Sesamoid Bones (Foot)
Ossa Sesamoidea Pedis
location_on Plantar surface of the first metatarsophalangeal joint, beneath the great toe
The two sesamoid bones of the great toe (tibial/medial and fibular/lateral) are embedded within the tendons of the flexor hallucis brevis beneath the first metatarsal head. They function like pulleys, increasing the mechanical advantage of the flexor hallucis brevis and absorbing weight-bearing stress under the first metatarsal head. These are the most clinically significant sesamoids in the body after the patella.
Key Anatomical Features
- Two constant sesamoids: tibial (medial) and fibular (lateral) beneath the first metatarsal head
- Embedded within the two heads of the flexor hallucis brevis tendon
- Articular surface on the superior side articulates with facets on the plantar first metatarsal head
- Intersesamoid ligament connects the two sesamoids and creates a channel for the flexor hallucis longus tendon
- Tibial (medial) sesamoid is larger and bears more weight than the fibular (lateral)
Muscle Attachments
| Muscle | Attachment | Action |
|---|---|---|
| Flexor hallucis brevis (medial head) | Tibial (medial) sesamoid | Flexes the great toe MTP joint |
| Flexor hallucis brevis (lateral head) | Fibular (lateral) sesamoid | Flexes the great toe MTP joint |
| Adductor hallucis | Fibular (lateral) sesamoid | Adducts the great toe |
| Abductor hallucis | Tibial (medial) sesamoid | Abducts the great toe |
| Flexor hallucis longus tendon | Passes between the two sesamoids in a groove | Flexes the great toe IP joint |
Joints and Articulations
| Joint | Type | Connects to |
|---|---|---|
| First metatarsosesamoid joints | Synovial plane | Plantar facets of first metatarsal head |
| Intersesamoid ligament | Fibrous | Connects tibial and fibular sesamoids |
Common Pathologies
Sesamoiditis
Chronic inflammation and pain of the sesamoid bones or surrounding structures, common in dancers, runners, and people who wear high heels. Causes pain under the ball of the great toe.
Sesamoid fracture
Acute fracture from direct impact or stress fracture from repetitive loading. Must be distinguished from bipartite sesamoid (congenital two-piece sesamoid present in 10-30% of people).
Sesamoid avascular necrosis
Death of sesamoid bone tissue from disrupted blood supply, causing persistent plantar forefoot pain. More common in the tibial (medial) sesamoid.
Hallux valgus (sesamoid subluxation)
In bunion deformity, the sesamoids sublux laterally relative to the metatarsal head, exacerbating the deformity and causing weight-bearing dysfunction.
Clinical Relevance
Bipartite sesamoid (present in 10-30% of people, usually the tibial sesamoid) must be distinguished from fracture. Bipartite sesamoids have smooth, rounded edges and are often bilateral, while fractures have irregular edges. Sesamoid axial (skyline) radiographs and MRI help differentiate. The sesamoid position is used to grade hallux valgus severity. Sesamoidectomy can be performed for intractable sesamoiditis but should preserve at least one sesamoid to maintain great toe flexion strength.
Development and Ossification
The sesamoid bones of the great toe begin ossifying between ages 8 and 12, with the tibial sesamoid appearing slightly before the fibular. Bipartite or multipartite sesamoids (from multiple ossification centers that fail to fuse) are common normal variants.
Did You Know?
- Sesamoid means sesame-seed-shaped, from the Greek sesamon
- The human body contains numerous sesamoid bones, but only the patella and the hallucal sesamoids are constant; others are variable
- Bipartite tibial sesamoid is one of the most common normal variants in foot radiology and is often mistaken for a fracture
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