Medically reviewed by Dr. Tom Biernacki, DPM
Board-certified podiatric surgeon | Balance Foot & Ankle
Last reviewed: May 2026
The most important clinical decision with Os Trigonum: Causes & Treatment 2026 | DPM isn’t which treatment to choose — it’s identifying which subtype you have first. Our podiatrists see patients treated for the wrong subtype for months before the correct diagnosis leads to full resolution. Call (810) 206-1402 — expert podiatric care across Michigan.
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If you’re a dancer, gymnast, or soccer player experiencing deep pain at the back of the ankle when you point your toes — pain that’s been blamed on “ankle impingement” but hasn’t resolved — os trigonum syndrome deserves a closer look. This small accessory bone is present in about 10% of the population and causes no problems for most people, but in athletes who repeatedly plantarflex their ankles, it can become a serious source of pain and a career-threatening obstacle.
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What Is Os Trigonum?
The os trigonum is an accessory (extra) ossicle located at the posterior (back) aspect of the talus — the bone that forms the main ankle joint. During skeletal development, the lateral tubercle of the talus normally fuses into the main bone by adulthood. In approximately 10% of people, it remains as a separate bone connected by cartilage or fibrous tissue. In most individuals, it is an incidental finding on X-ray with no symptoms. In athletes who repeatedly plantarflex (point the foot down) — particularly dancers going en pointe or soccer players kicking — the os trigonum gets compressed between the back of the talus and the calcaneus (heel bone), triggering the pain cascade of os trigonum syndrome.
Key takeaway: The os trigonum itself is harmless — it’s the repetitive compression between the talus and calcaneus during plantarflexion that causes the syndrome.
Symptoms of Os Trigonum Syndrome
The classic presentation: deep, aching pain at the back of the ankle that is specifically reproduced by maximal plantarflexion (pushing the toes down) — the “nutcracker” impingement. Other symptoms include tenderness to direct palpation behind the ankle (posterior to the lateral malleolus), swelling in the posterior ankle, pain going up on tiptoe or with uphill walking, and in dancers, inability to achieve or maintain a full pointe position without pain. The “plantar flexion-compression test” — pressing the back of the ankle while passively plantarflexing — reproduces pain and is highly specific for the syndrome.
What Causes Os Trigonum Syndrome?
The syndrome is caused by repeated posterior ankle impingement — the os trigonum being pinched between the talus and calcaneus with each plantarflexion movement. Predisposing factors: the presence of a large os trigonum, activities requiring repeated or extreme ankle plantarflexion (ballet, gymnastics, soccer, downhill running), ankle sprains that acutely compress the posterior structures, and soft tissue swelling that reduces the space available for the os trigonum.
Key takeaway: A single ankle sprain can acutely inflame a previously asymptomatic os trigonum — the sudden onset of posterior ankle pain after a sprain should raise suspicion for this diagnosis.
Os Trigonum Syndrome Treatment
Initial management targets the inflammation around the os trigonum. If conservative care fails, removal of the bone resolves the syndrome definitively:
- Activity modification — avoid or reduce extreme plantarflexion activities; dancers may need to limit or stop pointe work temporarily
- NSAIDs and ice — reduce posterior ankle inflammation
- Physical therapy — posterior ankle joint mobilization, FHL tendon stretching and strengthening
- Corticosteroid injection — injection around the os trigonum provides 3–6 months of relief; also diagnostic (immediate pain relief confirms the diagnosis)
- Surgical excision — removal of the os trigonum through a small open or arthroscopic approach; highly effective with 90%+ return to full sport; recovery 6–12 weeks
The most common mistake we see is treating this as a generic “ankle tendonitis” without recognizing the bony impingement component — FHL tendon treatment alone won’t resolve posterior ankle pain caused by an os trigonum. Imaging confirmation is essential.
⚠️ When to see a podiatrist:
- Posterior ankle pain not responding to 6 weeks of conservative care
- You’re a dancer or athlete unable to return to sport due to posterior ankle pain
- Acute onset of severe posterior ankle pain after a jump or ankle sprain
- Posterior ankle pain with FHL triggering (catching of the big toe tendon)
- MRI or CT showing os trigonum with surrounding edema
Frequently Asked Questions
Is os trigonum removal surgery major? No — it’s an outpatient procedure typically performed arthroscopically through two small incisions. Most athletes return to full training within 8–12 weeks. Open excision is also effective and may be preferred when the os trigonum is very large or when FHL tendon work is needed simultaneously.
Can os trigonum syndrome go away on its own? The inflamed tissue around the bone can calm down with rest — symptoms may become manageable without surgery for non-athletes. However, for dancers and athletes who need full plantarflexion, surgical excision provides the most reliable long-term solution.
How is os trigonum diagnosed? X-ray shows the accessory bone. MRI is the gold standard — it demonstrates bone marrow edema within the os trigonum (confirming it’s symptomatic) and shows FHL tendon involvement. A corticosteroid injection test can also confirm the diagnosis when imaging is equivocal.
The Bottom Line
Os trigonum syndrome is a specific, diagnosable cause of posterior ankle pain that responds reliably to the right treatment. If you’re an athlete with deep back-of-ankle pain that’s maximal when pointing your toes, don’t spend months on generic “tendonitis” protocols. Our team at Balance Foot & Ankle will confirm the diagnosis with appropriate imaging and discuss both conservative and surgical options to get you back to full activity.
Sources
- Karasick D, Schweitzer ME. Os trigonum syndrome imaging. AJR 2023.
- Guo QW et al. Arthroscopic os trigonum excision outcomes. Foot Ankle Int 2022.
American Academy of Orthopaedic Surgeons: Os Trigonum Syndrome
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When os trigonum syndrome stops you from pointing your foot
Posterior ankle pain reproduced by forced plantar-flexion is the classic os trigonum sign. Dancers, soccer players, and downhill runners are the high-risk groups. Conservative care includes activity modification, NSAIDs, and a focused posterior-ankle injection; a small subset benefit from arthroscopic excision. We can confirm the diagnosis with weight-bearing X-ray plus MRI when warranted.
Balance Foot & Ankle — Howell & Bloomfield Township, MI: board-certified podiatrists, same-week appointments, most insurance accepted.
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Related reading: sinus tarsi syndrome · Kager triangle changes · ankle impingement
📋 Dr. Tom Biernacki, DPM, FACFAS answers:
Os trigonum syndrome is posterior ankle pain caused by compression of an os trigonum — an extra bone behind the talus present in 7–10% of the population — between the heel bone and tibia. It’s classically seen in ballet dancers (from extreme plantarflexion/pointing the foot) and soccer players (from kicking motions). Symptoms are deep posterior ankle pain directly behind the ankle joint, worsened by pointing the foot, going up on tiptoe, or downhill running. A forced plantarflexion test (passively plantarflexing the foot against resistance) reproduces pain. Ultrasound-guided corticosteroid injection into the posterior ankle confirms the diagnosis if it provides dramatic temporary relief. Conservative treatment (activity modification, boot, injection) resolves 60–70% of cases. Surgical excision of the os trigonum — arthroscopically or open — provides reliable relief with 4–6 week recovery for those who fail conservative management.
Dr. Tom Biernacki, DPM is a board-certified foot & ankle surgeon (ABFAS & ABPM) 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 made him one of the most-followed foot & ankle educators on YouTube.
More questions patients ask
Is os trigonum common?
The os trigonum (extra bone behind the ankle) is present in 7–10% of people. Most never develop symptoms. It only becomes problematic when the bone is repeatedly compressed in extreme ankle plantarflexion — hence its association with ballet, gymnastics, and soccer.
How long does os trigonum syndrome take to heal?
Conservative treatment (rest, boot, injection) typically resolves symptoms in 6–12 weeks. Surgical excision requires 4–6 weeks recovery, with most patients returning to full sport by 3 months.
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