Accessory Bones of the Foot: Os Trigonum, Accessory Navicular, and Others

Quick answer: Os Trigonum Accessory Navicular Accessory Bones Foot is a common foot/ankle topic that affects many patients. Effective treatment starts with a targeted diagnosis, conservative-first treatment, and escalation only when needed. We treat this regularly at our Howell and Bloomfield Hills practices. Call (810) 206-1402.

Medically reviewed by Dr. Tom Biernacki, DPM — Board-Certified Podiatric Surgeon — Balance Foot & Ankle, Howell & Bloomfield Hills, MI. Last updated April 2026.

Accessory bones are small supplementary ossicles adjacent to normal foot bones that develop from separate ossification centers during skeletal development. Most are asymptomatic incidental findings on X-ray, but several — particularly the os trigonum and accessory navicular — become significant sources of pain in active individuals. Understanding which accessory bones cause pain and how to treat them prevents both underdiagnosis of genuine pathology and overtreatment of normal variants.

Os Trigonum

The os trigonum is a small oval bone posterior to the talus, present in approximately 7–14% of the population. It represents a failure of fusion of the posterior lateral tubercle of the talus — this ossicle normally fuses to the talus between ages 8–11; when it fails to fuse, the os trigonum persists as a separate bone connected by fibrocartilage to the talus.

Symptomatic os trigonum (os trigonum syndrome) occurs when the ossicle is compressed between the calcaneus and posterior tibia during forced plantarflexion. Classic presentation: posterior ankle pain with plantarflexion activities in ballet dancers, gymnasts, or soccer players. Diagnosis is confirmed by MRI (bone marrow edema in the os trigonum and adjacent talus on STIR sequences) or bone scan. Treatment: conservative management (activity modification, boot immobilization, corticosteroid injection) succeeds in approximately 50–60% of cases; arthroscopic or open excision achieves excellent results in surgical cases.

Accessory Navicular (Os Naviculare)

The accessory navicular is present in approximately 4–14% of the population and is bilateral in 50–90% of cases. Three types are recognized: Type 1 (os tibiale externum) — a sesamoid bone within the posterior tibial tendon, rarely symptomatic. Type 2 — an ossicle connected to the navicular by a fibrocartilaginous synchondrosis, 2–6 mm from the navicular body; this is the type that becomes symptomatic. Type 3 (cornuate navicular) — a completely fused prominence of the navicular, asymptomatic.

Type 2 accessory navicular syndrome presents as medial midfoot pain over the prominent accessory navicular in active children and adolescents (ages 8–14) and in adults with pes planus. The prominence of the accessory navicular increases with flatfoot from posterior tibial tendon dysfunction; the synchondrosis becomes stressed during push-off. Treatment: custom orthotics with medial arch support reduce PTT tension; a short course of immobilization manages acute flares. Surgical excision (Kidner procedure — excision of the accessory navicular with PTT advancement) is effective for refractory cases.

Os Vesalianum (Base of Fifth Metatarsal)

The os vesalianum is an accessory ossicle adjacent to the proximal fifth metatarsal base, present in approximately 1–5% of the population. Its significance lies in radiographic differentiation from fifth metatarsal base avulsion fracture — the os vesalianum has smooth, rounded, corticated edges; a fracture has sharp, irregular, non-corticated edges. MRI is definitive when X-ray is ambiguous. Most os vesalianum are asymptomatic; symptomatic cases respond to activity modification and orthotics.

Sesamoids: Bipartite vs. Fractured

As discussed in detail separately, bipartite sesamoids (present in 10–30% of people) are frequently confused with sesamoid fractures on X-ray. Bipartite sesamoids have corticated, smooth margins and are typically bilateral; fractures have irregular, non-corticated edges. MRI with bone marrow edema at the fracture site confirms a fracture; absence of edema supports bipartite sesamoid.

Other Accessory Bones

The os supranaviculare lies dorsal to the talonavicular joint and can cause dorsal midfoot pain with shoe pressure. The os peroneum lies within the peroneus longus tendon at the cuboid; injury to the os peroneum can indicate peroneus longus tendon rupture. The os subfibulare lies adjacent to the distal fibula and may be confused with an avulsion fracture of the anterolateral talofibular ligament after ankle sprain.

At Balance Foot & Ankle, Dr. Biernacki evaluates foot pain with weight-bearing X-rays at both Bloomfield Hills and Howell offices, accurately distinguishing symptomatic accessory bones from fractures and other pathology. Call (810) 206-1402 for an evaluation.

Differential Diagnosis: What Else Could It Be?

Not every case of accessory navicular syndrome is straightforward. In our clinic we routinely rule out three look-alike conditions before confirming the diagnosis. If your symptoms don’t match the classic presentation, one of these may explain the pain — which is why physical exam matters more than self-diagnosis.

Condition	How It Differs
Posterior tibial tendon dysfunction	Pain along the tendon course with progressive flatfoot; may coexist.
Medial midfoot sprain	Ligamentous tenderness without a prominent bony bump.
Navicular stress fracture	Dorsal midfoot pain with impact; confirmed on MRI, not an accessory bone.

Red Flags — When to See a Podiatrist Now

In Our Clinic: What We See

In-Office Treatment at Balance Foot & Ankle

If home treatment isn’t providing relief for your foot and ankle pain, our podiatry team at Balance Foot & Ankle can help with same-day evaluations and advanced in-office care.

Frequently Asked Questions

When should I see a podiatrist?

If symptoms persist past 2 weeks, affect your normal activity, or are accompanied by red-flag symptoms (warmth, redness, swelling, inability to bear weight).

What does treatment cost?

Most diagnostic visits and conservative treatments are covered by Medicare and major insurers. Out-of-pocket costs vary by your specific plan.

How quickly can I get an appointment?

Most non-urgent cases see us within 5 business days. Urgent cases (sudden pain, possible fracture) typically same or next business day.

Related Care at Balance Foot & Ankle

Clinical navicular services at our Howell and Bloomfield Hills offices.

Custom OrthoticsFoot BracingFlat Feet Treatment