A case report on the bilateral absence of fourth tendinous slip of the flexor digitorum brevis muscle in the foot: Exploring evolutionary and surgical relevance

The flexor digitorum brevis (FDB) muscle extends across the central region of the sole, positioned deep beneath the plantar aponeurosis. It inserts into the lateral four toes through four slender musculotendinous slips. Functionally, this muscle reinforces the foot arch by facilitating flexion at the interphalangeal and metatarsophalangeal joints of the lateral toes. In clinical contexts, the FDB muscle serves as a musculocutaneous flap in reconstructive surgeries, addressing various foot deformities. Despite its small size, the FDB muscle carries significant evolutionary importance, indicating potential phylogenetic degeneration in humans due to adaptations to diverse lifestyles. The anatomical variation presented in this case report holds importance, as the presence or absence of the FDB muscle can play a crucial role in maintaining arch integrity and holds relevance from a surgical perspective.