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

Table of Contents

What Is the os trigonum?

The os trigonum is an accessory ossicle — an extra bone — located at the posterior aspect of the talus, present in approximately 10 to 15 percent of the population as a normal variant. In most individuals, the os trigonum is asymptomatic. However, in athletes and dancers who repeatedly plantarflex the ankle maximally — particularly ballet dancers going en pointe, soccer players kicking with the top of the foot, and swimmers performing flutter kicks — the os trigonum can become compressed between the tibia and the calcaneus during maximum plantarflexion, causing posterior ankle pain. This compression syndrome is called posterior ankle impingement or os trigonum syndrome.

Symptoms and Diagnosis

Os trigonum syndrome presents as pain at the back of the ankle — directly behind and below the Achilles tendon — that worsens with forced plantarflexion and is reproduced by passive plantarflexion of the ankle under examination. Dancers describe pain specifically when going en pointe or in demi-pointe; soccer players note pain when kicking with a plantarflexed ankle; and swimmers may experience posterior ankle aching during freestyle or butterfly kick. Plain radiographs with a lateral view of the ankle identify the os trigonum as a round or triangular accessory bone at the posterior talar process. MRI confirms inflammation and edema around the ossicle and assesses the adjacent posterior structures, including the flexor hallucis longus tendon — which runs in a groove adjacent to the os trigonum and is commonly affected secondarily.

Conservative Treatment

Conservative management includes activity modification to avoid end-range plantarflexion, immobilization in a walking boot for 4 to 6 weeks to allow inflammation to settle, and anti-inflammatory therapy. Ultrasound-guided corticosteroid injection around the os trigonum and into the posterior ankle recess reduces the acute inflammatory component and provides diagnostic confirmation — temporary complete relief with injection confirms the os trigonum as the pain source and predicts a good surgical outcome if symptoms recur.

Surgical Treatment: Os Trigonum Excision

Os trigonum excision is performed when symptoms are recurrent or persistent after adequate conservative management. The procedure can be performed through an open posterolateral incision or endoscopically using two posterior portals with a 4-millimeter arthroscope and instruments. The os trigonum is identified, mobilized, and removed along with any fibrotic tissue in the posterior ankle recess. Endoscopic excision minimizes soft tissue disruption and allows return to sport in 6 to 8 weeks — significantly faster than open surgery. Published outcomes from experienced centers consistently demonstrate excellent pain relief and return to pre-injury activity level in athletes and dancers after os trigonum excision.

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Recommended for recovery: The BraceAbility Short Walking Boot provides ankle immobilization during the initial recovery phase after os trigonum excision. In our clinic, patients transition from the boot to supportive athletic shoes within 2 to 3 weeks.

Frequently Asked Questions

What causes os trigonum syndrome?

The os trigonum is an extra bone behind the ankle that about 10 to 15% of the population has from birth. It becomes symptomatic when repetitive plantarflexion (pointing the foot down) compresses the bone between the ankle and heel bone. This is especially common in ballet dancers during en pointe work and soccer players during forceful kicking.

Can os trigonum syndrome heal without surgery?

Many patients improve with conservative treatment including rest, anti-inflammatory medication, physical therapy, and activity modification. A corticosteroid injection can confirm the diagnosis and provide temporary relief. Surgery is only recommended when 3 to 6 months of conservative care fails to adequately control symptoms.

How long until I can dance or play sports after os trigonum surgery?

After arthroscopic os trigonum excision, most athletes return to sport-specific training at 6 to 8 weeks and full competition at 8 to 12 weeks. Dancers may need slightly longer before returning to full pointe work. In our clinic, we use a structured rehabilitation protocol to safely progress each athlete based on their specific demands.

The Bottom Line

Os trigonum syndrome is a treatable cause of posterior ankle pain that affects athletes and dancers at all levels. Whether managed conservatively or through minimally invasive surgery, most patients return to their full activity level. Early evaluation ensures the right diagnosis and prevents unnecessary time away from the activities you love.

Os Trigonum Treatment in Michigan

Os trigonum syndrome causes posterior ankle pain especially in dancers, gymnasts, and soccer players. Our podiatric surgeons offer both conservative care and arthroscopic excision at our Howell and Bloomfield Hills offices.

Learn About Ankle Surgery Options | Book Your Appointment | Call (810) 206-1402

Clinical References

1. Hedrick MR, McBryde AM. Posterior ankle impingement. Foot Ankle Int. 1994;15(1):2-8.
2. Abramowitz Y, et al. Outcome of resection of a symptomatic os trigonum. J Bone Joint Surg Am. 2003;85(6):1051-1057.
3. Nault ML, et al. Posterior ankle impingement syndrome: a systematic review of the literature and analysis of outcomes. Arthroscopy. 2014;30(10):1366-1371.