Abstract
BACKGROUND: Several patient reported outcome measures (PROMs) are available for assessing the outcomes of ankle fracture but few have been compared for recommended measurement properties. This study compares the measurement properties of the Lower Extremity Function Scale (LEFS), Olerud Molander Ankle Score (OMAS) and Self-Reported Foot and Ankle Score (SEFAS) following ankle surgery. METHODS: The retrospective cohort study included 959 patients aged 18 years and over who underwent surgical treatment (ORIF) for unstable and closed ankle fractures in SE Norway. The PROMs were included in a postal questionnaire sent to patients' homes in 2015, three years after surgery. Missing data, structural validity, internal consistency, test-retest reliability and validity were assessed. RESULTS: Confirmatory factor analysis results showed model fit for the SEFAS and a bi-dimensional LEFS with scales of easy and difficult items. The OMAS performed less satisfactorily. Cronbach's alpha and test-retest correlations ranged from 0.82 to 0.96 and 0.91 to 0.93 respectively. The smallest detectable differences for group and individual comparisons were 14.1 to 20.6 and 0.93 to 1.55; SEFAS performed best. As hypothesised, instrument scores were highly correlated and with those for the EQ-5D and SF-36 physical functioning. Mean imputation where half or more items are completed increased usable scores by 1.4-15.7% without affecting measurement properties. CONCLUSIONS: The three instruments largely performed satisfactorily in relation to important measurement properties but the LEFS had evidence for two dimensions relating to easier and more difficult aspects of function. Mean imputation where half or more items are completed increased the number of usable responses for all three instruments. The three instruments represent different approaches to measuring outcomes and their content should be considered carefully when choosing between them. The SEFAS is designed for a range of foot disorders including ankle fractures and has the best measurement properties in this population.