Posterior Ankle Impingement (Os Trigonum Syndrome)

The VerdictMODERATE CONVICTION

The back of your ankle is getting pinched when you point your foot down.

Gently point your foot down as far as it will go. If a deep pain shows up at the back-and-outside of your ankle, that is the pinch. That clinical sign matters more than any scan.

Here's what's really happening: the tissues at the back of your ankle get pinched between two bones when you point your foot down hard or a lot.
What most people get wrong: they trust the scan. An extra little bone or a "swollen-looking" MRI is present in loads of pain-free people, so the scan alone is not the diagnosis.
Start here: ease off the hard "pointing-down" loads (pointe, kicking, downhill running), keep training everything else, and rebuild your calf and big-toe strength.

Think of the back of your ankle like a door hinge with a loose chip of wood sitting in the gap. When you swing the door fully shut (point your foot), the chip gets squeezed and it hurts. The fix usually is not removing the chip. It is stopping the full slam for a while and rebuilding the muscles so the joint moves cleanly, because plenty of people have that same chip and no pain at all.

What Works

Cinematic anatomy of the posterior ankle

1. Reduce the load + rehab MODERATE

Cut the forced "pointing-down" load that provokes it (pointe volume, kicking, downhill running, deep jump landings), then rebuild strength and control. This is the starting point and where most cases resolve.

Exercise Prescription: Controlled calf raises (3×10–15, slow up and down, staying out of the painful end-range at first). Big-toe (flexor hallucis longus) strengthening — press the pad of the big toe into the floor and hold, 3×10. Single-leg balance work, 3×30s. Progress by comfort. Specific sets/reps are not established in the research, so these are pragmatic starting points.

See Tier 2 and Tier 3 (injection and surgery)

2. Image-guided cortisone injection LOW

Used both to confirm the pain source and to calm a stubborn case before considering surgery. A bridge, not a first move.

3. Surgery — keyhole beats open MODERATE

Only after a genuine conservative trial fails. The one solid comparative finding in the whole literature: endoscopic (keyhole) resection has a lower complication rate (7.2% vs 15.9%) and faster return to activity (11.3 vs 16.0 weeks) than open excision.

What Doesn't Work

Operating on an incidental os trigonum seen on a scan when the clinical picture doesn't match. That extra bone is common and usually harmless — this treats the image, not the patient.
Prolonged complete rest with no graded reloading — deconditions without fixing the load-capacity mismatch.
Missing the coexisting big-toe tendon problem (flexor hallucis longus tendinopathy, "dancer's tendinitis"), a common reason symptoms persist after the bone is addressed.

Return to Training

Gate the return on what your ankle can do, not on the calendar:

Forced plantarflexion (pointing the foot down) no longer reproduces the pain
Full, comfortable pointing-down range restored
Calf and big-toe strength symmetrical with the other side
Can do sport-specific loading (pointe, kicking, jumping) without a flare
No pain or swelling 24 hours after loading, for 2 consecutive weeks

Red Flags — When to Get Checked

Most back-of-ankle pain is mechanical and settles. See a doctor first if any of these apply:

A clear injury and you can't put weight on it, or a specific tender spot on the bone — possible fracture. Get it imaged before loading.
A teenager with this pain — growing bone needs checking first (apophyseal or avulsion injury).
Calf or leg pain that comes on with exercise and eases when you stop — a vascular problem (popliteal artery entrapment) that needs a different check.
A bony bump and pain at the back of the heel — that's Haglund's, a different condition.
Night pain, feeling unwell, or pain with no "pointing-down" trigger — needs review for non-mechanical causes.

Refer to: Orthopedics (foot & ankle) for fracture or refractory cases · Vascular for suspected artery entrapment · GP for non-mechanical or systemic pain.

Gently point your foot down as far as it goes. If a deep pain shows up at the back-and-outside of your ankle, that's the pinch.

That clinical sign, in someone who dances, kicks, or runs downhill, matters more than any scan finding. It's the reproduction of the pinch that makes the diagnosis.

Takes less than 2 minutes. No equipment needed.

Conviction

MODERATE–LOW

The strongest teaching (diagnose clinically, not by the scan) and the mechanism are on solid ground. Conservative care rests on consistent but uncontrolled case series, and the surgical comparison (keyhole beats open) is convergent but low-level. There's no randomized trial of conservative management, no diagnostic-accuracy data, and no formal clinical guideline for this condition.

What would change the "diagnose clinically, not by scan" claim

A study reporting the sensitivity and specificity of the forced-plantarflexion test against a reference standard, with an asymptomatic imaging-matched control arm, would move this from moderate to high.

What would change the "conservative-first" claim

A prospective cohort or RCT of a fully-specified conservative protocol in a mixed recreational-and-elite population reporting resolution rates at 6 and 12 months and predictors of failure.

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The Full Picture — Anatomy, Diagnosis & Evidence

What's Actually Going On

In full plantarflexion (pointing the foot down), the structures at the back of the ankle get compressed between the back of the shin bone and the heel bone — a "nutcracker" pinch. What gets caught varies, which is why the modern view is that this is multifactorial, "not only about the os trigonum":

Bony: a symptomatic os trigonum (an extra bone behind the talus that never fused) or an elongated Stieda process. Soft tissue: the posterior capsule, synovium, or an inflamed joint lining. Tendon: the flexor hallucis longus (big-toe) tendon runs right through the zone, so its tendinopathy ("dancer's tendinitis") very commonly co-travels.

Key point: the os trigonum is present in roughly 1.7–32.5% of people and is usually painless. Finding it on a scan doesn't, by itself, explain the pain.

How to Identify It

Clinical assessment of the ankle, cinematic

It's a clinical pattern: a plantarflexion-loading history plus posterolateral pain plus a positive provocation test. No published sensitivity or specificity exists for these tests — the diagnosis is the pattern, not one number.

Forced passive plantarflexion test — reproduces the deep back-of-ankle pain Sn: n/a | Sp: n/a
Resisted big-toe flexion — screens the coexisting flexor hallucis longus tendon Sn: n/a | Sp: n/a

Imaging (X-ray, MRI, CT) is used to exclude a fracture and support the picture, not to make the diagnosis — because the same findings show up in pain-free ankles.

The Debate

Is the os trigonum the problem, or a red herring?

Traditional view

An os trigonum on imaging explains the pain; open excision is the standard surgery.

2021–2025 evidence (PMID 39586987, 34013446, 36315819, 33874783)

The ossicle is a common incidental finding and posterior MRI changes are ubiquitous in pain-free elite athletes; clinical features don't track imaging, and no study has ever compared PAIS imaging to an asymptomatic control group.

Diagnose clinically. Use imaging to exclude a fracture and support the picture — not to define the condition. And if surgery is needed, endoscopic beats open.

Honest Limitations

The evidence is surgical and uncontrolled

The literature is dominated by surgical case series and technique comparisons. There's no RCT of conservative management, so "conservative-first" rests on consistent low-level series (best data point: 69% non-surgical resolution in elite footballers).

Elite-athlete skew and no dosing

Nearly all the informative data come from professional dancers and footballers at full workload. And the physical therapy that "works" is described only as a category — no sets, reps, or load are specified, so real-world delivery varies widely.

The Nuance

Surgical versus conservative decision, cinematic

Conservative care resolves most symptomatic cases (about 69% non-surgical in the best-documented elite series). When it genuinely fails, surgery works and the keyhole approach is the better-supported choice, with return to activity around 11–16 weeks. The biggest avoidable error runs the other way: operating on an os trigonum seen on a scan when the clinical picture doesn't match, because that ossicle is common and usually harmless.

Sources

Ribbans WJ et al., 2013 — SR of 16 surgical trials; endoscopic vs open complication 7.2% vs 15.9%, return to activity 11.3 vs 16.0 weeks. (PMID 23541613)
Zwiers R et al., 2022 — meta-analysis, open vs endoscopic PAIS surgery; endoscopic favored. (PMID 34048272)
Minimally invasive surgery for os trigonum SR, 2024 — 17 studies, N=435, good outcomes (Level 4). (PMID 38348483)
PAIS + flexor hallucis longus tendinopathy in dancers SR, 2018 — 27 operative studies, 376 ankles; the two entities coincide. (PMID 29510786)
Football case series, 2016 — 26 elite players; 69.2% resolved without surgery. (PMID 27919560)
Clinical-vs-imaging case-control, 2022 — clinical features not associated with MRI findings. (PMID 36315819)
MRI prevalence in elite performers, 2021 — posterior effusion-synovitis 90.8% in pain-free athletes. (PMID 34013446)
Os trigonum prevalence meta-analysis, 2025 — prevalence 1.7–32.5%. (PMID 39586987)