Development of the patient-based outcome instrument for foot and ankle: part 2: results from the second field survey: validity of the outcome instrument for the foot and ankle version 2

The Clinical Outcomes Committee of the Japanese Society for Surgery of the Foot (JSSF) has conducted the second Field Survey of the Outcome Instrument for the Foot and Ankle version 2. The survey of the Outcome Instrument version 2, which was composed of 43 items, was performed in 313 patients (154 men and 159 women) who had pathological conditions related to the foot and ankle. Optional sports items in the Outcome Instrument version 2 were analyzed in 123 patients. Internal consistency and construct validity of the Outcome Instrument version 2 were assessed. Correlation of the Outcome Instrument version 2 score with Short Form 36 (SF36) and JSSF scores was analyzed to evaluate criterion validity. Both the EFA and CFA demonstrated good alignment of questionnaire items with their intended subscales in most cases. Sports items were not clearly classified into subgroups. Therefore, it seemed reasonable to use those as a set of questions in a single subscale. The present subscales, having similar names as the SF36 subscales, were closely correlated with the respective subscales. In those cases, the magnitude of the correlation coefficient was > 0.6 (p < 0.001) except the present subscale called General Health and Well-being. Comparison of the present scores with JSSF evaluation scores showed satisfactory results except in patients with rheumatoid arthritis. The Outcome Instrument version 2 demonstrated acceptable psychometric performances as outcome measures for patients with pathological conditions related to the foot and ankle. This outcome instrument would be helpful to evaluate patients with foot and/or ankle impairment. However, the analyses of the test-retest reliability and the influence of background factors such as age and gender, etc., on Outcome Instrument version 2 are needed in the third field survey.