Structural validation of the Manchester-Oxford Foot Questionnaire (MOxFQ) for use in foot and ankle surgery

R. Goodall, K. Borsky, C. Harrison, M. Welck, K. Malhotra, J. Rodrigues

Background: The Manchester-Oxford Foot Questionnaire (MOxFQ) is a condition specific patient reported outcome measure (PROM) for foot and ankle surgery. It consists of 16 items across three subscales measuring distinct, but related traits: walking/standing ability, pain, and social interaction. Although it is the most used foot and ankle PROM in the UK, initial MOxFQ validation involved analysis of only 100 individuals undergoing hallux valgus surgery. This project aimed to establish whether an individual’s response to the MOxFQ varies with anatomical region of disease (measurement invariance), and to explore structural validity of the factor structure (subscale items) of the MOxFQ.

Methods: This was a single-centre, prospective cohort study involving 6640 patients (mean age 52, range 10-90 years) presenting with a wide range of foot and ankle pathologies between 2013 and 2021. Firstly, to assess whether the MOxFQ responses vary by anatomical region of foot and ankle disease, we performed multi-group confirmatory factor analysis. Secondly, to assess the structural validity of the subscale items, exploratory and confirmatory factor analyses were performed.

Results: Measurement invariance by pathology was confirmed suggesting the same model can be used across all foot and ankle anatomical regions. Exploratory factor analysis demonstrated a 2-3 factor model, and suggested that item 13 (inability to carry out my work/everyday activities) and item 14 (inability to undertake social/recreational activities) loaded more positively onto the walking/standing subscale than their original social interaction subscale.

Conclusions: This large-cohort study supports the current widespread use of the MOxFQ across a broad range of foot and ankle pathologies. Items 13 and 14 might be better moved from the “social interaction” to the “walking/standing” subscale and this may have future implications for deriving/analysing subscale scores.