The Reliability of Smartphone and Goniometric Measurements of Hip Range of Motion

Background: Range of motion is an essential component of the hip examination. Handling issues with the goniometer often create challenges when measuring hip passive range of motion (PROM). Recent generations of smartphones have emerged as an alternative instrument for the measurement of joint ROM. The purpose of this study was to investigate the intra-rater, inter-rater and interinstrument reliability of smartphone and goniometric hip PROM. Methods: Two investigators measured hip PROM to a designated end position on 30 asymptomatic participants in a blinded within study design using two measurement methods, smartphone and goniometer. Relative reliability of smartphone and goniometric measurements of hip PROM was assessed using intraclass correlation coefficients (ICC). Absolute reliability of both measurement methods was assessed using paired t-tests, standard errors of measurement (SEM), and 95% limits of agreement (LOA). Results: Relative reliability ICCs ranged from 0.47-0.99 (intra-rater), 0.05- 0.99 (inter-rater) and 0.25 -0.97 (inter-instrument). Inter-rater differences of smartphone hip measurements were non-significant, however, significant differences were found for all inter-rater goniometric hip measurements (P<0.02). The comparison of the smartphone to goniometric measurements showed bias was present in 7 out to 12 hip measurements (P<0.04). SEM ranged from 1° to 3° (intra-rater, inter-rater, and inter-instrument). LOA ranged from -6.8° - 5.1° (inter-rater) and -8.9° - 13.8° (inter-instrument). Conclusion: These findings support intra-rater reliability of both instruments when measuring hip PROM. Inter-rater reliability, however, was supported only for the smartphone. Due to systematic bias of inter-instrument measurements performed by one rater, caution should be used if the instruments are to be used interchangeably in order to quantify within session hip PROM.