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Second Plantar Interosseous of the Foot

musculus interosseus plantaris secundus pedis

The second plantar interosseous adducts the fourth toe toward the midline, occupying the space plantar to the fourth metatarsal. It works antagonistically to the third dorsal interosseous to maintain fourth toe alignment during gait. Its functional role becomes apparent in forefoot deformity where fourth toe crossover occurs.

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

Anatomical Data

Origin, Insertion & Supply

Origin	Medial side and base of the fourth metatarsal (unipennate)
Insertion	Medial 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	Adducts the fourth toe toward the second toe axis; Assists MTP flexion and IP extension of the fourth toe

Clinical Relevance

Clinical Notes

The second plantar interosseous is involved in fourth toe deformities including crossover toe syndrome and hammer toe. Synovitis of the fourth MTP joint displaces the plantar plate and stretches this muscle, contributing to progressive deformity. Weil osteotomy of the fourth metatarsal indirectly addresses the biomechanical imbalance at this muscle's insertion.

Palpation

Not directly palpable. Assessed by fourth toe adduction resistance testing or by observing passive deformity correction.

Pathology

Common Injuries & Conditions

Fourth Toe Crossover Deformity

Progressive adduction and dorsal subluxation of the fourth toe from plantar plate failure and second plantar interosseous dysfunction, requiring plantar plate repair and possible Weil osteotomy for correction.