The dorsal interossei of the foot are four muscles on each side which act to:
- abduct the second to fourth toes from the axis of the second toe
- assist in:
- flexing the metatarsal-phalangeal (MTP) joints
- extending the interphalangeal (ITP) joints
The dorsal interossei are larger than the plantar interossei. They sit in the fourth and deepest layer of muscles of the sole of the foot.
The origin of the interossei is:
- first interossei: bipennate origin from the lateral side of the first metatarsal and the medial side of the second metatarsal
- second to fourth interossei: bipennate from similar sites between second and third, third and fourth and fourth and fifth metatarsals respectively
Similarly, they have differing insertions:
- first dorsal interossei: inserts into medial side of base of proximal phalanx of second toe
- second to fourth dorsal interossei: insert into lateral side of base of proximal phalanx of toes two to four
- all interossei: also insert into dorsal extensor expansions of respective toe
The innervation of the dorsal interossei of the foot is the lateral plantar nerve (S2, S3), either its deep branch for the first to third interossei or its superficial branch for the fourth interossei.