The Spanish Version of the Functional Rating Index in Patients With Low Back Pain: Preliminary Results of the Validation Study

OBJECTIVE: To assess the reliability, validity, and the psychometric properties of the Spanish version of the Functional Rating Index (Sp-FRI) in a preliminary cohort of patients with low back pain (LBP). DESIGN: Prospective observational multicenter study. SETTING: Outpatient physical therapy clinics and units from public and private settings. PARTICIPANTS: Patients with LBP (N=22; 52.5±12.5y) entered the study. INTERVENTIONS: The translation and cross-cultural adaptation were performed following international guidelines through a 5-step procedure. MAIN OUTCOME MEASURES: The Sp-FRI was administered along with the Spanish version of Roland-Morris Disability Questionnaire (Sp-RMDQ) and numeric pain rating scale (NPRS) index. Preliminary testing included readability, comprehensibility, ceiling and floor effects, reliability, and validity. Statistical analysis was based on the Fernandez-Huerta index, and the calculation of Cronbach alpha, intraclass correlation coefficient (ICC), and Spearmanś correlation coefficient, respectively. All patients completed the Sp-FRI again after 1-2 days to assess its test-retest reliability. RESULTS: None of the participants requested clarification of any of the items at the time of completion. The test-retest reliability of the FRI score was substantial (ICC 0.77). Cronbach alpha was 0.859. Spearman correlation coefficient between Sp-FRI and Sp-RMDQ was 0.66; P<.0001, and between Sp-FRI and NPRS was 0.66; P<.0001. No ceiling or floor effects were detected. CONCLUSIONS: In light of these preliminary data, the Sp-FRI appears to be linguistically accurate and has been adapted to the Spanish-speaking population. It demonstrated reliability and validity and is suitable for clinical and research use among Spanish patients with LBP, with an acceptable degree of internal consistency and concurrent validity.