It’s very common practice for people with lower back pain to think oh I need to get a MRI scan and get it as quick as possible. Yes, an MRI is very good at taking very sensitive and specific images in order to show what damage has occurred to your lower back. However, there are countless studies that show that the damage shown on MRI scans are not necessarily related to the amount of pain, reduced movement or symptoms from your lower back. So, if it’s not necessarily going to give you information or change how you treat it then why bother at all. This article will explore why it may or may not be appropriate for you to get one.
What is an MRI?
An MRI scan is a magnetic resonance imaging machine which is a type of scan that uses strong magnetic and radio fields to create a detail picture of an area of your body. An MRI scan be used for almost every part of the body including the brain, organs like your stomach, liver, womb, breasts, bones, muscles, tendons and spinal cord. Therefore, it can be used to diagnosis a lot of different conditions. During the scan, you will lie on a flat bed and move into a scanner which can be very loud. The radiographer will be in another room but you can speak to them through an intercom and they will be able to see you through a camera. The scan can take anything from 15 mins to an hour and a half depending on what part of the body you are getting scanned and the type of image they are going.
So, for the science bit, your body is mainly made up of water which is H2O, which is 2 hydrogen and 1 oxygen atoms. The magnets in the scan detect the protons that are found in the hydrogen atoms. When the MRI is on, the magnets will lie up the protons in the cells and then when it is turned off the protons will then move back to their normal place. The radio signals will tell the scanner what type of substance the molecule is like a bone or tendon as each area will realign differently. All the different protons will create a picture the same way pixels will in your camera or tv.
What does an MRI of my Back show up?
An MRI of your lower back will be very detailed and sensitive causing it to show many different things. The sensitivity will vary depending on the structure but it’s between 89-100%.
Different things that can show up on a MRI:
• Disc problems including, Bulge/ Herniation, Protrusion and extrusion.
There are many different causes and reasons you can get a problem with the disc it can be from a trauma, an acquired deformity, genetic or from another health condition. The scan will show how much if any of the matter inside the disc has come out. This is often called a bulge, protrusion, extrusion or sequestration. A disc bulge is normally when 50-100% has extended past the vertebral body. A displacement is normally 25-50% and a focal herniation is less than 25%.
ϖ A Protrusion is when the base of the disc is wider than the matter that has come out.
ϖ An extension is when the disc matter is more than the base of where the matter has come out the joint.
ϖ A sequestration is when there is a gap between the main disc and the disc matter than has come out.
• Foramen compromise
• Canal Stenosis (is a compression of the nerve roots at the thecal sac this can cause cauda equina which is an medical emergency and you will require immediate surgery.
• Conditions like Ankylosing spondylitis which is an inflammatory condition that can cause the bones in your lower back to look more like a square.
• Nerve root compression (When the nerve exiting your lower back gets squashed.
• Spondylolthesis (misalignment of the bones in your spine when the bone has moved forwards compared to the bones above it.)
• Annular fissures – A separation of the annular fibres that make up the disc it can often occur when the disc is slightly worn. It can be from a traumatic event though it can happen naturally.
If it’s so specific why isn’t it always helpful?
Just because you have something come up on the scan doesn’t actually mean that you will have any pain or even realise that there is something wrong! It is suggested that in most cases it is not possible to identify the actual tissue causing source of lower back pain. Therefore, MRI’s are not initially recommended by the NHS unless it changes the management plan, often positive findings are reported on MRI scans however the patient doesn’t actually have any lower back symptoms at all. Therefore, it cannot be concluded that it can confidently diagnosis lower back pain. Additionally, research shows that the best estimate that your pain is coming from a positive disc pathology is only in 40% of patients. Therefore, despite the vast amounts of research and money the health industry has put into research there is no gold standard for diagnosing lower back pain.
Generally speaking there is research to show that features such as disc degeneration, modic and herniation’s are more common in people with lower back pain than people without. Also, that there is a good correlation between findings and clinical features even if not all of the features actually match the symptoms of all patients. There also doesn’t seem to be one finding that shows up in an MRI that is more important than others though significant rather than mild disc degeneration seems to be the best indictor to whether you will develop pain. The MRI will give you a good indication and may help what your future treatments options are in terms of needing surgery extra but it worth bearing in mind they don’t always have a clinical significance.
How else can you diagnosis a lower back problem?
• Straight leg raise: (This is the most common special test for lower back pain especially if the clinician is thinking of a discal or compression of neurological tissues. It is a neurodynamic test and checks the movement of the nerves in response to mechanical stress or compression. The test is performed with the patient lying down and the medical practitioner slowly bring their leg up in the air. It is then increased with the patient lifting his head forward to see if it reproduces any symptoms down the patient’s leg. If there is pain at less than 30 degrees it might indicate a discal injury or a tissue such as a tumour compressing the nerves. If there is pain after 70 degrees it is more likely to be tension in the muscles for example to hamstrings, or glutes.
• Slump test (This test’s if there is any tension on the nerves in the lower back and is performed like its name by essentially slumping forwards. However, the specificity and accuracy of this test is up for debate.)
• Quadrant Test (This test’s if there is inflammation in the vertebral joints causing local pain to the lower back by increasing the load of the joint. The test involved reaching backward and down the back of the leg)
• Movements – This is when the practitioner will get you to do different movements to see if you have an reduced movement or pain.
• Neurological testing including sensation, power and reflexes. Your practitioner will go through a neurological testing to see if the nervous system has been affected. Often with lower back pain especially if it has compromised the nerves it can cause symptoms of pins and needles, numbness and tingling and this testing will test the different nerve to pin point which one is causing the symptoms.
NICE Guidelines (2016). Low back pain and sciatica in over 16s: assessment and management. [NG59] [online] Available at: https://www.nice.org.uk/guidance/NG59/chapter/Recommendations#assessment-of-low-back-pain-and-sciatica Accessed: 27/5/2017.
Rahman MH, Islam KMT, Islam MR, Haque M, Devnath H, Hossain MA, Barua KK. Association between clinically diagnosed lumbar intervertebral discprolapse and Magnetic resonance image findings. Bangabandhu Sheikh MujibMed University Journal 9:146-150
Hancock et al 2011 MRI findings are more common in selected patients with acute low
back pain than controls?