The accessory heads of the muscles flexor pollicis longus and flexor digitorum profundus (Gantzer muscle) – An anatomical study in Brazilian cadavers

•The neurovascular structures that supply the forearm are subject to compressions.•The prevalence of Gantzer's muscle is variable and related from the flexor pollicis longus muscle.•There is a causal relationship between the variant head of the flexor pollicis longus muscle called Gantzer resulting in the neuropathic AIN syndrome.•In this study, the prevalence of variant muscle formation (Gantzer) was 50% with a predominantly fusiform aspect.•The compressive neuropathy of the anterior interosseous nerve (AIN) results in the Kiloh–Nevin syndrome.