ROTATIONAL CHANGES OF THE VERTEBRAL PELVIC AXIS AFTER SUBLAMINAR INSTRUMENTATION IN ADOLESCENT IDIOPATHIC SCOLIOSIS

Study Design, The authors studied the rotational effect of sublaminar wiring on the spinal pelvic axis on 20 patients who were being treated for adolescent idiopathic scoliosis. Objectives. To determine if subl aminar wiring effectively derotates the scoliotic spine. Summary of Ba ckground Data. The correction of the rotational deformity in adolescen t scoliosis via sublaminar wiring is not well quantified in the litera ture. The derotation maneuver of Cotrel-Dubousset has been shown to pr oduce variable and unpredictable amounts of axial derotation. Methods. Twenty patients who underwent posterior spine fusion for adolescent i diopathic scoliosis were evaluated using computed tomography scans and plain radiography before and after surgery and at a subsequent follow -up examination (average time of follow-up examination, 35 months afte r surgery). The degree of angle of vertebral rotation about the sagitt al plane and that relative to the pelvis were measured before and afte r surgery and at a follow-up examination. Results. The primary thoraci c curves were not derotated significantly relative to the pelvis with sublaminar wiring. Primary thoracolumbar curves instrumented on the co nvexity with pedicle screws were derotated significantly relative to t he pelvis (P = .001). The average initial correction was 57%. On final follow-up examination, the correction was 24% (18 of 20 twenty indivi duals lost axial correction by an average of 34%). In nine of 20 patie nts the spine was more rotated, relative to the pelvis, than it had be en before surgery. No coronal or sagittal decompensation was seen in a ny curve type. Conclusions. Coronal and sagittal plane correction of s coliotic curves may be achieved with sublaminar instrumentation, The a bility to derotate axially the scoliotic spine appears to be variable, however,and, in most cases, curve-type dependent. Overtime, much corr ection appears to be lost, and in many patients the scoliosis actually becomes worse than it was before surgery. Nonetheless, the apical der otation that takes place appears to be reasonably true: the percent co rrection of angle of rotation about the sagittal plane and the percent correction of angle of rotation about the sagittal plain relative to the pelvis were closely correlated. Derotation forces applied to the i nstrumented spine do not appear to be transmitted to more distal segme nts.