The Reliability and Validity of Active Range of Motion Measurement for Fingers Using Three-Dimensional Motion Analysis

The Fugl–Meyer Assessment (FMA) and Range of Motion (ROM) are well-known measures for evaluating finger motor function. However, the finger FMA has a narrow scoring range, and goniometer ROM measurements lack reliability. Therefore, we investigated ROM measurement using a 3D motion capture system (Ultraleap Stereo IR 170, Ultraleap Ltd., Bristol, UK, hereinafter referred to as Ultraleap). This study aimed to evaluate the intra- and inter-rater reliability of finger Active ROM (A-ROM) using Ultraleap, and its criterion-related validity compared to a goniometer, in stroke patients with upper limb hemiplegia. A-ROM was evaluated over a 3-day period. For Ultraleap reliability, flexion intraclass correlation coefficients (ICCs) showed variability (intra-rater: 0.576–0.896; inter-rater: 0.426–0.841), whereas extension ICCs were ≥0.81 for all joints except the thumb interphalangeal (IP) joint. Regarding criterion-related validity, correlation coefficients ranged from −0.0706 to 0.493 for flexion, and 0.698 to 0.814 for extension (excluding the thumb IP joint). Ultraleap extension measurements demonstrated acceptable-to-high reliability and moderate-to-strong correlations with manual goniometry in most joints, except for the thumb IP joint. However, Bland–Altman analyses revealed systematic and proportional biases, indicating limited agreement for absolute ROM values. While the system cannot be directly interchangeable with manual goniometry for absolute ROM assessment, it may serve as an efficient supplementary tool for repeated measurements of finger extension in clinical settings.