Cultural adaptation and validation of the knee injury and osteoarthritis outcome score into Sinhala language in patients with primary knee osteoarthritis: a cross-sectional study.

ABSTRACT

BACKGROUND: Knee Injury and Osteoarthritis Outcome Score (KOOS) scale is a patient-reported outcome measurement tool. It evaluates both short- and long-term consequences of knee injury and primary osteoarthritis. This study aims to translate and validate the KOOS scale for a Sinhala-speaking Sri Lankan population. METHODS: A cross sectional study was conducted in three hospitals. Four hundred and fifteen patients comprising 185 males and 227 females (3 subjects did not reveal their gender) with knee osteoarthritis (KOA) participated in the study. Seventy nine participants without KOA were recruited as controls. The functionality and quality of life level in patients and healthy participants were assessed using translated versions of the KOOS and Short Form-36 (SF-36) scales. Internal consistency of the instrument was assessed by Cronbach alpha. Construct validity and test-retest reliability were examined using the Intraclass Correlation Coefficient (ICC). Confirmatory Factor Analysis (CFA) was used to assess factorial validity. RESULTS: The mean age (± sd) of the KOA subjects was 54.9 (± 9.2) years and for the control group was 49.2 (± 8.0) years. Majority of the respondents were female and Sinhalese in both groups. Internal consistency reliability was high (Cronbach's alpha values ≥ 0.70). The test-retest reliability was excellent with the intraclass correlation coefficient for all subscales being above 0.90. Construct validity was assessed by the magnitude of the correlation coefficient between KOOS and SF-36 subscale scores. KOOS Pain scale moderately correlated with SF-36 bodily pain (Pearson's r = 0.41). SF-36 physical function scores had a weak positive correlation with all KOOS subscales and SF-36 emotional wellbeing was not significantly correlated with KOOS Quality of Life (QoL) subscale. A five-factor Confirmatory Factor Analysis (CFA) model yielded a Comparative Fit Index (CFI) = 0.950, Tucker Lewis Index (TLI) = 0.946, Root Mean Square Error of Approximation (RMSEA) = 0.082 and Standardised Root Mean squared Residual (SRMR) = 0.072. CONCLUSION: The Sinhala translation of the KOOS scale is a reliable and valid instrument to assess KOA in a Sinhala-speaking Sri Lankan population. Studies to assess its use as a scale to evaluate responsiveness are recommended.