A Study of Vertebral Displacement Due to Disc Loading and Its Risks when Using Lumbar Assist Devices

This paper examines the displacement of the vertebral body caused by the difference in the reduction rate of compression and shear forces on the intervertebral disc, which is suggested by the use of lumbar assist devices, and the risks associated with such displacement. Lumbar assist devices are being developed by various research institutes as a method of assisting workers. Although there are many reports on the effectiveness of lumbar assist devices in terms of performance, there are few reports describing the effects on the spine when the devices are used. Therefore, we calculated the reduction rate of compression force and shear force on the intervertebral disc using a lumbar load evaluation model with a passive-type assist suit, and found that the reduction rate of compression force was greater than that of shear force. In this case, the vertebral body may be displaced significantly in the vertical direction of the vertebral column because the force of the vertebral body holding down the intervertebral disc is weakened. In addition, the vertebral displacement in the shear direction was measured by simultaneously applying compression and shear forces to an animal specimen, and it was shown that the reduction of compression force affects the displacement in the shear direction.