Lying plantar to the first metatarsal head are two sesamoids, the tibial (medial) and fibular (lateral) hallucal sesamoids. The sesamoids nestle within apposing concave facets of the plantar surface of the first metatarsal, with the crista, a small bony ridge separating the two facets. The respectively named hallucal sesamoids lie within the tibial and fibular heads of the tendon of the flexor hallucis brevis muscle and the surface of each sesamoid is covered by hyaline cartilage.

The tibial and fibular hallucal sesamoids are susceptible to a variety of pathologies including fracture and/or dislocation.

The tibial sesamoid is more likely to be fractured and this is thought to be due its more critical role in weight bearing.

With regards to a potential injury of the tibial sesamoid, one of the main differentials is ruling out a bipartite sesamoid as the cause of the appearance. However a bipartite fibular sesamoid is very rare and therefore this is rarely a concern.