Os Trigonum Posterior Ankle Impingement 2026 | DPM

Condition	Pain Location	Provocative Maneuver	Imaging	Population	Treatment
Os Trigonum Syndrome	Posterior ankle; deep to Achilles; lateral to FHL	Forced plantarflexion (nutcracker test); positive in ballet relevé	X-ray: os trigonum (separate ossicle posterior talus); MRI: bone edema around os	Dancers, soccer players, gymnasts	Injection; endoscopic excision if persistent
Posterior Ankle Impingement (soft tissue)	Same; may be more medial with FHL involvement	Plantarflexion test; FHL resistance positive if tendon involved	MRI: posterior capsular thickening; synovitis; no os trigonum	Athletes with repetitive plantarflexion	PT, injection; arthroscopic debridement
FHL Tenosynovitis	Posteromedial; along FHL course	FHL resistance (resisted hallux plantarflexion); triggering	US/MRI: FHL tenosynovial fluid; possible nodule	Ballet dancers (en pointe)	Injection; FHL sheath release
Stieda Process (Elongated Posterior Talar Process)	Posterior ankle; similar to os trigonum	Forced plantarflexion	X-ray: elongated posterior talar process (not separate)	Same athletic populations	Same as os trigonum — injection or excision

Treatment	Indication	Details	Outcome
Activity Modification + PT	All posterior impingement — first-line	Avoid forced plantarflexion; posterior ankle mobilization; 4–6 weeks	Resolves in 30–40% of mild cases without injection
Corticosteroid Injection (posterior ankle)	Persistent symptoms after 4–6 weeks PT	Ultrasound-guided; posterior approach; 1–2 injections	65–75% significant relief; diagnostic and therapeutic
Endoscopic Os Trigonum Excision	Failed 3–6 months conservative; os trigonum confirmed symptomatic	Two-portal posterior endoscopic approach; removes os and posterior capsule	85–95% return to sport; faster than open (6–8 weeks vs 3–4 months)
Open Posterior Ankle Surgery	Complex lesions; FHL involvement requiring repair; revision	Posterolateral or posteromedial approach; more extensive access	Good outcomes; longer recovery (3–4 months to sport)
FHL Sheath Release (concurrent)	Os trigonum with FHL tenosynovitis (common combination)	Performed endoscopically at same time as os excision	Addresses both pathologies; no additional recovery time

The os trigonum is an accessory ossicle — a small extra bone — located posterior to the talus that is present in approximately 10% of the general population. In most people, the os trigonum causes no problems whatsoever. But in athletes and performers who repeatedly force the ankle into extreme plantarflexion — ballet dancers going en pointe, soccer players kicking with the instep, swimmers performing flutter kicks, or downhill runners with forced heel push-off — the os trigonum can become a source of significant posterior ankle pain from impingement between the tibia and calcaneus.

At Balance Foot & Ankle PLLC in Howell, Michigan, Dr. Tom Biernacki diagnoses and treats os trigonum syndrome for dancers, athletes, and active patients who experience posterior ankle pain that has resisted standard ankle sprain treatment. Many of these patients have been misdiagnosed with chronic ankle sprain or Achilles tendinopathy before the true diagnosis is identified on MRI or CT.

What Is the Os Trigonum?

During skeletal development, a secondary ossification center forms behind the posterior process of the talus. In most individuals, this center fuses with the main talus body by age 16. In approximately 10% of people, it fails to fuse and persists as a separate ossicle — the os trigonum — connected to the talus by fibrocartilaginous tissue. Radiographically, the os trigonum appears as a small, round or triangular bone immediately posterior to the talus on lateral X-ray.

The os trigonum lies adjacent to the flexor hallucis longus (FHL) tendon tunnel, and os trigonum syndrome is often accompanied by FHL tenosynovitis from compression and friction. The FHL tendon component frequently contributes to the overall posterior ankle pain syndrome and must be addressed simultaneously in surgical planning.

Symptoms of Os Trigonum Syndrome

Posterior ankle pain is the hallmark symptom — specifically deep pain behind the ankle that is reproduced by forced plantarflexion (pointing the foot maximally). In ballet dancers, pain typically occurs when going en pointe or demi-pointe. Soccer players notice pain when striking the ball with the dorsum of the foot. Tenderness on palpation posterior to the lateral malleolus and between the Achilles tendon and the fibula is characteristic. FHL involvement produces additional catching or triggering of the big toe as described in the FHL tendinopathy section.

Symptoms commonly develop acutely after a forced plantarflexion injury or insidiously from repetitive athletic loading. The condition is often intermittent initially — present during activity and resolving with rest — but can become constant and function-limiting as the syndrome progresses.

Diagnosis

Lateral X-ray or CT scan demonstrates the os trigonum and its relationship to the surrounding bony anatomy. MRI provides the most comprehensive evaluation, showing bone marrow edema within the os trigonum (indicating active impingement), FHL tendon sheath fluid, synovitis, and soft tissue edema. A diagnostic local anesthetic injection into the posterior ankle confirms that the pain is arising from this anatomical region — if injection abolishes the pain, surgical excision is very likely to be effective.

Conservative Treatment

Acute os trigonum syndrome is initially managed with activity modification to avoid forced plantarflexion, immobilization in a walking boot for 4–6 weeks, NSAIDs, and physical therapy. Corticosteroid injection into the posterior ankle provides anti-inflammatory relief and serves as a diagnostic tool. In dancers and athletes whose activity cannot be fully modified, technique adjustments to reduce extreme plantarflexion loading may help control symptoms during competitive seasons.

Surgical Os Trigonum Excision

Surgical excision of the os trigonum is performed when conservative management fails after 3–6 months or when the patient’s activity demands make non-operative management impractical. The procedure is performed through a posteromedial or posterolateral approach, or endoscopically (arthroscopic excision) in appropriate candidates. The os trigonum is identified, its fibrocartilaginous connection to the talus is divided, and the bone is excised in its entirety. Associated FHL tenosynovitis is addressed simultaneously with tenolysis of the FHL tendon sheath. Recovery involves 2–3 weeks of protected weight-bearing, with return to dance or sport at 3–4 months post-operatively. Endoscopic excision typically offers faster recovery than open techniques. Surgical outcomes are excellent, with the vast majority of patients returning to full sport or dance activity without posterior ankle pain. Call Balance Foot & Ankle at (517) 315-6969 for a posterior ankle impingement evaluation in Howell, Michigan.

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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. If you’re dealing with heel pain, ingrown toenails, or a foot injury, we have same-day appointment availability.