Sesamoid Fracture vs Bipartite Sesamoid Explained

Quick answer

The sesamoid bones are two small bones embedded within the tendon under the big toe joint — the tibial sesamoid (medial) and the fibular sesamoid (lateral). They act like pulleys, redirecting force during push-off. A fracture in either sesamoid is uncommon but real, and is often misdiagnosed as sesamoiditis — the bones look similar enough on X-ray that distinguishing requires careful evaluation. Fractures take longer to heal because the sesamoids have poor blood supply.

The other thing a sesamoid fracture is confused with is a bipartite sesamoid — a normal congenital variant where the sesamoid is naturally in two pieces, present in roughly 10–30% of people. The difference matters: a bipartite sesamoid is harmless and needs no treatment, while a true fracture needs offloading and time to heal. The two can look nearly identical on a single X-ray, and the distinction is the most common diagnostic question with sesamoid two-piece appearance — covered in detail below.

Two types of fracture

Acute fracture

A sudden, traumatic break — typically from:

• Landing forcefully on the ball of the foot from a jump or fall
• High-impact running on a hard surface
• A direct blow to the bottom of the big toe joint
• Forced extension of the big toe (similar mechanism to severe turf toe)

Stress fracture

A gradual fatigue fracture from repetitive load:

• High-mileage runners
• Dancers (especially ballet, en pointe)
• Athletes with rapid increases in training volume
• People with high arches (cavus foot) — concentrates load on the sesamoids

How to distinguish from sesamoiditis

Bipartite sesamoid — the most common mimic

A bipartite sesamoid is a normal anatomic variant in which the sesamoid bone forms in two (or sometimes three — tripartite) pieces rather than one. It is present in roughly 10–25% of people depending on the series, occurs more often in the tibial (medial) sesamoid than the fibular, and is bilateral in about 25–85% of cases. On a standard X-ray, a bipartite sesamoid can look strikingly like a fracture — so much so that telling them apart is one of the more common diagnostic pitfalls in foot radiology.

Features that suggest bipartite (normal variant) rather than fracture:

• Smooth, rounded, well-corticated edges at the split — fractures show sharp, irregular, non-corticated edges
• Total combined size larger than expected — the bipartite halves together are usually bigger than a normal single sesamoid
• No significant pain or tenderness when pressed directly over the sesamoid (although a bipartite sesamoid can develop its own painful problems)
• No clear history of acute injury or escalating overuse

A practical clinical tip: because bipartite sesamoids are bilateral in a large minority of patients, comparing an X-ray of the other foot can help confirm the diagnosis. If the contralateral foot shows the same bipartite pattern, the appearance on the symptomatic side is more likely to be a normal variant than a fracture. (The reverse is not absolute — a unilateral bipartite is still possible — so a symptomatic patient with X-ray findings still needs careful clinical correlation, and MRI when in doubt.)

When the X-ray is genuinely ambiguous, MRI is the most useful next step. A true acute fracture shows bone marrow edema across the line; a quiet bipartite sesamoid does not. A symptomatic bipartite sesamoid (sometimes called bipartite sesamoiditis, where the cartilaginous junction between the two parts becomes inflamed or disrupted) can show edema too — at which point the management overlaps with sesamoiditis and stress fracture care.

How to recognize it

• Sharp, focal pain under the big toe joint
• Pain with push-off, especially during running or walking on hard surfaces
• Tenderness directly over the affected sesamoid
• Swelling and possible bruising under the joint
• Painful big toe extension (bending the toe up stretches the tendon and sesamoid)
• Pain wearing high heels (loads the sesamoid)
• Limp in acute cases

Diagnosis

• History and exam — pinpoint tenderness over the sesamoid, pain with toe extension
• X-rays — including standard views and a sesamoid axial view which best shows the bones. Compare to the other foot if needed
• MRI — gold standard. Shows fracture, bone marrow edema, and helps distinguish from bipartite sesamoid or sesamoiditis
• Bone scan or CT — sometimes used in stress fracture cases

Treatment

Conservative care (most cases)

The sesamoids’ poor blood supply means healing is slow. Treatment focuses on complete unloading of the sesamoid:

• Walking boot or stiff-soled rocker shoe for 6–8 weeks
• Carbon fiber turf toe plate to limit big toe extension
• Sesamoid pad / J-pad orthotic to offload the affected bone
• Activity modification — no running, jumping, or pivoting until cleared
• Crutches in the early phase if pain is severe
• NSAIDs for inflammation
• Bone stimulator — sometimes used in stress fractures with delayed healing
• Imaging follow-up at 6–8 weeks to confirm healing

Healing time:

• Acute fractures: typically 6–12 weeks
• Stress fractures: 3–6 months
• Some cases progress to avascular necrosis (bone death) requiring different management

Surgery

Considered for fractures that don’t heal with prolonged conservative care, or for displaced fractures with poor alignment:

• Sesamoidectomy — removal of the affected sesamoid. Reliable for pain relief
• Bone graft / fixation — preservation surgery, less common but used in selected cases
• Recovery — 6–8 weeks in a boot; full recovery 3–6 months

Removing both sesamoids is generally avoided — it can cause secondary big toe deformity. Single sesamoidectomy is generally well tolerated.

Bottom line

A sesamoid fracture is slow to heal, easy to confuse with sesamoiditis or a bipartite sesamoid, and benefits from early protected weight-bearing. MRI is the most useful imaging test for confirming the diagnosis. Most cases heal with patient conservative care; persistent pain points to sesamoidectomy. Athletes should expect 3–6 months for full return to sport — trying to push through is the most common cause of progression to avascular necrosis.