The three plantar interossei adduct the third, fourth, and fifth toes toward the second toe axis, working with the dorsal interossei to provide the toe positioning and MTP joint stability needed during the push-off phase of gait. Their PAD mnemonic (Plantar interossei ADduct) complements the DAB of the dorsal interossei, providing the adductor forces that counterbalance the lateral spread of the toes under loading.
| Origin | Medial sides of the 3rd, 4th, and 5th metatarsals — three plantar interossei, one for each lateral toe |
|---|---|
| Insertion | Medial sides of the bases of the proximal phalanges and extensor expansions of toes 3, 4, and 5 |
| Nerve Supply | Lateral plantar nerve (S1, S2) |
| Blood Supply | Plantar metatarsal arteries |
| Actions | Adduction of toes 3, 4, and 5 toward the second toe axis (PAD — Plantar Adduct); MTP joint flexion; IP joint extension through the extensor expansion |
|---|
Plantar interosseous adduction keeps the lesser toes in alignment with their metatarsals during push-off, preventing the lateral splaying that would reduce propulsive efficiency and accelerate degenerative joint changes at the MTP joints.
Plantar interosseous atrophy from neuropathy allows the lesser toes to splay apart and the MTP joints to hyperextend, producing the characteristic foot deformity of cavovarus foot in Charcot-Marie-Tooth disease. Intrinsic foot muscle strengthening programmes targeting the plantar interossei alongside the lumbricals and flexor digitorum brevis can partially compensate for neuropathic weakness in early stages.
The plantar interossei are not individually palpable due to their deep plantar position but are assessed functionally by resisting toe adduction in the less common clinical scenario requiring their specific assessment.
Neuropathic or atrophic interosseous loss producing lateral toe splaying and MTP joint instability contributing to cavovarus foot deformity.
