Hallux sesamoid

The hallux sesamoid bones are paired ossicles of the foot. They function as a fulcrum to increase the leverage of both flexor hallucis brevis and longus. 

Gross anatomy

The hallux sesamoids are ovoid-shaped ossicles, separated from each other by the intersesamoidal ridge. There is a medial (tibial) and lateral (fibular) hallux sesamoid and, which are embedded within the substance of the medial and lateral slips of the tendon of the flexor hallucis brevis muscle respectively ¹. They are usually 1.3 cm long x 0.3 cm wide ². The medial sesamoid is generally larger than the lateral seasmoid. 

During dorsiflexion of the hallux, the seasmoids lie below the first metatarsal head, offering protection to the otherwise exposed plantar aspect of the first metatarsal head.

Along with the tendons/ligaments listed below, the sesamoid bones form the hallux sesamoid complex.

Articulations

• cartilaginous dorsal surface articulates with the grooved undersurface of the first metatarsal head

Attachments

• intersesamoid ligament:

  • connects the two hallux sesamoids strongly to form one functional unit ²

  • forms the floor of the tendinous canal for the tendon of flexor hallucis longus

• medial and lateral collateral ligaments

• abductor hallucis tendon: medial aspect of hallux sesamoid complex

• adductor hallucis tendon: lateral aspect of hallux sesamoid complex

Blood supply

• considerable variation but mostly branches from the medial plantar artery but often additional branches from the lateral plantar artery as well as a perforating branch of dorsalis pedis ^1,2

Innervation

• plantar digital nerves

Development

Ossification

• occurs between 8-10 years of age ¹

Variant anatomy

• multipartite hallux sesamoid

Related pathology

• hallux sesamoid fracture
• sesamoiditis
• avascular necrosis or osteochondritis
• subluxation or dislocation
• osteoarthritis (of sesamoid-metatarsal articulation)