Impact of volumetric muscle loss injury on persistent motoneuron axotomy

IntroductionVolumetric muscle loss (VML) occurs following significant traumatic injury or surgical removal of skeletal muscle, resulting in nonrecoverable loss of tissue and long-term dysfunction. Perhaps less recognized is that VML injuries inherently disrupt the neuromuscular unit, resulting in fiber denervation and presumptive motor unit rearrangement, expansion, and/or loss. To characterize neural dysfunction we quantified motoneuron axotomy, in efforts to understand how this relates to the temporal coordination of neuromuscular and morphological alterations due to injury. MethodsIn an established rat tibialis anterior (TA) VML injury model, we examined the motoneuron, skeletal muscle, and maximal isometric torque at 3, 7, 14, and 21 days postinjury. ResultsSignificant axotomy of 57-79% of all TA muscle motoneurons was observed through 21 days postinjury, which was coupled with a 45-90% TA maximal torque deficit. DiscussionA approximate to 20% partial ablation of the TA muscle causes disproportionate damage across the motor unit acutely postinjury. Muscle Nerve57: 799-807, 2018