Effect of rotation on frontal plane deformity in idiopathic scoliosis

To analyze the effect of rotation on frontal plane deformity in idiopathic scoliosis, 44 patients with idiopathic scoliosis aged 11 to 18 years were e xamined using standing anteroposterior and true AP radiographs. Axial rotat ion was measured by computed tomography. Patients were divided into two gro ups according to Cobb angle: patients with angles <30<degrees> comprised gr oup 1 and patients with angles >30 degrees comprised group 2. Cobb angle in creased with true-AP projection a mean of 21.2% in group 1 and 16.7% in gro up 2. Rotation degree was significantly correlated with increasing degree o f frontal plane deformity (P<.01) in group 1 but not in group 2 (P>.05). Th ese results demonstrate the influence of rotation over frontal plane deform ity and is more apparent at curves >30 degrees.