The flexor hallucis brevis arises from the midfoot and divides into medial and lateral heads that each contain a sesamoid bone, wrapping around the plantar first metatarsal head to insert on the great toe proximal phalanx. The sesamoids distribute the enormous loads at the first MTP joint during push-off and protect the underlying flexor hallucis longus tendon. Sesamoid pathology from stress fracture, osteonecrosis, or sesamoiditis is a significant source of forefoot pain in runners and dancers.
| Origin | Plantar surface of the cuboid and lateral cuneiforms |
|---|---|
| Insertion | Both sides of the base of the proximal phalanx of the great toe via medial and lateral heads, each containing a sesamoid bone |
| Nerve Supply | Medial plantar nerve (L4, L5) |
| Blood Supply | First plantar metatarsal artery |
| Actions | Flexion of the great toe MCP joint; Stabilises the first metatarsal head and sesamoid complex during push-off |
|---|
The sesamoids within its two heads act as a biological pulley increasing the mechanical advantage of the FHB and the windlass mechanism, while distributing the up to eight times body weight loads at the first MTP joint during sprinting.
Sesamoid stress fractures in runners and dancers produce focal plantar pain directly under the first metatarsal head that worsens with push-off and is reproduced by direct sesamoid palpation and passive great toe dorsiflexion. The medial (tibial) sesamoid is fractured more frequently than the lateral. A bipartite sesamoid is a normal variant present in 10 to 30 percent of people and must be distinguished from fracture by the smooth corticated margins on radiograph.
The sesamoids within the FHB are palpable as two firm nodules under the first metatarsal head on the plantar forefoot, and their direct tenderness distinguishes sesamoid pathology from metatarsal stress fractures located more proximally.
Inflammation and stress reaction of the sesamoid bones within the FHB producing plantar first MTP pain in runners and dancers, managed with cushioned orthotics, activity modification, and rarely sesamoid excision.
