Whole body balance control in Lenke 1 thoracic adolescent idiopathic scoliosis during level walking

INTRODUCTION: Altered trunk shape and body alignment in Lenke 1 thoracic adolescent idiopathic scoliosis (AIS) may affect the body’s balance control during activities. The current study aimed to identify the effects of Lenke 1 thoracic AIS on the balance control during level walking in terms of the inclination angles (IA) of the center of mass (COM) relative to the center of pressure (COP), the rate of change of IA (RCIA), and the jerk index of IA. The association between the Cobb angle, IA and RCIA was also evaluated. MATERIALS AND METHODS: Sixteen adolescents with AIS (age: 14.0±1.8 years, height: 154.8±4.7 cm, mass: 42.0±7.5 kg) and sixteen healthy controls (age: 14.4±2.0 years, height: 158.4±6.2 cm, body mass: 48.6±8.9 kg) performed level walking in a gait laboratory. The kinematic and ground reaction force data were measured for both concave-side and convex-side limb cycles, and used to calculate the IA and RCIA, the jerk index of IA, and the temporal-spatial parameters. Correlations between the Cobb angle, IA and RCIA were quantified using Pearson’s correlation coefficients (r). RESULTS: The patients showed less smooth COM-COP motion with increased jerk index of IA in the sagittal plane during single limb support (SLS) of the concave-limb (p = 0.05) and in the frontal plane during double limb support (DLS) (p < 0.05). The patients also showed significantly increased posterior RCIA on both the concave and convex side during initial (p = 0.04, p = 0.03) and terminal (p = 0.04, p = 0.03) DLS when compared to healthy controls. In the frontal plane, the patients walking on the concave-side limb showed decreased IA over SLS (p = 0.01), and at contralateral toe-off (p<0.01) and contralateral heel-strike (p = 0.02), but increased mean IA magnitude over terminal DLS (p = 0.01). The frontal IA at contralateral toe-off and SLS for AIS-A showed a moderate to strong correlation with Cobb angles (r = -0.46 and -0.61), and the sagittal RCIA over the initial DLS for AIS-A also showed a significant, strong correlation with Cobb angles (r = -0.50). CONCLUSIONS: The patients with Lenke 1 thoracic scoliosis in the current study showed altered and jerkier COM-COP control during level walking when compared to healthy controls. During DLS, the patients increased the posterior RCIA in the sagittal plane with increased IA jerk index in the frontal plane for both the concave- and the convex-side limb, indicating their difficulty in maintaining a smooth transfer of the body weight. During SLS of the concave-side limb, the patients adopted a conservative COM-COP control strategy, as indicated by a decreased IA in the frontal plane, but showed a jerky COM-COP control in the sagittal plane. The COM-COP control of the patients was associated with the severity of the spinal deformity. The current results suggest that this patient group should be monitored for signs of an increased risk of loss of balance during weight transfer on the concave-side limb.