Ultrasonic evaluation of the abductor hallucis muscle in hallux valgus: a cross-sectional observational study.

Background: The aim of the study was to investigate the abductor hallucis muscle characteristics, defined as dorso-plantar (DP) thickness, medio-lateral (ML) width, and cross-sectional area (CSA) in relation to the severity of hallux valgus using musculoskeletal ultrasound. One hundred and two feet, mean (SD) age of 60.3 (20.54) years old, displaying varying severities of hallux valgus were stratified into four groups representing the four grades of the Manchester Scale (grade 0: no deformity, grade 1: mild deformity, grade 2: moderate deformity and grade 3: severe deformity).

Methods: The abductor hallucis muscle was imaged in each foot using a portable ultrasound system. The mean (SD) DP thickness, ML width, and CSA measurements were compared across the four Manchester Scale grades using a one-way ANOVA.

Results: Significant differences in DP thickness were found between feet with no hallux valgus (grade 0) and feet with hallux valgus grade 2 (p=0.001) and 3 (p<0.001). Significant differences were also found in ML width between feet with no hallux valgus (grade 0) and feet with grade 2 hallux valgus (p=0.010). Significant differences in CSA were found between feet with no hallux valgus (grade 0) and feet with grade 2 (p<0.001) and grade 3 (p<0.001) hallux valgus. No significant differences in these three muscle characteristics were found between grades 1, 2 and 3 (p>0.0125).

Conclusions: We speculate that morphological changes to the abductor hallucis muscle occur early in the development of the deformity.