Background: Hallux valgus is a progressive foot deformity that commonly affects middle-aged women. The aim of this study was to develop a novel method using only top-view photographs to assess hallux valgus severity.
Methods: A top-view digital photograph was taken of each foot of 70 female participants. Two straight lines were drawn along the medial edge of the great toe and forefoot, and the included angle (termed bunion angle) was measured using a free software program. 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 angles of the 140 feet were 6.7°, 13.5°, and 16.2° for Manchester grades 1, 2, and 3, respectively (no foot was in grade 4). The reliability was excellent for both intrarater (intraclass correlation coefficient [ICC] = 0.93-0.95) and interrater (ICC = 0.90) assessments. Receiver operating characteristic curves determined the optimal bunion angle cutoff value for screening hallux valgus to be 9°, which gives 89.2% sensitivity and 74.2% specificity.
Conclusions: The bunion angle is a reliable, clinician-free method that can potentially be integrated into a smartphone app for easy and inexpensive self-assessment of hallux valgus.