
 
Discogenic pain is generally self-limiting and compatible with a normal life.
 
In some individuals, however, it may lead to more persisting and disabling pain and when less invasive forms of treatment fail, surgery may be considered.
 
Traditionally, surgery has consisted in fusing and/or stabilising the segment affected with bone and/or metal instrumentation.
 
Since the early 1980s, European Surgeons have developed artificial disc implants to replace the affected disc as a way of treating back pain.
 
This procedure has gradually gained popularity in the English speaking world and a number of Surgeons, including Dr Osti, are now performing it in Australia.  Dr Osti performed the first Charite artificial disc replacement operation in Australia in 1996.
 
 
Whilst the indications and reported outcomes of this procedure remain controversial, such technique is becoming more accepted and should not be considered experimental.
 
 TECHNIQUE
 
The procedure is performed through an anterior retroperitoneal approach, similar to the one used for anterior spinal fusion.  The skin incision (figure 1) is generally vertical below the umbilicus although in certain individuals, a transverse incision may be used for cosmetic reasons.
 


Artificial Disc Replacement Surgery for Discogenic Low Back Pain Image

The bowels are protected and retracted onto the right side to expose the front of the spine.  The large vessels, anterior to the spine, are carefully retracted and then the intervertebral disc, considered to be responsible for the pain, is removed.  The empty space between the two vertebrae is then replaced by using an artificial disc implant which consists of two metal plates and a plastic (polyethylene) core in between (fig.2).


 Image

These plastic inserts allow movement, which is similar, although not identical, to a normal disc.  The wound is then closed and the patient is allowed to stand up and walk the day after the operation.  A corset may be worn for the first four weeks, although it is not mandatory.  No additional procedures are performed.
 
 RISKS/COMPLICATIONS
 
This operation is associated with risks, which are common to any other spinal operation.  Due to the handling of the large vessels at the front of the spine, disc replacement surgery is associated with an increased risk of blood clots in the legs and/or lungs (DVT/Pulmonary Embolus).
 
Some patients, therefore, may be considered unsuitable if the risk of thrombo-embolic accidents is too high and/or their arteries/veins are significantly affected by disease before the surgery.  All patients are given anti-coagulants after the surgery and asked to wear special stockings for a minimum of two weeks after the operation.
Other risks of the operation include infection, vascular damage during the procedure due to the close proximity of the vessels to the disc, nerve damage, damage to the bowels and/or the bladder and hernias through the anterior incision of the muscles.  In addition, in men, there is a well recognised risk of interference with ejaculation due to some of the nerves responsible being close to the lumbosacral disc.  There is also a risk of interference with the sympathetic chain which may lead to the left leg being warmer than the right.
Overall, the complication rate of artificial disc replacement surgery in suitable individuals should be quantified at less than 5% and is similar to other major spinal operations such as interbody fusions and pedicle screw fixation.
 
The risk of paralysis and/or severe neurological deficit is remote as with this approach, in most cases, the nerves are not interfered with.
 
There is a possibility that the prosthesis may fail and this could include breakage of the metal plates, displacement of the plastic insert and/or abnormal movement with increasing symptoms. This may lead to further surgery, although such complications should be considered rare.
 
In a percentage of patients, despite a satisfactory technical outcome, the pre-operative back pain may remain and may not be substantially better than prior to the surgery.  It is accepted that if the patient is selected appropriately, the probability of the patient being satisfied with the outcome should be quantified at approximately 80%.
 
As indicated previously, less than one in 20 patients would suffer from a complication which may lead to permanent worsening of his/her pre-operative state.  Most complications may be considered mild although, as indicated in the previous paragraph, some of the complications may theoretically be life threatening and may require intensive further medical/surgical treatment.
 
It is indispensable that the patient be positive about the treatment before the operation and that any doubt he/she may have be cleared with the Surgeon prior to the operation.
Results of medical treatment have been proven in many studies to be linked to the degree of motivation by the patient and his/her positive attitude towards the treatment.
 
 POST-OPERATIVE INSTRUCTIONS
 
All patients are encouraged to stand up and walk the day after the operation.  The bladder catheter, which is used as routine in this operation, is removed the morning after the surgery and, in most cases, the blood drain is removed a few hours later.  Most patients are able to leave hospital within the first three days.  Patients are instructed not to drive for approximately two weeks and not to perform any heavy repetitive physical activities for a period of approximately two months.
 
This would include Tennis, Squash, Golf and/or any contact sports.  At two weeks, most patients should be able to use an exercise bike and/or swim for short periods.
 
All patients should avoid any prolonged bending and/or heavy lifting for a period of four weeks following the surgery.  A graduated gentle exercise programme should be commenced two weeks after the operation and this may require some supervision by an experienced Physiotherapist.
 
You will be assessed by a Physiotherapist during your hospital stay, before the surgery and prior to discharge.
 
 CONTRA-INDICATION FOR DISC REPLACEMENT SURGERY
 
Such technique is contra-indicated in patients with significant nerve involvement due to pressure on nerves by either bone or disc. 
 
Patients suffering from osteoporosis and/or requiring systemic steroid treatment should not undergo this procedure in view of the possibility of fracture to the vertebrae, either during and/or after the operation and/or bony failure around the metal plates of the prosthesis subsequently.
 
The procedure should not be performed in individuals with arterial and/or vein disease which may expose them to a significant risks of either vascular injury and/or clot due to the handling of the vessel at the time of the operation.
 
Dr Osti does not recommend this procedure in elderly patients and/or patients that have undergone extensive abdominal surgery because of an increased intra-operative risk due to scarring.
 
Dr Osti would also not recommend this operation if more than two discs are involved as the results appear to be much less satisfactory when the implants are used at more than two levels.
This operation is also less successful when previous spinal surgery has been performed.  In some individuals, however, especially after simple discectomy, the results of artificial disc replacement surgery may still be highly satisfactory. 
 
No patient should be given the option of artificial disc replacement surgery for back pain if their pain is not disabling and/or extensive conservative treatment for a minimum period of six months has not been attempted. 
 
The prospective candidate should be made aware that back pain is a benign condition which, in most cases with regular exercise and good mental health, is compatible with a highly satisfactory quality of life. (Please refer to Dr Osti’s information on Principles of Management of Back Pain).
 
 COST
 
The cost of the artificial disc implant is rebatable in Australia through all major health funds.  Dr Osti’s fee is not covered fully by either Medicare and/or the health funds.  The patient, therefore, is expected to pay the difference between Dr Osti’s fee and the government/health fund rebate prior to surgery.
 
 CONCLUSION
 
Artificial disc replacement surgery for disabling low back pain may, in some individuals, offer a high probability of a good outcome. 
 
Overall, its results, however, should not be considered, at this stage, better than conventional spinal fusion and this technique does expose patients to risks which should be justified by the patient’s disability.  Depression, litigation and poor general health are, by far, the most important long term factors for disabling chronic low back pain.



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