Fifth-Toe Deformities

Anatomically, the forefoot is considered the portion of the foot that extends from the tarsal-metatarsal joint to the tips of the toes, and pathology of the toes are typically subdivided into the pathology of the hallux, or great toe, and pathology of the lesser toes. The fifth toe is the most distal and lateral structure in the forefoot is comprised of the proximal, middle, and distal phalanges. The proximal phalanx articulates with the metatarsal at the metatarsophalangeal joint, and in turn, the proximal phalanx articulates with the middle phalanx at the proximal interphalangeal joint, and the middle phalanx articulates with the distal phalanx at the distal interphalangeal joint.Layer 1, or the most superficial layer, is comprised of the following structures. The abductor hallucis muscle serves to abduct the great toe, the flexor digitorum brevis muscle which inserts on the base of the middle phalanx of toes 2 to 5 and flexes the proximal interphalangeal joints and the abductor digiti minimi muscle which serves to abduct the fifth toe.Layer 2 is immediately deep to layer one and is comprised of the flexor digitorum longus (FDL) tendons, which insert on the base of the distal phalanx of toes 2to 5 and serve to flex the proximal and distal interphalangeal joints. The flexor hallucis longus (FHL) tendon, which inserts on the base of the distal phalanx of the great toe and serves to flex the interphalangeal joint of the great toe. The quadratus plantae muscle, which inserts on the tendon of the flexor digitorum longus, assists with flexion of toes 2 to 5. Finally, the lumbrical muscles which originate from the tendon of FDL and insert on EDL serve to flex the metatarsophalangeal joints and extend the interphalangeal joints of toes 2 to 5Layer 3 is comprised of the flexor hallucis brevis muscle, which inserts on the base of the proximal phalanx of the hallux and flexes the great toe. Within the two heads of the flexor hallucis, brevis lie the sesamoid bones of the great toe. The adductor hallucis muscle, which is comprised of an oblique and transverse head serves to adduct the great toe. Finally, the flexor digiti minimi brevis muscle which inserts on the base of the fifth toe proximal phalanx flexes the fifth toe at the metatarsophalangeal jointLayer 4 is the deepest and is comprised of the dorsal interosseous muscles which serve to abduct the toes at the metatarsophalangeal joints while the plantar interosseous muscles serve to adduct the toes at the metatarsophalangeal joints. The peroneus longus tendon travels from lateral to medial within the foot and inserts on the medial cuneiform providing eversion and flexion to the ankle joint. Finally, the tibialis posterior tendon inserts on the navicular and acts as a foot supinator and invertor, and is crucial to the maintenance of the arch of the footThe dorsum of the foot contains the muscle bellies of extensor digitorum brevis and extensor hallucis brevis. The extensor digitorum longus originates in the anterior compartment of the lower leg and inserts on the dorsum of the middle and distal phalanges of toes 2 to 5 serving to extend the toes and assist in ankle dorsiflexion while the extensor hallucis longus inserts on the dorsal base of the distal phalanx of the great toe and thus extends the interphalangeal (IP) joint of the hallux.Understanding the anatomy of the foot is critical to understanding its various deformities. Deformities of the fifth toe are often congenital and include deformities such as an overlapping fifth toe or a congenital curly toe.