Imaging of Tendinous and Muscular Anatomical Variants Around the Ankle

Tendinous and muscular anatomical variants around the ankle are usually an unexpected finding on imaging. Magnetic resonance imaging offers the best visualization of the accessory muscles; however, they can also be detected on radiography, ultrasonography, and computed tomography. Their accurate identification facilitates appropriate management of the rare symptomatic cases, mostly caused by accessory muscles in the posteromedial compartment. Symptomatic patients present with chronic ankle pain, most commonly as tarsal tunnel syndrome. The most frequently observed accessory muscle around the ankle is the peroneus tertius muscle, an accessory muscle in the anterior compartment. The tibiocalcaneus internus and peroneocalcaneus internus are uncommon; anterior fibulocalcaneus is rarely mentioned. We describe the anatomy of the accessory muscles with their anatomical relations accompanied by schematic drawings and radiologic images from clinical practice.