Effects of pedicle subtraction osteotomy on spino-pelvic parameters of ankylosing spondylitis

Abstract

Pedicle subtraction osteotomy (PSO) is a spinal realignment technique of correcting the sagittal spinal imbalance. Theoretically, the level and degree of resection via a PSO should impact the degree of sagittal correction. However, the quantitative effect of PSO level and focal angular change on postoperative spino-pelvic parameters has not been fully elucidated. The purpose of this study was to analyze the relationship between the level/degree of PSO and changes in global sagittal balance and spino-pelvic parameters. Retrospective analysis was conducted for 34 patients undergoing PSO surgery for ankylosing spondylitis. Preoperative and postoperative free-standing sagittal radiographs were obtained and analyzed by regional curves (lumbar lordosis, thoracic kyphosis), pelvic parameters of pelvic tilt (PT), pelvic incidence (PI) and sacral slope (SS) and global balance of sagittal vertical axis (SVA). And the correlations between PSO parameters (level and degree) and spino-pelvic parameters were analyzed. There were significant changes in spino-pelvic parameters including decreased thoracic kyphosis, increased lumbar lordosis, decreased SVA, decreased PT and increased SS. The decreased SVA were 3.94 ± 3.38 and 3.97 ± 1.91 in lumbar/thoracic osteotomy respectively (P > 0.05). The decreased values of PT were 9.71 ± 6.46 and 5.20 ± 2.74 respectively (P < 0.05). Larger degree of osteotomy (≥ 22°) had greater SVA and PT decreases (P < 0.05). PSO is a quite useful technique of restoring spinal alignment. Lumbar and larger degrees of osteotomy have greater effects on spino-pelvic parameters.