An analysis of the effect of the Zielke operation on S-shaped curves in idiopathic scoliosis. A follow-up study revealing some skeletal and soft tissue factors involved in curve progression.

This article analyzes the fate of S-shaped idiopathic spinal curves during follow-up in 18 patients having the Zielke VDS operation. The spinal radiographs were evaluated by Cobb angle, end-vertebra angles (EVAs), vertebral rotation, and by a new method using the tilt of the surgically fused spinal block in the frontal plane. Spinal growth was measured. Using the conventional criterion for Cobb angle progression, 83% of the lower curves and 50% of the upper curves progress. The use of EVAs shows that progression occurs mainly in the middle (thoracolumbar) segment of the spine. Curve progression occurs in the frontal plane without any significant change in vertebral rotation. The progression of the upper curve Cobb angle is not related to the progression of the Cobb angle of the lower curve; but it is related to 1) tilt of the spinal block, 2) growth of the spine below the block and 3) overall linear spinal growth (T1-S1). Progression of the upper EVA of the upper curve is associated with skeletal immaturity. The key features leading to curve progression after the Zielke operation appear to be spinal asymmetry in the frontal plane, linear spinal growth, and concave lumbar muscle tether (myostatic contracture). The surgical implications of the findings are outlined.