Background: The hallux valgus interphalangeus (HVI) deformity has a common association with hallux valgus and hallux rigidus. The HVI is formed by the angle between the long axes of the proximal and distal phalanges. The normal value for this angular deformity in the coronal plane is less than 10°. The aim of this study was to analyze the intra- and inter-observer reliability of measuring the interphalangeal angle by orthopaedic surgeons. This study is the first study to evaluate specifically the reliability and reproducibility of measuring the HVI angle.
Methods: Twenty-one X-ray prints of weightbearing feet constituted a set. Sixteen qualified orthopaedic surgeons were asked to measure the HVI angle of all 21 X-ray images in the set. Three randomized sets were sent to each evaluator at 4-week intervals. After all 3 sets were measured, data were retrieved and statistically analyzed to determine the inter- and intraobserver variability and reliability in the measurement of the HVI angle. Reproducibility of the HVI measurement was assessed using 3 categories, which included the ability to measure the same angle 3 times and achieve: 3° or less, 5° or less, and more than 5° variation.
Results: The intraobserver reliability was found to be 5° or less in 85.2% of participants and the interobserver reliability was 81.2%. The researcher did not find significant correlation between the surgeons' level of experience with regard to the reliability of measuring the HVI angle.
Conclusion: The inter- and intraobserver reliabilities of measuring the HVI angle is 81.2% and 85.2%, respectively. The level of experience of the surgeon does not improve this reliability.
Levels of evidence: Level II.
Keywords: bunions; complex foot and ankle conditions; diagnostic and therapeutic techniques; foot surgery techniques; forefoot; hallux abducto valgus; midfoot; reconstructive foot and ankle surgery; toe.