An analysis of the effect of the Zielke operation on the rib cage of S-shaped curves in idiopathic scoliosis.

This report evaluates the rib cage in 16 patients with S-shaped idiopathic scoliosis having the Zielke operation and followed-up for an average period of 30 months. Methods used include Cobb angle and a segmental evaluation (T7-T12) of each of convex and concave rib-vertebra angles (RVAs), rib-vertebra angle differences (RVADs), vertebral rotation, tilt and displacement. Preoperatively, the apical convex ribs droop more than the concave ribs, but the most striking difference is an asymmetry of RVAs, with increasing droop of the concave RVAs from T7-T12. The effect of the Zielke operation (on the lower curve) is: (a) to correct the Cobb angle, vertebral tilt, and displacement of the upper (thoracic) curve; (b) to derotate the spine; (c) to elevate the mobile concave ribs; (d) to have little or no effect on the stiff apical convex ribs; and (e) to increase the droop of the mobile lower convex ribs. During follow-up, six of the upper (thoracic) curves progressed. The apical RVAD and apical convex RVA are not prognostic. The concave RVAs maintain their position while convex RVAs elevate relative to the concave ribs.