Muscle imbalance in hallux valgus: an electromyographic study

Hallux valgus is a very common foot deformity in modern societies. Muscle imbalance in abductor and adductor muscles was cited as a major factor in the production of hallux valgus. Our aim in this study was to evaluate the role of certain muscles in this deformity.

Twenty hallux valgus patients and 20 healthy volunteers participated in the study. After thorough physical, neurologic, and radiographic investigations, we performed an electromyographic study to observe the relationship of hallux valgus deformity with the muscles coordinating first metatarsophalangeal joint movements. Voluntary extension, flexion, abduction, and adduction at the hallux with maximum resistance were performed. Firing rates and amplitudes of motor unit potentials of four muscles: musculus abductor hallucis, musculus adductor hallucis, musculus extensor hallucis longus, and musculus flexor hallucis brevis were recorded. Statistical analysis, including Spearman's correlation analysis and Mann-Whitney U tests were performed with SPSS 8.0 for Windows.

We observed that in the hallux valgus group, abduction activity of musculus abductor hallucis was markedly decreased when compared with adduction of musculus adductor hallucis. Motor unit potential amplitude of abductor activity recorded from musculus abductor hallucis was slightly more than half of the activity in flexion.

Muscle imbalance in abductor and adductor muscles is apparent in hallux valgus deformity, and this imbalance may be the reason or the result of joint deformity.