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 back 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 puzzling complication in its surgical treatment was postoperative persistent stooping.
METHODS: This study analyzed 26 surgically treated patients with preoperative gait analysis. Patients were divided into two groups according to postoperative improvement in stooping: Group 1 with marked improvement in stooping and Group 2 with persistent stooping. Various radiographic and gait parameters were compared between the two groups.
RESULTS: Comparison of radiographic parameters, representing the static status 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 groups. Among various gait parameters compared, pelvic tilt seemed to be the most 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 surgery improved the stooping. In the latter, corrective surgery was ineffective, resulting in postoperative persistent stooping.