Lumbar stress distribution in sitting posture with considering spinal alignment: A finite element analysis

BackgroundSitting on a chair is an essential part of daily life, however the posture is a heavy burden on the lower back, leading to lower back pain.ObjectiveIn this study, lumbar stress distribution was analyzed when sitting on a chair with different backrest inclination, sitting distance and seat pan inclination in order to visualize the stress on intervertebral discs and sacroiliac joints (SIJs).MethodsBody pressure distribution was measured on backrests and seat pans of six subjects. Each sitting posture on a chair was reproduced using a finite element model of a spine and pelvis, and the stress distribution in the lower back was analyzed based on the results of the body pressure distribution measurements.ResultsWhen the seat pan was tilted forward, the pressure on the backrest decreased, whereas the pressure increased with large sitting distance. Finite element analyses showed that equivalent stresses on the SIJs and intervertebral discs was decreased when sitting on a chair shallowly and with the seat pan tilted forward.ConclusionBoth sitting shallowly and with a forward-tilted seat are postures that increase the trunk-thigh angle, and the load on the lower back was reduced by reducing the moment applied to the sacrum.