Inter-rater and inter-instrument reliability of goniometric thumb active and passive flexion range of motion measurements in healthy hands

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Abstract
Introduction: Goniometry is a common measure of range of motion and may be assessed by different therapists and goniometers. To date, there is limited psychometric data on active and passive range of motion measurements of individual thumb joints. The purpose of this study was to analyze inter-rater and inter-instrument reliability of passive and active flexion goniometric measures of thumb joints in healthy adults. Methods: A within-subjects psychometric design was utilized. Two raters each used two goniometers (Baseline™ Flexion-Hyper Extension and Baseline™ 180 Degree Digit) to measure each participant’s (n = 48) thumb carpometacarpal, metacarpophalangeal, and interphalangeal flexion range of motion. Inter-rater and inter-instrument reliability and stability were evaluated through use of intraclass correlation coefficient, standard error of the measurement, and minimal detectable change test statistics. Results: Inter-rater reliability was poor for carpometacarpal flexion and good-to-excellent for metacarpophalangeal and IP flexion. Between-rater error ranged between 3.9 and 6.3 degrees for active measurements and between 3.9 and 7.9 degrees for passive. Error was generally less when using the Baseline™ 180 Degree Digit goniometer. Inter-instrument reliability was excellent for all joints. Discussion: These findings validate the concerns that thumb goniometry inter-rater reliability may differ in clinical and non-clinical populations, support further study in clinical populations, and support a common assumption that the same rater should test the same client with the same goniometer to minimize measurement error. When compared to the Baseline™ Flexion-Hyper Extension Goniometer, the Baseline™ 180 Degree Digit had higher repeatability across raters. Further research on within-rater reliability is required as is study on clinical populations.

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