Virtual goniometric measurement of the forearm, wrist, and hand: A double-blind psychometric study of a digital goniometer.

Background: Various virtual goniometers have been used for photographic measurements. However, there is no single method that is both reliable and valid for measuring the forearm, wrist, and finger joints.

Purpose: This study aimed to investigate the criterion validity and intra- and inter-rater reliability of a virtual goniometer for assessing forearm, wrist, and finger joints using screenshots from video recordings and to calculate the standard error of measurement (SEM) and minimum detectable change (MDC).

Study design: This is a clinical measurement study.

Methods: Goniometric measurements were performed independently by two observers in 26 healthy participants (49 hands) using a virtual goniometer. Criterion validity was assessed by examining the agreement between virtual and manual goniometer measurements. Reliability was calculated using the intraclass correlation coefficient (ICC) to assess agreement between virtual and manual goniometers and interobserver agreement for virtual measurements. The difference between measurements was analyzed using the Student test and Bland-Altman plots. SEM and MDC were both used to determine the error associated with the measurements.

Results: Strong agreement between measurements (ICC = 0.69-0.98) and positive moderate to high correlation (r = 0.52-0.96; p < 0.001) were observed. Bland-Altman plots showed the agreement between the two measurement methods. Intra-rater (ICC = 0.80-0.99) and inter-rater reliability (ICC = 0.76-0.99) were high. SEM was low (2°-4°) and MDC ranged from 4°-12°.

Conclusions: The virtual goniometer proved to be a valid and reliable method for measuring joint angles from screenshots. The inter-rater and intra-rater reliability of the virtual goniometer was high. The average bias between the virtual and manual goniometer was small. Measurement errors were low for forearm, wrist, and hand movements, with the largest measurement errors observed for the second and third fingers.