Measurement of Lower Extremity Alignment Using a Smartphone Application

Identification of lower extremity misalignment requires radiation exposure and complex imaging. We developed and tested a smartphone application to facilitate quick identification of misalignment using photographs. Lower extremity alignment was measured by two independent researchers using a proprietary smartphone application and conventional radiographs. The results were compared between the methods and evaluators for interrater and intrarater reliability. Ninety datasets were obtained from 45 patients, with 90 lower extremity alignment angles measured via radiographs and the smartphone application. The intrarater reliability of the hip–knee–ankle angle (HKAA), measured twice by evaluator A using the radiographic imaging program, was 0.985, whereas that measured by evaluator B was 0.995. The intrarater reliability of the predicted lower extremity alignment angle (PLEAA) measured using the smartphone application was 0.970 and 0.968 for evaluators A and B, respectively. Thus, all results showed excellent reliability. In validity analysis, the correlation between PLEAA and HKAA measured twice by evaluators A and B was analyzed using Pearson’s correlation coefficient. HKAA (A) and PLEAA (A) had a positive correlation coefficient of 0.608 (<i>p</i> < 0.01), whereas HKAA (B) and PLEAA (B) had a positive correlation coefficient of 0.627 (<i>p</i> < 0.01). Thus, our smartphone application can facilitate for self-diagnosis of lower extremity misalignment.