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

What Is Posterior Ankle Impingement?

Posterior ankle impingement syndrome (PAIS) occurs when soft tissues or bony structures are pinched between the tibia and calcaneus during forceful plantarflexion — the movement of pointing the toes downward. The posterior ankle contains several structures that can become impinged: the os trigonum (a small accessory bone present in about 10 percent of the population), a hypertrophied posterior talar process, the posterior joint capsule, or scar tissue from prior injury. The result is deep posterior ankle pain with activities that require extreme plantarflexion.

Who Gets Posterior Ankle Impingement?

PAIS is classically associated with athletes whose sport demands extreme plantarflexion. Ballet dancers are the most frequently affected group — the en pointe and demi-pointe positions maximally compress the posterior ankle. Soccer players experience impingement from the plantarflexed shooting motion. Gymnasts and swimmers performing flutter kicks, downhill skiers in the forward-lean position, and sprinters with aggressive toe-off mechanics are additional athletic populations at risk. The condition can also develop in non-athletes following ankle sprains that produce posterior capsular scarring.

The Os Trigonum: The Most Common Structural Cause

The os trigonum is an accessory bone behind the talus that fails to fuse with the main talus body during development. Present in approximately 7 to 10 percent of the population, most os trigona are asymptomatic. When an acute ankle plantarflexion injury (nutcracker mechanism) fractures the fibrocartilaginous synchondrosis between the os trigonum and talus, or when repetitive impingement produces chronic irritation, the os trigonum becomes a painful focus. Ballet dancers are uniquely susceptible because of the sustained extreme plantarflexion of pointe work.

Diagnosis

Clinical diagnosis relies on the plantar flexion sign: passive forced plantarflexion reproduces deep posterior ankle pain. Tenderness is palpable directly behind the ankle, between the Achilles and the peroneal tendons. Resisted big toe flexion may also elicit pain if the adjacent flexor hallucis longus (FHL) tendon is involved — a common associated finding in dancers. X-rays may show an os trigonum or enlarged posterior talar process. MRI confirms os trigonum pathology, assesses FHL tenosynovitis, and evaluates the posterior joint capsule. Diagnostic injection of local anesthetic into the posterior ankle is both diagnostic and temporarily therapeutic.

Conservative Treatment

Initial treatment involves activity modification to avoid extreme plantarflexion, NSAIDs for acute inflammation, physical therapy for posterior ankle strengthening and biomechanical optimization, and corticosteroid injection around the os trigonum. Dancers may need technique modification with coaching. Conservative care resolves PAIS in approximately 50 to 60 percent of patients who comply with a structured program and are willing to modify activity.

Surgical Treatment: Excision of the Os Trigonum

When conservative care fails after 3 to 6 months, surgical excision of the os trigonum reliably resolves symptoms. Traditional open excision through a posteromedial or posterolateral approach provides direct visualization. Posterior ankle arthroscopy — the modern alternative — uses small portals to introduce the arthroscope and instruments, allowing removal of the os trigonum and decompression of the posterior compartment with lower complication rates, smaller scars, and faster recovery. FHL tendon decompression can be performed simultaneously through the same portals when indicated. Return to sport following arthroscopic excision typically occurs at 6 to 10 weeks.

If you experience deep posterior ankle pain with activities requiring pointed toes, the team at Balance Foot & Ankle can evaluate for posterior ankle impingement and provide the full range of treatment options from injection therapy to arthroscopic surgery.

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Balance Foot & Ankle — Howell & Bloomfield Township, MI

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Posterior Ankle Impingement Treatment

Posterior ankle impingement causes pain at the back of the ankle during pointing the foot down. Dr. Tom Biernacki diagnoses and treats posterior impingement including os trigonum syndrome at Balance Foot & Ankle.

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Clinical References

1. Giannini S, et al. “Posterior ankle impingement.” Foot Ankle Clin. 2006;11(3):569-583.
2. Ribbans WJ, et al. “The management of posterior ankle impingement syndrome in sport.” Clin Sports Med. 2015;34(2):371-385.
3. Zwiers R, et al. “Prevalence of the os trigonum on CT imaging.” Foot Ankle Int. 2018;39(3):338-342.

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.