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Impact of Ethnicity on Adult Spinal Deformity Surgical Outcomes: An Analysis of Japanese and North American Databases

Introduction Adult spinal deformity (ASD) research and treatment has continued to evolve and grow globally. International studies are now frequently presented at the SRS, but surgeons are unsure of the data comparisons and global relevance of conclusions across ethnicities. We compared HRQOL and radiographs between two countries (United States and Japan) to help define the effect of geographic variation. Materials and Methods Retrospective, multicenter case series of 337 operative patients with ASD with baseline radiographs and ODI from 11 sites across USA ( n = 235) and Japan (JPN, n = 102). Patients were compared preoperatively and postoperatively in ODI, ODI need for improvement (ODIni, using age/ethnic normative values), and radiographs. Regression was used to define thresholds for disability: USA ODI 41.9, JPN ODI 33.7. Results Differences in age (USA 55 years, JPN 65 years, p < 0.001) and primary cases (USA 59%, JPN 98%, p < 0.001) existed at baseline (BL), but not gender (USA 84%, JPN 84%). BL ODIni was significantly higher in JPN, without a difference in BL ODI. JPN was significantly more deformed at BL (Table). At 2-year follow-up, both cohorts improved significantly (p < 0.05), however, JPN had significantly higher ODIni without a difference in 2-year ODI (Table). Both cohorts improved significantly radiographically (p < 0.05); however, JPN was more malaligned (Table). Applying thresholds of deformity, 46% United States (n = 54) were disabled compared with 60% JPN (n = 36; p = 0.014). Conclusion Despite having a greater deformity at BL, there were no significant differences in BL ODI. Although both the groups improved in ODI and alignment, JPN cohort still had higher offset from the normative age-/ethnicity-matched values and more spino-pelvic malalignment at 2 years—for the same ODI, JPN patients may be masking a greater disability than represented by the score. When population-specific thresholds of disability were applied, JPN patients had a large percentage over the threshold, revealing that 60% were still with lower scores at 2 years. The ethnicity of a patient should be considered when interpreting ODI and comparing surgical outcomes for ASD using standard metrics.