On the Variations of the Muscle Flexor Digitorum Brevis: Anatomical Insight Variaciones del Músculo Flexor Corto de los Dedos: Experiencias de Anatomía

Flexor digitorum brevis is an intrinsic muscle of the sole of the foot that lies immediately superior to the central part of the plantar aponeurosis and inferior to the tendons of flexor digitorum longus. Its flat spindle shaped muscle belly arises as a thin tendon from the medial process of tuber calcanei, proximal part of plantar aponeurosis, intermuscular septa and other adjacent fascial layers. The muscle fibers converge anteriorly forming four tendons, one each for the four lateral toes. At the base of the proximal phalanges, each tendon of the flexor digitorum brevis, splits into two slips and spirals around the tendons of the flexor digitorum longus, reunites in a chiasma, divides again and inserts into the margins of the intermediate phalanges of lateral four toes. The tendons of the flexor digitorum brevis enter fibrous digital tunnels on the plantar aspect of the digits, where they are surrounded by digital synovial sheaths. These fibrous digital tunnels or sheaths hold the flexor digitorum brevis tendons to the bony plane and prevent them from bowing when the toes are flexed (Romanes, 1986; Williams et al., 2000). Flexor digitorum brevis is innervated by the major sensory nerve in the sole of the foot, medial plantar nerve, a branch of the tibial nerve and vascularized by medial and lateral planter arteries, plantar metatarsal arteries and plantar digital arteries (Williams et al.). Flexor digitorum brevis function in flexion of the four lateral toes at the proximal inter-phalangeal and metatarso-phalangeal joints, regardless of the position of the ankle joint (Romanes; Williams et al.). Along with other muscles of the foot, it reinforces the longitudinal arch of the foot (Romanes; Rosse & GaddumRosse, 1997). Paralysis of the flexor digitorum brevis results in distortion of the arches of the foot (Rosse & GaddumRosse).