The plantar interosseous muscles are part of the fourth and deepest layer of muscles in the sole of the foot. There are three plantar interossei and they are smaller than the dorsal interossei.
They arise from the inferior and medial side of the third, fourth and fifth metatarsals. On the same toe as they arise, each insert into the:
- medial sides of the bases of the proximal phalanx
- dorsal extensor expansion
The plantar interossei have several functions:
- adduct the third, fourth and fifth toes to the axis of the second toe
- facilitate extension of the interphalangeal joints and flexion of the metatarsophalangeal joint
They are innervated by the deep branch of the lateral plantar nerve (S2, S3).