Axial rotation of the pelvis and its influencing factors in adolescent idiopathic scoliosis with primary thoracic curve

Abstract

Objective To explore the influencing factors and possible mechanism of axial rotation of the pelvis in adolescent idiopathic scoliosis (AIS) with primary thoracic curve.Methods 91 AIS patients with primary thoracic curve were recruited in this retrospective study. There were 81females and 10 males with a mean age of 14.5 ± 1.7yrs and a mean Cobb angle of 48 ± 8.6.Axial pelvic rotation can be quantified using the left/right hemipelvis width ratio (L/R ratio) as measured on standing posterior-anterior scoliosis radiographs.According to the L/R ratio,the subjects were divided into two groups:Group A (L/R ratio ≤1) and Group B (L/R ratio ＞1).Descriptive statistics were done to determine the means and standard deviations.Correlation and linear regression were used for statistic analysis.Results 75.8％ (n =69) of AIS patients with primary thoracic curve had a trend of axial pelvic rotation in the same direction as the thoracic curve; two variables were associated with axial rotation of the pelvis:more flexibility of the lumbar curve in AIS patients with axial pelvic rotation to the right (0.87 ± 0.27 vs 0.69 ± 0.24,P =0.007) ; and greater axial pelvic rotation in AIS patients with less rotation of the lumbar apex (P =0.008).The L/R ratio correlated with the lumbar apical vertebral rotation (P =0.003) and the lumbar Cobb angle (P =0.002),but not with thoracic curve severity.There was a correlation between lumbar and thoracic Cobb angles (P＜0.001 ).Conclusions The majority of AIS patients with primary thoracic curve had significant axial pelvic rotation in the same direction as the thoracic curve.Moreover,although the axial pelvic rotation did not correlate with the magnitude of thoracic curve directly,there were overlapping correlations from the thoracic spine to the pelvis.Thus it was speculated that the pelvis might compensate for the deformity of thoracic curve through the lumbar spine. Key words: Scoliosis; Adolescent; Pelvic rotation