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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, 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 and it also occupies a more distal and superficial (plantar) position.
During dorsiflexion of the hallux, the sesamoids lie below the first metatarsal head, offering protection to the otherwise exposed plantar aspect of the first metatarsal head.
Along with the tendons and ligaments listed below, the sesamoid bones form the hallux sesamoid complex.
- cartilaginous dorsal surface articulates with the grooved undersurface of the first metatarsal head
- 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
- 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
- each sesamoid receives a single artery at its proximal pole and there is a general lack of collateralisation, this increases the risk of osteonecrosis and poor fracture healing 4
- veins correspond to the supplying arteries
- occurs between 8-10 years of age 1