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Lateral sesamoid phalangeal ligament

The lateral sesamoid–phalangeal ligament is a key stabilizing structure of the first metatarsophalangeal (MTP) joint complex. It connects the lateral sesamoid bone to the base of the proximal phalanx of the hallux, contributing to medial–lateral balance, joint stability, and the mechanical efficiency of the first ray during gait.

This ligament forms part of the sesamoid apparatus, which includes the medial and lateral sesamoids, intersesamoid ligament, and the plantar plate. Together, these components stabilize the flexor hallucis longus (FHL) tendon as it passes between the sesamoids and maintain congruency of the first MTP joint during push-off.

The lateral sesamoid–phalangeal ligament is thinner and shorter than its medial counterpart but plays an equally vital role in controlling lateral translation and preventing excessive abduction of the hallux.

Synonyms

  • Lateral sesamoid–phalangeal band

  • Lateral phalangeo-sesamoid ligament

  • Lateral metatarsosesamoid–phalangeal connection

Location and Structure

  • Position: Extends from the lateral sesamoid bone to the lateral tubercle of the base of the proximal phalanx of the great toe.

  • Orientation: Oblique and slightly transverse, reinforcing the lateral aspect of the plantar plate.

  • Composition: Dense collagenous fibers forming a short, strong band; blends with the plantar capsule of the first MTP joint.

  • Continuity: Laterally continuous with the fibers of the lateral collateral ligament and fibrous sheath of the FHL tendon.

Relations

  • Superiorly: Head of the first metatarsal bone and articular cartilage of the MTP joint

  • Inferiorly: Flexor hallucis longus tendon coursing between the sesamoids

  • Medially: Inter-sesamoid ligament connecting to the medial sesamoid

  • Laterally: Fibers blending with the lateral collateral ligament and joint capsule

  • Anteriorly: Base of the proximal phalanx of the hallux

  • Posteriorly: Plantar aponeurosis and surrounding connective tissue

Attachments

  • Proximal attachment: Lateral sesamoid bone

  • Distal attachment: Lateral tubercle of the base of the proximal phalanx of the hallux

  • Associated structures: Blends with fibers of the plantar plate, joint capsule, and flexor hallucis brevis tendon sheath

Nerve Supply

  • Digital branches of the medial plantar nerve (branch of the tibial nerve, roots S1–S2)

Function

  • Joint stabilization: Prevents excessive lateral displacement of the hallux at the first MTP joint

  • Load transmission: Distributes plantar load between sesamoids and proximal phalanx during toe-off

  • Protection: Shields the flexor hallucis longus tendon from shear forces

  • Coordination: Works with the medial sesamoid–phalangeal ligament to maintain balanced joint mechanics

  • Arch support: Contributes to stability of the medial longitudinal arch indirectly via sesamoid support

Clinical Significance

  • Ligament sprain or tear: Occurs in hallux valgus, turf toe injuries, or sesamoid dislocations

  • Chronic strain: Seen in repetitive push-off activities (running, ballet, jumping)

  • Association with sesamoiditis: Inflammation may involve adjacent capsule and ligament

  • Disruption: May lead to hallux valgus deformity, instability, or altered pressure under the first metatarsal head

  • Imaging relevance: MRI and CT critical for evaluating ligament continuity, integrity, and relation to sesamoid fractures or FHL tendon pathology

MRI Appearance

  • T1-weighted images:

    • Ligament: Low signal (dark), sharply defined linear band

    • Adjacent bone marrow: Bright signal in sesamoid and phalangeal base (fatty marrow)

    • Cartilage and capsule: Intermediate-to-low signal overlying metatarsal head and phalangeal base

    • Tears or sprains: Appear as discontinuity or intermediate signal thickening of the ligament

  • T2-weighted images:

    • Normal ligament: Low signal, appearing as a thin dark line connecting the sesamoid to phalanx

    • Cartilage: Intermediate-to-bright

    • Joint fluid: Bright hyperintense signal surrounding ligament margins

    • Pathology: Partial or complete tears appear as bright linear gaps or thickened, hyperintense fibers

  • STIR:

    • Normal ligament: Intermediate-to-dark signal

    • Pathologic ligament: Bright hyperintense regions indicating edema or strain

    • Associated findings: Marrow edema in the sesamoid or phalanx may appear bright

  • Proton Density Fat-Saturated (PD FS):

    • Normal ligament: Intermediate-to-dark with smooth contour

    • Partial tear or inflammation: Bright hyperintense signal replacing or surrounding ligament fibers

    • Excellent for detecting subtle sprains, capsulitis, or periligamentous fluid

  • T1 Fat-Sat Post-Contrast:

    • Normal ligament: Minimal enhancement

    • Inflamed ligament or capsule: Focal or diffuse enhancement along lateral plantar joint margin

    • Chronic degeneration: Shows peripheral enhancement with central low-signal fibrosis

CT Appearance

Non-Contrast CT:

  • Ligament: Not directly visualized but inferred by position between lateral sesamoid and phalanx

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

  • Pathology: May reveal sesamoid fractures, sclerosis, or calcifications near ligament attachment

  • Joint surface: Smooth in normal state; irregularity indicates degenerative or post-traumatic change

Post-Contrast CT (standard):

  • Ligamentous region: Enhancing periligamentous tissues indicate inflammation

  • Soft-tissue thickening: Seen in chronic strain or scarring

  • Usefulness: Helpful in identifying periarticular fibrosis, calcific enthesopathy, or adjacent joint inflammation when MRI is unavailable

MRI images

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

MRI images

Lateral sesamoid phalangeal ligament of foot coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001