Biomechanical Influence of Treatment Table Axis Location on Axial Rotation of Lumbar Spine

Abstract

Various treatment devices or tables have been developed for generating axial rotation of the lumbar spine during spinal mobilization. However, the effects of the design of such treatment devices on the axial rotation of the lumbar spine have not been thoroughly investigated. In this study, the influences of the location of the treatment table rotational axis on the biomechanical behaviors of the lumbar spine were investigated for spinal mobilization using finite element analysis. The axial rotation of spinal mobilization with a supine posture on a treatment table was simulated. The sacrum was rotated by 10° along the axial rotation axis. The initial axis location was around the posterior edge of the nucleus pulposus of the L5–S intervertebral disc. The axis location was varied in the posterior direction from 0 to 200 mm in increments of 50 mm. Changes in the spine biomechanics, such as the intersegmental rotation, intradiscal pressure, and stresses on the ligaments and fibers of the annulus fibrosus, were investigated. Upon movement of the rotation axis towards the posterior direction, (1) the rotation angle along the lateral bending direction increased, (2) the intradiscal pressure increased, (3) the stresses on fibers of the annulus fibrosus and ligaments increased, and (4) the facet joint forces increased. Based on these findings, we conclude that careful consideration of the rotation axis location is important and necessary in the development of treatment beds for spinal manipulation.