Background This study test if the frequency coherence calculated for the overall, low and high frequency bandwidths of the center of pressure excursions and free-moment calculated during standing balance are similar between scoliotic and non-scoliotic girls and if the coherence values within each frequency band are comparable for a given group of girls. Methods Twenty-nine girls with adolescent idiopathic scoliosis formed the scoliotic group and 22 able-bodied girls formed the non-scoliotic group. Each girl maintained a quiet upright stance on a force plate. Three trials were performed at a sampling frequency of 64 Hz for 64 s. Mean anterio-posterior, medio-lateral center of pressure positions and free-moment were measured and their frequency content calculated. The magnitude of the coherence was calculated for each signal pairs for three frequency ranges. Results The magnitude of the medio-lateral center of pressure/free-moment coherence in the low and high frequency bands was significantly different between the groups. Within each group, the magnitude of the medio-lateral center of pressure/free-moment coherence was significantly higher than the other two coherence pairs at low frequencies (P < 0.001). Factor analysis revealed that able-bodied girls exhibited a mixed standing balance modality consisting of posture (center of pressure) and proprioceptive information (free-moment). Scoliotic girls adopted an adaptive modality mostly based on proprioception information to maintain their standing balance. Interpretation Scoliotic girls systematically depend on the free-moment to modulate their antero-posterior center of pressure displacements. These results suggest a postural reeducation program aimed at improving proprioception while repositioning the mean center of pressure by postural corrections.
