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

Poststroke spasticity significantly impairs function, particularly through the development of pes equinovarus. Botulinum toxin A (BoNT) injections into the medial gastrocnemius (MG) are a first-line treatment. Treatment outcomes and long-term responses to interventions can vary significantly between individual patients. Additionally, there is increasing concern about potential adverse effects on muscle morphology. Further research is essential to optimize treatment strategies and improve long-term outcomes in this population. Three-dimensional freehand ultrasound (3DfUS) and instrumented spasticity assessment (ISA) are two recently developed techniques that enable the evaluation of changes in muscle, tendon, and neural properties following BoNT injections for post-stroke spastic equinovarus. These methods hold promise for providing new insights into treatment effects. Before implementing these techniques in large-scale studies, a pilot study is required for accurate sample size calculations for a prospective observational study. This study includes a protocol for a non-blinded, non-randomized open-label longitudinal pilot study. The study was approved by the European Medicines Agency ( EU CT Number 2024-513158-32) by the University Hospitals Leuven ethical committee (ID S68672). Standard deviations and effect sizes of outcome measures obtained longitudinally with 3DfUS and ISA before and after BoNT injection into MG will inform sample size calculations for future research.