Flexor Digitorum Accessorius Longus in the Tarsal Tunnel: A Rare Anatomical Variant

During the routine dissection of an 80-year-old male cadaver, an unusual variant of the Flexor Digitorum Accessorius Longus (FDAL) muscle was identified in the left ankle. The FDAL, with two distinct heads- medial (tibial) and lateral (calcaneal)- was found occupying the tarsal tunnel and partially obscuring the deep flexor tendons and neurovascular structures. This variant crossed over the posterior tibial nerve, which had bifurcated into its medial and lateral plantar branches, contributing to a potential site for compression. The FDAL’s rare muscular form in the lower tarsal tunnel and its anatomical positioning suggest a predisposition to Tarsal Tunnel Syndrome (TTS), which may present with pain, paraesthesia, or movement restriction. Magentic Resonance Imaging (MRI) is essential for accurate diagnosis. This case supports evolutionary and embryological theories of muscle descent and highlights the clinical significance of FDAL in differential diagnosis and surgical planning for TTS. Awareness of such variations is crucial for anatomists, clinicians, and surgeons.