Posterior ankle impingement syndrome (PAIS) — pain from soft tissue or bony compression in the posterior ankle with forced plantarflexion — is among the most common ankle conditions in ballet dancers, soccer players, and athletes who repeatedly load the ankle in terminal plantarflexion. The os trigonum, a posterior talar accessory ossicle present in 5–14% of the population, is frequently the osseous driver of posterior impingement when present and symptomatic.

Anatomy and Pathomechanics

The posterior talar process (Stieda process) projects posteriorly from the talus, adjacent to the posterior capsule, posterior inferior tibiofibular ligament, and flexor hallucis longus (FHL) tendon sheath. The os trigonum develops from a secondary ossification center of the posterior talar process that fails to fuse — creating a separate ossicle connected to the talus by a fibrocartilaginous synchondrosis. During forced plantarflexion, the posterior talar process (or os trigonum) is compressed between the posterior tibia and calcaneus — producing the characteristic posterior ankle pain of PAIS that limits the en pointe position in dance and the follow-through in kicking sports.

Clinical Presentation and Diagnosis

Patients describe deep posterior ankle pain exacerbated by forced plantarflexion — the “nutcracker test” (passive forced plantarflexion) reproduces posterior ankle pain and is positive in PAIS. FHL tendinopathy frequently coexists (FHL tendon runs immediately medial to the posterior process), contributing medial posterior ankle pain that worsens with hallux flexion. Tenderness is present on direct palpation posterior to the lateral ankle malleolus adjacent to the Achilles tendon. Weight-bearing lateral X-ray identifies the os trigonum or elongated Stieda process; MRI demonstrates bone marrow edema at the posterior talar process/os trigonum and any associated FHL tendinopathy or synovitis.

Conservative Treatment

Initial conservative management includes relative rest from plantarflexion-demanding activities, corticosteroid injection posterior to the talar process under ultrasound guidance, physical therapy addressing ankle dorsiflexion mobility (reducing plantarflexion demand), and dancer’s rehabilitation programs modifying technique to reduce posterior ankle compressive loading. Conservative care resolves PAIS in 40–60% of patients within 3–4 months.

Surgical Treatment: Os Trigonum Excision

Os trigonum excision is indicated for symptomatic PAIS failing 3–6 months of conservative care. Arthroscopic posterior ankle two-portal excision has largely replaced open excision, achieving equivalent ossicle removal with substantially reduced soft tissue disruption, scar formation, and recovery time. The FHL tendon is examined and debrided concurrently if tendinopathic. Return to dance or sport averages 3–4 months following arthroscopic excision, with over 90% of patients returning to their previous activity level.

Posterior Ankle Evaluation at Balance Foot & Ankle

Dr. Biernacki at Balance Foot & Ankle evaluates posterior ankle pain with weight-bearing lateral radiographs, ultrasound-guided posterior ankle injection, and MRI coordination for patients with suspected os trigonum syndrome or FHL tendinopathy. Surgical excision planning for posterior ankle arthroscopy is available. Call (810) 206-1402 for a same-week posterior ankle evaluation.

Dr. Tom Biernacki, DPM

Dr. Tom Biernacki, DPM is a double board-certified podiatrist and foot & ankle surgeon at Balance Foot & Ankle Specialists in Southeast Michigan. With over a decade of clinical experience, he specializes in heel pain, bunions, diabetic foot care, sports injuries, and minimally invasive surgery. Dr. Biernacki is a member of the APMA and ACFAS, and his patient education content on MichiganFootDoctors.com and YouTube has reached over one million views.