As discussed in my previous article, the causes of lower back pain can be divided into ‘mechanical’ and ‘pathological’ types.
Mechanical lower back pain accounts for 97% of all cases and includes problems such as lumbar muscle strains, disc injuries and arthritis of the facet joints of the lumbar spine. Pathological lower back pain is caused by non-mechanical spinal conditions, such as arthritis, infections and cancers, as well as conditions that refer pain to the back, such as some kidney and gut diseases.
Research has shown that in the primary care setting the exact cause of lower back pain cannot be determined accurately on history and examination. Yet to investigate all cases of lower back pain to identify the exact cause of the problem is unnecessary in the vast majority of cases. In addition, given how common lower back pain is, investigating all these cases would simply not be financially viable. Rather, the aim of assessing a patient with lower back pain is to exclude emergency or serious conditions that would suggest a diagnosis of pathological lower back pain.
To do this, the doctor takes a history and examines the patient for the presence of ‘red flags’ and ‘yellow flags’.
‘Red flags’ are signs and symptoms of more severe causes of lower back pain. Perhaps the most important ‘red flag’ is pain.
Pain that wakes the patient from sleep, severe pain that doesn’t respond to standard management, pain that is unchanged with different postures and any change in the character of pain are indications that the cause of the lower back pain is ‘pathological’. In addition, other ‘red flags’ include leg weakness or numbness, bladder or bowel dysfunction, a history of cancer and unexplained loss of weight. Failure of lower back pain to improve after four to six weeks of treatment is also a ‘red flag’.
‘Yellow flags’, on the other hand, are risk factors for long term disability and work loss and should also be taken seriously as they are strong predictors of a poor outcome of lower back pain. ‘Yellow flags’ can include a negative belief that pain is harmful, the expectation that passive rather than active treatment is beneficial, a depressed mood and co-existing social or financial problems.
There is good evidence in the medical literature that, when there are no ‘red flags’ or ‘yellow flags’, no initial investigation needs to be done. In fact, doing investigations in these patients has been shown to not improve their outcomes. For example, an x-ray of the lumbar spine in a patient with no signs or symptoms of pathological lower back pain has been shown to do little more than “buy” reassurance for the patient. So instead of spending money inappropriately on these patients, they should rather commence the correct treatment.
Of course, if pathological lower back pain is suspected, then a specific series of investigations is indicated. This should include an x-ray, various blood investigations and perhaps an MRI or CT scan of the lumbar spine. The decision regarding these investigations is best left to the doctor managing the case.
Dr Mike Marshall