Structural and mechanical alterations of the medial head of the gastrocnemius after stroke assessed by high-frequency ultrasound: a prospective study.

Background: Little is known about the use of ultrasonography to evaluate lower-limb function during early stroke-induced hemiparesis rehabilitation.

Objective: To investigate the changes in structural and mechanical parameters using high-frequency ultrasonography to identify parameters correlating with functional improvement.

Methods: Forty-five patients with first-ever stroke within the past 6 months and unilateral lower-limb motor dysfunction were prospectively included. The patients were divided into groups based on the change in their Fugl-Meyer Assessment-Lower Extremities score after a 4-week comprehensive physical rehabilitation therapy: markedly effective (≥4 point increase), effective (1-3 point increase), and ineffective (no change/decrease). High-frequency ultrasonography was used to measure the ankle pennation angle (PA), muscle thickness (MT), fascicle length (FL), and shear wave velocity at the medial head of the gastrocnemius with patients in the neutral position. Pre-treatment and post-treatment comparisons were also performed.

Results: The markedly effective, effective, and ineffective groups included 21, 18, and six patients, respectively. Before treatment, the PA, MT, and FL of the medial head of the gastrocnemius on the affected side were significantly lower than those on the unaffected side (p < 0.05). After treatment, PA and FL increased significantly in the markedly effective and effective groups (p < 0.05), but not in the ineffective group. No changes in these parameters were observed in the ineffective group.

Conclusions: High-frequency ultrasonography provides a quantitative method to distinguish between paretic and non-paretic limbs and identify patients who benefit from treatment. PA and FL of the medial head of the gastrocnemius may be effective indicators of functional improvement.