Changes in Shape of the Spine with Idiopathic Scoliosis after Harrington or C-D Instrumentation: The Plan View

The ability of C-D instrumentation (CDI - 23 patients) was compared with that of Harrington distraction instrumentation (HDI - 6 patients) to change the orientation of the best-fit plane of the instrumented part of the spine of patients with idiopathic scoliosis. Each patient was radiographed pre- and post-operatively using stereo-xray methods to obtain the three-dimensional position and orientation of each lumbar and thoracic vertebra. A plane image was then created in which the vertebrae were projected on to a plane perpendicular to the regional axis defined by the lower-most instrumented vertebra (origin) and the upper-most instrumented vertebra (z axis direction). The lateral (y) axis lay in the global frontal plane. The vertebrae in the instrumented part of the spine were found to lie approximately on a straight line in this projection. Therefore, linear regression was used to obtain a measure of the rotation of the best-fit plane of this part of the spine from the regional frontal plane. Differences were found in the post-operative changes in spinal shape between these two groups of patients. It was found that both operations produced a straighter (less curved) spine in the best-fit plane. The major difference was that CDI achieved much greater derotation of the best-fit plane of the instrumented region of the spine. The regional plan view (based on the instrumented region of the spine) was particularly useful for demonstrating changes in spinal shape in individual patients, and in demonstrating differences between the two groups of patients.