Vertebral Rotation in Adolescent Idiopathic Scoliosis Is Primarily Curve-Magnitude Driven Rather than Age-Dependent

The relationship between vertebral rotation (VR), curve magnitude, and age in adolescent idiopathic scoliosis (AIS) is not yet fully understood. Although VR represents a defining feature of scoliotic deformity, it remains unclear whether rotational progression is age-related or curve magnitude-related. It has been suggested that in early scoliosis the intervertebral disc is initially deformed or wedged, driving the formation of the Cobb angle, with secondary vertebral and rotational deformity.The present study aimed to analyze the associations between age, Cobb angle, and VR in an AIS cohort, and to determine the independent predictors of axial rotation.

This retrospective study included 255 AIS patients (183 females, 72 males, age 10-18 years) at first presentation. Radiographic measurements included Cobb angle of the primary curve and apical vertebral rotation (AVR - Raimondi method). Univariate linear regression models evaluated associations between age and AVR, and age and Cobb angle. A multivariable linear regression model was constructed with AVR as the dependent variable, incorporating age, Cobb angle, primary curve location, number of curves, and gender as independent variables.

The mean age was 14.0 ± 1.6 years, with a mean primary Cobb angle was 26.5 ± 11.2°(10-78) and mean AVR 17.3 ± 6.6°(2-40) In univariate analysis, age showed a modest but statistically significant association with VR (B=0.664, p=0.009), whereas no significant association was observed between age and Cobb angle (B=0.360, p=0.406). In multivariable regression analysis (Table 1), Cobb angle emerged as the strongest independent predictor of VR (B=0.286, p<0.001). Age retained a smaller but significant independent effect (B=0.566, p=0.011). Curve location, number of curves, and gender were not significant predictors of VR.

Although VR showed a modest increase with age in univariate analysis, curve magnitude emerged as the primary independent determinant. The absence of a significant age-related increase in Cobb angle suggests that rotational progression is not simply an age-dependent phenomenon. These findings support the concept that axial deformity in AIS is predominantly magnitude-driven, with age contributing only modestly. In the context of existing biomechanical evidence, the results are consistent with the hypothesis that early scoliotic deformity may originate at the intervertebral disc level, with VR developing secondary to curve progression rather than aging itself. Further studies in larger stratified cohorts by curve severity and skeletal maturity are warranted to better clarify the temporal relationship between disc deformation and VR in AIS.