The two sesamoid bones of the great toe are embedded in the tendons of the flexor hallucis brevis (medial and lateral sesamoid), lying in grooves on the plantar surface of the first metatarsal head. They protect the FHL tendon and transmit the weight-bearing forces through the first metatarsal head during the toe-off phase. Sesamoiditis, bipartite sesamoid (medial in 20%), and sesamoid stress fractures are the primary pathological entities.
| Articulations | |
|---|---|
| Landmarks |
|
| Ossification | The medial sesamoid ossifies at 8-12 years; the lateral at 10-12 years. The medial sesamoid is bipartite in 20%, the most common lower extremity sesamoid variant. |
Sesamoiditis (sesamoid inflammation from overload) produces first metatarsal head plantar pain in dancers and runners. Differentiation from sesamoid fracture uses MRI. The bipartite sesamoid has smooth corticated edges (normal variant) while a fracture has irregular margins and bone marrow oedema. Sesamoid excision for chronic non-union or sesamoiditis requires meticulous plantar plate and FHB tendon repair to prevent hallux valgus (medial excision) or varus (lateral excision).
Pull the big toe gently upward to tension the area under the ball of the foot. Press up under the first metatarsal head: two small, firm, pea-sized bones can be felt side by side, the medial (tibial) sesamoid more prominent. Moving the toe up and down makes them glide under your thumb.
Overload inflammation of the hallux sesamoids, common in dancers and runners, causing pain under the big toe joint.
Acute or stress fractures, usually of the medial sesamoid, which must be distinguished from a bipartite sesamoid.
Hyperextension injury of the first MTP plantar plate, which may displace the sesamoids proximally.
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