There is a need for non-radiographic, objective outcome measures for children with Adolescent Idiopathic Scoliosis (AIS). Standing balance and stability is altered in children with AIS. The Margin of Stability (MoS) has been used to compare gait stability in clinical populations. Our objective was to compare the MoS in anterior-posterior (MoS_AP) and mediolateral (MoS_ML) directions in girls with AIS to Controls.

Girls with AIS and healthy girls walked at three speeds on an instrumented treadmill wearing retroreflective markers, surrounded by motion capture cameras. The MoS_AP/ML was calculated at left and right heel strike. Data was processed in Visual 3D. A two-way ANOVA was used to compare MoS_AP/ML between group, speed and the interaction between group and speed. Pearson's correlation coefficient was used to compare the MoS to Cobb angle. Statistical significance was accepted when p > 0.05.

A priori power analysis suggested 12 participants per group. Three Cases and four Controls were recruited. Girls with AIS all had right-sided main thoracic curves (Lenke type 1a, 61.3° ± 10.0°). MoS_AP was significantly bigger for Cases compared to Controls on the left (p=0.038) and right foot (p=0.041). There was no significant difference between Cases and Controls for MoS_ML, but there was a visual trend for a smaller MoS_ML in Cases. There was no significant difference for speed or the interaction between group and speed for MoS_AP or MoS_ML. In Cases, MoS_AP increased with increasing Cobb angle on the left (r²=0.687, p=0.054) and right (r²=0.634, p=0.067) and MoS_ML decreased with increasing Cobb angle on the left (r²=-0.912, p=0.002). Further subjects are being recruited.

Girls with Lenke type 1a AIS are more stable in the AP direction and less stable in the ML direction than Controls during treadmill walking. AP stability increases and ML stability decreases with increasing Cobb angle. This research suggests that the MoS could be used as an outcome measure for children with AIS. Continued work is required to increase the power of this study. Further work could consider these changes during walking overground, measuring an MoS or MoS-like measure using a wearable device, and in different curve types.

Purpose of the study

We propose a simple classification for adolescent idiopathic scoliosis (AIS) based on two components which include the curve type and shoulder level and suggest a treatment algorithm for AIS.