Spinal fusion for chronic low back pain: A ‘magic bullet’ or wishful thinking?

          Spinal fusion for chronic low back pain: A ‘magic bullet’ or wishful thinking?
                                 
                                            Dr KS Dhillon FRCS

Abstract
Chronic low back pain represents a common disabling and costly health problem but unfortunately in 80% to 95% of the patients a pathoanatomical diagnosis cannot be made despite the existence of modern imaging techniques. Specific spinal pathology that fits into a classic disease model which can be accurately diagnosed and appropriately treated is seen in only about 5% to 7% of the patients. This small group of patients with specific diagnosis can be successfully treated with good outcome. The back pain in majority of the patients where no specific pathology exists has been unscientifically labeled as non-specific low back pain.  To date there is no imaging technique or diagnostic test which can localize the source of pain in patients with non-specific back pain. Imaging findings such as degenerated disc, facet arthritis, spondylosis, spondylolysis and spondylolisthesis has no causal relationship to the pain in these patients. The outcome of spinal fusion in these patients is no better than nonsurgical treatment, and spinal fusion is associated with significant morbidity and occasional mortality. Yet there is rapid rise in the rates of spinal fusion. There is a growing tension between ethics and conflicts of interest for surgeons. The spine unfortunately has been labeled as profit center and there are allegations of conflicts of interest in the relationships of doctors with the multi-billion dollar spinal devices industry. The devices industry has a significant influence on not only research publications in peer review journals but also on decisions made by doctors which can have a detrimental effect on the welfare of the patient.

Key Words
Chronic low back pain, spinal fusion, conflicts of interest.









Introduction
Low back pain represents a common disabling and costly health problem. Unfortunately the cause of back pain can be accurately diagnosed and treated in only a small proportion of the patients, where specific spinal pathology such as tumours, infection, fractures and nerve root pain caused by prolapsed disc or spinal stenosis, is present. In vast majority of the patients the cause of the pain is not known and such pain has been unscientifically labeled as non-specific back pain. A pathoanatomical diagnosis cannot be made in these patients, even with modern diagnostic imaging techniques such as magnetic imaging of the spine, and this makes the treatment of nonspecific back pain difficult. Surgeons are treating the symptom (back pain) and not a disease, with surgery, when they offer spinal fusion as a modality of treatment to such patients. The rates of spinal fusion are rapidly increasing in most countries. Is there justification for spinal fusion in the treatment of patients with nonspecific low back pain or are there some conflicts of interest?



















Definition and classification of chronic low back pain
Uniformity of definitions is essential to study prevalence and management outcome of low back pain. There is a lack of uniform definitions of chronic low back pain in the literature. The most widely used definition of chronic low back pain is persistent low back pain that is present for at least 12 weeks. Acute back pain lasts for less than 6 weeks and subacute back pain lasts between 6 and 12 weeks. There will be patients with a history of back pain for many years who have repeated bouts of acute or subacute back pain but will not be classified as having chronic low back pain unless the episode of pain lasts at least 12 weeks. A recurrence of an episode of low back pain is defined as a return of low back pain lasting at least 24 hours and recurrent low back pain is defined as low back pain which has occurred at least two times over the past year with each episode lasting at least 24 hours1.
There are several classifications of low back pain; the most widely accepted is that proposed by Waddell. Waddell’s diagnostic triage divides low back pain into three categories;
Specific spinal pathology such as tumour, infection, fractures, cauda equina syndrome which occurs in about 1 to 2 % of the patients.
Nerve root pain such as that caused by disc prolapse and spinal stenosis which occurs in about 5% of the patients.
Non-specific low back pain which occurs in about 85 to 95% of the patients2.
The first two categories fit into the classical disease model where the disease can be accurately diagnosed and appropriately treated. However, the third category does not fit into this model, where a proper clinical diagnosis can be made. Such a diagnosis of non-specific low back pain according to Waddell is ‘intellectually and scientifically inadequate and fails to provide any biological basis for real understanding’ which results in treatment remaining ‘empirical or based on unproven hypotheses’ 2. Claims of diagnoses such lumbar strain or degenerative spine disease as a cause of chronic low back pain remain unfounded and leaves room for uncertainty about treatment, prognosis and clinical outcome2.

Pathoanatomical diagnosis of non-specific low back pain
For spinal fusion to be successful in the treatment of chronic or recurrent low back pain there has to be a pathoanatomical diagnosis which accounts for the pain. The role of spinal fusion in progressive or unstable spondylolisthesis, spinal trauma, tumours and spinal infections is well established. However in patients with non-specific chronic low back pain a pathoanatomical diagnosis is often impossible to establish.
The degenerated intervertebral disc is most often implicated as the cause of pain in patients with nonspecific low back pain. Such pain is usually referred to as discogenic back pain. Disc degeneration leading to abnormal shock loading of the disc and micro trauma to annulus and the endplate is believed to cause the pain. This trauma to the annulus and the endplate also allows blood vessel and nerve ingrowth into the normally avascular and aneural disc3. The disc is implicated in about 40% of the patients with nonspecific low back pain4. The facet joints is believed to be the source of low back pain in 15 to 40% of the patients5 while the sacroiliac joint is implicated in about 15% of the patients6. Though we know that these three are the main sources (but not the only source) of chronic low back pain, no conventional clinical test can discriminate the source of pain in patients with disc, facet joint or sacroiliac joint abnormalities4,5,6.
A simple relationship of radiographic structural abnormalities of the lumbar spine and low back pain cannot exist because many individuals with such structural spinal abnormalities are asymptomatic7. Systematic review of published studies show that there is a lack of firm evidence for a causal relationship, between radiographic findings of degeneration of the spine as defined by disc space narrowing, osteophytes and sclerosis, and nonspecific back pain. Neither does a causal relationship exist between radiographic evidence of spondylosis, spondylolysis, spondylolisthesis, spina bifida, transitional vertebra or Scheuermann’s disease and nonspecific back pain8.
Modern imaging techniques can now allow us to accurately depict the anatomical changes that occur with the degeneration of the disc. However, the clinical significance of these changes depicted on magnetic resonance imaging (MRI) remains elusive and often confusing9. In asymptomatic adults, degeneration of the disc can be seen in about 40 to 80% of individuals and it increases with age, while disc protrusion can be seen 40 to 70%, end plate changes in 10 to 30% and annular disruption in 25 to 70% of adults who are asymptomatic10. Jansen et al11 in a study of 98 asymptomatic individuals, found that an MRI examination of the spine revealed a normal disc in only 36% of the individuals.Fifty-twoo percent had a disc bulge at one level, 27% had disc protrusion and 1% had disc extrusion. Nineteen percent had Schmorl’s nodes, 14 % had annular tears and facet arthropathy was present in 8% of the subjects. The findings were the same in males and females. The high prevalence of these findings in asymptomatic individuals and a high prevalence of back pain in general population suggest that the MRI findings of bulges or protrusions in people with low back pain may frequently be coincidental. Hence it makes sense that abnormalities on magnetic resonance images must be strictly correlated with age and any clinical signs and symptoms present before surgery is contemplated.
Since anatomical diagnostic tests such as radiographs and magnetic resonance imaging (the gold standard) are of not much help in elucidating the cause of non-specific low back pain, can other tests help in making a decision as to which of the patients with non-specific low back pain will benefit from surgery? Discography has in the past been advocated (by some proponents) as a useful decision making tool.



Lumbar discography
Discography is used to determine if the low back pain the patient is experiencing is caused by disc pathology. In this procedure dye is injected at pressure of between 15-25 psi, under fluoroscopy, into the suspected disc while the patient is sedated. If the injection reproduces the pain at the same site that the patient has been experiencing before the procedure (concordant pain) then it is believed that the disc is the source of the patient’s low back pain (positive discogram). However there is no universally accepted definition as to what a concordant pain response is and there is a lack of reliability studies on discography12. It is important to know whether discography can accurately define the disc that is generating the patient’s pain for it to be any use in spinal surgery.
We know that imaging of the spine with scans can reveal the degenerated morphology of the disc but the scans cannot tell us that the disc is the source of the pain. This is obvious from the fact that the imaging morphology of the disc does not change over short periods of time but the patient’s symptoms do. Can a discogram which is an invasive procedure with potentially serious complications such as discitis, provide us with the information needed regarding the source of the patient’s pain?
Sackett and Hayes13 have proposed that a critical test of validity of a diagnostic procedure involves measuring it against a gold standard in a clinical setting. The test should be able to distinguish between patients with and those without the target disorder (in this case low back pain) and furthermore patients who undergo the test should fare better compared to those patients who did not have the test (ultimate health outcome). Unfortunately there is no reasonable gold standard against which to test discography. Despite the lack of proven validity against a gold standard, discography has been used to recommend spinal fusion in patients with non-specific low back pain.
Carragee et al14 did a study to test the hypothesis that positive provocative discography will accurately identify patients with low back pain due to a primary discogenic lesion and a clinical cure will be achieved in such patients with a successful spinal fusion. This prospective study was carried out between 1996 and 2000. The first cohort of 32 patients had an episode of low back pain for 6 to 12 months which did not respond to conservative treatment and the discogram was positive at one level with a normal discogram at adjoining levels. The second cohort included 34 patients with an unstable spondylolisthesis who did not respond to conservative treatment. Patients with selection co-morbidities such as compensation claim, abnormal psychometric test, occupational disabilities and prior lumbar surgery were excluded. The patients were followed up for 2 years.
When a high level criterion of successful outcome (highly effective) was adopted, 71.9% of patients in the spondylolisthesis group had a successful outcome after spinal fusion and in the discogenic group only 26.6% had a successful outcome. When a low level criterion of successful outcome (minimal acceptable outcome) was used 91.7% of the spondylolisthesis group had a successful outcome as compared to 43% in the discogenic group. After ‘adjusting for surgical morbidity and drop out failure, by either criteria of success, the best-case positive predictive value of discography was calculated to be 50% to 60%’14. The study showed that provocative discography is not highly predictive in identifying intradiscal lesions as a cause of chronic low back pain. The usefulness of the test hence remains to be proven.
False positive findings on discography are also common. Carragee et al15 did an experimental disc injection in patients who had no past history of low back pain but developed back/buttock pain after posterior iliac graft harvesting for non-thoracolumbar surgical procedures.  They studied 8 subjects who had 24 disc injections and 14 disc injections produced some pain response, 35.7% produced non-concordant pain, 50% produced similar pain and 14.3% of the injections produced the ‘exact’ pain. By the usual criteria for positive discography, 50% would have been classified as positive in this group of patients who had no back pain prior to the graft harvest. The response of concordant pain on discography appears to be less meaningful than is often believed.
Systematic review of accuracy of other tests such as orthosis immobilization and temporary external fixation of the spine to identify patients with chronic low back pain for whom spinal fusion is a predictable and effective treatment has not proved to be useful16.
Can spinal fusion be an effective procedure for treatment of chronic non-specific low back pain when there are no accurate diagnostic tests to identify patients who will benefit from such treatment?

Outcome of spinal fusion for non-specific low back pain
None of the imaging studies or other diagnostic test is able to accurately localise the source of pain in patients with non-specific low back pain. How can we then expect lumbar fusion to effectively treat the patient’s pain? Yet there has been a rapid increase in fusion rates (336%) of the lumbar spine from 1996 to 2001in the United States of America17. In England there has been an almost direct relationship between the numbers of operations performed per year and number of orthopaedic and neurosurgeons per head of population18. Do the results of spinal fusion justify the increase in fusion rates or are there some conflicts of interest?
Fairbank et al19, in 2005, published the results of a randomised controlled trial which assessed the clinical effectiveness of spinal stabilization/fusion compared to intensive rehabilitation for patients with chronic low back pain. Their cohort included 349 patients between the ages of 18 to 55 years with at least one year of low back pain who were considered by an experienced surgeon that they were candidates for spinal fusion. The patients were randomised into two groups, 176 to the surgical group and 173 to the rehabilitation group. The cohort was followed up for 2 years.
At 2 years the clinical outcome was assessed using the Oswestry low back pain disability index, which is scored 0% (no disability) to 100% (totally disabled or bed ridden) and is designed to assess the limitation of activities of daily living. Other assessments included the shuttle walking test, short form (SF) general health questionnaire, and psychological distress and risk assessment (DRAM).
The mean Oswestry disability index changed favourably from 46.5 to 34 in the surgical group and from 44.8 to 36.1 in the rehabilitation group. The mean difference between the groups was about -4.1 in favour of the surgical group. There was no difference between the groups in the shuttle walking test and other outcome measures. There were surgical complications in 19 patients. Eleven patients in the surgical group had reoperations. Complications included dural tears, excessive bleeding, implant problems, fractures and vascular injury.
The study showed that there was no clear evidence that primary spinal fusion surgery was any more beneficial than intensive rehabilitation in patients with chronic low back pain. Surgery while not having any superiority over conservative management was associated with potential risk and increased cost.
Brox et al20 did a 4 years follow up of patients to compare surgical versus non-surgical therapy in the treatment of chronic low back pain. In this study of two merged randomised clinical trials the authors compared instrumented transpedicular fusion with cognitive intervention and exercises in 124 patients who had disc degeneration and one year of symptoms. This study included some patients who had previous surgery for disc herniation while others had no previous spinal surgery. Of the 124 patients 66 patients were assigned to the surgical group and 58 to the non-surgical group.
The study showed that lumbar fusion was not superior to cognitive intervention and exercises at reliving back pain, improving function and return to work at 4 years. However there were 14 patients (24%) randomised to the non-surgical group who underwent subsequent surgery (non- adherence to protocol) while 15 patients (23%) in the surgical group had to undergo reoperation.
These studies lack placebo controls. The improvements in the surgical group may be placebo mediated. Hence it is not possible to know whether the marginal positive outcome in these patients reflect the natural course of the disease, placebo effect, patient expectation, or the care provided20. It is a fallacy to believe that new technical solutions in the hands of a skilled surgeon will provide faster and greater improvements in the patient’s symptoms unless the solutions are based on sound knowledge backed by good randomised studies. At the present time there is insufficient evidence to determine the effect of fusion compared to non-surgical treatment. Methodological limitations of the published randomised trials prevent any firm conclusions to be drawn on the effectiveness of spinal fusion for chronic low back pain21.
The Agency for Healthcare Research and Quality (ACHR), U.S. Department of Health and Human Services which conducts the effective health care program as part of its mission to organise knowledge, has conducted an extensive comparative effectiveness review of spinal fusion for treating painful lumbar degenerated discs or joints and has come to the conclusion that there is insufficient evidence to determine the benefits of lumbar fusion compared to more intensive rehabilitation programs22.
In the absences of sufficient evidence of benefits of spinal fusion for chronic non-specific low back pain, is it safe to recommend the procedure to patients?

Complications of spinal fusion
Spinal fusion is a major surgical procedure which involves extensive dissection, decortication of bone, blood loss and longer operating time. Often implants have to be used. More extensive and prolonged procedures are usually associated with more complications. There is a tendency among spinal surgeons to correct all anatomical abnormalities to prevent future symptoms, leading to more complex fusions, although there is no evidence that such ‘prophylactic’ surgery has any benefits. Complex fusions include multi-level surgery involving multiply approaches.
Deyo et al23 did a study to evaluate major complications in Medicare patients undergoing surgery for spinal stenosis in the United States in 2007. Their study of Medicare data avoided the bias which is often associated with studies by surgeons of selected patients from select centres. They were able to obtain nearly complete data on repeat hospitalization and mortality.
They studied 32,152 patients who had surgery for spinal stenosis in the first 11 months of 2007. The patients were 66 years and above. They analysed major medical complications, wound complications and the 30 day mortality. The major medical complications included those that needed cardiopulmonary resuscitation or repeat endotracheal intubation and mechanical ventilation due to cardiorespiratory arrest, acute myocardial infarct, respiratory failure, pulmonary embolism, pneumonia and stroke. The wound complications included haemorrhage, haematoma, seroma, wound break down and post-operative infections. Mortality included all deaths within 30 days of hospital discharge.
In patients who had complex spinal fusion, there was a 5.6% rate of major complication and the 30 day mortality was 0.6%. Complex fusions had an odds ratio of 2.95(95%CI) for life-threatening complications compared to decompression without fusion. The re-hospitalization rate was 13% in patients who had complex fusions. The wound complications were also higher in patients who had complex procedures.
In a study by Fritzell et al24 comparing surgical with non-surgical treatment for low back pain 18% of the patients in the fusion group developed early (within 2 weeks) complications and 6% had late complications. Complications included, bleeding, neural injury, heart failure, major GI bleeding, pulmonary oedema, aspiration sepsis, pulmonary embolism, dural tears, haematomas, pseudoarthrosis and even wrong level surgery. In patients who had complex fusion the complication rate was 31%. The reoperation rate in the surgical group was 6%.
Brox et al25 (2003) in a study comparing instrumented lumbar fusion with conservative treatment for chronic low back reported a 18% complication rate in the surgical group. In the Fairbank19 study the complication rate in the surgical group was 10.7% and the reoperation rate was 0.6%. In the Brox study (2010)20 the reoperation rate in the surgical group was higher at 23%.
There are wide variations in the complication and the reoperation rates in these studies because of insufficient reporting and variations in surgical techniques. This makes it difficult to determine conclusively the complication rates of lumbar fusion in these patients22. Nevertheless, complications associated with spinal fusion are not uncommon and can be life-threatening.
Despite a lack of superiority of spinal fusion over non-operative treatment of patients with chronic non-specific low back pain, there has been a steep rise in the rates of spinal fusion over the last two decades. Spinal fusion is also associated with morbidity and mortality. This begs the question as to why there is such a trend.

‘Spine as a profit centre’
 There is growing tension between ethics and conflicts of interest with some surgeons becoming less altruistic and allegations of unethical behaviour among doctors becoming more rampant. The American press is often inundated with reports of unethical behaviour among doctors and these include accusations of exorbitant professional charges, royalties paid to doctors without intellectual property and marketing of medical products and services by doctors for economic gain. Spinal fusion for chronic low back is one such service. Spinal fusion is one of the most lucrative areas of medicine and it generates billions of dollars for the hospitals and the surgeons26.
In the year 2001 in the United States, 122,000 lumbar fusions were carried out for degenerative disease of the spine and this represented a 220% increase from 1990. This increase became more obvious after 1996 when fusion cages for spinal fusion became available. The increase in lumbar fusion from 1996 to 2001 was 113%, while for hip and knee arthroplasty it was only 13% and 15% respectively27. Studies show that a higher proportion of fusion procedures and the introduction of new spinal implants between the years 1993 to 1997 did not reduce re-operation rates. In fact the reoperation rates were higher in the late 1990’s as compared to the early 1990’s27. The authors were of the opinion that introduction and marketing of new surgical devices and the influence of key opinion leaders is the likely reason for invasive procedures in the absences of new indications. Other possible reasons being financial incentives to hospitals and surgeons as well as the desire of surgeons to be innovators.
The influence of key opinion leaders and financial incentives for surgeons has hit the headlines in major U.S. newspapers in recent years. Allegations of kickbacks to spine surgeons to use their products, relationship of surgeons to biomedical firms with financial arrangements involving multibillion dollar medical devices industry have been highlighted28.
One such debacle was that of the use of recombinant human bone morphogenetic protein-2 (rhBMP-2), a bone growth factor for spinal fusion.  The Spine Journal, June issue 2011, gained attention from surgeons, researchers, patients, media, and industry when it focused attention on the controversial rhBMP-2 synthetic bone growth factor for use in spinal fusion surgery. It highlighted the limitation of industry sponsored research, bias in research development and reporting as well as weaknesses of peer review publications and inadequate disclosures and ethical shortcomings. The industry sponsored doctors involved in the promotion of rhBMP-2 through publication of studies in peer review journals which showed no complications with the use of rhBMP-2, received millions of dollars in royalties from Medtronic, the manufacturer of the product29. Subsequent non-industry studies showed that the use of rhBMP-2 was associated with many complications30.
Conflicts of interest through consulting ties and other relationship with device manufactures aside, doctors have now started becoming investors in spinal implant manufacture and distribution. As of Oct 2012, there were at least 20 states in U.S. with multiple active physician owned distributorships (PODs) which supply devices to hospital, with California alone having 40 such distributorships31. This has sparked fears that this would provide extra financial incentive for surgeons to recommend spinal fusion.
This prompted the Congress in the U.S. to ask the U.S. Department of Health and Human Services to investigate the prevalence and use of spinal devices supplied by physician-owned distributorships (PODs) 32. In 2011 PODs supplied devices used in one in five spinal surgeries billed to Medicare and contrary to claims by such distributorships the cost were not lower. A third of hospitals surveyed purchased devices from PODs. After hospitals started buying devices from PODs, the rates of spinal fusions grew faster in hospitals that bought devices from PODs compared to fusion rates in hospitals overall. In 2012 surgeons did more spinal surgeries at hospitals that purchased spinal devices from PODs than at hospitals that did not get their devices from PODs.
This new and growing area of partnership between surgeons and the device manufacturers has led some surgeons to express concern about such partnerships, because they believe that it is unethical and it will bias the doctor’s choice of what is best for the patient. Others have described such partnerships as ‘an awfully pernicious conflict of interest’ for doctors26. Some have gone further to described this new business model as ‘low hanging fruits’ waiting to be plucked and not to be deprived of the opportunity Malaysian surgeons have jumped on the bandwagon33.








Conclusions

The definition of chronic low back pain varies in different studies that are published. There is a need for uniformity of definitions to effectively study, the prevalence and outcome of treatment, of chronic low back pain. The most widely used definition is persistent low back pain which last at least 12 weeks.
Chronic back pain is a symptom and not a disease. Specific spinal pathology which fits into a classical disease model, where treatment can be effective, can be found in only about 6% to 7% of the patients. In about 85 to 95% of the patients with back pain no pathoanatomical diagnosis can be made and such pain gets labelled as non-specific back pain.
In the vast majority of patients the degenerated disc is implicated as the cause of chronic low back pain while in others the facet joints and sacroiliac joint is believed to be the cause of the pain. Although MRI scans can accurately depict the anatomical changes seen in the spine as degeneration of the spine sets in, the clinical significance of these changes remain elusive and the scans cannot help in elucidating the cause of the pain. Provocative discography which was in the past touted as a valid diagnostic test, has also failed to stand up to its usefulness.
Despite the inability to make a diagnosis in patients with non-specific low back pain, there has been a sharp increase in the number of patient undergoing spinal fusion for low back pain over the last two decades. Spinal fusion in patients with non-specific back pain is akin to treating a symptom (not a disease) with surgery. Logic dictates that such an approach cannot be very successful.
There is a dearth of level 1 studies in the medical literature comparing spinal fusion to non-surgical treatment of chronic low back pain. There are two relatively good level 1 studies with two to four years follow up comparing surgical to non-surgical treatment published so far, but they do not show superiority of surgical treatment over nonsurgical treatment. Furthermore spinal fusion is associated with significant and sometimes serious medical complications including mortality.
The growth in the number fusions carried out for chronic low back pain despite the lack of evidence of its efficacy has raised concerns about conflicts of interests and unethical behaviour on the part of the surgeons. In recent years, allegations of kickbacks to spine surgeons from the multibillion dollar medical devices industry, to use their products, have made the headlines in major U.S newspapers. To make matters worse surgeons have now become investors in the manufacture and distribution of medical devices used in spinal surgery, raising concerns of pernicious conflicts of interest for the surgeons. The growing partnership between surgeons and the manufacturing and distribution industry has been blamed for an increasing number of spinal fusions and bias in the doctor’s choice of what is in best for the patient.
The frequent allegations of financial conflicts of interest and the absence of scientific evidence of superiority of spinal fusion over non-surgical treatment for chronic low back pain should be reason enough for surgeons to seriously reconsider their indications for spinal fusion, since their decision may have future medico-legal implications and in some countries it may run afoul of existing legislations.

























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