Can pelvic incidence be used to analyse the sagittal profile in adolescent idiopathic scoliosis? A retrospective analysis of 100 patients.

Abstract

To evaluate pelvic incidence (PI) as a reliable parameter for analysing sagittal profiles in patients with adolescent idiopathic scoliosis (AIS). This retrospective cohort study included 100 patients with AIS (aged 12-17 years) who underwent posterior spinal deformity correction and had a 2-year follow-up. Radiographic parameters-Pelvic Incidence (PI), pelvic tilt (PT), sacral slope (SS), lumbar lordosis (LL), thoracic kyphosis (TK), sagittal vertical axis (SVA), and T1 pelvic angle (TPA)-were evaluated preoperatively, at 6 months, and at 2 years postoperatively. Sagittal profiles were classified using the theoretical Roussouly system. Statistical analysis used repeated-measures ANOVA with Tukey HSD post hoc testing to assess temporal variability and Pearson correlation coefficients to assess associations between pelvic and spinal parameters. The mean age was 13.3 years, with females comprising 66% of the cohort; Lenke type 5 was the most common curve type. Roussouly type 3 predominated at all time points. Pelvic parameters (PI and SS) remained stable (p > 0.1), whereas spinal parameters showed significant changes in LL (p = 0.000) and TK (p = 0.001). Global alignment shifted in SVA (p = 0.014), while TPA remained unchanged (p > 0.3). PI consistently correlated with PT (r = 0.60), SS (r = 0.64), and LL (r = - 0.55) across intervals. PI showed minimal temporal variability, confirming its reliability as a morphological parameter in AIS. These findings support the role of PI in sagittal alignment assessment and reinforce the applicability of the Roussouly classification in AIS patients.