Os Trigonum 2026: Posterior Ankle Pain | DPM

Feature	Os Trigonum Syndrome	FHL Tenosynovitis	Achilles Tendinopathy (Insertional)
Pain location	Deep posterior ankle; behind lateral malleolus	Posteromedial ankle; along FHL tendon toward great toe	Posterior heel at Achilles insertion on calcaneus
Provocative test	Forced plantarflexion (nutcracker) test	Resisted great toe flexion in plantarflexion	Palpation at Achilles insertion; pain with heel raises
Imaging	Os trigonum on lateral X-ray; edema on MRI	Fluid in FHL sheath on MRI; may coexist with os trigonum	Achilles thickening/calcification on X-ray and MRI
Common in	Ballet dancers, gymnasts, soccer players (repeated plantarflexion)	Ballet dancers, runners (big toe push-off demands)	Masters runners, middle-aged active adults, hill runners
Conservative success	60–70% with injection + immobilization	70–80% with rest + PT	60–70% with eccentric exercises + PT
Surgical option	Arthroscopic or open os trigonum excision	FHL tendon sheath release + debridement	Insertional debridement + calcaneal osteotomy (Haglund)

Treatment	Timeline	Success Rate	Notes
Immobilization (boot or cast)	4–6 weeks	50–65%	Eliminates plantarflexion loading; most effective in acute onset cases
Corticosteroid injection (posterior ankle)	Relief in 1–2 weeks; lasts 2–4 months	60–75%	Targets posterior capsule/os trigonum synchondrosis; avoid intratendinous injection near FHL
Physical therapy (equinus correction)	6–8 weeks	50–60%	Addresses tight posterior chain contributing to impingement
Arthroscopic excision	NWB 2–3 weeks; return to sport 6–8 weeks	85–95%	Gold standard surgical approach; preserves FHL function; dancers return to full pointe rapidly
Open excision	NWB 3–4 weeks; return to sport 8–12 weeks	80–90%	Preferred when os trigonum is large or FHL release needed simultaneously

What Is the Os Trigonum?

The os trigonum is an accessory bone located posterior to the talus (heel bone), just behind the ankle joint. It is present in approximately 7–10% of the population and arises from a secondary ossification center that fails to fuse with the main body of the talus during adolescent skeletal development. In most people, the os trigonum is an incidental finding on X-ray that causes no problems whatsoever.

However, in certain patients — particularly dancers, gymnasts, soccer players, and others who repeatedly plantarflex (point) the foot — the os trigonum can be compressed between the posterior tibia and the calcaneus during extreme plantarflexion, causing significant pain and functional limitation. This condition is called os trigonum syndrome or posterior ankle impingement syndrome.

At Balance Foot & Ankle, Dr. Tom Biernacki provides expert diagnosis and treatment for os trigonum syndrome using a structured approach from activity modification and corticosteroid injection to minimally invasive endoscopic or open os trigonum excision when conservative care fails.

Who Gets Os Trigonum Syndrome?

Os trigonum syndrome has a strong association with activities that require extreme plantarflexion. Classic patient profiles include:

• Ballet dancers: The en pointe and demi-pointe positions create maximum plantarflexion — repeatedly compressing any posterior bony prominence with every relevé. Os trigonum syndrome is so common in dancers that it is sometimes called “dancer’s ankle.”
• Soccer players: Kicking with the pointed foot compresses the posterior ankle. Receiving and deflecting balls with the top of the foot also creates acute plantarflexion stress.
• Gymnasts: Beam work, floor exercise, and vault approaches involve significant repetitive ankle plantarflexion.
• Track and field athletes: Sprinters, jumpers, and hurdlers generate substantial plantarflexion forces with every push-off.
• Recreational athletes: Any active adult with an os trigonum who increases activity volume or starts a new plantarflexion-intensive sport can develop symptoms.

Symptoms of Os Trigonum Syndrome

The hallmark symptom is posterior ankle pain with plantarflexion — pain at the back of the ankle when pointing the foot. Specific findings include:

• Deep posterior ankle pain with forced plantarflexion (the “nutcracker test” — passive forced plantarflexion that reproduces pain is the key clinical test)
• Tenderness on palpation just posterior to the peroneal tendons and behind the lateral malleolus
• Swelling in the posterior ankle
• Symptoms reproduced by descending stairs (which loads the plantarflexed position) and sports activities requiring point loading

Diagnosing Os Trigonum in Michigan

Dr. Biernacki diagnoses os trigonum syndrome through a combination of:

Clinical examination: Passive forced plantarflexion reproducing the characteristic posterior pain, with tenderness localized to the posterolateral ankle posterior to the fibula.

X-ray: Lateral ankle view demonstrates the os trigonum posterior to the talus. The size of the os trigonum varies — larger bones create more impingement potential but size does not always correlate perfectly with symptoms.

MRI: The gold standard for confirming symptomatic os trigonum syndrome. T2 bone marrow edema within the os trigonum or at the synchondrosis, associated soft tissue edema in the posterior ankle, and assessment of the flexor hallucis longus (FHL) tendon (which passes through a groove adjacent to the os trigonum and is frequently involved in posterior ankle impingement).

Diagnostic injection: Fluoroscopy or ultrasound-guided injection of local anesthetic around the os trigonum provides confirmatory evidence — if symptoms are reproduced by the injection site and then briefly eliminated by the local anesthetic, the diagnosis is confirmed.

Conservative Treatment

Activity modification: Reducing or eliminating plantarflexion-intensive activities during the acute phase. For dancers, modified training that avoids pointe work until acute inflammation resolves.

Immobilization: A short leg walking boot or cast for 4–6 weeks rests the posterior ankle and allows the os trigonum synchondrosis inflammation to resolve.

Corticosteroid injection: A precisely targeted injection of corticosteroid and local anesthetic into the posterior ankle under ultrasound or fluoroscopic guidance provides significant anti-inflammatory effect. Response to injection is also diagnostically informative.

Physical therapy: FHL strengthening, posterior ankle flexibility work, and proprioceptive training help optimize return to sport after acute symptoms resolve.

Surgical Excision of the Os Trigonum

When conservative management fails (typically after 3–6 months without adequate improvement), surgical excision provides excellent results. Dr. Biernacki performs os trigonum excision via:

Endoscopic (arthroscopic) excision: Two small portals are made at the posterolateral ankle. The os trigonum is identified and removed with a shaver and burr under direct visualization. Minimally invasive technique with faster recovery and return to sport than open excision — the preferred approach for most patients.

Open excision: Through a posterolateral incision for complex cases with associated FHL tendon pathology, large os trigonum, or when endoscopic anatomy is challenging.

Recovery after endoscopic excision: 2 weeks in a boot, then progressive return to activity over 4–6 weeks. Most athletes return to full sport participation by 6–8 weeks post-surgery.

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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.

Visit Balance Foot & Ankle — Same-Day Appointments Available

Our podiatry team serves patients throughout Michigan including Howell, Brighton, and Bloomfield Hills. Whether you’re dealing with heel pain, ingrown toenails, or a foot injury, we have same-day appointment availability.