Os Trigonum Syndrome: Posterior Ankle Impingement, Diagnosis, and Surgical Excision

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

Os trigonum syndrome — posterior ankle impingement from a symptomatic os trigonum (an accessory ossicle of the posterolateral talus present in 7–14% of the population) — is the most common cause of posterior ankle pain in ballet dancers and soccer players who perform repetitive forced plantarflexion, but it also occurs in runners and patients with acute plantarflexion ankle injuries who experience fragmentation or synovitis around a previously asymptomatic os trigonum. Recognition of this condition prevents delays in diagnosis and guides prompt conservative and surgical treatment.

Anatomy, Pathophysiology, and Diagnosis

Os trigonum anatomy: an accessory ossification center at the posterior process of the talus — when it fails to fuse with the talus (completing ossification by age 11–13), it remains as a separate ossicle connected by a fibrocartilaginous synchondrosis (‘talar tail’); the os trigonum is located immediately adjacent to the flexor hallucis longus (FHL) tendon, whose sheath passes through the groove between the medial and lateral posterior talar processes. Mechanism of impingement: forced plantarflexion (grand plié in ballet, kicks in soccer, push-off in running) compresses the os trigonum between the posterior tibial plafond and the calcaneus; the synchondrosis can acutely fragment, or chronic repetitive microimpingement produces synovitis, fibrocartilaginous enlargement, and FHL tenosynovitis from the adjacent tendon. Clinical features: posterior ankle pain with forced plantarflexion; the ‘nutcracker test’ — passive forced plantarflexion reproduces posterior ankle pain; FHL tenosynovitis produces triggering or pain with great toe flexion against resistance. Imaging: lateral ankle X-ray with plantarflexion view shows the os trigonum and any fragmentation; MRI confirms bone marrow edema within the os trigonum, synchondrosis inflammation, and FHL tenosynovitis.

Treatment

Conservative: activity modification; NSAID therapy; posterior ankle corticosteroid injection (ultrasound-guided, posterior approach between Achilles and FHL — highly effective for acute synovitis); boot immobilization for 4–6 weeks; physical therapy for posterior ankle mobility and eccentric calf strengthening. Surgical excision: indicated for refractory symptoms after 3–6 months of conservative care — endoscopic (posterior two-portal arthroscopic approach) os trigonum excision and FHL tenosynovitis release; faster recovery than open excision (return to sport 6–8 weeks); complication rate <5%; open posteromedial approach for complex cases. Outcomes: 85–90% return to pre-injury activity level within 3–4 months; FHL tendon release concurrent with os trigonum excision reduces FHL tenosynovitis recurrence. Dr. Biernacki at Balance Foot & Ankle diagnoses and treats os trigonum syndrome and posterior ankle impingement at our Bloomfield Township and Howell offices. Call (810) 206-1402.

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In-Office Treatment at Balance Foot & Ankle

If home care isn’t resolving your your foot or ankle concern, a visit with a board-certified podiatrist is the fastest path to accurate diagnosis and a personalized plan. At Balance Foot & Ankle Specialists, Dr. Tom Biernacki, Dr. Carl Jay, and Dr. Daria Gutkin offer same-day and next-day appointments at both our Howell and Bloomfield Township offices. We perform on-site diagnostic ultrasound, digital X-ray, conservative care, advanced regenerative treatments, and minimally invasive surgery when indicated.

Call (810) 206-1402 or request an appointment online. Most insurance plans accepted, including Medicare, Blue Cross Blue Shield, Aetna, Cigna, and United Healthcare.

Frequently Asked Questions

How do I know if I sprained or broke my ankle?

Both cause pain, swelling, and difficulty walking. Key differences: fractures often cause more immediate severe pain, tenderness directly over bone (not just ligament), and inability to bear any weight. X-rays and the Ottawa Ankle Rules help determine if imaging is needed.

How long does an ankle sprain take to heal?

Grade I (mild): 1–2 weeks. Grade II (moderate): 3–6 weeks. Grade III (complete tear): 2–3 months. Chronic instability from improperly treated sprains can persist and may require surgery.

What is the best treatment for a sprained ankle?

RICE protocol (Rest, Ice, Compression, Elevation) for the first 48–72 hours, followed by protected weight-bearing as tolerated. Physical therapy rehabilitation is critical for high-grade sprains to restore strength and proprioception and prevent chronic instability.

Need Treatment at Balance Foot & Ankle?

Dr. Tom Biernacki, Dr. Carl Jay, and Dr. Daria Gutkin see patients at our Howell and Bloomfield Township offices.

Book Online or call (810) 206-1402

Most Common Mistake We See

The most common mistake we see is: Waiting too long before seeking care. Fix: any foot pain lasting more than 4 weeks, or any sudden severe symptom, deserves a professional evaluation rather than more rest.

Warning Signs That Need Same-Day Care

Frequently Asked Questions

What causes this condition?

Causes include mechanical stress, biomechanical imbalance, age-related changes, and sometimes systemic disease. Our clinical exam plus imaging identifies the specific driver.

Can it go away on its own?

Mild cases sometimes resolve with rest and supportive footwear. Persistent symptoms past 4-6 weeks rarely resolve without active treatment.

Is surgery required?

Most patients resolve with non-surgical care. Surgery is reserved for refractory cases or structural deformity.

Related Care at Balance Foot & Ankle

Clinical ankle services at our Howell and Bloomfield Township offices.

Ankle Sprain & InstabilityFoot BracingAnkle Arthroscopy