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Medial sesamoid phalangeal ligament

The medial sesamoid-phalangeal ligament is a strong fibrous connective structure located beneath the first metatarsophalangeal (MTP) joint, connecting the medial sesamoid bone to the base of the proximal phalanx of the hallux. It plays a critical role in stabilizing the medial sesamoid apparatus and the great toe joint, ensuring smooth load transmission during push-off in gait.

This ligament is part of the plantar complex of the first MTP joint, working in conjunction with the lateral sesamoid-phalangeal ligament, plantar plate, and inter-sesamoid ligament to stabilize the flexor hallucis brevis tendons and maintain alignment of the sesamoid bones beneath the metatarsal head.

Synonyms

  • Medial sesamoid ligament

  • Medial phalangeal-sesamoid ligament

  • Medial component of the plantar plate complex

Location and Structure

  • Location: Plantar aspect of the first MTP joint

  • Attachments: Extends from the medial sesamoid bone to the plantar base of the proximal phalanx of the hallux

  • Structure: Short, dense, fibrous band with a slightly oblique orientation; blends with the plantar plate and capsule of the MTP joint

  • Composition: Collagen-rich ligament with fibrocartilaginous transition zones near its attachments to bone and sesamoid

  • Orientation: Runs anteromedially, forming part of the medial stabilizing complex of the hallux

Relations

  • Superiorly: Head of the first metatarsal bone and flexor hallucis brevis tendon

  • Inferiorly: Plantar aponeurosis and subcutaneous fat pad

  • Medially: Abductor hallucis muscle and tendon

  • Laterally: Flexor hallucis longus tendon and inter-sesamoid ligament

  • Distally: Base of the proximal phalanx of the hallux

Attachments

  • Proximal attachment: Medial sesamoid bone and adjacent fibrous sheath of flexor hallucis brevis

  • Distal attachment: Plantar aspect of the base of the proximal phalanx

  • Additional fibers: Blend with the medial capsule and plantar plate of the first MTP joint

  • Provides a stabilizing sling around the flexor hallucis longus tendon

Nerve Supply

  • Medial plantar nerve (branch of the tibial nerve, S1–S2) — provides sensory and proprioceptive innervation to the joint capsule and ligament

Function

  • Stabilization: Anchors the medial sesamoid bone to the proximal phalanx, preventing displacement during toe-off

  • Load distribution: Assists in transmitting pressure from the metatarsal head to the sesamoid apparatus and plantar surface

  • Support: Reinforces the plantar capsule and helps maintain alignment of the sesamoids beneath the first metatarsal head

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

  • Assists flexion: Facilitates smooth hallux flexion by guiding the motion of the flexor hallucis brevis tendons

Clinical Significance

  • Sprain or rupture: May occur due to forced dorsiflexion or repetitive push-off (common in runners and dancers)

  • Sesamoiditis: Chronic inflammation of the sesamoid complex can cause medial plantar pain under the great toe

  • Hallux valgus: Chronic strain or attenuation of the medial sesamoid-phalangeal ligament contributes to medial drift and instability

  • Post-traumatic changes: Partial tears can result in sesamoid migration or subluxation

  • Surgical importance: Must be preserved during bunion correction procedures to prevent postoperative hallux weakness

MRI Appearance

  • T1-weighted images:

    • Ligament: Low signal (dark band) connecting medial sesamoid to the base of the proximal phalanx

    • Adjacent fat: Bright, delineating ligament borders

    • Sesamoid bone marrow: Bright due to fatty content

    • Pathology: Partial tears appear as focal discontinuity or irregular thickening

  • T2-weighted images:

    • Normal ligament: Low signal (dark) structure

    • Mild surrounding fluid or bursal changes may appear intermediate-to-bright

    • Partial or complete tear: Hyperintense signal disruption with loss of continuity

    • Sesamoid bone marrow edema: Bright signal when inflamed

  • STIR:

    • Normal ligament: Intermediate-to-dark signal

    • Pathology: Bright hyperintense signal in ligament or periligamentous soft tissue (strain, inflammation, or edema)

    • Sensitive for early detection of sesamoiditis and ligament strain

  • Proton Density Fat-Saturated (PD FS):

    • Normal: Intermediate-to-dark, well-defined band

    • Partial tear or inflammation: Bright focal signal with thickening or irregularity

    • Useful for evaluating periligamentous edema and subtle fiber disruption

  • T1 Fat-Sat Post-Contrast:

    • Normal: Mild uniform enhancement of surrounding soft tissues

    • Inflamed or torn ligament: Focal or diffuse enhancement

    • Chronic degeneration: Poorly enhancing fibrotic thickening with irregular margins

CT Appearance

Non-Contrast CT:

  • Ligament: Not directly visualized (soft-tissue density)

  • Sesamoid bone: High-density ovoid structure beneath first metatarsal head

  • Pathology: Chronic stress may cause cortical irregularity, sclerosis, or fragmentation of the medial sesamoid

  • Indirect findings: Peri-sesamoid soft-tissue thickening, sesamoid subluxation, or small avulsion fragments

Post-Contrast CT (standard):

  • Enhancing periligamentous soft tissue suggests inflammation or bursitis

  • Helpful in assessing postoperative or chronic degenerative changes around the sesamoid apparatus

  • Provides excellent delineation of osseous morphology and joint alignment

MRI images

Medial sesamoid phalangeal ligament of foot coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

Medial sesamoid phalangeal ligament of foot sag cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000