I. Function of Sesamoids
A. To protect the flexor hallucis longus muscle
B. A pulley for the flexor hallucis brevis muscle to increase moment arm
C. To disperse forces on the first metatarsal head
II. Incidence of Bipartite Sesamoids1
A. Reported incidence of 6% to 31%.
B. More common in the tibial sesamoid with 80% of incidences occurring in the tibial sesamoid and 20% occurring in the fibular sesamoid
C. 25% of bipartite sesamoids occur bilaterally.
III. Acute Sesamoid Fractures
A. Occurs in the tibial sesamoid more frequently than the fibular sesamoid.2
B. Mechanism of injury:
1. Direct trauma
2. Hyperdorsiflexion injury
C. May be difficult to distinguish an acute sesamoid fracture from a bipartite sesamoid. Magnetic resonance imaging (MRI) or a bone scan can help make the diagnosis
D. Treatment for an acute sesamoid fracture:
1. Nondisplaced: Non-weight bearing in a cam walker boot or cast for 3 weeks to 6 weeks
2. Displaced: Partial or total sesamoidectomy and bone grafting
IV. Sesamoid Stress Fracture
A. Caused by chronic repetitive overload, an injury that is common to runners
B. Plain radiographs can be normal
C. Diagnosis by an MRI or bone scan can show bone marrow edema or increased uptake
D. Treatment consists of a non-weight-bearing cast or boot for 6 weeks, activity modification, nonsteroidal anti-inflammatory drugs, and orthotics
E. If patient does not respond to conservative care after 6 months of treatment, then consider a sesamoidectomy
V. Sesamoid Osteonecrosis
A. Commonly occurs in young women.3
B. May have a history of single or repetitive trauma
C. Common in runners and dancers
D. Plain radiographs can show fragmentation, lysis, sclerosis, and flattening
E. Treat with symptomatic care. If symptoms last greater than 6 months then consider a sesamoidectomy.
VI. Sesamoid Arthritis
A. Associated with subluxation, longstanding hallux valgus, rheumatoid arthritis, and osteonecrosis
B. If only 1 sesamoid is involved, then consider a sesamoidectomy
C. If both sesamoids are affected then:
1. Both sesamoids because cannot be removed because this will result in cock-up toe deformity
2. Do a first metatarsophalangeal fusion
- Dobas DC, Silvers MD. The frequency of partite sesamoids of the first metatarsophalangeal joint. J Am Podiatry Assoc. 1977: 67;880–882.
- Hobart MH. Fracture of sesamoid bones of the foot: With report of a case. J Bone Joint Surg. 1929: 11;298-302.
- Waizy H, Jäger M, Abbara-Czardybon M, Schmidt TG, Frank D. Surgical treatment of AVN of the fibular (lateral) sesamoid. Foot Ankle Int. 2008: 29;231-236.