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Intersesamoid ligament

The intersesamoid ligament is a strong, transverse fibrous band connecting the medial and lateral sesamoid bones beneath the head of the first metatarsal. It forms part of the plantar plate complex of the first metatarsophalangeal (MTP) joint and plays a crucial role in stabilizing the hallux sesamoid apparatus.

Located on the plantar aspect of the great toe joint, it bridges the two sesamoids and provides a smooth gliding channel for the flexor hallucis longus (FHL) tendon, which passes between them. The ligament is integral to maintaining the structural integrity and biomechanics of the first MTP joint, allowing efficient weight transfer during toe-off in gait.

Synonyms

  • Transverse sesamoid ligament

  • Inter-sesamoid ligament

  • Sesamoid band of the first MTP joint

Location and Structure

  • Found on the plantar aspect of the first MTP joint, deep to the flexor hallucis brevis tendons.

  • Extends transversely between the medial and lateral sesamoid bones.

  • Composed of dense regular collagen fibers forming a strong, slightly concave band.

  • The flexor hallucis longus tendon passes between the sesamoids and beneath the ligament in a synovial sheath.

  • Forms the distal portion of the plantar plate, blending with the joint capsule and collateral ligaments.

Relations

  • Superiorly: Head of the first metatarsal and articular cartilage

  • Inferiorly: Plantar skin and subcutaneous tissue

  • Medially: Medial sesamoid bone and tendon of flexor hallucis brevis (medial head)

  • Laterally: Lateral sesamoid bone and tendon of flexor hallucis brevis (lateral head)

  • Posteriorly: Tendon of flexor hallucis longus passing between sesamoids

  • Anteriorly: Plantar plate blending with fibrous capsule of the first MTP joint

Attachments

  • Medial attachment: To the medial sesamoid bone and the fibrous sheath of the medial head of the flexor hallucis brevis

  • Lateral attachment: To the lateral sesamoid bone and the fibrous sheath of the lateral head of the flexor hallucis brevis

  • Superior fibers: Merge with the plantar capsule of the first MTP joint

  • Inferior fibers: Blend with the plantar fascia and subcutaneous tissue

Nerve Supply

  • Medial plantar nerve and lateral plantar nerve (branches of tibial nerve), providing sensory and proprioceptive input to the plantar aspect of the first MTP joint

Function

  • Sesamoid stabilization: Prevents excessive medial or lateral displacement of sesamoid bones

  • Weight distribution: Transfers and balances pressure across the first MTP joint during gait

  • Tendon protection: Provides a pulley system and protection for the flexor hallucis longus tendon

  • Joint stability: Reinforces plantar aspect of first MTP joint capsule and plantar plate

  • Arch support: Contributes indirectly to medial longitudinal arch stability during toe-off

Clinical Significance

  • Injury: Common in athletes, dancers, and runners due to repetitive forefoot stress

  • Sesamoiditis: Inflammation may extend to or involve the intersesamoid ligament, causing plantar medial forefoot pain

  • Tears or rupture: May result from acute hyperextension or chronic overload, leading to sesamoid separation or hallux instability

  • Degeneration or fibrosis: Thickening and loss of elasticity can cause restricted joint motion or sesamoid maltracking

  • Surgical relevance: Identified during sesamoidectomy and plantar plate repair; crucial to preserve to maintain hallux stability

  • Imaging importance: MRI and CT provide detailed assessment in sesamoid complex injuries, particularly when radiographs are inconclusive

MRI Appearance

  • T1-weighted images:

    • Ligament: Low signal (dark linear band) connecting medial and lateral sesamoids

    • Surrounding fat and marrow of sesamoids: Bright

    • Flexor hallucis longus tendon: Low-signal band passing beneath ligament

    • Pathology: Partial tear shows focal signal discontinuity or thickening; complete tear shows separation of sesamoids

  • T2-weighted images:

    • Normal ligament: Low signal

    • Marrow of sesamoids: Bright (fatty content)

    • Pathology: Bright hyperintense areas at attachment sites in edema or strain

    • Fluid between sesamoids indicates ligament disruption

  • STIR:

    • Normal ligament: Intermediate-to-dark signal

    • Pathologic ligament: Bright hyperintense signal in partial tear or inflammation

    • Adjacent soft-tissue edema well visualized

  • Proton Density Fat-Saturated (PD FS):

    • Normal: Intermediate-to-dark ligament band

    • Partial tear: Bright hyperintense focus within or around ligament

    • Useful for differentiating ligament injury from sesamoid stress reaction

  • T1 Fat-Sat Post-Contrast:

    • Normal ligament: Minimal or no enhancement

    • Inflamed or torn ligament: Peripheral or focal enhancement

    • Adjacent capsular or periligamentous enhancement suggests synovitis or bursitis

CT Appearance

Non-Contrast CT:

  • Ligament: Thin soft-tissue density band between sesamoids (may be difficult to delineate directly)

  • Sesamoid bones: Dense ovoid structures beneath the first metatarsal head

  • Pathology: Widened intersesamoid space, soft-tissue swelling, or ossification may indicate chronic strain or tear

  • Excellent for detecting sesamoid fractures, alignment abnormalities, and ossified ligament remnants

Post-Contrast CT (standard):

  • Ligament itself does not enhance significantly

  • Adjacent soft-tissue or periligamentous enhancement may be seen in inflammatory or post-traumatic conditions

  • Helpful in evaluating chronic plantar plate injuries, sesamoiditis, or postoperative scarring

MRI image

intersesamoid ligament of foot axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

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

CT image

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