Reliability of sagittal vertical axis measurement and association with measures of age-related hyperkyphosis

[Purpose] Persons with age-related hyperkyphosis often have concomitant sagittal plane imbalance of the spine. This study investigated the reliability of sagittal vertical axis (SVA) measurement of sagittal balance, association between thoracic Cobb angle of kyphosis and SVA measure of sagittal balance, and compared the degree of SVA in males and females with age-related hyperkyphosis. [Participants and Methods] Measurements of SVA and Cobb angle of kyphosis were obtained from baseline radiographs of 112 community-dwelling males and females, mean age 70.0 (SD=5.7) years with kyphosis ≥40 degrees, recruited for a randomized controlled trial. Spearman correlation coefficients were used to determine associations between SVA and kyphosis, and Wilcoxon nonparametric tests to compare SVA between genders. [Results] SVA was acquired with excellent intra-rater [0.95 (95% CI: 0.88, 0.98)] and inter-rater reliability [0.93 (95% CI: 0.83,0.97)]. There was no significant correlation between Cobb angle of thoracic kyphosis and SVA, (r=-0.05). More males than females had sagittal imbalance (SVA≥5 cm). [Conclusion] In older adults with hyperkyphosis, SVA was a reliable measure of sagittal balance, and more extreme in males. SVA was not associated with Cobb angle of thoracic kyphosis, and could be considered an independent phenotype of age-related hyperkyphosis to be targeted in future intervention trials.