Usability evaluation of smartphone-based goniometer applications for shoulder range of motion

Range of motion (ROM) measurements are performed every day in clinical practice. The ROM is usually measured using conventional goniometers; however, studies have shown considerable variability in interrater and intrarater reliability. Despite the growing availability of smartphone-based goniometry, studies on the usability of these tools are highly limited. The aim of this study was to evaluate shoulder ROM applications (apps), with a focus on their usability and handling. Eleven apps were identified and tested by two physicians using the same smartphone. A healthy volunteer subject performed defined movements with each arm measured three times per app by both users. The apps were evaluated in terms of usability on a grading scale, with 1 representing the best result and 6 representing the worst result, on the basis of two key factors: intuitiveness and quality of description. The learning time of the physicians was also measured and recorded in minutes. The usability of the apps showed considerable variability. The usability is statistically correlated with the learning time of the raters (p = 0.021; τb = 0.607 for quality of description and p = 0.039; τb = 0.551 for intuitiveness). The quality of description and intuitiveness are significantly correlated with each other (p < 0.001; τb = 0.941). The interrater reliability was high, with an ICC of 0.88 for the quality of the description and 0.95 for intuitiveness, suggesting consistent evaluations between the raters. Two apps were rated as the best apps, with 1.0 and 1.25 in usability. Overall, there seems to be wide variation in the usability of smartphone-based apps. While smartphone-based goniometers show potential benefits, further research is required to establish their applicability before routine use.