Background: Radiographs of the feet are the reference standard for measuring the hallux valgus angle. However, the availability and use of radiographs are constrained due to cost and radiation exposure. Less invasive, nonradiographic assessments have been proposed, although measurement using self-photography has not been reported.
Objectives: To determine (1) reliability of photographic hallux valgus angle (pHVA) measurement using the same photographs of the feet, (2) reliability of repeated self-photography trials, and (3) measurement error when the radiographic hallux valgus angle (rHVA) is estimated using the pHVA.
Methods: In this reliability study, participants took photographs of their own feet using a digital camera. The intrarater and interrater reliability of pHVA measurements were then assessed using the intraclass correlation coefficient (ICC) and 95% minimum detectable change (MDC). The participants took photographs twice, and the reliability of repeated self-photography trials was examined. Participants also received radiographs of their feet, from which the rHVA was measured. The measurement error was assessed using the mean difference and 95% limits of agreement.
Results: The intrarater and interrater ICC of pHVA measurement was 0.99, with MDCs less than 2°. The ICC of pHVA measurement for repeated self-photography was 0.96, and the MDC was 6.9°. The pHVA was systematically lower than the rHVA, by 5.3°.
Conclusion: Measurement of the pHVA using self-photography was reproducible, although pHVA measurement underestimated the rHVA. The pHVA can be a useful nonradiographic method to quantify hallux valgus deformity. J Orthop Sports Phys Ther 2019;49(2):80-86. Epub 12 Sep 2018. doi: 10.2519/jospt.2019.8280.
Keywords: clinical measurement; digital camera; foot; hallux valgus; radiology; self-photography.