Restoration of Lumbar Lordosis in Flat Back Deformity: Optimal Degree of Correction

STUDY DESIGN: A retrospective comparative study. PURPOSE: To provide an ideal correction angle of lumbar lordosis (LL) in degenerative flat back deformity. OVERVIEW OF LITERATURE: The degree of correction in degenerative flat back in relation to pelvic incidence (PI) remains controversial. METHODS: Forty-nine patients with flat back deformity who underwent corrective surgery were enrolled. Posterior-anterior-posterior sequential operation was performed. Mean age and mean follow-up period was 65.6 years and 24.2 months, respectively. We divided the patients into two groups based on immediate postoperative radiographs-optimal correction (OC) group (PI-9°≤LL<PI+9°) and under-correction (UC) group (LL<PI-9°). We also classified the patients according to the PI of each patient-low PI group (PI<55°) and high PI group (PI≥55°). Radiological and clinical results were analyzed. RESULTS: Patients in OC group had significantly less correction loss and maintained normal sagittal alignment (sagittal vertical axis<5 cm), as compared to patients in UC group (p<0.05). LL of low PI group significantly maintained within 9° better than high PI group (p<0.05). Oswestry disability index (ODI) significantly decreased at last follow-up, as compared to preoperative state. However, there was no significant difference in last follow-up ODI between the groups. CONCLUSIONS: In flat back deformity, correction of LL to within 9° of PI will result in better sagittal balance. Thus, we recommend sufficient LL to prevent correction loss, especially in patients with high PI.