Negative Sagittal Balance Following Adult Spinal Deformity Surgery

Study Design: Retrospective cohort study. Objective: Elucidate negative sagittal balance following adult spinal deformity surgery. Methods: We conducted a retrospective review of adult spinal deformity patients who underwent long fusion (>5 levels) to the sacrum by a single surgeon at a single institution between 2011 and 2015. Patients were divided into cohorts of postoperative sagittal vertical axis (SVA) <−10 mm, between −10 and +10 mm, or >+10 mm, denoted as groups 1, 2, and 3, respectively. Univariate analysis compared preoperative factors between the groups, and a multivariable logistic regression model was used to determine independent risk factors for developing a negative sagittal balance (SVA<−10 mm) following adult spinal deformity correction. Results: We reviewed 8 patients in group 1, 9 patients in group 2, and 25 patients in group 3. The average postoperative SVA for group 1, group 2, and group 3 were −30.99, +3.67, and +55.56 mm, respectively. There was a trend toward higher upper-instrumented vertebra (UIV) in group 1 (T2) compared with group 2 (T10) and group 3 (T9) (P =.05). A trend toward lower preoperative SVA in groups 1 and 2 compared with group 3 was also seen (+53.36 vs +71.73 vs +122.80 mm) (P =.06). Finally, we found a trend toward lower body mass index in group 1 compared with groups 2 and 3 (24.71 vs 25.92 vs 29.33 kg/m²) (P =.07). Based on multivariable regression, higher UIV was found to be a statistically significant independent predictor for developing a postoperative negative sagittal balance of <−10 mm (P =.02, odds ratio = 0.67). Conclusions: Our results demonstrate that a higher UIV may predispose patients undergoing adult spinal deformity correction to have a postoperative negative sagittal balance.