The first dorsal interosseous of the foot abducts the second toe toward the hallux. The foot's abduction-adduction axis passes through the second toe (unlike the hand where it is the middle finger). The first DI is the muscle most subject to overload in hallux valgus.
| Origin | Adjacent sides of the first and second metatarsal shafts |
|---|---|
| Insertion | Medial base of the second toe proximal phalanx — the foot axis abducts toward the midfoot axis from the second toe |
| Nerve Supply | Lateral plantar nerve — deep branch (S2, S3) |
| Blood Supply | First dorsal metatarsal artery from dorsalis pedis |
| Actions | Abducts the second toe medially — toward the great toe; Flexes the second toe MTP joint |
|---|
In severe hallux valgus, the first web space first dorsal interosseous becomes stretched and overloaded as the hallux deviates laterally. In second toe MTP synovitis (second toe "crossover toe"), the first DI is implicated in the early lateral instability. Its anatomy is relevant in first web space reconstruction after trauma.
Palpated in the first web space on the dorsal foot during second toe medial abduction.
Stretching and fatigue of the first dorsal interosseous foot from lateral hallux deviation producing first web space pain and second toe instability.
