ANTERIOR SPINAL CORRECTION FOR SCOLIOSIS WITH AO UNIVERSAL SPINE SYSTEM: MAINTENANCE OF CORONAL AND SAGITI’AL BALANCE

Introduction: Historically, anterior spinal surgery for scoliosis has led to better coronal correction, though at the expense of sagittal alignment specifically at the thoracolumbar junction. The purpose of the study was to ascertain the effectiveness in maintenance of coronal and sagittal balance of anterior spinal surgery and instrumentation for AIS. Methods: 17 patients with idiopathic scoliosis treated with anterior spinal fusion using a single rod AO USS construct were reviewed in a retrospective fashion. Inclusion in study group required a minimum two years follow-up with complete radiographic and clinical follow up. Results: There were 14 lumbar curves of which seven were King I and seven thoracolumbar / lumbar curves. Seven patients had supplemental structural anterior support in the lumbar spine. Four had femoral allograft rings and three had cages (2 Harms, 1 Synex cages). Three thoracic curves were operated on of which two were King III, and one King II. The mean pre-operative Cobb angle was corrected from 48° to 14° post-op and 16° on the last follow-up (24 to 53 months) representing 71% of correction. Apical vertebral translation was corrected to 70%, comparable to the 60% correction of trunk shift at last follow-up. Sagittal contour of instrumented segment for the thoracic curve did not change. The pre-operative sagittal contour across the instrumented levels for the 14 1umbar was 5.6° of lordosis which changed to 0.5° of lordosis post-operatively. At last follow-up it was 2° of kyphosis. Specifically there were 7 of 14 that had greater that 10° of surgically induced kyphosis across the fusion mass. At last follow-up three patients had further kyphosis across the instrumented levels. The overall sagittal vertical axis did not change irrespective of the focal sagittal alignment. There was a net increase in lumbar lordosis below the fusion mass. Three patients had asymptomatic pseudoarthroses. There was no failure of instrumentation and no patient required further surgery. Conclusion: The authors conclude that single rod anterior spinal instrumentation for AIS is effective in maintaining coronal and sagittal alignment though one needs to pay particular attention to sagittal contour. The increase in lumbar lordosis below the fusion may well explain the maintained sagittal balance.