Flexibility in the scoliotic spine: three-dimensional analysis.

The purpose of this study was to measure the three-dimensional geometry of scoliosis by using biplane radiographic photogrammetry and to evaluate the flexibility of the deformed spine. Thirty-one patients with idiopathic scoliosis underwent analysis. There was a significant correlation between the degree of the scoliotic angle in the frontal plane, kyphotic angle in the sagittal plane, and the rotational angle of the apical vertebra. Hypokyphosis was associated with a scoliotic angle > 40 degrees in the frontal plane. Similarly, hypokyphosis was related to increased rotation of the apical vertebra (p < 0.01). Although the scoliotic angle was decreased by traction in all cases, axial rotation was less corrected in those patients with scoliotic angle > 40 degrees. This suggests that the rotational stiffness at the apex is related to the degree of the rotational angle of the apical vertebra and to the degree of the frontal curve.