Supernumerary Muscles in the Posterior Leg Compartment: a Case Report

The leg muscles are organized in anterior, lateral and posterior compartments. The posterior compartment is usually divided in two layers: superficial and deep. The deep muscles of the posterior compartment of the leg are known to mainly plantar flexion and toes flexion. In comparison to the other leg compartments, variations of the posterior one are rare. These variants often involve the presence or absence of one or more muscles, and they have differences among origin and insertion, which leads to confusion between anatomists. We aim to describe a case of a male cadaver that possessed three supernumerary muscles in the lateral and posterior compartments of both legs: the peroneus quartus muscle and two accessory bellies of the flexor digitorum longus. This presentation seems to be very rare and scarcely reported in the literature. These variants have the potential of causing nervous or vascular compression, thus leading to tarsal tunnel syndrome or a symptomatic peroneus quartus. The clinical and surgical implications of this abnormal presentation is discussed.