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Flexor Digitorum Brevis Second Slip

musculus flexor digitorum brevis (fasciculus secundus)

The second slip of flexor digitorum brevis is the most medially placed FDB tendon, inserting into the middle phalanx of the second toe after splitting to allow the flexor digitorum longus to pass through. The FDB second slip is the primary PIP flexor of the second toe and works synergistically with the FDL in toe purchase during propulsion.

Nerve: Medial plantar nerve (S1, S2) Blood Supply: Medial plantar artery Region: Foot & Ankle

Anatomical Data

Origin, Insertion & Supply

Origin	Medial process of the calcaneal tuberosity and central plantar fascia
Insertion	Middle phalanx of the second toe via two slips (splitting for FDP passage)
Nerve Supply	Medial plantar nerve (S1, S2)
Blood Supply	Medial plantar artery

Biomechanics

Function & Actions

Actions	Flexes the PIP joint of the second toe; Assists MTP joint flexion of the second toe

Clinical Relevance

Clinical Notes

The FDB second slip is disrupted in second toe plantar plate tears and hammer toe deformity, where its loss combined with FDL dominance produces PIP hyperflexion and MTP hyperextension. Isolated FDB second slip pathology produces plantar second toe pain reproduced by PIP flexion resistance. Weil osteotomy for second MTP joint instability addresses the biomechanical imbalance at this slip.

Palpation

Palpated on the plantar aspect of the second toe at the level of the proximal phalanx during resisted PIP flexion.

Pathology

Common Injuries & Conditions

Second Toe Hammer Toe

Progressive PIP flexion contracture from FDB second slip fibrosis and imbalance with FDL dominance, requiring FDL to FDB transfer or PIP fusion for correction.