The role of muscle ultrasound in stroke rehabilitation: a review of calf muscle alterations and clinical implications.

Background: Post-stroke morphological and structural alterations in lower-leg muscles-including changes in muscle thickness, pennation angle, fascicle length, and echo intensity-are key factors contributing to gait impairment and functional disability in stroke survivors. Conventional clinical assessments, such as the Modified Ashworth Scale and Fugl-Meyer Assessment, are limited by subjectivity and an inability to quantify intramuscular structural changes. Musculoskeletal ultrasonography, as a non-invasive, real-time, and quantitative imaging tool, has emerged as a valuable technique for evaluating post-stroke muscle alterations. Objective: This systematic review aims to synthesize the literature published in the past 5 years on the application of musculoskeletal ultrasound-including B-mode, shear wave elastography, dynamic ultrasound, and quantitative ultrasound-in assessing morphological and functional changes of lower-leg muscles in stroke patients, and to explore its correlations with clinical outcomes and its utility in guiding rehabilitation interventions. Methods: PubMed, CNKI, and Wanfang Data were searched from January 2020 to December 2025 following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. Studies were included if they were original research involving stroke patients, utilized ultrasound to assess lower-leg muscles, and reported at least one morphological or functional parameter. Results: A total of 8 studies published between 2020 and 2025 were included. The most frequently assessed muscles were the gastrocnemius and tibialis anterior. Compared with the non-paretic side or healthy controls, the paretic lower-leg muscles commonly exhibited reduced muscle thickness and cross-sectional area, altered pennation angle, shortened fascicle length, increased echo intensity (indicating fat infiltration or fibrosis), and elevated shear wave velocity or Young's modulus (indicating increased stiffness). These ultrasound parameters showed significant correlations with clinical measures of spasticity (e.g., Modified Ashworth Scale), motor function (e.g., Fugl-Meyer Assessment), and muscle strength. Ultrasound was also effectively used to monitor treatment responses, including changes following botulinum toxin injection and rehabilitation training. Conclusion: Musculoskeletal ultrasonography is a promising imaging modality for objectively assessing structural and biomechanical alterations in lower-leg muscles after stroke. Recent evidence from the past 5 years confirms its value in providing insights into the pathophysiology of post-stroke muscle changes, correlating with functional outcomes, and guiding personalized rehabilitation. Future efforts should focus on establishing standardized imaging protocols to enhance clinical applicability and cross-study comparability.