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Flexor hallucis brevis tendons

The tendons of the flexor hallucis brevis (FHB) are the terminal extensions of the muscle’s medial and lateral heads. These paired tendons insert on either side of the base of the proximal phalanx of the great toe and each encloses a sesamoid bone within its substance — the medial and lateral sesamoids.

Together, these tendons act to flex the proximal phalanx of the great toe, stabilize the first metatarsophalangeal (MTP) joint, and protect the flexor hallucis longus (FHL) tendon, which passes between them in a fibrous tunnel. The tendons’ unique sesamoid configuration improves leverage during push-off and prevents tendon compression during locomotion.

Synonyms

  • Tendons of flexor hallucis brevis

  • Medial and lateral FHB tendons

  • Hallucal sesamoid tendons

Origin, Course, and Insertion

  • Origin: The FHB muscle arises from the plantar surface of the cuboid and lateral cuneiform bones, and the tendon of tibialis posterior.

  • Course: The muscle splits into medial and lateral tendinous heads at the level of the first metatarsal head, separated by the FHL tendon.

  • Insertion:

    • Medial tendon: Inserts into the medial side of the base of the proximal phalanx of the great toe, enclosing the medial sesamoid bone.

    • Lateral tendon: Inserts into the lateral base of the proximal phalanx, enclosing the lateral sesamoid bone.

    • Both tendons blend with the joint capsule and plantar plate of the first MTP joint.

Tendon Structure and Attachments

  • Each tendon contains a sesamoid bone acting as a pulley to improve flexion efficiency.

  • The flexor hallucis longus tendon passes between them through a fibrous tunnel, reducing friction during toe flexion.

  • Strong fibrous slips anchor the tendons to the plantar plate and joint capsule, providing medial-lateral stability.

  • The medial tendon may fuse partially with the abductor hallucis, while the lateral tendon may join the adductor hallucis.

Relations

  • Superiorly: Flexor hallucis longus tendon passing between the sesamoids

  • Inferiorly: Plantar aponeurosis

  • Medially: Abductor hallucis muscle and medial plantar nerve

  • Laterally: Adductor hallucis (oblique and transverse heads)

  • Posteriorly: Plantar nerves and digital vessels

  • Anteriorly: Base of proximal phalanx and MTP joint capsule

Nerve Supply

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

Function

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

  • Load support: Stabilizes the first MTP joint during stance and push-off

  • Arch support: Helps maintain the medial longitudinal arch

  • Dynamic stabilization: Coordinates with abductor and adductor hallucis for medial-lateral balance

  • Protection: Shields the flexor hallucis longus tendon as it passes between the sesamoids

Clinical Significance

  • Sesamoiditis: Inflammation of the sesamoid bones or tendons from repetitive loading or overuse (runners, dancers)

  • Tendinopathy: Degeneration or microtears in the FHB tendons from excessive toe-off forces

  • Tendon rupture: Partial or complete tears may occur after trauma or hallux valgus deformity

  • Entrapment neuropathy: Medial plantar nerve irritation can affect tendon function and cause plantar pain

  • Surgical relevance: Critical in sesamoid excision, bunion correction, and plantar plate repair surgeries

MRI Appearance

  • T1-weighted images:

    • Tendons: low signal intensity (dark linear bands) along plantar surface of the hallux

    • Sesamoid bones: low-signal cortical margins with intermediate marrow signal

    • Muscle belly (FHB): intermediate signal, clearly defined from surrounding fat

    • Peritendinous fat and connective tissue: bright

  • T2-weighted images:

    • Normal tendons: low signal (dark)

    • Sesamoids: dark cortex, bright marrow center if non-sclerotic

    • Pathology: bright hyperintense signal in tendon substance or at insertion (tendinitis, tear, or sesamoiditis)

    • Surrounding soft-tissue edema or fluid collection: hyperintense signal

  • STIR:

    • Normal tendons and muscle: intermediate-to-dark signal

    • Pathology: bright hyperintense signal indicating edema, inflammation, or interstitial tear

    • Perisesamoid edema and capsulitis clearly visualized

  • Proton Density Fat-Saturated (PD FS):

    • Normal: intermediate-to-dark, smooth low-signal tendons and uniform muscle

    • Abnormal: focal or diffuse bright signal within tendons (tendinitis, strain, or partial tear)

    • Surrounding fluid or reactive synovitis: high-signal hyperintensity

  • T1 Fat-Sat Post-Contrast:

    • Normal: minimal or homogeneous mild enhancement

    • Inflamed tendon sheath or sesamoiditis: shows focal enhancement

    • Chronic tendinopathy: peripheral rim enhancement with central low-signal fibrosis

CT Appearance

Non-Contrast CT:

  • Tendons: thin soft-tissue bands inserting on proximal phalanx

  • Sesamoids: dense, ovoid ossicles beneath first metatarsal head

  • Chronic inflammation: cortical irregularity or sclerosis of sesamoids

  • Calcific tendinopathy: punctate or linear calcifications within tendon substance

Post-Contrast CT (standard):

  • Tendons and surrounding muscle enhance homogeneously

  • Inflamed peritendinous soft tissues or sesamoid regions show focal enhancement

  • Useful for detecting osseous changes, calcifications, or chronic scar tissue near the MTP joint

MRI image

Flexor hallucis brevis tendons of the Foot axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

MRI image

Flexor hallucis brevis tendons of the Foot coronalcross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Flexor hallucis brevis tendons of the Foot sagcross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00002

CT image

Flexor hallucis brevis tendons ct