Comparable effect of simulated side bending and side gliding positions on the direction and magnitude of lumbar disc hydration shift: in vivo MRI mechanistic study

Hiroshi Takasaki

To investigate the direction and magnitude of mechanical influence to the lumbar disc in side bending and side gliding positions by considering shift of disc hydration. Twenty asymptomatic subjects completed this study. Direction of the hydration shift (θ), magnitude of the shift, and segmental lateral flexion and rotation angles from L1/L2 to L5/S1 during left side bend and side glide in lying were measured by magnetic resonance imaging (MRI) and compared using paired t-tests. A significant difference (P<0.001) was detected in the segmental lateral flexion angle at L1/L2 between the side bending position (mean [SD], 5.1° [2.2°] left lateral flexion) and the side gliding position (mean [SD], 2.1° [2.7°] left lateral flexion). However, there was neither significant difference (P>0.05) in the lateral flexion angle at other segments nor rotation angles at each segment between the two lumbar positions. There was also no significant difference (P>0.05) in the θ value and magnitude of the hydration shift between the two lumbar positions. The disc hydration generally shifted to the right in the left side bending and side gliding positions at all disc levels. This is the first study to investigate mechanical influence to each lumbar disc in the side gliding position using the shift of disc hydration on axial MRI. The comparability in the direction and magnitude of the hydration shift in the side bending and side gliding positions indicates that the maneuver of side gliding can produce comparable ipsilateral mechanical influence to each lumbar disc in comparison to side bending.