Background
Since trunk morphology and curve types were reported to affect standing in adolescent idiopathic scoliosis (AIS), it is reasonable to assume that bracing could perturb standing balance in this population. The objective here was to use time- and frequency-domain analyses to test if the Boston brace affects balance in AIS.
Material and Method
Fifteen AIS girls were fitted with a Boston brace. At the four-month follow-up, standing balance was assessed using center of pressure (COP) displacements measured from a force plate. The subjects were tested with and without the brace.
Results
The mean position of the COP and the sway area were similar with and without the brace. Though the first peak in the power spectra was not statistically significant, the second peak was statistically smaller with the brace in the antero-posterior direction (p=0.012) and larger along the medio-lateral axis (p=0.022). In the antero-posterior direction there was a statistically significant shift towards higher mean (p=0.012) and median (p=0.003) frequencies with the brace, whereas no difference was noted in the medio-lateral direction. Time-domain parameters did not prove useful in differentiating between the in- and out-of-brace conditions in AIS individuals. The second peak in the power spectra could be associated with an inverse double-pendulum motion.
Conclusions
The time-dependent parameters used in this study did not prove useful in differentiating between in-brace and out-of-brace conditions. Spectral analysis highlighted increased stiffness in the antero-posterior direction and less control in the medio-lateral axis in standing balance between in-brace and out-of-brace conditions in AIS.

Keywords: Pressure, Posture - physiology, Postural Balance - physiology, Scoliosis - physiopathology, Child, Braces, Adolescent