Contribution of ribcage movement to thoracolumbar posteroanterior stiffness

Abstract

Objective To investigate (1) whether thoracolumbar posteroanterior (PA) stiffness differs between 2 conditions of ribcage movement: unconstrained and constrained, and (2) whether the effect of ribcage constraint on PA stiffness varies according to where the PA force is applied. Design Two-factor within-subjects design. Setting Spinal Mechanics Laboratory, University of Sydney. Intervention A convenience sample of 41 subjects, asymptomatic for back pain, participated. PA stiffness at T12-L4 was measured in the unconstrained and constrained ribcage conditions with a mechanical device. For the constrained condition, we used a clamping device to apply a force to the subject’s lower thorax to reduce movement. Main outcome measures PA stiffness at T12-L4 under both ribcage conditions. Results PA stiffness at T12-L4 significantly increased when the ribcage was constrained ( P< .05). However, the effect of ribcage movement did not depend on the location of the PA force. Conclusions These findings suggest that the properties of the ribcage influence measures of PA stiffness in the thoracolumbar (T12-L4) spine uniformly. Variations in PA stiffness in segments T12-L4 may reflect the properties of the intervertebral joints.