Complications and Predictive Factors for the Successful Treatment of Flatback Deformity (Fixed Sagittal Imbalance)

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Abstract
This is an analysis of consecutive cases of flatback deformity (fixed sagittal imbalance), treated by one of two surgeons at a university hospital. To define factors that contribute to results with treatment of flatback syndrome, classify types of sagittal deformities, and discuss complications. There are few reports that detail the results and complications of current instrumentation and osteotomy techniques for correction of fixed sagittal deformities. Twenty-eight patients treated with osteotomies for sagittal imbalance were eligible for 2-year minimum follow-up (average, 3.6 years). Patients were classified (segmental imbalance, Type 1; or global imbalance, Type 2) and evaluated by upright radiographs, chart review, and a questionnaire. Twenty-eight (100%) patients returned the questionnaire, and 28 had current radiographs. Five treatment groups were evaluated based on osteotomy type (anterior, posterior [Smith–Petersen], both, or pedicle subtraction) and use of anterior structural grafting. All patients were treated with modern bilateral hook–rod–screw constructs. Mean correction at the osteotomy levels was 25° for Type 1 deformities and 30° for Type 2 (P < 0.05). Sagittal correction averaged 6.6 cm in Type 2 deformities (P < 0.05). Questionnaire analysis showed a significant and persistent reduction in subjective pain level. There were seven patients with 11 total complications and no neurologic deficits. Associations among patients who were not satisfied with their results (n = 4) included insufficient sagittal correction (P = 0.045), pseudarthrosis (P = 0.045), coronal imbalance, and four or more medical comorbidities (P = 0.03). Satisfaction with the results of treatment may be reduced in patients with four or more major coexistent medical problems, insufficient sagittal correction, and resultant pseudarthrosis.