Cross-Cultural Adaptation, Reliability, Internal Consistency and Validation of the Spinal Function Sort (SFS) for French- and German-Speaking Patients with Back Complaints

Introduction Functional subjective evaluation through questionnaire is fundamental, but not often realized in patients with back complaints, lacking validated tools. The Spinal Function Sort (SFS) was only validated in English. We aimed to translate, adapt and validate the French (SFS-F) and German (SFS-G) versions of the SFS. Methods Three hundred and forty-four patients, experiencing various back complaints, were recruited in a French (n = 87) and a German-speaking (n = 257) center. Construct validity was estimated via correlations with SF-36 physical and mental scales, pain intensity and hospital anxiety and depression scales (HADS). Scale homogeneities were assessed by Cronbach’s α. Test–retest reliability was assessed on 65 additional patients using intraclass correlation (IC). Results For the French and German translations, respectively, α were 0.98 and 0.98; IC 0.98 (95% CI: [0.97; 1.00]) and 0.94 (0.90; 0.98). Correlations with physical functioning were 0.63 (0.48; 0.74) and 0.67 (0.59; 0.73); with physical summary 0.60 (0.44; 0.72) and 0.52 (0.43; 0.61); with pain −0.33 (−0.51; −0.13) and −0.51 (−0.60; −0.42); with mental health −0.08 (−0.29; 0.14) and 0.25 (0.13; 0.36); with mental summary 0.01 (−0.21; 0.23) and 0.28 (0.16; 0.39); with depression −0.26 (−0.45; −0.05) and −0.42 (−0.52; −0.32); with anxiety −0.17 (−0.37; −0.04) and −0.45 (−0.54; −0.35). Conclusions Reliability was excellent for both languages. Convergent validity was good with SF-36 physical scales, moderate with VAS pain. Divergent validity was low with SF-36 mental scales in both translated versions and with HADS for the SFS-F (moderate in SFS-G). Both versions seem to be valid and reliable for evaluating perceived functional capacity in patients with back complaints.