Relation between spinal load factors and the high-risk probability of occupational low-back disorder.

Spinal compression is traditionally assumed the principal biomechanical mechanism associated with occupationally related low-back disorders (LBD). However, there is little conclusive evidence demonstrating that compression is related to occupational LBD. The objective of this research was to examine whether axial compression in the lumbar spine can predict the probability that a lifting task should be classified as high risk for LBD. Furthermore, the improvement in predictive ability was examined when analyses include 3-D, dynamic biomechanical factors. Ten experienced warehouse workers transferred 12 pallet loads of boxes in a simulation of warehouse working conditions. Biomechanical estimates of 2-D static and 3-D dynamic spinal compression, shear loads and tissue strains were achieved from the subjects during each lifting exertion. Each lift was also assessed for probability of high LBD risk classification. Regression analyses were performed to examine the relationship between biomechanical and epidemiological factors. Results indicate 2-D static estimates of spinal compression describe approximately 13% of the probability of high LBD risk variability. Dynamic estimates of spinal compression describe > 44% of the variability. A multifactor regression model including 3-D spinal loads and tissue strains further improved the predictive ability, but the improvement was not statistically significant. This research demonstrates the biomechanical source of low-back pain is dynamic, multifaceted and multidimensional. Significant improvements in ergonomics assessments can be achieved by examining interactions of dynamic biomechanical factors. Unfortunately, this improved predictive ability is generated at the high cost of computational complexity. However, less realistic biomechanical representations may ignore the injury mechanisms associated with the greater number of workplace injuries. Thus, improved understanding of the dynamic biomechanical interactions influencing the tolerance and injury mechanisms of the spine may permit more accurate assessments of workplace injury factors associated with LBD and reduced incidence of occupationally related low-back pain.