Post-stroke muscle atrophy and intramuscular fat content in hemiparetic subjects
Date
2010
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Publisher
University of Delaware
Abstract
Stroke is a leading cause of long term disability in adults, affecting approximately 795,000 adults a year in the United States alone. Following stroke, muscle weakness contralateral to the brain lesion, or hemiparesis, is the most common impairment. Post-stroke hemiparesis is a concern clinically because it restricts many daily living tasks including reaching and grasping, stair-climbing, and most importantly, walking. Among many factors involved in post-stroke hemiparesis is muscle atrophy – a loss of muscle tissue resulting from immobilization, disuse, inactivation, or a combination thereof. Since muscle force is a function of muscle size, the amount of atrophy a post-stroke muscle undergoes is important in adequately describing any changes to its force-generating capability as a result of stroke. Few studies have measured muscle atrophy in post-stroke individuals, and none have attempted to quantify muscle atrophy for individual paretic and non-paretic muscle. In this thesis, Magnetic Resonance Imaging (MRI) and digital reconstruction software were used to measure muscle volumes for individual muscles as well as specific muscle groups in the hemiparetic lower extremity. All muscle volumes were adjusted to exclude non-contractile tissue content, and muscle atrophy was quantified by comparing the volumes between paretic and non-paretic sides. The results of this study suggest that all individual paretic muscles atrophy in relation to the non-paretic side except the gracilis muscle. Besides the gracilis, an average decrease in muscle volume of 23% was observed for the paretic muscles. The gracilis was larger, with an increase of approximately 11%. The gracilis acts not only as a knee flexor, but also as a hip flexor and hip adductor and may increase in volume as ipsilateral hip flexors have been shown to compensate for plantar flexor weakness. The results also suggest that the gastrocnemius atrophies preferentially in the plantar flexor group. Results observed for the muscle groups suggest that the plantar flexor group atrophies preferentially over the dorsiflexors, and that paretic and non-paretic knee flexors and extensors atrophy approximately the same amount. This thesis successfully quantified individual muscle and muscle group atrophy between paretic and non-paretic sides of post-stroke lower extremities. The findings can be used in future studies to develop stroke-specific musculoskeletal models that address additional changes to movement strategies following stroke.