The Reliability and Validity of DrGoniometer, a Smartphone Application for Measuring Elbow Flexion

This study evaluated the reliability and validity of the DrGoniometer smartphone application for measuring elbow flexion compared to the Universal Goniometer (UG). Fifty-six healthy participants were assessed by two physiotherapists, with anatomical landmarks marked by an independent examiner. Intra- and inter-rater reliability were calculated using intraclass correlation coefficients (ICC), and measurement error was assessed via the standard error of measurement (SEM) and Bland - Altman analysis. DrGoniometer showed excellent intra-rater reliability (ICC = 0.99; SEM = 0.69 degrees) and higher inter-rater reliability (ICC = 0.87; SEM = 1.28 degrees) than UG (ICC = 0.54; SEM = 3.87 degrees). Cronbach's alpha values were also higher for DrG (0.929) than UG (0.704). Although Bland - Altman plots indicated no systematic bias, they revealed wide limits of agreement, suggesting limited interchangeability between tools. These findings support the DrGoniometer as a reliable tool for elbow flexion assessment, especially in contexts requiring high intra-rater consistency and digital precision.