Diagnostic confusion and use of inappropriate terms such as ‘slipped disc’ demonstrate the difficulties of undertaking any objective research into spondylosis. It is therefore important to distinguish studies of reported symptoms from studies of objective findings such as MRI studies. It is also important to recognise limitations in MRI technology and associated variations in reporting, and the considerable limitations of X-ray studies which do not adequately show any soft tissue pathologies in the spine.
Any study considering a historical cause, or assessing activity levels, will usually rely in recall which may be very inaccurate. Broad titles for job types may not reflect the actual activity levels in any particular role. Furthermore the wide variation in military deployments and activities can mean that individuals may be placed in roles involving much greater, or much less, physical activity than other individuals with the same job or role title. Musculoskeletal injuries often result from sports activities rather than military activities, and sports and adventure training exposures usually decrease on operational deployments.
A literature search for spondylosis in military personnel found little evidence of use for this study, while searching for back pain produced several useful studies. Back pain does not, however, correlate well to underlying degenerative change. The only study that did use MRI showed no correlation between the degenerative changes found and symptoms of back pain.
Chronic back pain is often considered to be a form of somatisation, and there is evidence that there is altered central processing of pain in those presenting with low back pain (Flor et al., 2001, Flor, 2003, Mouraux et al., 2011, Legrain et al., 2011). In many cases of somatisation there is no indication of any underlying physical cause for symptoms. The patient experience of pain is either due to a ‘software error’ of pain generation within the pain centres of the brain, or is a reflection of psychological ‘pain’ as physical pain, an issue covered elsewhere on this website. Clinicians should always be alert to a diagnosis of somatisation, exaggeration and increased central sensitisation. Psychological factors should always be taken into account and appropriate support offered.
Back pain can often become a surrogate reason for someone not coping, and this is not helped by inappropriate advice and treatment resulting from medicalization of the symptoms. The epidemiology of back pain does not therefore always follow the pattern expected from studies of pathological changes (Halligan and Aylward, 2006, Waddell et al., 2002, Waddell, 2004).
Acute low back pain with associated structural injury tends to follow fairly soon after an event or after trauma. There is often a delay of one to three days before pain ensues, but rarely longer. Annular tears are not always painful, but when pain does arise it is usually within two weeks of injury. Longer delays would need a convincing explanation such as distracting fractures elsewhere. Onset of root pain, or pain related to disc degeneration may be delayed for much longer.
The legal concept of causation differs from the scientific concept and is a particularly challenging area in low back pain. Degeneration is an ongoing process, and a disc may inevitably have prolapsed at some point, so a particular activity on a particular day may seem irrelevant scientifically if it represents say 0.01% of lifetime forces on the spine. If, however, the 'final straw' was a particular work activity, it may be argued that legally this caused the disc prolapse. While it may be unlikely that a disc prolapse can be clearly attributed to one event at work, if it can, an argument may well be made that this is a 'qualifying injury' in relation to pensions, or justification for compensation. It is particularly important when taking a history at the time or shortly afterwards to identify all activities at or around the time of the alleged qualifying injury. Many military personnel, police and firefighters undertake other activities, or reservists may have other employment that may be much more physical than their military, police or firefighting role. The combination of unreliable memories and secondary gain should always be considered when taking a later history. Contemporaneous sources such as accident records and GP records should be considered before forming an opinion on causation.
There is evidence that significant acute injury to the spine may be caused by a specific incident at work, particularly when there is clear evidence of acute trauma at the time. An applicant in these circumstances would be expected to have attended for acute medical care either as a result of back pain or as a result of other trauma, with demonstrable signs and symptoms of an acute injury.
Several studies have shown that smoking significantly increases the risk of intervertebral disc degeneration. Disc degeneration and low back pain are significantly increased in patients with aortic calcification and lumbar artery atheroma linked to smoking and high cholesterol levels (Kauppila, 2009).
Tobacco smoke condensate greatly induced an inflammatory response and gene expression of metalloproteinases, and reduced active matrix synthesis and expression of matrix structural genes in disc cells. This suggests a direct effect on human disc cell viability and metabolic activity (Vo et al., 2011).
There is a clear link between back pain and current and former smoking, athough the effect was modest (OR 1.31, CI 1.02-1.55) in a meta-analysis (Shiri et al., 2010).
A study of construction workers in Japan found a clear link between low back pain and heavy smoking (Ueno et al., 1999).
A Norwegian study found a job involving heavy lifting and much standing was a strong predictor of low back pain in smokers four years later (OR 5.53, 95% CI 1.93-15.84) but was not associated with low back pain in non-smokers (Eriksen et al., 1999).
Logically, an increase in long-term loading on the spine would be expected to increase degenerative changes.
A study in Spain found a significant increase in incidence of Modic changes, disc contour abnormalities, spondylolisthesis and disc degeneration in obese patients with chronic back pain (Arana et al., 2011).
A study in Finland found a link between smoking, overweight and obesity and high physical activity with lumbar radicular pain (Shiri et al., 2007).
A clear association between BMI over 25 at young age and disc degeneration (RR 3.8, 95% CI 1.4-10.4) was shown in working middle-aged men (Liuke et al., 2005).
A US Military review of acute low back pain found an overall incidence rate of 37.74 per 1000 person years, with the lowest rate of 30.7 among Asians/Pacific Islanders, and the highest rate of 43.7 among blacks. Female sex and older age were also significant risk factors in this study and among whites there was a 36% difference between the rates in the youngest and oldest age groups, while there was a 126% difference for Native Americans/Alaskans (Knox et al., 2012).
A prospective study of all patients referred to Colchester Garrison Sports Injury and Rehabilitation Centre found female soldiers had an odds ratio of 2.71 (p<0.0001) for back pain compared to male soldiers. No difference was found for sport or road traffic accidents, suggesting that the main cause of back pain was military training, work and other recreation (Strowbridge, 2002). A further four year study found an odds ratio of 3.17 (95% CI 2.13-4.35) for female soldiers with new cases of back pain and again there was no link to sport or road traffic accidents (Strowbridge, 2005).
A Finnish study of 982 recruits found an increased risk for incidence of low back pain in conscripts with low dynamic trunk muscle endurance, low aerobic endurance and low educational level (Taanila et al., 2012).
Psychosocial issues have a significant part to play in presentation and disability from low back pain. A major international study compared prevalence of disabling low back pain across eighteen different countries. Established risk factors such as occupational physical activities, psychosocial aspects of work and tendency to somatise were confirmed by this study, however after allowing for these risk factors and systems of compensation and financial support, an up to 8-fold difference in prevalence remained between countries, suggesting a cultural difference (Coggon et al., 2013).
In a Finnish prospective cohort study, recruits with low back pain hindering military service were followed up over seventeen years. Disc herniation was found in 76% of previously dehydrated discs and only 29% of well-hydrated discs, but this was not associated with severe low back pain or increased frequency of spinal surgery (Waris et al., 2007).
As noted above, there are substantial limitations in all studies and evidence. Overall, obesity and smoking are associated with more back pain and earlier degenerative changes , and fitness appears to be protective. Psychological issues play a major role in the presentation and experience of back pain. Occupationalcauses of back pain are considered elsewhere on the website.
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