Tibial Sesamoid Fracture: Diagnosis, Bipartite Sesamoid Differential, and Treatment

The sesamoid bones beneath the first metatarsophalangeal (MTP) joint — the tibial (medial) and fibular (lateral) sesamoids — are embedded within the flexor hallucis brevis tendon and function to protect the flexor hallucis longus tendon, reduce friction during hallux push-off, and increase the mechanical advantage of the intrinsic toe flexors. The tibial sesamoid bears approximately 60% of the load transmitted through the first MTP joint during normal gait and up to 300% of body weight during push-off in running — making it one of the most biomechanically stressed bones relative to its size in the body. Tibial sesamoid fractures can be acute (from direct impact, jamming injury, or repetitive hyperextension of the hallux) or stress-type (from cumulative repetitive loading in dancers, runners, and ballet performers). The most important diagnostic challenge is distinguishing a tibial sesamoid fracture from a bipartite sesamoid — a normal anatomical variant in which the tibial sesamoid develops from two ossification centers that fail to fully fuse, present in 10-30% of the population — and from sesamoiditis, which is inflammation without fracture. This distinction determines whether immobilization, continued conservative care, or surgery is appropriate.

Tibial Sesamoid Fracture vs. Bipartite Sesamoid vs. Sesamoiditis: Differential Diagnosis

Feature	Acute Sesamoid Fracture	Stress Sesamoid Fracture	Bipartite Sesamoid (Normal Variant)	Sesamoiditis (No Fracture)
Mechanism	Single traumatic event: hyperextension jamming injury (stubbed toe, landing awkwardly), direct blow to forefoot, fall from height; sudden onset severe pain	Gradual onset with repetitive loading; no single injury; dancers (releve), runners (mileage increase), military recruits; weeks to months of progressive forefoot pain	Congenital — present since adolescent ossification; no injury; bilateral in 25% of cases (useful diagnostic clue)	Insidious onset with overuse or biomechanical overload; ill-fitting shoes; forefoot valgus biomechanics; no acute injury; gradual onset
Radiographic appearance	Fracture line with IRREGULAR, jagged margins; non-smooth fracture edges; displacement of fragments; loss of normal smooth cortical surface; acute cortical disruption	Fracture line may be subtle initially; sclerosis at fracture margin over time; MRI shows linear T1 signal loss and T2 STIR edema within sesamoid body; periosteal reaction	SMOOTH, corticated edges at the gap between the two ossification centers (both edges have smooth rounded cortex — this is the key radiographic differentiator from fracture); gap typically transverse orientation; bilateral in 25%	Normal plain X-ray (no fracture); MRI: diffuse T2 edema throughout sesamoid without fracture line; periosteal edema; FHB tendon signal change
Pain pattern	Immediate severe pain at injury; point tenderness directly over tibial sesamoid on plantar forefoot; pain with any first MTP extension; antalgic gait	Chronic insidious forefoot pain worsening with activity; pain after activity then at rest; tibial sesamoid plantar tenderness; worse on hard surfaces/dancing surface	Typically ASYMPTOMATIC (incidental finding); if symptomatic: chronic low-grade ache; bilateral symptoms possible; no acute onset; compare with contralateral foot X-ray	Diffuse plantar first metatarsal head tenderness; not always isolated to sesamoid; aggravated by tight shoes, high heels, forefoot loading
Key diagnostic test	X-ray: axial sesamoid view + lateral; CT confirms displacement; MRI shows soft tissue extension and FHB injury	MRI gold standard: T1 signal loss + STIR hyperintensity; plain X-rays often normal for weeks; bone scan positive earlier than X-ray	Bilateral X-ray comparison (25% bilateral); corticated smooth edges; check contralateral foot for matching bipartite; no MRI edema if asymptomatic	MRI: diffuse edema without fracture line; normal X-ray; ultrasound shows peritendinous fluid around FHB; trial of offloading diagnostic
Population	Any age; acute trauma; athletic injury in hyperextension mechanism	Dancers (especially ballet — releve position places maximum sesamoid load); runners; military recruits; young females with forefoot valgus	Incidental finding on X-ray; not a disease; present in 10-30% of population; tibial sesamoid more commonly bipartite than fibular	Middle-aged adults; biomechanical causes; inflammatory arthritis (first MTP involvement in RA, gout, psoriatic)

Sesamoid Fracture: Treatment Algorithm and Surgical Decision-Making

Stage	Treatment	Details / Duration
Phase 1 — Acute offloading (0-6 weeks)	Non-weight-bearing in below-knee cast or CAM boot; dancer’s pad (felt or foam padding with cutout under sesamoid region); rigid sole shoe modification to limit first MTP dorsiflexion; NSAIDs for pain	Non-weight-bearing preferred for acute fractures; protective weight-bearing in boot acceptable for stress fractures without displacement; cutout dancer’s pad reduces direct sesamoid pressure by redistributing load to surrounding metatarsal heads
Phase 2 — Protected weight-bearing (6-12 weeks)	Transition to boot with dancer’s pad insert; progress to athletic shoe with custom sesamoid offloading orthosis; Morton’s extension orthotics limit first MTP dorsiflexion; physical therapy for ROM	Monitor for healing on serial X-rays or MRI; stress fractures require longer offloading (12+ weeks for healing); non-union risk is significant — tibial sesamoid has tenuous blood supply from single medial branch
Phase 3 — Non-union management (3-6 months)	Trial of bone stimulator (electrical or ultrasound) for delayed union; bone marrow aspirate injection (orthobiologic); continue offloading orthosis; if no healing at 4-6 months → surgical consultation	Non-union is the most common complication of sesamoid fracture (30-40% of tibial sesamoid fractures); avascular necrosis (AVN) of sesamoid from disrupted blood supply occurs in 10-20%; AVN appears as sclerotic dense sesamoid on X-ray; MRI confirms
Surgical — partial sesamoidectomy	Excision of the smaller/non-viable fragment of a comminuted or non-union fracture, preserving the larger fragment and the FHB tendon attachment; medial plantar approach for tibial sesamoid	Preferred surgical option — preserves sesamoid function and biomechanics; avoids hallux valgus deformity risk of total excision; indicated for AVN of smaller fragment, non-union with minimal bone stock, symptomatic bipartite
Surgical — total tibial sesamoidectomy	Complete excision of tibial sesamoid when entire sesamoid is non-viable (complete AVN), severely comminuted, or chronically infected (osteomyelitis); FHB tibial head tendon repair essential after excision	Risk: hallux valgus deformity from loss of medial sesamoid restraint (fibular sesamoid pulls great toe laterally without medial counterbalance); meticulous FHB repair minimizes this risk; outcomes good in 80-85% when FHB repair performed; total fibular sesamoidectomy risk: hallux varus

At Balance Foot & Ankle in Howell and Bloomfield Hills, tibial sesamoid fractures are distinguished from bipartite sesamoids by the smoothness of the cortical margins and bilateral X-ray comparison — an acute fracture has irregular jagged edges while a bipartite sesamoid has smooth corticated margins on both sides of the gap — and MRI is ordered when plain films are inconclusive, because correctly identifying a true fracture allows early aggressive offloading that significantly reduces the risk of non-union and avascular necrosis. Call (810) 206-1402.