The Effect of Altered Neural Inputs and Botulinum Neurotoxin Chemical Denervation on the Passive Biomechanical Properties of Hand and Wrist Muscles in Chronic Hemiparetic Stroke

Abstract

Background and Purpose: Following a hemiparetic stroke, prolonged altered motor neuronal inputs may drive passive mechanical changes within muscle that further amplify the brain injury induced motor impairments, reducing optimal recovery. However, due to confounding factors, i.e. muscle hyperactivity and botulinum neurotoxin (BoNT) chemical denervation, there is no consensus on how altered neural inputs following a stroke may affect the muscle s passive mechanical properties. Therefore, the goal of this study is to understand how passive mechanical properties of muscles adapt to prolonged altered neural inputs by minimizing and controlling for muscle hyperactivity and BoNT. Methods: Passive torques about the wrist and metacarpophalangeal (MCP) joints were quantified in the paretic and non-paretic wrist/fingers of 34 individuals with chronic hemiparetic stroke. Participants hand impairments ranged from severe to mild and included a group who received BoNT injections. Torques were quantified with the subjects in a sleep or near-sleep state to mitigate muscle hyperactivity and EMGs were continuously monitored to ensure no muscle activity during data collection. Results: Our findings indicate that the passive mechanics of wrist/fingers do not substantially change following a hemiparetic stroke unless the individual previously received BoNT injections. Substantial increases in passive flexion torques were observed in individuals who had received BoNT which resulted in a decrease of up to 68 degrees in passive MCP range of motion in extension. Conclusions: To the best of our knowledge this study is the most thorough investigation of in vivo passive elastic torques at the wrist and fingers in chronic hemiparetic stroke. The results indicate increased stiffness observed clinically and in previous studies are likely a result of muscle hyperactivity, or are the result of BoNT injections. Thus, loss of hand function post-stroke is predominately due to motor impairments post stroke suggesting future studies and rehabilitation techniques should focus on these deficits.