Structural and Textural Ultrasound Features of Gastrocnemius Medialis in Chronic Stroke: Associations with Functional Outcomes and Spasticity.

Background/Objectives: Stroke is a leading cause of disability, and post-stroke spasticity frequently impairs ankle mobility, strength, and gait. The gastrocnemius medialis (GM) is central to these deficits, yet the relationship between its ultrasound characteristics, functional outcomes, and spasticity severity remains unclear. This study aimed to compare structural and textural ultrasound features of the GM between individuals with chronic stroke presenting ankle spasticity and healthy controls, and to examine their associations with functional performance and spasticity severity. Methods: This case-control study included 26 individuals with stroke and 26 matched controls. Ultrasound assessments were performed using B-mode imaging to obtain parameters such as muscle thickness, pennation angle, and textural features (first-, second-, and higher-order). Functional measures included mobility (Timed Up and Go), walking speed (10-Meter Walk Test), ankle strength (dynamometry), and range of motion (goniometry). Spasticity was evaluated separately using the Modified Ashworth Scale. Results: No significant differences in GM ultrasound parameters were observed between groups or limbs (p > 0.05). Participants with stroke showed significantly reduced dorsiflexion mobility and lower strength for both plantarflexors and dorsalflexors. Correlations between ultrasound parameters and functional measures were not statistically significant; however, the effect size was consistently small. Spasticity severity did not significantly influence ultrasound findings. Conclusions: GM ultrasound parameters did not distinguish participants with stroke from controls or meaningfully correlate with function or spasticity. Functional impairments may stem primarily from neural mechanisms and compensatory motor strategies rather than muscle alterations detectable by ultrasound.