<em>Botulinum Neurotoxin</em> A Injections Influence Stretching of the Gastrocnemius Muscle-Tendon Unit in an Animal Model

Abstract

<em>Botulinum Neurotoxin</em> A (BoNT-A) injections have been used for the treatment of muscle contractures and spasticity. This study assessed the influence of (BoNT-A) injections on passive biomechanical properties of the muscle-tendon unit. Mouse<strong> </strong>gastrocnemius muscle (GC) was injected with BoNT-A (<em>n</em> = 18) or normal saline (<em>n</em> = 18) and passive, non-destructive, <em>in vivo</em> load relaxation experimentation was performed to examine how the muscle-tendon unit behaves after chemical denervation with BoNT-A. Injection of BoNT-A impaired passive muscle recovery (15% <em>vs.</em> 35% recovery to pre-stretching baseline, <em>p</em> < 0.05) and decreased GC stiffness (0.531 ± 0.061 N/mm <em>vs.</em> 0.780 ± 0.037 N/mm, <em>p</em> < 0.05) compared to saline controls. The successful use of BoNT-A injections as an adjunct to physical therapy may be in part attributed to the disruption of the stretch reflex; thereby modulating <em>in vivo</em> passive muscle properties. However, it is also possible that BoNT-A injection may alter the structure of skeletal muscle; thus modulating the <em>in vivo</em> passive biomechanical properties of the muscle-tendon unit.

Keywords

• &lt;em&gt;Botulinum Neurotoxin&lt;/em&gt;
• spasticity treatment
• muscle tone
• passive muscle biomechanics