Validation of the Ankle Osteoarthritis Scale Instrument for Preoperative Evaluation of End-Stage Ankle Arthritis Patients Using Item Response Theory.

BACKGROUND:: Significant ankle arthritis results in functional limitations and patient morbidity. There is a need to measure symptoms and the impact of interventions on patient's quality of life using valid and reliable patient-reported measurement instruments. The objective of this research was to validate the Ankle Osteoarthritis Scale instrument in the preoperative setting using factor analysis, item response theory, and differential item function methods.

METHODS:: This research is based on secondary analysis of patients scheduled for ankle arthrodesis or total ankle replacement in Vancouver, Canada. Participants completed the instrument between September 2014 and August 2017. Item response theory was used to estimate item difficulty and discrimination parameters, controlling for study participants' underlying level of ankle function. Differential item function was examined for sex, age group, and surgery. There were 88 participants.

RESULTS:: Modification indices suggested that item 10, "walking around the house," would better fit the pain domain rather than the disability domain. Items in the pain domain displayed a range of discrimination and difficulty. Items in the disability domain exhibited a range of discrimination, though the disability domain had low difficulty. Differential item functioning for sex, age group, and ankle arthrodesis or total ankle replacement appeared to be ignorable.

CONCLUSION:: This evaluation of the Ankle Osteoarthritis Scale found the instrument to be a strong measure of the effect of pain and dysfunction among patients with end-stage ankle arthritis, even when removing items 7 and 8, supporting its prior use in numerous clinical studies.

LEVEL OF EVIDENCE:: Level II, prospective comparative study.