The first dorsal interosseous of the foot is the largest of the four dorsal interossei, occupying the first intermetatarsal space. It is the primary abductor of the second toe, the axis of which passes through the second ray. It contributes to transverse arch support and MTP joint stability.
| Origin | Adjacent surfaces of the first and second metatarsals (bipennate) |
|---|---|
| Insertion | Medial base of the proximal phalanx of the second toe and extensor hood |
| Nerve Supply | Lateral plantar nerve (deep branch) |
| Blood Supply | Plantar metatarsal arteries |
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It abducts the second toe toward the big toe side and assists flexion at the MTP joint, helping stabilise the forefoot during push-off.
The first dorsal interosseous is frequently atrophied in peripheral neuropathy, producing the characteristic visible hollowing of the first intermetatarsal space. It is palpable and visible on the dorsum of the foot in lean individuals. Wasting is assessed clinically in diabetes, Charcot-Marie-Tooth disease, and compression neuropathies.
Palpated by placing the thumb in the first intermetatarsal space on the dorsum of the foot, with the muscle belly visible during active second toe abduction.
Denervation wasting of the first dorsal interosseous producing a visible depression in the first intermetatarsal space, commonly from peripheral neuropathy, tarsal tunnel syndrome, or intrinsic muscle weakness in cavus foot.
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