Nucleus pulposus deformation in response to lumbar spine torsion

[Truncated abstract] Background: The lumbar intervertebral disc (IVD) is comprised of the collagenous anulus fibrosus (AF) and the proteoglycan based, hydrophilic nucleus pulposus (NP). The primary role of the NP is load attenuation which it achieves by deforming within the confines of the anulus via a hydrostatic mechanism. The pattern of deformation is assumed to be away from the position of offset loading. Changes in spinal posture result in variable loading. Sagittal plane positioning has been shown to result in deformation of the NP towards the convexity in most cases. Primary uniplanar lumbar segment movement results in additional movement in a secondary plane. Spinal rotation, though small in range intersegmentally, plays an important role in locomotion and contributes to multiplanar motion and spinal flexibility. Rotation is also implicated as a common mechanism by which the IVD may be injured. Few data exist reporting the direction of NP deformation relative to rotated positions. Such information may inform the knowledge base on injuring mechanisms and normal lumbar spine mechanics. Purpose: The primary purpose of this thesis investigation was to quantify the in vivo effect of rotation postures on lumbar NP deformation and to report the predictability of the direction of that deformation. Additionally, the effects of coincident coronal plane positions, age related changes and spinal deformity (scoliosis) were examined to determine the relative influences of such factors on the internal mechanism of the IVD. The principal hypothesis was that the NP would deform in all cases and conditions in a predictable direction and with a magnitude proportional to the resultant segmental angulation. Methods: This investigation is divided into two main themes.