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 chang es of the trunkal balance in King II curves treated with selective posterio r 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 analyz ing the changes in shoulder level, pelvic tilt, trunk shift, centering of f usion mass, changes in the T11-L1 sagittal angle, and behavior of the unfus ed 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 arres t of lumbar curve progression in selected cases. Detailed quantitative anal ysis of the longitudinal changes and correlation between various clinical a nd radiologic parameters was not readily available in the literature. Methods. This study investigated 24 patients with King II adolescent idiopa thic 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 preopera tive 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 c enter sacral line together with progressive leveling and stabilization of t he shoulder and pelvic tilt was noted during the first year after surgery. Gradual movement of the Harrington rod toward the center sacral line assumi ng 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 wit h no significant residual junctional kyphosis also was found. The unfused l umbar curve improved in both the coronal and sagittal plane and did not sho w any further progression. Patients whose lower end level of fusion was at T12 had a better percentage of lumbar curve correction than those that ende d at L1. Conclusions. Selective thoracic fusion for King II idiopathic scoliosis cur ve 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.