Effect of Posture on Biomechanics of Human Lumbar Spine in Combined Loadings

Changes in the sagittal curvature of the human lumbar spine (ie, lordosis) has been recorded under external loads and in microgravity [1-3]. Smaller lordosis has been observed in standing radiographs of low-back pain population compared with those of normal volunteers [4]. The preservation of lordosis and its biomechanical consequences during daily activities and heavy lifting tasks remain still as a controversial issue. In this study, following our earlier studies on the mechanics of the entire lumbar spine under single moments [5,6] and small axial compression forces [7], the effect of changes in the sagittal posture (ie, lordosis) on mechanics of the lumbar spine is studied under axial compression forces up to 800 N with and without right axial torques of up to 10 N-m. The forces on facets, strain in disc fibres, and primary and coupled motions at all levels are evaluated and compared. Attention is focused on the effect of posture on the stability of the spine in compression. The influence of facet gap distance, removal of facets, and disc fluid loss on results are also investigated.