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Medial head of flexor hallucis brevis muscle

The medial head of the flexor hallucis brevis (FHB) is one of the two terminal portions of the FHB muscle, located on the plantar aspect of the foot in the third muscular layer. It contributes to the flexion and stabilization of the proximal phalanx of the great toe at the first metatarsophalangeal (MTP) joint.

This head arises medially and inserts into the medial side of the base of the proximal phalanx, via a tendon that contains the medial sesamoid bone. It works in close association with the abductor hallucis and the flexor hallucis longus to stabilize and flex the great toe during the push-off phase of gait.

Synonyms

  • Medial belly of flexor hallucis brevis

  • Medial portion of short flexor of the great toe

Origin, Course, and Insertion

  • Origin: Plantar surface of the cuboid and medial part of the lateral cuneiform bone, and the medial division of the tendon of the tibialis posterior

  • Course: Fibers pass anteriorly and slightly medially, forming a tendon that passes beneath the head of the first metatarsal bone

  • Insertion: Medial side of the base of the proximal phalanx of the hallux, incorporating the medial sesamoid bone within its tendon

Tendon Attachments

  • The tendon of the medial head contains the medial sesamoid bone, which serves as a pulley for the flexor hallucis longus tendon

  • The flexor hallucis longus (FHL) tendon runs between the medial and lateral heads of FHB

  • The tendon blends with fibers of the abductor hallucis, contributing to joint stabilization at the medial aspect of the first MTP joint

Relations

  • Superiorly: Tendon of flexor hallucis longus

  • Inferiorly: Plantar aponeurosis

  • Medially: Abductor hallucis muscle

  • Laterally: Lateral head of the flexor hallucis brevis

  • Anteriorly: Base of proximal phalanx and medial sesamoid bone

  • Posteriorly: Medial plantar nerve and artery branches

Nerve Supply

  • Medial plantar nerve (branch of tibial nerve, roots S1–S2)

Arterial Supply

  • Medial plantar artery (from posterior tibial artery)

  • Contribution from first plantar metatarsal artery

Venous Drainage

  • Medial plantar vein and deep plantar venous plexus, draining into the posterior tibial vein

Function

  • Flexion of the great toe: Flexes the proximal phalanx at the MTP joint

  • Medial stabilization: Works with abductor hallucis to stabilize the medial aspect of the great toe during toe-off

  • Arch support: Reinforces the medial longitudinal arch of the foot

  • Synergistic action: Assists the flexor hallucis longus during powerful plantarflexion and push-off

Clinical Significance

  • Medial sesamoiditis: Overuse or impact may cause pain and inflammation beneath the first metatarsal head

  • FHB tendinopathy: May result from repetitive plantar flexion and excessive load in runners or dancers

  • Hallux valgus deformity: Medial head displacement may occur with progressive bunion formation

  • Post-surgical relevance: Recognizing its anatomy is crucial during sesamoidectomy and bunion correction surgery

  • Imaging relevance: Important to differentiate from adductor hallucis or abductor hallucis on MRI in cases of medial forefoot pain

MRI Appearance

  • T1-weighted images:

    • Normal muscle: intermediate signal intensity with visible fascicular pattern

    • Tendon: low signal (dark) inserting into base of proximal phalanx

    • Medial sesamoid: low cortical rim with internal intermediate marrow signal

    • Surrounding fat planes: bright

  • T2-weighted images:

    • Normal muscle: slightly darker than on T1, intermediate-to-low signal

    • Tendon: very low signal, continuous

    • Pathology: bright focal hyperintense areas in the tendon or muscle indicating tendinitis or strain

    • Medial sesamoid inflammation: localized bright signal near tendon attachment

  • STIR:

    • Normal muscle: intermediate-to-dark

    • Pathology: hyperintense signal in muscle or peritendinous tissue consistent with edema or inflammation

    • Distinguishes normal muscle from areas of strain or sesamoiditis

  • Proton Density Fat-Saturated (PD FS):

    • Normal muscle: intermediate-to-dark, homogeneous signal

    • Pathology: bright hyperintensity in muscle belly, tendon, or perisesamoid region

    • Best for early detection of low-grade muscle injury, tendinopathy, or fluid accumulation

  • T1 Fat-Sat Post-Contrast:

    • Normal: mild uniform enhancement

    • Inflamed tendon or sesamoid capsule: focal or rim-like enhancement

    • Chronic fibrosis or scarring: low central signal with peripheral enhancement

CT Appearance

Non-Contrast CT:

  • Muscle: homogeneous soft-tissue density on plantar aspect of first metatarsal region

  • Tendon: linear soft-tissue structure inserting medially on base of proximal phalanx

  • Medial sesamoid: dense ovoid bone beneath first metatarsal head

  • Chronic stress or inflammation: sclerosis, flattening, or fragmentation of medial sesamoid

Post-Contrast CT (standard):

  • Muscle enhances uniformly

  • Inflamed tendon sheath or sesamoid region: focal increased enhancement

  • Useful for evaluating sesamoid morphology, calcification, or chronic degenerative changes around MTP joint

MRI images

medial head of flexor hallucis brevis muscle axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

medial head of flexor hallucis brevis muscle coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

CT image

medial head of flexor hallucis brevis muscle ct axial anatomy