The foot has four dorsal and three plantar interossei muscles analogous to those in the hand, providing the MTP stabilisation and toe control critical for the push-off phase of gait. Their atrophy from intrinsic muscle weakness produces lesser toe deformity including hammertoes and claw toes, as the MTP joints hyperextend without intrinsic stabilisation. Morton neuroma pain arises between the interosseous muscles in the intermetatarsal spaces.
| Origin | Adjacent surfaces of the metatarsal bones — dorsal interossei from two adjacent metatarsals, plantar interossei from single metatarsals |
|---|---|
| Insertion | Bases of the proximal phalanges and extensor expansions of toes 2 through 4 |
| Nerve Supply | Lateral plantar nerve (S1, S2) |
| Blood Supply | Plantar metatarsal arteries |
| Actions | Abduction (dorsal) and adduction (plantar) of the toes; MTP joint flexion; IP joint extension through the extensor expansion; Stabilisation of the lesser toe MTP joints during push-off |
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During push-off the interossei stabilise the MTP joints against the massive ground reaction force dorsiflexing them, preventing the dynamic collapse into MTP hyperextension that creates forefoot pain and lesser toe deformity.
Interosseous atrophy from peripheral neuropathy (diabetes, Charcot-Marie-Tooth), prolonged tight footwear, or Morton neuroma produces progressive lesser toe clawing and forefoot pain. Intrinsic foot muscle strengthening through toe curling and towel pickup exercises is a primary intervention for lesser toe deformity prevention. The intermetatarsal spaces between the interosseous muscles are where Morton neuromas develop from interdigital nerve compression.
The interossei are not individually palpable but interosseous atrophy produces visible metatarsal gutter prominence on the dorsal foot between the metacarpals, and interosseous space tenderness during Mulder squeeze test suggests Morton neuroma.
Perineural fibrosis of the interdigital nerve in the third web space (most commonly) between the interosseous muscles, producing burning forefoot pain and numbness reproduced by the Mulder click on lateral compression.
