The effect of tone-reducing ankle-foot orthoses for the treatment of lower limb spasticity

Submission note: A thesis submitted in total fulfillment of the requirements for the degree of Doctor of Philosophy to the National Centre for Prosthetics and Orthotics, Division of Allied Health, Faculty of Health Sciences, La Trobe University, Bundoora.

Tone-reducing ankle-foot orthoses (TRAFOs) are prescribed for the specific purpose of reducing spasticity in the lower limbs to improve function. However, their effects on spasticity and function are unclear. Therefore, the aim of this thesis was to examine the tone-reducing (neurophysiological) effect of TRAFOs in subjects with lower limb spasticity. The first study conducted in this thesis aimed to determine the reliability of the Hoffmann reflex (H-reflex), which was the main measurement tool used in this thesis. The H-reflex is a measure of motoneuron (MN) excitability, and this study demonstrated that it was a reliable measure in the standing position. The H-reflex was subsequently used to examine the neurophysiological effect of TRAFOs on soleus MN excitability in able-bodied subjects, and subjects with spasticity while standing. The results of these studies demonstrated no significant effects of TRAFOs on MN excitability suggesting that they were ineffective in reducing spasticity neurophysiologically. While these results were true at the group level, some subjects demonstrated significant effects to the orthosis conditions when the results were analysed individually. This highlighted the fact that the way in which spasticity responds to treatments can be unique for each individual. Despite the main finding that TRAFOs had no significant effect on MN excitability, it was necessary to evaluate their effect on functional aspects of spasticity since the aim of TRAFO use is to improve spastic gait. The final study involved assessing the effect of TRAFOs using three-dimensional gait analysis and electromyography in subjects while walking. This study found no significant effect of TRAFOs on temporo-spatial gait parameters, joint kinematics or soleus muscle activity when compared with standard AFO designs. This thesis concluded that TRAFOs have no significant neurophysiological effect on soleus MN excitability, temporo-spatial and kinematic gait parameters or soleus muscle activity in subjects with spasticity.