Longitudinal changes in trunkal balance after selective fusion of King II curves in adolescent idiopathic scoliosis

Study Design. A retrospective study was performed on the longitudinal changes of the trunkal balance in King II curves treated with selective posterior fusion of the thoracic curve. Objectives. To determine the effect of selective fusion on the coronal and sagittal plane balance in King II adolescent idiopathic scoliosis by analyzing the changes in shoulder level, pelvic tilt, trunk shift, centering of fusion mass, changes in the T11-L1 sagittal angle, and behavior of the unfused lumbar curve and its correlation with the end level of fusion. Summary of Background Data. It has been shown that selective fusion of the thoracic curve in a King II curve is associated with good results and arrest of lumbar curve progression in selected cases. Detailed quantitative analysis of the longitudinal changes and correlation between various clinical and radiologic parameters was not readily available in the literature. Methods. This study investigated 24 patients with King II adolescent idiopathic scoliosis treated with Harrington rod and segmental spinous processes wiring in a 10-year period with follow-up periods of 3 to 8 years. Clinical and radiologic parameters were analyzed longitudinally during the preoperative and immediate postoperative period, then at 6 months, 1 year, 3 years, and final follow-up assessment. Results. Progressive improvement in the trunk shift to within 2 cm of the center sacral line together with progressive leveling and stabilization of the shoulder and pelvic tilt was noted during the first year after surgery. Gradual movement of the Harrington rod toward the center sacral line assuming a "straight rod sign" with a rod to center line distance of less than 1 cm was found in 90% of the cases. improvement of the sagittal alignment with no significant residual junctional kyphosis also was found. The unfused lumbar curve improved in both the coronal and sagittal plane and did not show any further progression. Patients whose lower end level of fusion was at T12 had a better percentage of lumbar curve correction than those that ended at L1. Conclusions. Selective thoracic fusion for King II idiopathic scoliosis curve can achieve acceptable coronal and sagittal plane balance of the spine. The rod to center sacral line distance is a helpful parameter in assessing the results and prognosis of surgically treated patients.