Ultrasound assessment of lower-limb muscle architecture in severe acquired brain injury. Prospective study

Objectives: Ultrasound (US) is a validated tool for the in vivo assessment of muscle architecture. Individuals with severe acquired brain injury (sABI) often develop profound alterations in muscle structure and function due to neurological impairment, prolonged immobilization, and systemic factors. This prospective study aims to (i) describe a standardized ultrasound protocol for lower-limb muscle architecture assessment in patients with sABI, (ii) illustrate typical ultrasound features with different clinical presentations compared with a healthy subject, and (iii) discuss the potential clinical implications for neurorehabilitation practice. Methods: Cross-sectional area (CSA), muscle thickness, and pennation angle were assessed bilaterally at the rectus femoris (RF) and medial gastrocnemius (MG) muscles using B-mode ultrasound, following a standardized protocol and anatomical landmarks. Results: The patient with a more severe clinical condition and spasticity showed marked alterations in muscle echostructure, characterized by a pronounced reduction in CSA, muscle thickness, and pennation angle, together with increased connective tissue and loss of normal fiber organization. In contrast, the patient with earlier functional recovery and absence of spasticity demonstrated only partial muscle architecture alterations, with overall preservation of muscle structure compared with the healthy subject. Conclusions: The proposed ultrasound protocol appears feasible, reliable, and suitable for patients with sABI across different rehabilitation settings. When integrated with clinical assessment, muscle ultrasound may support the evaluation of muscle status, guide rehabilitation strategies, and provide complementary prognostic information. © 2026 The Author(s).