Persian translation and validation of the Kujala Patellofemoral Scale in patients with patellofemoral pain syndrome

Purpose: To culturally translate and validate the Persian version of Kujala Patellofemoral Scale (KPS) and evaluate the test-retest reliability, internal consistency, construct validity and ceiling or floor effects of this instrument in patients with patellofemoral pain syndrome (PFPS). Method: After standard forward and backward translations, 100 patients with PFPS completed the Persian versions of the KPS and Short-Form 36 Health Survey (SF-36) in the first visit. With time interval of 2-3 days after the first visit, 47 patients filled out the KPS in the second visit. Test-retest reliability and internal consistency were assessed using intraclass correlation coefficient (ICC2,1) with 95% confidence interval (95% CI) and Cronbach's a coefficient, respectively. The Spearman's rank correlation (r(s)) was used to assess the correlations between the Persian KPS and SF-36 subscales. Results: The acceptable level of ICC >0.70 (ICC = 0.96, 95% CI = 0.93-0.98) and Cronbach's a coefficient >0.70 (alpha = 0.81) was obtained for the Persian KPS. There were low to moderate correlations (r(s) = 0.25-0.60, p < .01) between the Persian KPS and Persian SF-36 subscales of mental and physical health components. However, correlations between the Persian KPS and SF-36 physical components were higher than correlations between the Persian KPS and SF-36 mental components. No ceiling and floor effects were seen for the Persian KPS. Conclusions: The Persian version of KPS is a reliable and valid outcome measure of disability and seems to be a suitable instrument for use in clinical practice of Iranian patients with chronic PFPS.