Posterior Ankle Impingement & Os Trigonum 2026 | DPM

Condition	Anatomy	Pain Location	Provocative	Imaging	Treatment
Os Trigonum Syndrome	Unfused posterior talar ossicle compressed between tibia and calcaneus	Posterior ankle; deep to Achilles; lateral to FHL	Forced plantarflexion (dancers, downhill runners)	Lateral X-ray: os trigonum; MRI: bone edema, fluid	Rest, injection; arthroscopic excision if refractory
Posterior Talar Process Fracture (Shepherd Fracture)	Fracture of posterior lateral process of talus	Same as os trigonum	Plantarflexion injury; history of acute inversion	CT scan confirms fracture vs os trigonum	Boot immobilization 4–6 weeks; excision if non-union
FHL Tendinopathy	Flexor hallucis longus irritation in fibro-osseous tunnel	Medial posterior ankle; “dancer’s tendinitis”	Resisted hallux plantarflexion; triggering at MTP	US or MRI: FHL tenosynovitis	PT, injection; endoscopic FHL release if refractory

Treatment	Indication	Success	Notes
Activity modification + plantarflexion avoidance	All patients — first-line	60–70% resolve in 6–12 weeks	Avoid pointe position; limit downhill running
Boot immobilization	Acute flare; athletes in-season	70–80% symptom reduction	4–6 weeks; then gradual return to activity
Corticosteroid injection (posterior)	Persistent pain; confirms diagnosis	50–70% short-term relief	US or fluoroscopic guidance; posterior approach between Achilles and FHL
Arthroscopic os trigonum excision	Failed 3–6 months conservative care	85–95% excellent relief	Posterior 2-portal endoscopic; return to dance 3–4 months
Open excision	Failed arthroscopy; very large os; combined with FHL release	80–85%	Slightly longer recovery; lateral or posteromedial approach

https://www.youtube.com/watch?v=8opvH3qxkW4

While anterior ankle impingement affects the front of the ankle, posterior ankle impingement syndrome (PAIS) causes pain at the back of the ankle during plantarflexion — pointing the foot down. It is particularly common in ballet dancers (who perform in extreme plantarflexion), soccer players (who kick with the instep), and gymnasts. The condition can significantly impair performance and, when left untreated, become chronically disabling.

Anatomy: The Os Trigonum and Sternberg Process

The talus (ankle bone) has a posterior lateral tubercle at its back. In most people, this fuses seamlessly into the body of the talus. In approximately 5–10% of people, a secondary ossification center fails to fuse and remains as a separate bone — the os trigonum. When the ankle is forcefully plantarflexed, the os trigonum (or an enlarged Sternberg process — the unfused tubercle) becomes compressed between the calcaneus and the posterior tibia, causing pain, inflammation, and sometimes injury to the overlying flexor hallucis longus (FHL) tendon, which runs directly alongside.

Symptoms of Posterior Ankle Impingement

PAIS causes deep, posterior ankle pain specifically provoked by forced plantarflexion — particularly end-range plantarflexion. Dancers feel it in relevé and pointe. Soccer players feel it when striking the ball with the instep. Stair descent and running downhill may also trigger symptoms. There may be swelling and tenderness directly behind and below the lateral malleolus, and sometimes concomitant FHL tendon pain running along the inner ankle toward the big toe (a subtle sign distinguishing PAIS from simple posterior ankle pain).

Diagnosis

Lateral weight-bearing foot X-ray identifies an os trigonum or enlarged posterior talar process. The forced plantarflexion test — passive forced plantarflexion of the ankle by the examiner reproducing posterior ankle pain — is a sensitive clinical test. MRI provides definitive characterization: bone marrow edema in the os trigonum and surrounding structures confirms active impingement and inflammation. Ultrasound-guided injection of local anesthetic into the posterior ankle that eliminates pain during forced plantarflexion is both diagnostic and therapeutic.

Conservative Treatment

Activity modification to avoid forced plantarflexion during the acute phase is essential — dancers may need to temporarily avoid pointe work. NSAID anti-inflammatory medications reduce acute symptoms. An ultrasound-guided cortisone injection into the posterior ankle posterior to the os trigonum provides significant relief in many cases and has both diagnostic and therapeutic value. Physical therapy addressing FHL stretching, ankle proprioception, and posterior chain strengthening supports recovery. Most patients with symptomatic os trigonum will trial 6–12 weeks of conservative care before surgical consideration.

Surgical Excision: Arthroscopic and Open

When conservative management fails, surgical excision of the os trigonum provides reliable, durable relief. The procedure can be performed arthroscopically — using two posterior portals to visualize and remove the extra bone — or via a small open incision behind the lateral malleolus. Arthroscopic excision allows faster return to sport (6–10 weeks for dancers) compared to open surgery (10–16 weeks). Both approaches have excellent long-term outcomes with high patient satisfaction rates. The excised bone does not regenerate, providing permanent resolution of impingement.

Dr. Tom's Product Recommendations

In-Office Treatment at Balance Foot & Ankle

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