Mechanical Analysis of Harrington Rod Correction of Idiopathic Scoliosis*

ABSTRACT: Correction by Harrington instrumentation of six idiopathic scoliotic spines was studied through computer simulation. As the limit to lateral correction is approached, large force increases are needed to increase correction, beyond those likely to be achieved by improvements in hook fixation, for example. Significant derotation should not be expected in a Harrington procedure, and is likely to be achieved within a short time only by reducing intervertebral motion segment stiff nesses. Correction of the lateral curve and correction of the rotation were not de pendent on one another. Distraction by Harrington instrumentation is currently the surgical technique most widely used for correction of scoliosis when the curves measure 40 to 90 de grees. Many reports concerning the use of this technique have appeared in the literature. Citations to these reports are available in the study of Nachemson and Elfström. Whatever the etiology, scoliosis is defined in mechanical terms; that is, a patient has scoliosis when there are lateral deviations of several vertebrae from the longit