Prevalence and epidemiological variation of anomalous muscles at guyon's canal.

Ultrasound was performed in 116 wrists of asymptomatic volunteers to determine the prevalence and morphology of anomalous muscles in Guyon's canal in the normal population. The size of the muscle was correlated with sex, hand-dominance and occupation. Anomalous muscles were identified in 47% of volunteers and 35% of wrists (male prevalence (50%); female prevalence (21%)). All were variants of abductor digiti minimi. Bilateral muscles were present in 50% of index cases in both sexes. Mean muscle thickness was 1.7 mm overall with no inter-sex variation. Muscle thickness did not vary with hand dominance or manual employment. The prevalence of anomalous muscles is higher than previously reported and may be sex-linked. The size of the muscle may be an important factor in determining whether an anomalous muscle is significant in cases of ulnar nerve compression at Guyon's canal.