Frozen shoulder (FS) is a common disease which may cause restricted shoulder range of motion (ROM). Recently, studies have indicated that the smartphone goniometer apps could be reliable tools for shoulder ROM assessment. Nevertheless, patients with FS could not use most of these apps in normal measurement position due to shoulder capsular pattern. Hence, if we can design a new method in modified position to measure ROM with smartphones, it will be a helpful assessment for them. The purpose of this study was to investigate the reliability and validity of the smartphone goniometer app to measure shoulder ROM in modified position for healthy subjects.

Ten healthy subjects (5 male, 5 female; age=26.6±3.6 y/o) were recruited. Two physical therapists utilized the universal goniometer (UG) and ASUS Zenfone 4 smartphone with an accelerometer-based goniometer app to conduct various active shoulder ROM [flexion, abduction, external rotation (ER) and internal rotation (IR) at 0° abduction]. The smartphone was stabilized at the hand with an armband to reduce measurement errors. All measurements were taken for 3 times (2 measurements on the first day and 1 on the next day). Intraclass correlation coefficients (ICC) and Pearson's correlation coefficients (PCC) were used for statistical analysis. Significance level was set as α<0.05.

Both the UG and smartphone demonstrated high within-day and between-day reliability (ICC>0.800, P<0.001) except the flexion for which the ICC values was 0.622 (P=0.023, first day) and 0.787 (P=0.002, second day). The validity between the UG and the smartphone showed significant correlation (PCC>0.800, P<0.001) among all shoulder motions.

The smartphone goniometer app has good reliability and validity for shoulder ROM assessment in modified position, which indicates that the method is feasible to evaluate the restricted ROM for patients with FS.