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

Posterior ankle impingement causes deep ankle pain at the back of the heel when pointing the foot — a condition common in ballet dancers, soccer players, and gymnasts, and often caused by an os trigonum, an accessory bone that pinches soft tissue with plantarflexion. Dr. Tom Biernacki, DPM, at Balance Foot & Ankle in Howell and Bloomfield Hills, Michigan, evaluates and treats os trigonum syndrome and all causes of posterior ankle pain with conservative and surgical options.

Quick Answer: What Is Posterior Ankle Impingement?

Posterior ankle impingement is pain at the back of the ankle caused by compression of soft tissue or bone when the foot is maximally plantarflexed (pointed downward). The most common cause is an os trigonum — a small accessory ossicle at the posterior lateral talus present in approximately 10–15% of the population. When the foot is pointed, the os trigonum or the posterolateral talus (Stieda process) is compressed between the tibia and calcaneus. Most cases respond to cortisone injection and activity modification; surgical excision of the os trigonum reliably resolves the condition in refractory cases.

Anatomy: Os Trigonum and the Posterior Ankle

The os trigonum is a secondary ossification center of the posterior talus that fails to fuse with the main talus body, resulting in a separate small bone connected by a fibrocartilaginous synchondrosis. It is present bilaterally in approximately 50% of cases when found unilaterally. The os trigonum sits in close proximity to the flexor hallucis longus (FHL) tendon in the posterior ankle groove — FHL tenosynovitis frequently accompanies os trigonum syndrome and must be treated concurrently. The posterior ankle is also bounded by the posterior ankle capsule, the posterior talofibular ligament, and the posterior tibiofibular ligament — all of which can be sources of impingement independent of ossicle presence.

Who Gets Posterior Ankle Impingement?

Posterior ankle impingement is an occupational and sport-specific injury. Ballet dancers are the most commonly affected group — the en pointe and demi-pointe positions maximally compress the posterior ankle with every repetition. Soccer players develop it from repeated plantarflexion kicks and downhill running. Gymnasts, freestyle skiers, and synchronized swimmers have high rates from extreme plantarflexion demands. In non-athletes, posterior ankle pain is frequently triggered by a single forced plantarflexion injury — a missed step on stairs landing on a pointed foot, a car accident with the foot braced on the pedal, or a fall in heels. In our clinic, we also see a subset of patients with posterior ankle pain secondary to subtalar joint arthritis, which must be differentiated from os trigonum syndrome by CT scan.

Diagnosis: Clinical Tests and Imaging

Clinical diagnosis is made by the forced plantarflexion test: rapid passive plantarflexion of the ankle reproduces posterior ankle pain within 1–2 seconds. Sensitivity is approximately 84% for posterior impingement. Palpation of the posterolateral ankle between the Achilles and peroneal tendons elicits direct tenderness over the os trigonum or posterior talus. FHL tendon involvement is confirmed by asking the patient to flex and extend the great toe while palpating the posterior medial ankle — pain with active FHL glide indicates concomitant FHL tenosynovitis. Plain X-rays (lateral view) identify the os trigonum in 70% of cases; CT scan better characterizes the ossicle size and synchondrosis gap. MRI is the gold standard when plain X-ray is negative, demonstrating bone marrow edema in the os trigonum (indicating stress at the synchondrosis) and associated soft tissue inflammation.

Conservative Treatment Protocol

Conservative treatment is successful in approximately 60% of posterior ankle impingement cases. The protocol begins with 4–6 weeks of activity modification — eliminating all forced plantarflexion activities (ballet, kicking sports, stair descent barefoot). NSAIDs for 2 weeks reduce periossicle inflammation. A walking boot with the foot in slight dorsiflexion unloads the posterior ankle. Ultrasound-guided cortisone injection into the posterior ankle recess (not directly into the os trigonum synchondrosis, which risks fibrocartilage damage) provides excellent short-to-medium term relief. FHL stretching and gentle eccentric calf work address the tendon component. After pain-free period, a graduated return to sport program is initiated. In ballet dancers, technique correction — specifically avoiding sickling and winging — reduces recurrence.

Surgical Treatment: Os Trigonum Excision

Surgical excision of the os trigonum is indicated when 3–6 months of conservative treatment has failed to resolve symptoms or when the athlete cannot afford extended time away from their sport. Two surgical approaches are used. Open posterior approach: direct access between the Achilles and FHL tendons with excellent visualization — typically used when concomitant subtalar or posterior ankle pathology requires simultaneous treatment. Arthroscopic excision: two posterior portals using a posterior ankle arthroscopy technique — faster recovery (return to dance in 6–8 weeks versus 10–12 for open), less scar tissue formation, equal success rates for isolated os trigonum excision. Both approaches include release of the posterior ankle capsule and FHL tendon sheath to comprehensively address all posterior impingement sources. Success rate for complete symptom resolution: approximately 85–90% at 1 year. In ballet dancers, return to full pointe work occurs at 10–14 weeks after arthroscopic excision.

Flexor Hallucis Longus Tenosynovitis: The Often-Missed Component

FHL tenosynovitis accompanies os trigonum syndrome in approximately 40% of cases and is frequently the primary pain generator even when an os trigonum is present. The FHL tendon passes immediately medial to the os trigonum in a fibro-osseous tunnel behind the medial malleolus — inflammation causes catching, locking, or triggering of the big toe (hallux saltans). In ballet dancers, “trigger toe” — where the big toe catches or locks in flexion — is pathognomonic for FHL tenosynovitis. If not addressed concurrently with os trigonum excision, persistent FHL symptoms after surgery are a common cause of suboptimal outcomes. MRI with dynamic evaluation (foot in neutral and plantarflexion) best demonstrates the FHL tendon involvement.

Differential Diagnosis: Other Causes of Posterior Ankle Pain

Posterior ankle pain must be differentiated from several conditions before attributing it to os trigonum syndrome. Achilles tendon pathology (insertional or mid-substance tendinopathy) causes pain posterior to the ankle but is triggered by dorsiflexion loading, not plantarflexion — the opposite of os trigonum. Subtalar joint arthritis causes deep posterior-lateral ankle pain with walking on uneven surfaces; CT scan is diagnostic. Posterior ankle impingement from a bony Stieda process on the talus (without a separate os trigonum) is treated identically. Tarsal tunnel syndrome (posterior tibial nerve) produces burning and tingling on the medial ankle and plantar foot — positive Tinel’s at the medial ankle distinguishes it. Posterior tibial tendon dysfunction (PTTD) produces medial posterior ankle pain and progressive flat foot deformity — tested by single-leg heel rise.

Red Flags: When to Seek Urgent Evaluation

Seek same-day evaluation for posterior ankle pain if: there is sudden inability to plantarflex after a forced dorsiflexion injury (possible Achilles rupture — urgent); swelling is rapidly expanding with bruising spreading toward the midfoot (possible talus or posterior calcaneal fracture); the heel is painful at rest and at night with no mechanism of injury in a patient over 50 (possible calcaneal stress fracture or, rarely, tumor); or neurological symptoms are present (burning, tingling, weakness). Call (810) 206-1402 for same-day evaluation at Howell and Bloomfield Hills.

Book a Posterior Ankle Evaluation in Michigan

Dr. Tom Biernacki, DPM, evaluates posterior ankle impingement, os trigonum syndrome, FHL tenosynovitis, and all causes of posterior ankle pain at Balance Foot & Ankle in Howell (4330 E Grand River Ave, Howell MI 48843) and Bloomfield Hills (43494 Woodward Ave #208, Bloomfield Hills MI 48302). Same-day appointments available — call (810) 206-1402 or book online →.

Medically reviewed by Dr. Tom Biernacki, DPM — podiatric physician and surgeon, Howell and Bloomfield Hills, Michigan.

Ankle Impingement Treatment in Michigan

Posterior ankle impingement and os trigonum syndrome cause deep ankle pain that worsens with pointing the foot downward. Our board-certified podiatrists offer accurate diagnosis and treatment ranging from physical therapy to minimally invasive surgery.

Learn About Our Ankle Treatments → | Book Your Appointment | Call (810) 206-1402

Clinical References

1. Ribbans WJ, et al. “The os trigonum syndrome: a clinical review.” Foot and Ankle Clinics. 2015;20(1):167-181.
2. Smyth NA, et al. “Posterior ankle impingement in athletes: results of arthroscopic treatment.” American Journal of Sports Medicine. 2013;41(8):1869-1876.
3. Hamilton WG. “Posterior ankle pain in dancers.” Clinics in Sports Medicine. 2008;27(2):263-277.

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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.