Chemical Denervation With Botulinum Neurotoxin A Improves the Surgical Manipulation of the Muscle-Tendon Unit: An Experimental Study in an Animal Model

Purpose The chemical denervation that results from botulinum neurotoxin A (BoNT-A) causes a temporary, reversible paresis that can result in easier surgical manipulation of the muscle tendon unit in the context of tendon rupture and repair. The purpose of the study was to determine whether BoNT-A injections can be used to temporarily and reversibly modulate active and passive skeletal muscle properties. Methods Male CD1 mice weighing 40-50g were divided into a 1-week postinjection group (n = 13: n = 5 saline and n = 8 BoNT-A) and a 2-week postinjection group (n = 17: n = 7 saline and n = 10 BoNT-A). The animals had in vivo muscle force testing and in vivo biomechanical evaluation. Results There was a substantial decline in the maximal single twitch amplitude (p < .05) and tetanic amplitude (p < .05) at one week and at 2 weeks after BoNT-A injection, when compared to saline-injected controls. BoNT-A injection significantly reduced the peak passive properties of the muscle tendon unit as a function of displacement at one week (p < .05). Specifically, the stiffness of the BoNT-A injected muscle tendon unit was 0.417 N/mm compared to the control saline injected group, which was 0.634 N/mm, a 35% reduction in stiffness (p < .05). Conclusions Presurgical treatment with BoNT-A might improve the surgical manipulation of the muscle tendon unit, thus improving surgical outcomes. The results implicate neural tone as a substantial contributor to the passive repair tension of the muscle tendon unit. The modulation of neural tone through temporary, reversible paresis is a novel approach that might improve intraoperative and postoperative passive muscle properties, allowing for progressive rehabilitation while protecting the surgical repair site. (J Hand Surg 2011;36A:222-231. Copyright (C) 2011 by the American Society for Surgery of the Hand. All rights reserved.)