Lateral steps reveal adaptive biomechanical strategies in adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (characterized by a morphological deformation of the trunk) prompts the development of new postural control strategies. This adaptation has an influence on the dynamics of motor behaviour. The present study analysed ground reaction forces during lateral stepping in order to highlight the dynamic consequences of idiopathic scoliosis.

Ten adolescents suffering from idiopathic scoliosis with right thoracic curvature (Cobb angle>or=15 degrees) and 15 healthy adolescents participated in the study. We used two force platforms to record ground reaction forces for the right and left legs during large and small lateral steps (LSs).

Our results revealed intergroup and interlimb differences for both types of step. For small LSs, right-side (i.e. convexity side) initiation induced a significant increase in the ground reaction force impulse during the postural phase for the scoliotic group, when compared with the control group. For large LSs, left-side (i.e. concavity side) initiation induced a significant increase in ground reaction force impulse during the landing phase only. Patients always displayed slower dynamic behaviour than healthy controls. For both stepping sides, the asymmetry index (AI) was higher in the scoliotic group than in the control group (0.2or=85 in the scoliotic group versus 0.124.4 in the control group). Furthermore, the scoliotic group showed a significant increase in the variability of the dynamic parameters (>8%).

In scoliotic subjects, lateral stepping prompts specific dynamic behaviour affecting both limbs, in order to maintain balance during movement despite spinal deformation. This stepping task could be used in future studies to identify specific motor strategies.