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Fourth Dorsal Interosseous of the Foot

musculus interosseus dorsalis quartus pedis

The fourth dorsal interosseous is the most laterally placed of the dorsal interossei, occupying the fourth intermetatarsal space and abducting the fourth toe toward the little toe. It is the smallest of the four dorsal interossei. In combination with the abductor digiti minimi, it contributes to the lateral forefoot stability.

Nerve: Lateral plantar nerve (deep branch) Blood Supply: Fourth plantar metatarsal artery Region: Foot & Ankle

Anatomical Data

Origin, Insertion & Supply

Origin	Adjacent surfaces of the fourth and fifth metatarsals (bipennate)
Insertion	Lateral base of the proximal phalanx of the fourth toe and extensor hood
Nerve Supply	Lateral plantar nerve (deep branch)
Blood Supply	Fourth plantar metatarsal artery

Biomechanics

Function & Actions

Actions	Abducts the fourth toe toward the fifth toe; Assists MTP flexion of the fourth toe

Clinical Relevance

Clinical Notes

The fourth dorsal interosseous is the least clinically isolated but is relevant in fourth and fifth MTP joint pathology. Its atrophy in the fourth intermetatarsal space is a late sign of peripheral neuropathy. Fourth intermetatarsal space bursitis or neuroma is less common than the third interspace but follows the same clinical pattern. Resection of the fourth metatarsal head in metatarsalgia must consider the effect on this muscle.

Palpation

Palpated in the fourth intermetatarsal space on the dorsum of the foot, between the fourth and fifth metatarsal shafts. Often too small to palpate reliably in isolation.

Pathology

Common Injuries & Conditions

Fourth MTP Joint Instability

Plantar plate disruption at the fourth MTP joint with loss of fourth dorsal interosseous dynamic stabilisation, producing dorsal toe subluxation and crossover deformity.