Commentary on “Modified Global Alignment and Proportion Scoring With Body Mass Index and Bone Mineral Density Analysis in Global Alignment and Proportion Score of Each 3 Categories for Predicting Mechanical Complications After Adult Spinal Deformity Surgery”

Abstract

The authors have performed a retrospective review of 203 patients who underwent adult spinal deformity (ASD) surgery with minimum 2-year follow-up. 1 The authors have analyzed the global alignment and proportion (GAP) score, incorporating bone mineral density (BMD) and body mass index (BMI). The authors found that when incorporating BMI and BMI into the GAP score (GAPB), the GAPB score correlates with mechanical failure in patients when they are moderately or severe disproportioned in their alignment.I commend the authors for their work in incorporating BMI and BMD into the evaluation of mechanical failures in ASD surgery. This represents important work because Bari et al. 2 had reported that the GAP score alone-without the incorporation of BMI and BMDhas been unable to predict mechanical failure in ASD patients undergoing 4 or more levels of fusion. However, the original GAP score alone does not incorporate the BMI and BMD. Many mechanical failures can be related to poor bone quality because of the implant-bone junction interface failure. In our practice, all patient's bone densities are check prior to any fusion surgery, and by incorporating bone density into decision making, we have anecdotally seen fewer screw pull-out failures. Thus, it makes sense that the current authors' findings of incorporating BMD in the form of the GAPB score create a more accurate predictor of mechanical failure. In addition, the incorporation of BMI as a predictor makes sense. In patients with high BMI, the failure of mainly posterior-based constructs in the face of significant anterior trunk weight can potentially be predicted using the GAPB score instead of the GAP score. By incorporating BMI and BMD into the GAP score, the current authors have shown that incorporation of these 2 elements has made the GAP score more accurate by converting it into the GAPB score.The original GAP score takes into account age, pelvic incidence, sacral slope (SS), L4-S1