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Everything is Unreliable… Get Used to It
May 12, 2012 by Dr Matthew D. Long
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Everything is Unreliable… Get Used to It
May 12, 2012 by Dr Matthew D. Long
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Everything is Unreliable… Get Used to It
May 12, 2012 by Dr Matthew D. Long
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All of us want certainty in life, particularly in our professional life. Clear answers and reliable data allow us to make predictable decisions and minimise risk. Indeed, reducing risk is one of the prime motivators of human behaviour and drives much of our decision making. However, there is very little that is truly certain, and this includes the clinical decisions we all make every day. For this reason clinicians of all types tend to rely on 'tried and true' testing procedures to help us navigate the inherent uncertainty of dealing with individual human beings.
The question is, what can we truly rely on?
Clinical examination procedures are often singled out as being 'unreliable', and there has been a tendency to seek high-tech solutions to the problem of uncertainty. We would all be aware of the concept of 'sensitivity' and 'specificity' of clinical tests, but what about the reliability of MRI scans? Do they always give us a clear picture of what is going on? How sensitive is an MRI to the tissue changes occurring in a painful spine, and can we specifically correlate these features with a patient's symptoms?
You would probably recall that MRI scans are notorious for demonstrating disc protrusions in asymptomatic people. A study back in 1994 (1) confirmed that "52 percent of the subjects had a bulge at at least one level, 27 percent had a protrusion, and 1 percent had an extrusion." So we always have to be mindful of the fact that advanced imaging can show us abnormalities that are simply irrelevant.
But do MRI scans miss things?
A recent study published in the European Journal of Radiology (2) suggests that MRI scans do indeed miss relevant pathologies - largely due to the fact that most studies are done with the subject lying down. As such, the authors sought to compare images obtained in a relaxed supine position with those taken while the patient's spine was subjected to compression. An axial loading harness was used to apply approximately 50% of the patient's body weight while they remained supine. Comparisons were then made between loaded and unloaded images, specifically looking at disc herniation (protrusions/extrusions), bulging discs, facet joint synovial cysts, foraminal stenosis, and hypertrophy of the ligamentum flavum. Perhaps unsurprisingly, significantly more pathologies were visualised when compression was added.
The question is, what can we truly rely on?
Clinical examination procedures are often singled out as being 'unreliable', and there has been a tendency to seek high-tech solutions to the problem of uncertainty. We would all be aware of the concept of 'sensitivity' and 'specificity' of clinical tests, but what about the reliability of MRI scans? Do they always give us a clear picture of what is going on? How sensitive is an MRI to the tissue changes occurring in a painful spine, and can we specifically correlate these features with a patient's symptoms?
You would probably recall that MRI scans are notorious for demonstrating disc protrusions in asymptomatic people. A study back in 1994 (1) confirmed that "52 percent of the subjects had a bulge at at least one level, 27 percent had a protrusion, and 1 percent had an extrusion." So we always have to be mindful of the fact that advanced imaging can show us abnormalities that are simply irrelevant.
But do MRI scans miss things?
A recent study published in the European Journal of Radiology (2) suggests that MRI scans do indeed miss relevant pathologies - largely due to the fact that most studies are done with the subject lying down. As such, the authors sought to compare images obtained in a relaxed supine position with those taken while the patient's spine was subjected to compression. An axial loading harness was used to apply approximately 50% of the patient's body weight while they remained supine. Comparisons were then made between loaded and unloaded images, specifically looking at disc herniation (protrusions/extrusions), bulging discs, facet joint synovial cysts, foraminal stenosis, and hypertrophy of the ligamentum flavum. Perhaps unsurprisingly, significantly more pathologies were visualised when compression was added.
Fig 1. An occult facet joint cyst can be seen to develop when the patient’s spine is compressed in (B)
Fig 2. A significant reduction in the dimensions of the central canal and thecal sac occurs when the patient’s spine is compressed in (B)
The authors stated, "In conclusion, our results with axial-loaded lumbar spine MRI showed that the risk of failing to detect an essential spinal canal stenosis is considerable, if the examination uses only the traditional supine relaxed position. In this study, 81 patients (67.5%) and 138 disc spaces (38.3%) showed significant changes in the DSCA (dural sac of cross-sectional area) after axial load (>15 mm2 ). Of the levels considered normal (<100 mm2 ), 40% were reduced below than 100 mm2, a value considered by many to cause claudication symptoms."
So what does this mean for us, as front-line clinicians?
I think that one of the most significant messages to come from Kinder et al’s study is that our clinical findings and test results must always be viewed in context. Our job is to interpret ‘noisy’ information to find an accurate ‘signal’ - something that we can have confidence in and help us to predict the best course of action. So MRI scans can be a great tool for visualising a patient’s spine, but we must always interpret what we see and match it to their history and other examination findings.
Being a mature clinician means accepting that the world is not black and white. It exists as shades of gray. So we must become as knowledgable as possible about the advantages and limitations of our favourite examination protocols and constantly strive to make more informed clinical decisions. This goes for high-tech procedures and chiropractic technique systems alike - something to think about...
Dr Matthew D. Long
BSc (Syd) M.Chiro (Macq)
So what does this mean for us, as front-line clinicians?
I think that one of the most significant messages to come from Kinder et al’s study is that our clinical findings and test results must always be viewed in context. Our job is to interpret ‘noisy’ information to find an accurate ‘signal’ - something that we can have confidence in and help us to predict the best course of action. So MRI scans can be a great tool for visualising a patient’s spine, but we must always interpret what we see and match it to their history and other examination findings.
Being a mature clinician means accepting that the world is not black and white. It exists as shades of gray. So we must become as knowledgable as possible about the advantages and limitations of our favourite examination protocols and constantly strive to make more informed clinical decisions. This goes for high-tech procedures and chiropractic technique systems alike - something to think about...
Dr Matthew D. Long
BSc (Syd) M.Chiro (Macq)
References:
1. Jensen, M. C., Brant-Zawadzki, M. N., Obuchowski, N., Modic, M. T., Malkasian, D., & Ross, J. S. (1994). Magnetic resonance imaging of the lumbar spine in people without back pain. The New England journal of medicine, 331(2), 69–73.
2. Kinder, A., Filho, F. P., Ribeiro, E., Domingues, R. C., Domingues, R. C., Marchiori, E., & Gasparetto, E. (2012). Magnetic resonance imaging of the lumbar spine with axial loading: A review of 120 cases. European journal of radiology, 81(4), e561–e564. doi:10.1016/j.ejrad.2011.06.027
1. Jensen, M. C., Brant-Zawadzki, M. N., Obuchowski, N., Modic, M. T., Malkasian, D., & Ross, J. S. (1994). Magnetic resonance imaging of the lumbar spine in people without back pain. The New England journal of medicine, 331(2), 69–73.
2. Kinder, A., Filho, F. P., Ribeiro, E., Domingues, R. C., Domingues, R. C., Marchiori, E., & Gasparetto, E. (2012). Magnetic resonance imaging of the lumbar spine with axial loading: A review of 120 cases. European journal of radiology, 81(4), e561–e564. doi:10.1016/j.ejrad.2011.06.027