The influence of adolescent idiopathic scoliosis on the dynamic adaptive behaviour.

The idiopathic scoliosis is characterized by a three-dimensional spinal deformity involving new dynamical strategies to regulate the posture. The aim is to analyze the centre of pressure (CP) behaviour in forward stepping (FS) and lateral stepping (LS) to determine the dynamical consequences of scoliosis. Ten adolescents suffering from right thoracic scoliosis (Cobb>or=18 degrees ) and 15 healthy adolescents participated in this study. Two forceplates recorded the CP evolution in medio-lateral and antero-posterior axes resulting from FS and, LS with the dominant (D) and with the non-dominant (nD) limbs. Our results showed between groups and within groups differences respect to axis of motion. The comparison between groups in the LS showed the increase of the CP total displacement only when stepping with nD limb. Conversely no major evidence emerges from the FS analysis. Whatever the axis was, the CP total displacement of the D limb did not differ between groups. The comparison between lower limbs for healthy subjects was always different for FS whereas this comparison became non-significant for LS. For patients the same analysis showed results less systematically different. The correlation analysis, only when LS is initiated with nD limb, revealed opposite CP dynamical strategies between groups. These results may be explained by the influence of the spinal deformation on internal mass distribution and the asymmetrical neurophysiological factors previously described. Therefore, to perform LS the patients develop an asymmetry between both limbs to guarantee the balance despite scoliosis. Thus LS reveals the differences between groups and between initiation limbs.