Background: In clinical practice range of motion (RoM) is usually assessed with low-cost devices such as a tape measure (TM) or a digital inclinometer (DI). However, the intra- and inter-rater reliability of typical RoM tests differ, which impairs the evaluation of therapy progress. More objective and reliable kinematic data can be obtained with the inertial motion capture system (IMC) by Xsens. The aim of this study was to obtain the intra- and inter-rater reliability of the TM, DI and IMC methods in five RoM tests: modified Thomas test (DI), shoulder test modified after Janda (DI), retroflexion of the trunk modified after Janda (DI), lateral inclination (TM) and fingertip-to-floor test (TM).
Methods: Two raters executed the RoM tests (TM or DI) in a randomized order on 22 healthy individuals while, simultaneously, the IMC data (Xsens MVN) was collected. After 15 warm-up repetitions, each rater recorded five measurements.
Findings: Intra-rater reliabilities were (almost) perfect for tests in all three devices (ICCs 0.886-0.996). Inter-rater reliability was substantial to (almost) perfect in the DI (ICCs 0.71-0.87) and the IMC methods (ICCs 0.61-0.993) and (almost) perfect in the TM methods (ICCs 0.923-0.961). The measurement error (ME) for the tests measured in degree (°) was 0.9-3.3° for the DI methods and 0.5-1.2° for the IMC approaches. In the tests measured in centimeters the ME was 0.5-1.3cm for the TM methods and 0.6-2.7cm for the IMC methods. Pearson correlations between the results of the DI or the TM respectively with the IMC results were significant in all tests except for the shoulder test on the right body side (r = 0.41-0.81).
Interpretation: Measurement repetitions of either one or multiple trained raters can be considered reliable in all three devices.