GAP score potential in predicting post-operative spinal mechanical complications: a systematic review of the literature

Purpose: In 2017, the GAP score was proposed as a tool to reduce mechanical complications (MC) in adult spinal deformity (ASD) surgery: the reported MC rate for the GAP proportioned category was only 6%, which is clearly lower to the MC rate reported in the literature. The aim of this study is to analyse if the most recent literature confirms the promising results of the original article. Materials and methods: Using the PRISMA flow chart, we reviewed the literature to analyse GAP score capacity in predicting MC occurrence. We included articles clearly reporting ASD surgery MC stratified by GAP categories and the score's overall capacity to predict MC using the area under the curve (AUC). The quality of the included studies was evaluated using GRADE and MINORS systems. Results: Eleven retrospective articles (1,517 patients in total) were included. The MC distribution per GAP category was as follows: GAP-P, 32.8%; GAP-MD, 42.3%; GAP-SD, 55.4%. No statistically significant difference was observed between the different categories using the Kruskal-Wallis test (p = 0.08) and the two-by-two Pearson-Chi square test (P Vs MD, p = 0.300; P Vs SD, p = 0.275; MD Vs SD, p = 0.137). The global AUC was 0.68 ± 0.2 (moderate accuracy). The included studies were of poor quality according to the GRADE system and had a high risk of bias based on the MINORS criteria. Conclusion: The actual literature does not corroborate the excellent results reported by the original GAP score article. Further prospective studies, possibly stratified by type of MC and type of surgery, are necessary to validate this score.