Dynamic sagittal imbalance of the spine in degenerative flat back - Significance of pelvic tilt in surgical treatment

Study Design. A retrospective study of 26 patients with degenerative flat b ack treated with corrective osteotomy. Objective. To analyze dynamic sagittal imbalance and to elucidate the cause of postoperative persistent stooping in degenerative flat back. Summary of Background Data. Sagittal spinal imbalance in degenerative flat back was more evident on walking, suggesting its dynamic nature. The most p uzzling complication in its surgical treatment was postoperative persistent stooping. Methods. This study analyzed 26 surgically treated patients with preoperati ve gait analysis. Patients were divided into two groups according to postop erative improvement in stooping: Group 1 with marked improvement in stoopin g and Group 2 with persistent stooping. Various radiographic and gait param eters were compared between the two groups. Results. Comparison of radiographic parameters, representing the static sta tus of the spine, did not indicate any clue to the mechanism for persistent stooping. However, comparison of gait parameters, representing the dynamic status of the spine, revealed meaningful differences between the two group s. Among various gait parameters compared, pelvic tilt seemed to be the mos t important clue. Patients in Group 1 showed posterior pelvic tilt, whereas those in Group 2 showed marked anterior pelvic tilt. Conclusion. Degenerative flat back could be classified into two types based on pelvic position during walking: one with posterior pelvic tilt and the other with marked anterior pelvic tilt. In the former type, corrective surg ery improved the stooping. In the latter, corrective surgery was ineffectiv e, resulting in postoperative persistent stooping.