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QUANTIFYING ATROPHY OF INTRINSIC FOOT MUSCLES VIA MAGNETIC RESONANCE IMAGING: A PILOT STUDY

Abstract

L.J. Hinkle, J.K. Sponbeck, G.W. Fellingham, A.W. Johnson

Brigham Young University

Individuals with lower extremity injury are often prescribed a combination of interventions that result in them not walking or exercising for a period of time. Many interventions require muscle disuse. Disuse of muscles can lead to measurable muscle atrophy in as few as 12 hours. Understanding the effect disuse may have on an individual—in addition to the impact of the injury itself—can inform selection of interventions by clinicians and practitioners. PURPOSE: Examine adherence potential of a treatment, test measurement protocols on both feet of a single participant, confirm measurer reliability, and determine an expected amount of cross sectional area (CSA) and volume atrophy to (1) inform whether further studies are likely to find significant atrophy, (2) inform future hypotheses, and (3) reveal areas of concern for robustness in future studies. METHODS: We measured foot volume three times each for abductor hallucis, flexor digitorum brevis, and abductor digiti minimi in each of the subject’s feet before and after 10 days of disuse. The subject used a wheelchair for transport, walked fewer than 500 steps per day, and spent less than 30 minutes per day standing. RESULTS: We used a linear mixed model (LLM) to analyze measurements, accounting for muscle, left or right foot, and pre and post measurement. The LLM indicated an average loss of volume for each muscle of 1.0993 cm3. Standard error was 0.5442 cm3. We acknowledge and will need to address with another pilot (1) inter-measurer reliability and (2) subject to subject error (including both starting muscle sizes and protocol adherence). Based on a subject who was incentivized to adhere and a skilled CSA/volume measurer, we expect to find significant atrophy in three intrinsic muscles. CONCLUSION: With the noted caveats, we are confident moving forward with the planned series of studies, focusing on atrophy, recovery, and hypertrophy of foot intrinsics. We propose to add direct strength measurement of toe flexors to the measured variables. We expect our results to inform recovery from normally unaddressed atrophy that occurs as a result of clinical interventions of lower extremity injury.

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