Investigation of intra-rater reliability and measurement error of ultrasonographic measurements of finger flexor muscle thickness in individuals with chronic ischemic stroke

Ultrasonography is a practical, non-invasive method for assessing skeletal muscle morphology after stroke. Reliable measurement of finger flexor muscle thickness is essential for monitoring structural muscle changes associated with chronic spastic paresis and rehabilitation. This study investigated the intra-rater reliability, measurement error, and agreement of ultrasonographic measurements of the flexor digitorum superficialis and flexor digitorum profundus in individuals with chronic ischemic stroke. Twenty-four individuals with chronic ischemic stroke underwent two ultrasound examinations of finger flexor muscles performed by the same examiner 24 h apart. Intra-rater reliability was assessed using the two-way mixed-effects, single-measure intraclass correlation coefficient (2,1) with 95% confidence intervals. The standard error of measurement for agreement and smallest detectable change at the 95% confidence level were calculated. Agreement was also evaluated using Bland–Altman analysis. Excellent intra-rater reliability was observed for both muscles. Intraclass correlation coefficient (2,1) was 0.968 (95% confidence intervals: 0.919–0.986) for the flexor digitorum superficialis and 0.988 (95% confidence intervals: 0.972–0.995) for the flexor digitorum profundus. The standard error of measurement for agreement and smallest detectable change were 0.393 mm and 1.090 mm for the flexor digitorum superficialis, and 0.259 mm and 0.719 mm for the flexor digitorum profundus, respectively. Bland–Altman analysis demonstrated good agreement between repeated measurements. A small systematic bias was observed for the flexor digitorum superficialis (mean bias: −0.103 mm; 95% CI: −0.201 to − 0.006 mm, p = 0.038), whereas no systematic bias was observed for the flexor digitorum profundus (mean bias: −0.022 mm; 95% CI: −0.170 to 0.126 mm, p = 0.760). Ultrasonographic assessment of flexor digitorum superficialis and flexor digitorum profundus muscle thickness demonstrated excellent intra-rater reliability and low measurement error in individuals with chronic ischemic stroke. These findings support ultrasonography as a reliable tool for monitoring structural muscle changes during stroke rehabilitation. Not applicable.