Intra operative assessment of the coronal balance in spinal deformity surgery : a technical note and retrospective study

Obtaining a spine that is well balanced after fusion for scoliotic deformity is primordial for the patients' quality of life. A simple T-shaped instrument combined with standard intraoperative fluoroscopy can be of great help to evaluate the coronal alignment quickly. The aim of this study was to evaluate if a T-shaped device could predict the postoperative coronal balance. Before finalization of the rod fixation, the balance was checked by verifying the relationship between the T-shaped instrument and the upper instrumented vertebra (UIV), and final adjustments were made to correct the coronal balance. A retrospective study was conducted on 48 patients who underwent surgery to correct scoliotic deformity. Intraoperative and postoperative coronal alignment was measured independently by two observers. The mean intraoperative horizontal offset measured between T-shaped instrument and the center of the UIV was 1,69mm to the right with a standard deviation (SD) of 12,43 mm. On postoperative full spine radiographs, the mean offset between the centra sacral vertical line and the center of the UIV was 2,44mm to the left with a SD of 13,10mm. There is no significant difference in corona' balance between both measurements (p=0,12). With this technique we were able to predict the postoperative coronal balance in all but one patient (97,92%). We conclude that the use of a simple T-shaped instrument can provide adequate intraoperative assessment of coronal balance in correcting scoliotic deformity.