Predictors of operative duration in posterior spinal fusion for adolescent idiopathic scoliosis: A retrospective cohort study

and CA was positive (P < 0.001).The correlation between SS and SVA was negative (P < 0.001).The correlation between CA and concave LMA at upper or lower intervertebral level of the apical vertebra was positive (P 0.001); convex LMA at upper or lower intervertebral level was negatively correlated with CA (P < 0.001).Convex LMA at upper intervertebral level and concave LMA at lower intervertebral level of the apical vertebra were negatively correlated with the SVA (P 0.001).FJOA works similar to LMA (P<0.05).At upper intervertebral level, LMA on the concave side was positively correlated with CVA (P ¼ 0.028); LMA on the convex side was negatively correlated with CVA (P ¼ 0.012).PI was positively correlated with ODI (P < 0.001); PT (P < 0.001) and SS (P < 0.001) were negatively correlated with ODI.At lower intervertebral level, LMA on the concave side was positively correlated with ODI (P ¼ 0.038); LMA on the convex side was negatively correlated with ODI (P ¼ 0.011).PI was positively correlated with JOA (P < 0.001); PT (P < 0.001) and SS (P < 0.001) were negatively correlated with JOA.Conclusions: The parallelogram effect includes two parts: the asymmetric effect in the coronal plane and the diagonal effect in the sagittal plane.Asymmetrical LMA can aggravate the coronal deformity via the asymmetric effect, which may influence the conduction of gravity in the coronal plane (Figure 1 a).LMAs with similar severity on the diagonal through apical vertebra can balance the stress and secure the conduction of gravity in the sagittal plane via the diagonal effect, which is very important to maintain sagittal balance (Figure 1 b).LMA at lower intervertebral levels of apical vertebra may have a predictive effect on ODI.JOA score seems to be more correlated with spinopelvic parameters than LMA.