An index for back pain risk assessment in nursery activities

Back pain is one of the most significant socioeconomic problem in industrialized countries. Its origin is multifactorial, including physical, psychosocial and individual risk factors. Among the working population, nursery teachers are highly exposed to back pain diseases, but not many studies have dealt with this problem. So a suitable quantitative index is proposed, based on an unobtrusive video-analysis of established motor-tasks. In particular five nursery teachers were asked to perform lifting and lowering movements placing their feet at two different distances from a weight (a toy pet loaded with 8 kg, simulating a child) with different strategies (flexed, partially flexed and extended legs). The index is based on the idea that a greater trunk inclination angle determines increased loads on the lumbar spine, and so an augmented probability of spinal disorders. To validate our protocol, the same data were analyzed through a 3D biomechanical model (gold standard method), which computes the loads on L3-L4 intervertebral disc. Data show a good correspondence between the risk level suggested by the index and the one indicated by the mechanical loads: the antero-posterior shearing forces and the values of index coherently increase with the reduction of leg flexion.