Changes in Passive Mechanical Properties of the Gastrocnemius Muscle at the Muscle Fascicle and Joint Levels in Stroke Survivors

Objectives: To investigate the ankle joint-level and muscle fascicle-level changes and their correlations in stroke survivors with spasticity, contracture, and/or muscle weakness at the ankle. Design: To investigate the fascicular changes of the medial gastrocnemius muscle using ultrasonography and the biomechanical changes at the ankle joint across 0 degrees, 30 degrees, 60 degrees, and 90 degrees knee flexion in a case-control manner. Setting: Research laboratory in a rehabilitation hospital. Participants: Stroke survivors (n = 10) with ankle spasticity/contracture and healthy control subjects (n = 10). Interventions: Not applicable. Main Outcome Measurements: At the muscle fascicle level, medial gastrocnemius muscle architecture including the fascicular length, pennation angle, and thickness were evaluated in vivo with the knee and ankle flexion changed systematically. At the joint level, the ankle range of motion (ROM) and stiffness were determined across the range of 0 degrees to 90 degrees knee flexion. Results: At comparable joint positions, stroke survivors showed reduced muscle fascicle length, especially in ankle dorsiflexion (P <=.048) and smaller pennation angle, especially for more extended knee positions (P <=.049) than those of healthy control subjects. At comparable passive gastrocnemius force, stroke survivors showed higher fascicular stiffness (P <=.044) and shorter fascicle length (P <=.025) than controls. The fascicle-level changes of decreased muscle fascicle length and pennation angle and increased medial gastrocnemius fascicle stiffness in stroke were correlated with the joint level changes of increased joint stiffness and decreased ROM (P<.05). Conclusions: This study evaluated specific muscle fascicular changes as mechanisms underlying spasticity, contracture, and joint-level impairments, which may help improve stroke rehabilitation and outcome evaluation.