External Validation of the Global Alignment and Proportion Score as Prognostic Tool for Corrective Surgery in Adult Spinal Deformity: A Systematic Review and Meta-Analysis

Abstract

Since its proposal, the Global Alignment and Proportion (GAP) score has been the topic of several external validation studies, which have yielded conflicting results. Given the lack of consensus regarding this prognostic tool, the authors aim to assess the accuracy of GAP scores for predicting mechanical complications following adult spinal deformity correction surgery. A systematic search was performed using PubMed, Embase, and Cochrane Library for the purpose of identifying all studies evaluating the GAP score as a predictive tool for mechanical complications. GAP scores were pooled using a random-effects model to compare patients reporting mechanical complications after surgery versus those reporting no complications. Where receiver operator curves were provided, the area under the curve (AUC) was pooled. A total of 15 studies featuring 2092 patients were selected for inclusion. Qualitative analysis using Newcastle-Ottawa criteria revealed moderate quality among all included studies (5.99/9). With respect to sex, the cohort was predominantly female (82%). The pooled mean age among all patients in the cohort was 58.55years, with a mean follow-up of 33.86months after surgery. Upon pooled analysis, we found that mechanical complications were associated with higher mean GAP scores, albeit minimal (mean difference=0.571 [ 95% confidence interval: 0.163-0.979]; P= 0.006, n= 864). Additionally, age (P= 0.136, n= 202), fusion levels (P= 0.207, n= 358), and body mass index (P= 0.616, n= 350) were unassociated with mechanical complications. Pooled AUC revealed poor discrimination overall (AUC=0.69; n= 1206). GAP scores may have a minimal-to-moderate predictive capability for mechanical complications associated with adult spinal deformity correction.