Medial gastrocnemius muscle and tendon morphology in first-ever chronic stroke survivors using three-dimensional freehand ultrasound: a cross-sectional reliability and validity study

Morphological muscle–tendon (MMT) adaptations occur after stroke but remain insufficiently characterized because objective, clinically applicable assessment methods are limited. Three-dimensional freehand ultrasound (3DfUS) offers a promising approach for the simultaneous assessment of muscle–tendon morphology. This study aimed to (1) assess the repeatability of three-dimensional freehand ultrasound (3DfUS) for measuring GM MMT properties and (2) compare GM muscle length, tendon length, and muscle thickness between 35 first-ever chronic stroke survivors and 23 healthy controls. 3DfUS was used to assess GM MMT properties. Inter-/intra-operator as well as inter- and intra-processor repeatability were evaluated using intraclass correlation coefficients (ICC), standard error of measurement (SEM), minimum detectable change (MDC), and Bland–Altman analysis. Group comparisons were performed using Wilcoxon signed-rank and Mann–Whitney U tests. Inter- and intra-operator as well as inter- and intra-processor repeatability demonstrated ICC values ranging from 0.84 to 0.999, indicating good to excellent repeatability across all evaluated MMT parameters. Stroke survivors demonstrated significantly lower normalized muscle thickness in both the affected ( P = 0.005) and non-affected ( P < 0.001) limbs compared with healthy controls, whereas no significant differences were observed for normalized muscle belly length or tendon length. 3DfUS is a reliable method for the objective assessment of GM muscle–tendon morphology after stroke. The observed bilateral reduction in GM nMT indicates that structural muscle changes after stroke are not restricted to the affected limb. Furthermore, this study demonstrates the feasibility of simultaneously quantifying multiple clinically relevant MMT parameters using 3DfUS. Together, these findings provide preliminary evidence of the ability of 3DfUS to discriminate between chronic stroke survivors and healthy controls and warrant further evaluation in research and clinical practice. Trial registration ClinicalTrials.gov ID NCT04607486.