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 examined using standing anteroposterior and true AP radiographs. Axial rotation was measured by computed tomography. Patients were divided into two groups according to Cobb angle: patients with angles <30 degrees comprised group 1 and patients with angles >30 degrees comprised group 2. Cobb angle increased with true-AP projection a mean of 21.2% in group 1 and 16.7% in group 2. Rotation degree was significantly correlated with increasing degree of frontal plane deformity (P<.01) in group 1 but not in group 2 (P>.05). These results demonstrate the influence of rotation over frontal plane deformity and is more apparent at curves >30 degrees.