Correctional effect of Cotrel-Dubousset instrumentation for idiopathic scoliosis. An early follow-up study.

We reviewed the results of posterior spinal fusion with Cotrel-Dubousset Instrumentation for idiopathic scoliosis from fifty-six patients (sixty-five curves). The postoperative follow-up on them ranged six months to three years and seven months with an average of one year and nine months. From overall results, scoliotic curves were corrected by 36.5 from 60.3 degrees before operation to 23.8 degrees after operation on average. The rate of correction was 60.5%. On a sagittal plane, thoracic kyphosis improved from 22 to 35 degrees in the Cobb angle of T1-T12, to be more physiologically aligned. In addition, the derotational effect was elucidated by the measurement on pre- and post-operative CAT scan images in the apical vertebra, and on moiré topography. A reduction of the rib hump and the trunk inclination was also noted, but did not necessarily reflect the correctional gain of the scoliotic curvature. From the biomechanical point of view, the correction of rotational deformity by CD instrumentation is derived from a couple of the following movements: one is rotation of the apical vertebra around its axis and the other is revolutional displacement of that vertebra on a transverse plane (R-R movement).