The Effects of Global Alignment and Proportionality Scores on Postoperative Outcomes After Adult Spinal Deformity Correction

BACKGROUND: Recent studies have suggested achieving global alignment and proportionality (GAP) alignment may influence mechanical complications after adult spinal deformity (ASD) surgery. OBJECTIVE: To investigate the association between the GAP score and mechanical complications after ASD surgery. METHODS: Patients with ASD with at least 5-level fusion to pelvis and minimum 2-year data were included. Multivariate analysis was used to find an association between proportioned (P), GAP-moderately disproportioned, and severely disproportioned (GAP-SD) states and mechanical complications (inclusive of proximal junctional kyphosis [PJK], proximal junctional failure [PJF], and implant-related complications [IC]). Severe sagittal deformity was defined by a “++” in the Scoliosis Research Society (SRS)-Schwab criteria for sagittal vertebral axis or pelvic incidence and lumbar lordosis. RESULTS: Two hundred ninety patients with ASD were included. Controlling for age, Charlson comorbidity index, invasiveness and baseline deformity, and multivariate analysis showed no association of GAP-moderately disproportioned patients with proximal junctional kyphosis, PJF, or IC, while GAP-SD patients showed association with IC (odds ratio [OR]: 1.7, [1.1-3.3]; P = .043). Aligning in GAP-relative pelvic version led to lower likelihood of all 3 mechanical complications (all P < .04). In patients with severe sagittal deformity, GAP-SD was predictive of IC (OR: 2.1, [1.1-4.7]; P = .047), and in patients 70 years and older, GAP-SD was also predictive of PJF development (OR: 2.5, [1.1-14.9]; P = .045), while improving in GAP led to lower likelihood of PJF (OR: 0.2, [0.02-0.8]; P = .023). CONCLUSION: Severely disproportioned in GAP is associated with development of any IC and junctional failure specifically in older patients and those with severe baseline deformity. Therefore, incorporation of patient-specific factors into realignment goals may better strengthen the utility of this novel tool.