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An Analysis of the Effect of the Zielke Operation on S-Shaped Curves in Idiopathic Scoliosis: The Use of EVAs Showing that Correction of the Thoracic Curve Occurs in its Lower Part: Significance of the Thoracolumbar Spinal Segment

This paper analyzes the initial effect of the Zielke VDS operation on S-shaped idiopathic spinal curves in 17 patients with particular reference to the thoracic spine. The curves are evaluated by conventional methods (Cobb angle, apical vertebral rotation, kyphosis, and lordosis) and by a new method using end vertebra angles (EVAs). Three new surgical correction indices are used. In the lower curve, the surgical correction averaged 81%, and it is usually larger than that induced in the thoracic curve by about 48% (surgical correctability index). The lower curve correction is asymmetric, occurring more in its lower part (lower EVA) than in its upper part (upper EVA), a difference that the authors attribute to the restraint imposed by the rib cage on the upper EVA of the lower curve. In the upper (thoracic) curve, the surgically induced correction is variable and averages 33% (range, 6–69%). It is related significantly to preoperatlve bending film flexibility. The thoracic curve correction also is asymmetric, occurring more in its lower part (lower EVA) than in its upper part (upper EVA), which usually remains stable. The kyphosis angle decreases by an average of 7°. The thoracic apical vertebral rotation shows variable changes. The findings show that the correction of the upper curve occurs mainly in the thoracolumbar spinal segment. It is suggested that this junctional segment of the spine is of importance in determining the limits of both instrumentation and fusion for idiopathic scoliosis.