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Contribution of ribcage movement to thoracolumbar posteroanterior stiffness
Wunpen Chansirinukor1, Michael Lee, Jane Latimer
1School of Exercise and Sport Science, University of Sydney, 1/13 Mary Street, Lidcombe NSW 2141, Australia. wcha1745@mail.usyd.edu.au
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.