Reliability and Concurrent Validity of Smartphone Clinometer Application for Measuring Scapular Rotations in Subjects With and Without Shoulder Pain

Context: Clinical assessment of scapular motion is obscured by a lack of clinically accessible and feasible angular measurement tools. This study evaluates the reliability and validity of the smartphone "Clinometer" app in measuring scapular upward rotation (UR) and anteroposterior tilt. Design: Psychometric analysis. Methods: We recruited 57 participants-10 with and 47 without shoulder pain. Two physical therapists consecutively measured both scapular movements using the Clinometer app at the arm by the side (rest), 30 degrees, 60 degrees, 90 degrees, and 120 degrees of humeral elevation in the scapular plane; one therapist measured again after 2 days. For evaluating concurrent validity, we compared the Clinometer scores with those measured using an electromagnetic motion capture system in 10 healthy participants. Intraclass correlation coefficients (ICC) with standard error of measurement (SEM) and minimal detectable difference at 90% confidence intervals (MDD90) were calculated. Concurrent validity was evaluated using repeated-measures analysis of variance followed by post hoc testing with Tukey-Kramer test (P <.05). Results: We observed good intrarater reliability (ICC: UR =.76-.85, tilt =.69-.9; SEM: 2.2 degrees-3.5 degrees; MDD90: similar to 5 degrees-8 degrees) and moderate to good interrater reliability (ICC: UR =.66-.78, tilt =.66-.76; SEM: 3.6 degrees-8 degrees; MDD90: similar to 9 degrees- 18 degrees) for both rotations. The Clinometer scores for UR were comparable to electromagnetic motion capture system at all angles except 90 degrees (difference similar to 8 degrees); for scapular tilt, the scores were comparable only at rest and 30 degrees elevation. Conclusion: The Clinometer app is reliable and valid for measuring scapular UR throughout and for scapular tilt at lower humeral elevation angles. The MDD90 values for scapular rotations computed in this study can be helpful in rehabilitation planning and future research.