Of shiny pictures and poorer outcomes: Spinal MRI and back pain

Diagnosing low back pain is a nightmare. It established that apart from the 15% of back pain cases which can be attributed to a specific spinal pathology, the majority of cases fall under the unsatisfactory umbrella label of “non-specific low back pain”.

I was discussing with a colleague a new review that, while admittedly light on data, suggests that diagnostic tests offer little in the way of reassuring patients. This chimed with my (unreliable) anecdotal clinical experience with back pain wherein the results of X-Rays, MRI scans and the like often seem to strike fear into the hearts of patients and act as obstacles to resuming normal behaviour. In fairness to the technology it’s not really the scans that are the problem, it’s the way that they are (mis)used by clinicians. Powerful images of bulging discs, degenerating joints, partial dislocations or instability are evoked to help explain the patient’s symptoms, with the result that patients might be left with the plausible idea that their spine is what is technically referred to as “structurally buggered” (or “struggered”). Like Lorimer’s magic disc-popping action figure.

We’ve discussed the problems with this before. The best evidence strongly indicates that these stuctural findings on X-Ray and MRI are not clearly related to the onset, severity, duration or prognosis of low back pain. The presence of degenerative changes (see also here), disc pathology, muscle wasting, even spondylolisthesis and spondyolysis are common in those without pain and are poorly correlated with the signs and symptoms of low back pain. It’s counterintuitive but there you are. It is what it is. Be honest though, if you are a clinician – it’s hard not to blame that lack of recovery on “wear and tear” isn’t it? Neat, tidy but unsubstantiated  explanations are hard to shake off.

Recent clinical guidelines reflect this evidence by not recommending spinal imaging in the absence of clear indicators of specific pathology (or “red flags”). But beyond simply not telling us much a paper from last year suggests that MRI scans might achieve something worse.

These researchers analysed a large workers compensation database for back pain claims in the USA. They looked at the relationship between the early use of MRI imaging in people with work-related back pain and clinical outcomes. With this kind of retrospective data it is always difficult to attribute cause and effect. For example MRI might be associated with poor outcome because those with more severe injuries are more likely to get an MRI and at the same time are more likely to experience ongoing symptoms. To try to work around this the authors did a nifty trick by identifying first what factors actually increased the likelihood of somebody receiving an early MRI in their dataset and then dividing the groups into “high propensity and low propensity for MRI”. They then analysed the effect that having an MRI versus not having it had on outcomes in each of these groups while statistically controlling for things like symptom severity, age etc.  If MRI is itself an independent risk factor for poor outcome then we might expect to see it have an effect in the group that did not have those factors but that nonetheless still received an MRI. Like I said: nifty.

And that is precisely what they demonstrated. With big brass bells on. The statistically adjusted results indicate that folk in the MRI group came off of disability 200% slower (from a raw average of 134 days with MRI to 23 days without!) than those who did not have an MRI scan. Perhaps more worryingly while those in the no-MRI groups had a surgery rate of less than 10%, the MRI groups had surgery rates of 80-100%. To be clear in the group who had clinical characteristics that made them less likely to be offered an MRI, but who still received one, 100% underwent spinal surgery. These, you might notice, are large effect sizes.

How do we interpret these findings? Well maybe the results could be explained by the deleterious effects of spinal surgery or maybe they are due to the social and psychological impact of being given a structural diagnostic label that is likely to be spurious in the majority of cases. Perhaps there are influences in there specific to the opaque dynamics of a workers compensation system, with all of its competing agendas.  Most likely it is an murky combination of all of the above and more.

What the study does tell us is that as well as not being very informative, spinal imaging in this group was related to important differences in the treatment paths of these patients and also to a large and unhelpful change in clinical outcome. It’s time to listen to those clinical guidelines and be careful which spines we take pictures of.

About Neil

Neil O’Connell is a researcher in the Centre for Research in Rehabilitation, Brunel University, West London, UK. He divides his time between research and training new physiotherapists and previously worked extensively as a musculoskeletal physiotherapist. He also tweets! @NeilOConnell

Neil is currently fighting his way through a PhD investigating chronic low back pain and cortically directed treatment approaches. He is particularly interested in low back pain, pain generally and the rigorous testing of treatments. He also tends to get all geeky over controlled trials.

References
ResearchBlogging.org

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