American Orthopedic Foot and Ankle Society Hallux Metatarsophalangeal-Interphalangeal Joint Scale: A Cross-Cultural Adaptation and Validation Study in the Persian Language

Abstract

We evaluated the reliability and validity of the Persian translation of the American Orthopedic Foot and Ankle Society hallux metatarsophalangeal-interphalangeal joint scale (AOFAS Hallux MTP-IP). The translated AOFAS Hallux MTP-IP scale form was completed for 101 patients with hallux deformities; the subjective questions were answered by the patients, whereas the orthopedic foot and ankle surgeon and his assistant answered the objective questions. The validated Persian version of the 36-Item Short Form Survey Instrument (SF-36) was used for validity assessment. Eighty-five females and 16 males with a mean age of 49 years were enrolled. Hallux valgus and hallux rigidus was the diagnosis in 73 and 28 patients, respectively. Intrarater reliability had a high level of correlation (rho >0.6) for all subscales and total score. Although the correlation between the total score of the AOFAS Hallux MTP-IP scale and role: physical subscale of SF-36 was the highest (rho = 0.47), the total score of AOFAS Hallux MTP-IP scale and the other 7 domains of SF-36 had a correlation ranging between –0.17 and 0.43. Moreover, the correlation between total score of AOFAS-Hallux MTP-IP and SF-36 physical component summary scale was 0.50, which was higher than the correlation between total score of AOFAS and SF-36 mental component summary scale (rho = 0.35). Convergent validity was approved for MTP joint motion (0.59), IP joint motion (0.51), and callus (0.56) items of AOFAS-Hallux MTP-IP. Spearman's rank correlation coefficient between all items of the functional subscale of AOFAS Hallux MTP-IP scale with its own subscales was higher than the coefficient between these items and other subscales, including pain and alignment (discriminate validity). Floor and ceiling effects were calculated as 2% and 1%, respectively. Our findings indicate that the translated Persian version of the AOFAS Hallux MTP-IP scale is a reliable instrument, but its validity is not satisfactory.