Validation of the Persian version of Functional Index Questionnaire (FIQ) and Modified FIQ in patients with patellofemoral pain syndrome

Abstract

The aim of this investigation was to culturally translate and validate the Functional Index Questionnaire (FIQ) and Modified FIQ (MFIQ) in patients with patellofemoral pain syndrome (PFPS). A sample of 100 patients with PFPS completed the FIQ and MFIQ, and Short-Form 36 (SF-36) Health Survey in the first session. The FIQ and MFIQ were re-administered to a sample of 47 patients to evaluate test–retest reliability. Test–retest reliability and internal consistency were evaluated by the intraclass correlation coefficient (ICC) and Cronbach's alpha coefficient, respectively. Corrected item-total correlations and construct validity were assessed by Spearman's rank correlation. Factor analysis was performed on all items of the Persian FIQ and MFIQ to determine the number of underlying factors and the items which load on each factor. An acceptable level of test–retest reliability (ICC = 0.84, 0.85) and internal consistency (Cronbach's alpha = 0.79, 0.82) was obtained for both the Persian FIQ and MFIQ, respectively. Item-total correlations were greater than 0.40 for all but two questions of the Persian FIQ and all but four questions of the Persian MFIQ. A total of two factors were detected for each questionnaire. There were moderate to low correlations between the Persian FIQ/MFIQ and SF-36. Persian FIQ and MFIQ are two reliable and valid outcome measures of functional limitation and it seems that they are suitable for use in clinical practice of patients with chronic PFPS.