Definition of Sesamoid Bones
Sesamoids are:
small,
rounded bones,
partially or completely embedded within tendons.
They function as components of:
gliding mechanisms,
pressure-absorbing systems within tendon units.
Classification of Sesamoid Bones
Sesamoids may be classified as:
Constant
present consistently.
Inconstant
variably present.
The only constant sesamoid bones in the foot are:
the hallucal sesamoids.
Hallucal Sesamoids: Location and Anatomy
Two sesamoids are located on the plantar surface of the first metatarsal head:
Medial (tibial) sesamoid
Lateral (fibular) sesamoid
They are embedded within the plantar plate.
Typically, the two sesamoids are not equal in size.
Hallucal Sesamoid Complex: Anatomical Characteristics
Tibial Sesamoid
Larger in size.
Oval and elongated.
Associated with the medial head of the flexor hallucis brevis (FHB).
Bears a greater proportion of axial load.
Considered more susceptible to pathology.
Fibular Sesamoid
Smaller and more rounded.
Associated with the lateral head of the FHB.
Sesamoid Apparatus
The sesamoid mechanism consists of:
two sesamoid bones,
intersesamoid ligament,
medial and lateral metatarsosesamoid ligaments,
medial and lateral phalangeosesamoid ligaments.
Function of the Hallucal Sesamoids
During the push-off phase of gait, the sesamoids:
increase the lever arm of the FHB,
enhance plantarflexion strength of the first MTP joint.
Additional roles include:
shock absorption,
reduction of load transmitted to the first metatarsal head articular cartilage.
Load transmission:
approximately 50% of body weight during stance,
exceeds 300% during push-off.
Overview of Hallucal Sesamoid Disorders
Sesamoid-related disorders account for approximately 9% of foot and ankle injuries.
These conditions are:
relatively uncommon,
diagnostically challenging.
Common presenting complaint:
pain localized beneath the first MTP joint,
exacerbated during walking, particularly in push-off.
Physical examination findings:
localized tenderness on palpation,
pain with passive dorsiflexion of the first MTP joint,
pain most prominent at terminal range of motion.
Relative Distribution of Sesamoid Disorders
Stress fractures: ~40%
Sesamoiditis: ~30%
Acute fractures: ~10%
Osteochondritis / osteonecrosis: ~10%
Osteoarthritis: ~5%
Symptomatic bipartite sesamoid: ~5%
Sesamoiditis
Concept and Definition
Sesamoiditis is a descriptive umbrella term.
It represents:
a symptom complex rather than a distinct pathology.
Considered a diagnosis of exclusion.
Classical Definition
Painful inflammatory condition related to the sesamoid complex,
Occurs without radiographic abnormalities.
Differential Diagnoses to Exclude
Flexor hallucis tendonitis
Bursitis
Stress fracture
Osteonecrosis
Degenerative joint disease
Etiology
Commonly observed in young adults.
Associated with:
repetitive microtrauma,
pes cavus,
ankle equinus,
excessive first MTP joint loading.
Treatment
Conservative treatment is the initial approach:
activity modification,
immobilization if required,
custom orthoses.
Rigid insoles or Morton extension orthoses may be used to:
limit first MTP joint motion,
reduce sesamoid loading.
Acute Sesamoid Fractures
Epidemiology and Pattern
Most frequently involve the tibial sesamoid (~77%).
Likely related to increased load transmission.
Typical fracture orientation:
transverse.
Clinical Features
History of acute trauma.
Findings include:
plantar ecchymosis,
swelling,
localized tenderness,
pain with passive dorsiflexion of the first MTP joint.
Frequently underdiagnosed.
Imaging
Standard foot radiographs.
Oblique views:
medial oblique → tibial sesamoid,
lateral oblique → fibular sesamoid.
Bilateral AP comparison is useful for:
differentiation from bipartite sesamoid.
Sesamoid Stress Fractures
Represent the most common sesamoid pathology.
Common in athletes.
Associated activities:
running,
gymnastics,
dance,
football.
Clinical Course
Pain initially during activity.
Progression to pain at rest.
Swelling and painful dorsiflexion of the first MTP joint.
Diagnosis
Early radiographs may be normal.
Radiographic changes may appear up to one year after symptom onset.
CT or MRI is used for diagnostic confirmation.
Treatment Algorithm for Sesamoid Fractures
Conservative Management
First-line treatment.
Acute fractures:
6–8 weeks of immobilization,
restriction of weight bearing,
limitation of first MTP dorsiflexion.
Chronic stress fractures:
lower success rates,
prolonged immobilization may be required.
Healing may be impaired due to:
necrotic tissue,
fibrotic fracture interface.
Surgical Management
Acute Fractures
Nondisplaced (<3 mm), stable:
percutaneous screw fixation.
Displaced (>3 mm), unstable:
open reduction and internal fixation.
Chronic Stress Fractures
Anderson–McBryde procedure:
medial approach,
fracture site debridement,
autografting from the metatarsal head,
repair of the FHB tendon sheath.
Additional fixation if instability persists.
Osteochondritis / Osteonecrosis of the Sesamoids
Rare condition.
More commonly affects young women.
Etiology:
vascular insufficiency,
trauma is most frequently implicated.
Both sesamoids may be involved.
Imaging Findings
Early:
fragmentation,
irregularity,
cyst formation.
Late:
sclerosis,
collapse,
flattening and enlargement.
Radiographic changes may be absent for 9–12 months.
Bone scintigraphy, MRI, and CT may assist in diagnosis and staging.
Sesamoid Osteoarthritis
Most commonly secondary to:
hallux valgus with partial or complete sesamoid subluxation,
incongruity of the sesamoid–metatarsal articulation.
Frequently associated with:
hallux rigidus or limitus,
systemic inflammatory diseases (RA, psoriatic arthritis, DISH).
Treatment of Osteonecrosis and Osteoarthritis
Conservative Management
Custom orthoses.
Morton extension.
Taping to limit first MTP dorsiflexion.
Corticosteroid injections in selected cases.
Surgical Management
Curettage and bone grafting for osteonecrosis.
Partial sesamoidectomy:
<50% involvement,
combined with FHB repair and MANN procedure.
Total sesamoidectomy:
o 50% involvement or central necrosis.
Sesamoidectomy and Biomechanical Considerations
Tibial sesamoid excision:
associated with hallux valgus.
Fibular sesamoid excision:
associated with hallux varus.
Dual excision:
associated with cock-up deformity.
Total excision significantly alters:
FHB and FHL moment arms.
Partial excision better preserves joint biomechanics.
Dual sesamoid excision is currently avoided.
Intractable plantar keratosis.
Sesamoid-related osteophytes.
Congenital sesamoid anomalies.
Osteochondroma.
Nerve entrapment syndromes:
pain around the sesamoids,
possible positive Tinel sign.