The two sesamoid bones of the great toe (medial and lateral sesamoids) are embedded within the flexor hallucis brevis tendon on the plantar surface of the first metatarsal head. They protect the underlying flexor hallucis longus tendon, increase the mechanical advantage of the FHB, and distribute the enormous loads at the first metatarsophalangeal joint during walking (120% body weight) and running (800% body weight).
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| Landmarks |
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| Ossification | The medial sesamoid ossifies from age 8 to 10 and the lateral from age 10 to 12. Bipartite sesamoids from failure of ossification centres to fuse are common anatomical variants. |
Sesamoid fractures from direct impact or stress reaction produce plantarflexion-localised pain directly under the first metatarsal head. Bipartite sesamoids (present in 10 to 30 percent of people) are distinguished from fractures by their smooth corticated margins on radiograph and by the absence of acute onset. Sesamoiditis, stress reaction within the sesamoid without frank fracture, produces the same presentation and is managed with cushioned orthotics and activity restriction before considering sesamoid excision.
Overload inflammation of the hallux sesamoids under the first metatarsal head, common in dancers and runners.
Acute or stress fractures, most often of the medial (tibial) sesamoid, which must be distinguished from a normal bipartite sesamoid.
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