Spinal imbalance, involving the sagittal and/or coronal planes, is an essential index to the severity of spine deformity[15, 16]. The increasing imbalance on the coronal plane in patients with degenerative lumbar scoliosis (DLS) has become one of main underlying factor that leads them to abnormal appearance, functional decline, and back pain. The distance between C7 plumb line (C7PL) and central sacral vertical line (CSVL), named coronal balance difference, coronal balance distance, global coronal malalignment, and C7 migration, has been used to reflect coronal alignment. In this current study, we defined the global coronal parameter as coronal balance distance (CBD). The latest study demonstrated the threshold of CBD was 30mm, after analyzing those related-variables involving the health-related quality of life (HRQOL), radiographic data, and complications in adult spinal deformity (ASD) patients.
In our study, the prevalence rate of coronal imbalance was 19.25% (31/161) by the criterion of 30mm. According to previous studies[8, 11], structure curve had no influence on coronal imbalance in ASD patients. Comparisons in this current study revealed that although the degree of the main curvatures of patients in the two groups had no difference, the involving vertebras were less in patients with coronal imbalance (group A) than those with coronal balance (group B)(t=2.639, P=0.009). Additionally, Line Chart shows the number of vertebras in the major curve decreases gradually with the mean value of CBD increasing. According to compensatory mechanism of spine, the more the involved vertebras and the rotation degrees of apical vertebra, the larger the degrees of the structural curvatures, which can keep the global spinal balance. Contrarily, spine would be imbalance if the compensatory mechanism were broken. Therefore, according to the results in our study we deduce that DLS patients, with similar major Cobb angle, but less vertebras and more rotation degrees of those apical vertebras, would be at greater risk for coronal imbalance because of spinal decompensation.
Lewis et al. proposed that the coronal tilt of L4 and L5 were larger in ASD patients with CBD over 40mm, and the correction of coronal tilt of L4 and L5 had the greatest impact on restoration of global coronal balance, further prospective study involving larger number of participants is needed to verify that although. What’s more, the threshold of CBD being as 30mm would be more reasonable. Bao et al. proposed that the horizontalization of L5 was the foundation of coronal spinal alignment, in terms of addressing lumbosacral fractional curve. A population of 161 patients with DLS were absorbed in our study. Comparisons of regional radiographic data between coronal balance and imbalance patients showed significant difference only in L4 coronal tilt. Pearson correlation analysis showed that there were significant relationship between CBD and coronal tilt of L4 and L5, and weak relationship with fractional curve, however, only L4 coronal tilt was an independent predictor for CBD after multiple regression analysis. In other words, reconstruction of L4 coronal tilt would restore effectively the coronal imbalance in DLS patients.
Additionally, considering correction of main curve during long-fusion surgery in ASD patients, Zhang et al.  suggested that there is significant correlation among pre-operative CBD, rectified Cobb angle of main curves, and post-operative CBD. Unfortunately, they did not explore the relationship between major curve and CBD further. The current study explore the relationships between major Cobb and those regional parameters involving L4/L5 coronal tilt, fractional curve, and coronal pelvic tilt, and the results showed significant relationship between each other. Moreover, L4 coronal tilt was independent predictor of major Cobb following stepwise multiple regression analysis. Therefore, the correction of L4 tilt would play the essential role on rectification of scoliosis and restoration of coronal balance for degenerative lumbar scoliosis patients.
Regarding to sagittal full-body balance in patients with spinal deformity, Ferrero et al.  illustrated the key role of pelvis. Then, pelvis should be one of compensatory factor in global coronal balance. The results of this study revealed moderate relationship between coronal pelvic tilt and regional radiographic variables involving coronal tilt of L4/L5, major Cobb, and fractional curve, however, there was no relationship between pelvic tilt and CBD. Moreover, comparisons between balance and imbalance patients showed no difference of coronal pelvic tilt. In other words, pelvis would play less compensation on global coronal balance.
The limitation of this study should be mentioned. Although the number of patients was sufficient in this study, when all patients were divided into two groups, the patients in coronal imbalance group were much less(31 patients), and these may lead to bias. Furthermore, exploring the relationship between coronal balance distance and clinical findings, this current study did not consider those functional scores such as SRS-22 and ODI, and did not explore the role of those regional parameters on reconstruction surgery. Despite those limitations, we insist that the results from this study can be as the foundation for those purpose.