Translating and Validating a Hindi Version of the Spine Functional Index: Cross-cultural Adaptation and Psychometric Testing in an Indian Orthopedic Population.

Introduction: Existing Hindi patient-reported measures for spinal disorders assess the cervical and lumbar spine separately. The spine functional index (SFI) evaluates whole-spine functional limitation using 25 items, with validated Spanish, Turkish, and Chinese versions, but not Hindi. This study aimed to translate and culturally adapt the SFI into Hindi (SFI-Hi) and evaluate its measurement properties, including responsiveness and the minimal clinically important difference (MCID), in Indian patients with spinal disorders. Materials and Methods: The SFI was translated and culturally adapted using forward-backward translation, expert review, and pilot testing. One hundred eighty-six consecutive adults with chronic (≥12 weeks) cervical, lumbar, or combined spinal disorders completed the SFI-Hi, Hindi functional rating index (FRI-Hi), Hindi SF-12, and a pain visual analog scale (VAS); cervical patients also completed the Hindi neck disability index (NDI-Hi), and lumbar patients the Hindi Oswestry disability index (ODI-Hi). Ninety stable participants repeated the SFI-Hi after 5-7 days, and 92 treated patients were reassessed at 6 weeks for responsiveness and MCID. Internal consistency, test-retest reliability, measurement error, construct validity, principal component analysis (PCA), responsiveness, MCID, and floor/ceiling effects were assessed. Result: Mean SFI-Hi score was 49.0 ± 16.6 on a 0-100 disability scale. Internal consistency was high (Cronbach's α = 0.92), and test-retest reliability was excellent (ICC2,1 = 0.96, 95% CI 0.94-0.98), with a standard error of measurement of 2.8% and minimal detectable change of 6.5%. PCA identified a single dominant component explaining 35.0% of variance. Correlations were observed with the ODI-Hi (r = 0.64), FRI-Hi (r = 0.56), NDI-Hi (r = 0.53), VAS (r = 0.46), and SF-12 physical functioning (r = -0.54); only three of six prespecified hypotheses were confirmed. The SFI-Hi demonstrated good responsiveness (standardized response mean 0.84), with a 13.2-point improvement at 6 weeks (P < 0.001); the anchor-based MCID was 8 points (AUC 0.81). No clinically important floor or ceiling effect was observed. I was observed. Conclusion: The SFI-Hi demonstrated high internal consistency, excellent test-retest reliability, good responsiveness, and a predominantly unidimensional structure in this Indian cohort, with partial support for construct validity. It is a promising whole-spine outcome measure for Hindi-speaking patients, warranting further evaluation in larger, more diverse populations.