Reliability of measuring the passive range of shoulder horizontal adduction using a smartphone in the supine versus the side-lying position

[Purpose] The purpose of this study was to compare the reliability of the measurement of the passive range of motion (PROM) of shoulder horizontal adduction (SHA) measurements using a smartphone for the assessment posterior shoulder tightness (PST) between the side-lying and supine test positions. [Subjects and Methods] Forty-seven subjects (mean ± age, 24.9 ± 3.5 years) without shoulder pathology were included in this study. Intra-rater and inter-rater reliabilities were determined using intraclass correlation coefficients. The SHA PROM of each subject's dominant shoulder was measured using a smartphone by two investigators in two positions: the standard supine position, and a side-lying position on the tested side. [Results] The intra-rater reliability of the supine measurements was fair to good (ICC3,1 = 0.72-0.89), and for the side-lying measurements was excellent (ICC3,1 = 0.95-0.97). The inter-rater reliability of the supine measurements was fair (ICC2,2 = 0.79) and for the side-lying measurements was excellent (ICC2,2 = 0.94). [Conclusion] These results suggest that for healthy subjects, measurements of SHA using smartphones in the side-lying position has superior intra-rater and inter-rater reliabilities compared to the standard supine position.