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Diagnosis of Low Back Pain

The Clinical Picture

The first step in diagnosing your low back pain will occur during your consultation. Certain clues from the history and examination should help your clinician separate you into one of three groups; simple (or mechanical) back pain, nerve root pain or possible serious causes.

As a general rule, those who are otherwise well, with no previous medical history of serious disease and who have little or no leg pain will have simple or mechanical back pain and those with severe leg pain, possibly associated with numbness or tingling into the leg will have nerve root pain. Your clinician may confirm the suspicion of nerve root pain by raising your painful leg off the couch whilst you are lying on your back, thereby stretching the sciatic nerve and seeing if it reproduces your pain and by checking the feeling in your legs and the power of your leg muscles. Your clinician may be alerted to more serious causes of your low back pain if there are other symptoms present during questioning, such as unexplained weight loss, fever or a past history of serious disease such as cancer and in such circumstances further investigation may be necessary. Usually however no serious cause is found.

At a more specialist level, other clues in the history (such as your age, sex, how the pain began, the pattern and site of pain) and examination (such as how you move, where you are tender and whether pain is reproduced by certain examination techniques) may help your clinician to help diagnose the exact source of pain contributing to chronic mechanical low back pain, such as the disc itself, the facet joint or the sacroiliac joint.

Further information may however be gained by further investigations such as Xrays, MRI, CT or Isotope bone scans, electromyography and nerve conduction studies, blood tests or diagnostic injections.

Xrays

Xray of Lumbar Spine showing an addtional Lumbar Vertebra.

This Xray image shows a Lumbar Spine showing an additional Lumbar Vertebra (Lumbarised First Sacral Segment.)

In general terms, plain Xrays of the lumbar spine and pelvis have a limited role in diagnosing the source of back or leg pain. Often, Xrays will show minor abnormalities that are of little or no consequence and it is true to say that a lot of people with no back pain will have changes on their Xray, such as early degenerative changes, as it is that often patients with severe pain can have a normal Xray. Certainly, within the first few weeks of an episode of low back pain, Xrays are not routinely indicated. Xrays, may have a role however in certain situations:

1. When there is a suspicion of a more significant spinal injury or disease such as a fracture.

2. When there is a suspicion of a spondylolisthesis or spondylolysis.

3. At a more specialist level, when considering targeted spinal injections/interventions.

Historically, Xrays have arguably been overused in patients suffering with low back pain. As Xrays do show changes in almost everyone as they get older (normal wear and tear), this can lead to good intentioned misinformation given to patients when they are told that there are degenerative or arthritic changes accounting for their pain. Even though these changes are common, and often not associated with pain, the patient may be left with a feeling that their pain is going to be long term and progressive when often this is not the case. Xrays should therefore be used judiciously and the changes on them interpreted with caution.

In short; although your Xrays may show degenerative changes, these are common in people without pain, and are therefore not necessarily the cause. Therefore do not get alarmed or disheartened if you are told that your Xrays show degenerative changes. You can still recover!

MRI Scan

An MRI scan of the Lumbar Spine showing a prolapsed L5-S1 disc passing backwards into the Spinal Canal.

An MRI scan of the Lumbar Spine showing a prolapsed L5-S1 disc passing backwards into the Spinal Canal.

An MRI scanner is a large doughnut shaped magnet that the patient has to slide into. The magnet acts on the hydrogen atoms in the water molecules causing the water molecules to line up, like iron filings under the influence of a bar magnet. Shortly afterwards, the patient is exposed to a radio signal that causes the atoms to spin around and when this stops the hydrogen atoms try to line up again. Depending on the amount of water content in each organ of the body, the atoms line up at different speeds. A computer is then used to build up a 3-dimentional picture of the water density in the patient and this is provided as images. Structures in the body with little water content, therefore, such as bone, will appear as a different shade to high fluid structures, such as the cerebro-spinal fluid in the spinal canal. MRI scans are therefore good at detecting soft tissue problems such as disc bulges and prolapses and are also good at detecting more serious disease.

Due to the strong magnetic field, some people may not be suitable for scanning by magnetic resonance. If you have any of the following, or if you have any doubts about your suitability for MR imaging, then it is important for you to make contact with the scan department:

Heart pacemaker

Artificial heart valve

Metal fragments in the eye, head or body.

Aneurysm clips (these are metal clips inserted during some operations, especially of the blood vessels in the brain)

Pregnancy.

It is important for female patients to be aware that this investigation should not be used if you are pregnant or if you suspect that you may be pregnant. For that reason you will be asked when your last menstrual period started and it may mean that the examination has to be delayed to fit in with your monthly cycle.

CT Scan

A photograph of a CT Scaner.

A CT scan is a large, doughnut shaped machine. It has less depth than an MRI scan so only a small part of the patient’s body is within the scanner at any one time. There is some radiation exposure during the scan and the images produced are very good at looking at the bone rather than the soft tissues. It is therefore useful in assessing the condition of the spinal bones, looking for disease, fractures and overall structure.

A CT Scan of a Lumbar Vertebra showing the bony structure and stress fracture or Spondylolysis.

A CT Scan of a Lumbar Vertebra showing the bony structure and stress fracture or Spondylolysis.

It is important for female patients to be aware that this investigation should not be used if you are pregnant or if you suspect that you may be pregnant. For that reason you will be asked when your last menstrual period started and it may mean that the examination has to be delayed to fit in with your monthly cycle.

Isotope Bone Scan

An Isotope Bone Scan showing a normal uptake of radioisotope in the Vertebrae, Ribs and Pelvis.

An Isotope Bone Scan showing a normal uptake of radioisotope in the Vertebrae, Ribs and Pelvis.

A bone scan is a study of the bony skeleton and requires an injection of a slightly radioactive substance into a vein in the patient’s arm some hours before. The substance injected becomes concentrated in the bones and any area of increased concentration on the scan may indicate increased bony activity. This type of scan is often useful in identifying areas of injury or disease that may not always be obvious on an ordinary Xray.

It is important for female patients to be aware that this investigation should not be used if you are pregnant or if you suspect that you may be pregnant. For that reason you will be asked when your last menstrual period started and it may mean that the examination has to be delayed to fit in with your monthly cycle.

Electromyography (EMG) and Nerve Conduction Studies (NCS)

These investigations give information about a specific nerve or muscle that may be injured or not functioning. Small needles are inserted through the skin close to a nerve or into muscle and a small electrical impulse is passed between the two. By measuring the speed at which a muscle reacts to the nerve impulse, the size and the quality of the reaction, certain deductions can be made as to the specific cause of symptoms. This may be particularly useful in differentiating a spinal cause of nerve root compression as opposed to a local nerve or muscle problem.

Blood investigations

When there is a suspicion that there may be a potentially more serious source of back pain and sometimes, to reassure the patient and the doctor, blood tests can be ordered. Blood tests can look for non-specific changes such as thickening of the blood which may be associated with more serious diseases such as inflammatory joint disease (such a rheumatoid arthritis) or cancer or may show more specific abnormalities that may help your doctor reach a diagnosis and plan your further management. In the vast majority of cases, these blood tests will be normal.

Diagnostic injections

It is often the case, that despite having these investigations, the cause of back pain is still uncertain. In certain scenarios, particularly when pain remains significant and prevents return to normal function, sport or work, the source of pain can be further defined by performing injections. In principal this involves injecting a local anaesthetic into a specific area that is thought to be causing pain. The local anaesthetic will numb the area for up to a few hours and if during this time there is significant pain relief then the cause of pain will have been confirmed. This perhaps can be understood by the analogy of toothache. If your dentist numbs one tooth with an injection and your pain does not go, then he leaves that tooth alone and goes on to numb another with an injection. If the pain goes this time, then that is the tooth that he pulls out! In the same way, diagnostic injections aim to numb certain areas of the spine or adjacent joints, looking to see if the pain goes. If it does, then further treatment can be planned with more confidence.

In practice, this involves the insertion of a fine needle through the skin which, under the guidance of Xray images, is passed into a suspected painful joint, such as a facet joint or sacro iliac joint or on to the surface of the nerve that supplies pain sensation from the facet joints (medial branch of the posterior primary ramus) or on to the nerve root. With the joint injections and the nerve root injections, it is often the case that a small amount of anti inflammatory Cortisone is injected at the same time as the local anaesthetic. This brings with it the possibility of longer lasting pain relief than just the duration of the local anaesthetic.

A photograph of a C-arm with fluroscope.

A C-arm with fluroscope. The C-arm can take xrays at various angles during injections to help guide accurate and safe placement.

In the case of diagnosing pain arising from within a disc, a slightly different technique is employed, whereby the needle is directed into the disc and a small volume of fluid is then injected. If the patient’s pain is reproduced by this injection in terms of the type of pain experienced and the location of pain, this may provide evidence that this disc is the source of pain.