Introduction: Although the asymmetries of scoliotic gait in the adolescent idiopathic scoliosis (AIS) group were extensively studied, recent studies indicated conflicting results of the ground reaction forces (GRF) during gait in subjects with spinal deformity. The asymmetry during the stance phase might be clarified with 3D compensations of GRF between similar characteristics of subjects with and without AIS.

The purpose of this study was to compare the differences on three-dimensional (3D) GRFs, kinetic asymmetry indices (KAI) during gait, and the Cobb angle between subjects with and without right AIS.

Methods: There were 23 subjects with right convexity of thoracic idiopathic scoliosis and 22 age- and gender-matched control subjects. All subjects were right upper/lower limb dominant, and the outcome measures included the Cobb angles, normalized GRF, and KAI.

Results: The mediolateral third peak force on the dominant limb significantly decreased in the AIS group (t = 2.58, p = 0.01). Both groups demonstrated a significant interaction with the 3D indices (F = 5.41, p = 0.02). The post-hoc analysis identified that the mediolateral plane of asymmetry was significantly different between groups. The Cobb angles were negatively correlated with the vertical asymmetry index (r = -0.45, p = 0.03); however, there was no significant correlation with age (r = -0.10, p = 0.65) or body mass index (r = -0.28, p = 0.20).

Discussion: The AIS group demonstrated decreased GRF in the dominant limb mediolateral plane of the terminal stance phase. This compensatory motion was confirmed by a significant group difference on the mediolateral plane of the KAI. This KAI of vertical asymmetry correlated negatively with the Cobb angle. The asymmetric load transmission with compensatory vertical reactions was evident due to abnormal loading in the stance phase. These kinetic compensatory patterns need to be considered with asymmetry on the dominant limb when developing rehabilitation strategies for patients with AIS.