Pilot Study on Muscle, Tendon, and Neural Changes Post-Botulinum Toxin Injections in Post-stroke Spastic Equinovarus

Inclusion Criteria: * Voluntary written informed consent of the participant or their legally authorized representative has been obtained prior to any screening procedures * 2\. At least 18 years of age at the time of signing the Informed Consent Form (ICF) * 3\. Use of highly effective methods of birth control; defined as those that, alone or in combination, result in low failure rate (i.e., less than 1% per year) when used consistently and correctly; such as implants, injectables, combined oral contraceptives, some IUDs, true sexual abstinence (i.e. refraining from heterosexual intercourse during the entire period of risk associated with the Trial treatment(s)) or commitment to a vasectomised partner. * 4\. Pes equinovarus due to spasticity * 5\. Clinical need for BoNT injection at the lower leg * 6\. Any previous injection of BoNT into the muscles to be investigated was at least 3 months ago * 7\. First-ever, unilateral stroke Exclusion Criteria: * Musculoskeletal or other neurological problems affecting the lower limb * Presence of spinal cord pathology that could lead to spasticity, ataxia, dystonia * Cognitive problems that impede measurements * Severe co-morbidities * Irritated skin or open wounds where ultrasound will be placed * Pregnancy * Profound atrophy of the muscles in the target area(s) of injection * Participation in an interventional Trial with an investigational medicinal product (IMP) or device * The effect of botulinum toxin A can theoretically be potentiated by agents affecting neuromuscular transmission, such as aminoglycoside antibiotics (e.g., gentamicin, tobramycin), lithium salts, cholinesterase inhibitors and tubocurarine-like muscle relaxants ((cis)atracurium, rocuronium, suxamethonium, vecuronium). Therefore, patients on whom these medications are started during the course of the trail will be excluded.