Effect of Light and Heavy Touch on Transtibial Amputees’ Postural Control and Weight-Bearing Asymmetry

The objective of this thesis was to determine the effect of augmented sensory feedback and mechanical support on traumatic unilateral transtibial prosthesis users’ postural stability, neuromuscular control, and weight-bearing asymmetry during quiet stance. Our central hypothesis was that postural instability in traumatic unilateral transtibial prosthesis users is a sensory problem. To test this hypothesis 12 traumatic unilateral transtibial prosthesis users and 12 unimpaired age- and sex-matched adults were recruited, enrolled, and completed the study protocol. Participants postural stability, neuromuscular control, and weight-bearing asymmetry were assessed during quiet stance under three conditions: baseline no touch, light touch, which provides sensory feedback, and heavy touch, which provides mechanical support. Postural stability, neuromuscular control, and weight-bearing asymmetry were characterized by center of pressure mean velocity, total integrated area across select lower limb muscles, and a weight-bearing asymmetry index, respectively. In the first study of this thesis unilateral transtibial prosthesis users were found to have greater medial-lateral but not anterior-postural postural instability than age- and sex-matched adults. Importantly, this medial-lateral instability was only resolved relative to age- and sex-matched adults with mechanical support from heavy touch. In the second study we found that neither light touch (i.e., sensory) nor heavy touch (i.e., mechanical support) shifted traumatic unilateral transtibial prosthesis users’ neuromuscular control of postural stability towards proximal muscles during quiet stance. In contrast, we found that mechanical support from heavy touch significantly reduced the total muscle activity used by traumatic unilateral transtibial prosthesis users during quiet stance. In the third study of this thesis we found that despite improvements in postural stability via heavy touch, there was no accompanying reduction in weight-bearing asymmetry, suggesting that weight-bearing asymmetry is not used as a compensation to maintain stability The results of this thesis suggest that contrary to our central hypothesis postural instability in unilateral transtibial prosthesis users may be attributable to mechanical rather than sensory deficits.