Validity and Reliability of the American Orthopaedic Foot and Ankle Society Score for the English-Literate Singapore Population With Hallux Valgus.

Background: This study aimed to evaluate the reliability and validity of the American Orthopaedic Foot and Ankle Society Metatarsophalangeal-Interphalangeal (AOFAS MTP-IP) score in patients with hallux valgus in Singapore.

Method: A total of 121 English-literate patients with hallux valgus identified between October 2017 and May 2020 were analyzed. Reliability was assessed via Cronbach α. Construct validity was evaluated through 20 a priori hypotheses by correlating the AOFAS MTP-IP score for hallux and lesser toes with other patient-reported outcome measures (PROMs). Standardized response means (SRMs) were calculated to evaluate responsiveness at 6 months postoperative. Structural validity was evaluated via confirmatory factor analysis (CFA) whereby a good fit was indicated when comparative fit index (CFI) is >0.95, Tucker-Lewis index (TLI) is >0.95 and standardized root mean residual (SRMR) is <0.08.

Results: The AOFAS MTP-IP score demonstrated reliability with a Cronbach α of 0.837. Convergent construct validity was confirmed when all a priori hypotheses were fulfilled. Structural validity was established with our AOFAS MTP-IP score model that displayed good fit for a 1-factor structure (CFI = 0.988, TLI = 0.960, SRMR = 0.034). Responsiveness of the AOFAS MTP-IP score for hallux was demonstrated by an SRM score of 1.28.

Conclusion: The AOFAS MTP-IP score displayed adequate reliability and validity among English-literate patients in Singapore with an operatively managed hallux valgus.

Level of evidence: Level III: Retrospective cohort study.