A clinician-free method utilising top-view photograph for screening and monitoring hallux valgus

Background: Hallux valgus is a progressive foot deformity that commonly affect middle aged females. The aim of this study was to develop a novel method utilising only top-view photographs to assess hallux valgus severity.
Methods: Top-view digital photograph was taken on each foot of 70 female participants. Two straight lines were drawn along the medial edge of the great toe and the forefoot, and the included angle (termed ‘bunion angle’) was measured using a free software. Each foot was also assessed by a clinician using the Manchester scale as no (Grade 1), mild (Grade 2), moderate (Grade 3), or severe (Grade 4) deformity.
Results: The mean bunion angle of 140 feet was 6.7, 13.5, and 16.2 degrees for the first 3 Manchester grades (no foot was in Grade 4). The reliability was excellent for both intra-rater (intra-class correlation ICC = 0.93 to 0.95) and inter-rater assessments (ICC = 0.90). Receiver operating characteristics curve determined the optimal cut-off bunion angle value for screening hallux valgus to be 9 degrees, which gives 89.2% sensitivity and 74.2% specificity.
Conclusions: The ‘bunion angle’ is a reliable, clinician-free method that can potentially be implemented into smart phone app for easy and inexpensive self-assessment of hallux valgus.