Use of the iPhone for radiographic evaluation of hallux valgus

The purpose of this study was to compare the measurements made using a smartphone accelerometer and computerized measurements as a reference in a series of 32 hallux valgus patients.

Two observers used an iPhone to measure the hallux valgus angle (HVA), intermetatarsal angle (IMA), and distal metatarsal articular angle (of anteroposterior foot radiographs in 32 patients with symptomatic hallux valgus on a computer screen. Digital angular measurements on the computer were set as the reference standard for analysis and comparison. The difference between computerized measurements and all iPhone measurements, and the difference between the first and second iPhone measurements for each observer were calculated. Inter- and intraobserver reliability of the smartphone measurement method was also tested.

The variability of all measurements was similar for the iPhone and the computer-assisted techniques. The concordance between iPhone and computer-assisted angular measurements was excellent for the HVA, IMA, and DMAA. The maximum mean difference between the two techniques was 1.25 ± 1.02° for HVA, 0.92 ± 0.92° for IMA, and 1.10 ± 0.82° for DMAA. The interobserver reliability was excellent for HVA, IMA, and DMAA. The maximum mean difference between observers was 1.31 ± 0.89° for HVA, 0.90 ± 0.92° for IMA, and 0.78 ± 0.87° for DMAA. The intraobserver reliability was excellent for HVA, IMA, and DMAA.

We conclude that the Hallux Angles software for the iPhone can be used for measurement of hallux valgus angles in clinical practice and even for research purposes. It is an accurate and reproducible method.