Nearly 4 million people in Australia suffer from back pain at any one time [1
], with total treatment costs exceeding $1 billion a year [2
]. In the US, the figure is an astonishing US$32 billion a year [3
]. Back complaints are the seventh most common condition in patients consulting general practitioners in Australia, and the most common musculoskeletal condition [4
]. It is also the most common health problem for which an imaging test is ordered by a general practitioner [4
A potential solution to managing the problem of low back pain is the identification and control of modifiable risk factors. This approach is appealing and seemingly logical and there are notable examples where such an approach has provided major improvements in public health. For back pain this approach has not yet been fruitful: Cochrane reviews of workplace interventions [5
], insoles [6
] and lumbar supports [7
] have failed to support these traditional back pain prevention approaches. Prevention strategies have to date been largely based on controlling long-term exposure to risk factors, for example, modifying seats to control vibration in truck drivers. However it is likely that the full potential of prevention will not be reached unless we also consider commonly occurring, modifiable risk factors that happen just before the onset of back pain. In this regard we see our proposed research as complementary to, rather than in conflict with, research evaluating long term risk factors.
The existence of short term risk factors or 'triggers' is consistent with the time course of back pain. It is well established that most people will experience low back pain in their lifetime [8
], that pain is typically recurrent [9
] and that episodes are usually of sudden onset [10
]. For example research conducted by our group demonstrated that in an inception cohort of 969 subjects, 82% reported that their onset of low back pain was sudden [10
]. This pattern of low back pain suggests that rather than solely looking at long term exposure to risk factors it would be instructive to also look closely at events occurring immediately prior to the episode to identify modifiable triggers to the episode. This information is routinely sought by health practitioners when a patient with low back pain seeks care. The treating clinician commonly asks the patient what activity they were performing just prior to the onset of pain, in essence, "was the episode triggered by something unusual that happened just before?" The scientific method best suited to answer this question is the case-crossover design [11
We will use the case-crossover design to provide the first accurate estimates of the transient increase in risk of low back pain associated with transient exposure to various triggers. It is possible that we will identify several factors that are not modifiable but this information will be extremely important to our understanding and explanation of the causes of low back pain.
1) To quantify the transient increase in risk of an episode of sudden onset, acute, low back pain associated with exposure to a range of common physical and psychological factors listed in Table .
Factors that may trigger an episode of low back pain to be evaluated in the study
2) To determine if habitual physical activity moderates the transient increase in risk of an episode of sudden onset, acute, low back pain associated with exposure to the physical and psychological factors listed above.