Abstract
Introduction
Regression analysis of adult spinal deformity (ASD) databases in North America (NA) has yielded radiographic disability thresholds for sagittal vertical axis (SVA), pelvic tilt (PT), and pelvic incidence to lumbar lordosis (PI–LL), which have been used in formulating the Schwab–SRS ASD classification. These thresholds are often used as correction goals for surgery planning, but it is unclear whether these thresholds vary in other geographic regions or ethnicities. This is the first comparison of radiographic disability thresholds between NA and Asian populations of ASD.
Patients and Methods
Retrospective, multicenter case series of 595 operative patients with ASD with baseline radiographs and Oswestry disability index (ODI) from 11 sites across USA (n = 402) and Japan (JPN, n = 193). Patients were compared at baseline in ODI, ODI need for improvement (ODIni, calculated from age/ethnic normative values), and radiographs. Linear regression was used to define thresholds for disability.
Results
Differences existed in mean age (USA 52.5 ± 22.5 years vs. JPN was 56.5 ± 15.4 years, p = 0.012) and revisions (USA 48% vs. JPN 2%, p < 0.001), but not gender (USA 85% women and JPN 80% women). At baseline, there were no differences in sagittal parameters except PI, which was significantly smaller in the JPN cohort. Linear regression revealed differences in radiographic parameters corresponding to ODI of 30 to 40. JPN had higher PI–LL and PT for ODI 30 and 40 but similar SVA thresholds. Significant differences existed in Schwab classification curve type (JPN with more double curves, p < 0.001) and PT (JPN with lower grade) but not in PI–LL modifier. JPN had a significantly lower ODI (USA 43.7 vs. JPN 36.2, p < 0.001), without a significant difference in ODIni.
Conclusion
At baseline, patients in both cohorts had a similar sagittal deformity but different morphology. Disability thresholds for SVA appear to be maintained across ethnicities but with differences in pelvic morphology (PI–LL and PT). The JPN cohort had significantly smaller PI and multiple coronal curves compared with the USA cohort. Despite similar sagittal malalignment, the JPN cohort had a significantly lower ODI without a significant difference in ODIni.