Abstract
Although the effect of physical workload on the occurrence of low back pain (LBP) has been extensively investigated, few quantitative studies have examined the morphological changes visualized via magnetic resonance imaging (MRI) in relation to occupational variables. The relationship between the severity of some abnormalities such as lumbar spinal stenosis or spondylolisthesis and physical or psychosocial occupational risk factors has not been investigated previously. In this cross-sectional study patients fulfilled the following inclusion criteria: (1) long-standing (minimum 1-year) LBP radiating down the leg (or not); (2) age more than 40 years; (3) willingness to undergo an MRI of the lumbar spine; and (4) ability to speak Italian. Primary objective of the study was to investigate the association between occupational exposure and morphological MRI findings, while controlling for the individual risk factors for LBP. Secondarily, we looked at the influence of this exposure and the degenerative changes in the lumbar spine on clinical symptoms and the related disability. Lumbar MRI scans from 120 symptomatic patients were supplemented by the results of structured interviews, which provided personal, medical, and occupational histories. All occupational factors were arranged on scales of increasing exposure, whereas pain and disability were assessed using ad hoc validated questionnaires. Evidence of intervertebral disc narrowing or herniation and the occurrence and severity of spinal stenosis and spondylolisthesis was obtained from the MRI scans and a summative degenerative score was then calculated. We detected a direct association between increasing age and the global amount of degenerative change, the severity of intervertebral disc height loss, the number of narrowed discs, stenosis, the number of stenotic levels, and spondylolisthesis. Physical occupational exposure was not associated with the presence of lumbar disc degeneration and narrowing per se, but a higher degree of such an exposure was directly associated with a higher degree of degeneration (P=0.017). Spondylolistesis and stenosis were positively related to heavy workload (P=0.014) and the manual handling of materials (P=0.023), respectively. Psychosocial occupational discomfort was directly associated to stenosis (P=0.041) and number of stenotic levels (P=0.019). A heavier job workload was the only occupational factor positively related to the degree of disability at the multivariate analysis (P=0.002). Total amount of degeneration in the lumbar spine directly influenced pain duration (P=0.011) and degree of disability (P=0.050). These results suggest that caution should be exercised when symptomatic subjects with evidence of degenerative changes on MRI scans engage in strenuous physical labor.