Development of the patient-based outcome instrument for the foot and ankle. Part 1: project description and evaluation of the Outcome Instrument version 1.

BACKGROUND: The Clinical Outcomes Committee of the Japanese Society for Surgery of the Foot conducted a field survey using a novel foot and ankle outcome instrument. We report the development and evaluation of the Outcome Instrument version 1.

MATERIALS AND METHODS: A total of 108 potential questions were extracted from literature published in the interval between 1990 and 2006. Tentative subscales proposed were "Degree of Foot Pain," "Foot Pain-related," "Physical Functioning and Daily Living," "Social Functioning" and "General Health and Well-being." After pre-testing in two different groups of patients, the Outcome Instrument version 1, which was composed of 46 items selected from the 108 questions, was administered to 256 patients (111 men and 145 women) with foot-and-ankle-related pathologic conditions and 243 healthy volunteers (125 men and 118 women). Cronbach's alpha coefficients were used for assessment of internal consistency of the instrument. Exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) were utilized for evaluation of construct validity.

RESULTS: Neither a ceiling nor floor effect was observed in the responses from the patients. Significant differences were found in the responses to all of the questions between the patients and volunteers (P < 0.01 each). The Cronbach's alpha coefficients for each of the expected subscales indicated high reliability for most of the items and subscales. However, EFA extracted an additional subscale that should be interpreted as something related to shoe or shoe-fit. Further, both EFA and CFA indicated that "Degree of Foot Pain" and "Foot Pain-related" subscales were barely discernable with a factor correlation coefficient of 0.927.

CONCLUSIONS: The Committee partly revised the instrument, and the new subscales are as follows: "Foot Pain and Pain-related," "Physical Functioning and Daily Living," "Social Functioning," "General Health and Well-being" and "Shoe-related." Evaluation of the Outcome Instrument version 2 will be reported in the following paper.