Spinopelvic parameters in postfusion flatback deformity patients

Abstract

Background context Fixed sagittal imbalance (FSI) may result from loss of adequate lumbar lordosis (LL) after spinal fusion. Pelvic incidence (PI) is a fixed anatomical parameter that determines LL and overall spinal sagittal alignment. Purpose We describe the spinopelvic parameters in a series of patients with postfusion FSI. We hypothesize that patients who develop postfusion FSI may have a high PI and are thus more at risk from a loss of adequate LL. Study design Retrospective chart and image review. Patient sample Consecutive patients with degenerative spine disease with clinically significant postoperative FSI after fusion. Methods/outcome measures We evaluated 36-in full spine films for PI, LL, pelvic tilt (PT), thoracic kyphosis (TK), and C7 plumb line. Results Fifteen patients with clinically significant FSI were identified: 13 women and 2 men (mean age, 63.3 years). They had undergone a mean of 2.9 prior spine surgeries. The mean PI was elevated at 66.7° (normal 48–55°), mean PT was elevated at 35.5° (normal 12–18°), mean LL was reduced at 11.8° (normal 43–61°), mean TK was reduced at 19.3° (normal 41–48°), and mean C7 plumb line was elevated at 13.1 cm (normal <3 cm). Conclusions In the current series, patients with FSI after spinal fusion had an elevated PI and inadequate LL. They attempted to compensate for FSI with reduced TK and with increased pelvic retroversion (PT). Overall, it is important to identify sagittal spinopelvic parameters and promote sagittal balance when performing lumbar fusions.