Effectiveness of preoperative planning in the restoration of balance and view in ankylosing spondylitis

Object. The object of this study was to assess the effectiveness of preoperative planning in the restoration of balance and view angle in patients treated with lumbar osteotomy in ankylosing spondylitis (AS). Methods. The authors prospectively analyzed 8 patients with a thoracolumbar kyphotic deformity due to AS that was treated using a closing wedge osteotomy (CWO) of the lumbar spine to correct sagittal imbalance and horizontal view. Preoperative planning to predict postoperative balance, defined by the sagittal vertical axis (SVA) and the sacral endplate angle (SEA), and the view angle, defined by the chin-brow to vertical angle (CBVA), was performed using the ASKyphoplan computational program. Results. All patients were treated with a CWO at level L-4 and improved in balance and view angle. The mean correction angle was 35 degrees (range 24-47 degrees). The postoperative SEA improved from 21 to 36 degrees for a mean correction of 15 degrees. In addition, the SVA and CBVA improved significantly. Note, however, that the postoperative results did not exactly reflect the predicted values of the analyzed parameters. Conclusions. Preoperative planning for the restoration of balance and view angle in AS improves understanding of the biomechanical and clinical effects of a correction osteotomy of the lumbar spine. The adaptation of basic clinical and biomechanical principles to restore balance is advised in such a way that the individual SEA is corrected by 15 (maximum 40) in relation to the horizon and C-7 is balanced exactly above the posterosuperior corner of the sacrum.