Idiopathic scoliosis: relations between the Cobb angle and the dynamical strategies when sitting on a seesaw

The aim of this study was to determine the influence of the severity of the spinal curve on the postural regulation when self-imposed disturbances occur in a seated position in anteroposterior (AP) and mediolateral (ML) orientations. Twelve female adolescents with a right thoracic scoliosis (Cobb = 30.4° ± 9.7) were included in this study. The ground reaction forces (GRF) were studied while the subjects were maintaining their sitting on a seesaw (ML or AP destabilisation). Five conditions were tested: eyes open; with additional loads placed onto the subject's right or left shoulder; or onto the subject's right or left pelvis. We tested the correlation between the Cobb angle and the postural parameters (index of performance and GRF variability) for each condition. When the destabilisation was AP, the Cobb angle was significantly correlated with GRF variability and anterior and concavity index of performance. Two conditions showed higher correlations: stabilisation with the concavity pelvis load (GRF variability) and the open eyes (index of performance). In contrast, whatever the condition tested was, no link was found when the destabilisations were applied in ML direction. The destabilisation in a seated position highlights the influence of the curve severity on the postural organisation. In seated position, the postural control strategies specific to the scoliotic patients were always correlated by severity of curve, especially when the destabilisation is applied in AP directions. This study showed that the unstable seating position can be considered as a pertinent paradigm to help finding a postural clinical index for adolescent idiopathic scoliosis.