Posterior Ankle Impingement

Posterior ankle impingement is the pinching of structures at the back of the ankle during plantarflexion. The most common cause is an os trigonum or a prominent Stieda process, and the classic patients are ballet dancers and footballers.

The posterior talus. The back of the talus carries a medial and a lateral tubercle. The flexor hallucis longus (FHL) tendon runs in the groove between them and can become involved in posterior impingement.

Os trigonum and Stieda process. In a proportion of people the lateral tubercle of the posterior talar process develops as a separate ossicle, the os trigonum, an unfused secondary ossification centre. A Stieda process is the same tubercle elongated and still continuous with the talus. Both impinge posteriorly in plantarflexion.

How common is an os trigonum? A 2025 meta-analysis of 36,612 feet found a pooled prevalence of approximately 9%, with a wide reported range of 1.7-32.5% and the highest figures in East Asia. Read that with the imaging in mind: it was 8.2% on plain radiographs against 24.2% on MRI, so the "prevalence" of an os trigonum is substantially a statement about how hard you looked.

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The nutcracker. Forced or repetitive plantarflexion, as in dancing en pointe or kicking downward, compresses the os trigonum or Stieda process between the posterior tibial plafond and the calcaneus. Repetitive loading causes synovitis, capsular thickening and bone marrow oedema in the ossicle, and in chronic cases disruption of the synchondrosis between the os trigonum and the talus.

Impingement without an ossicle. Soft tissue can impinge on its own: the FHL, or the capsule through synovitis and scarring. A substantial minority of cases have no ossicle, but the true proportion, and the optimal treatment of pure soft-tissue impingement, are not well defined by high-level evidence.

The FHL. In its fibro-osseous tunnel the tendon lies immediately medial to the os trigonum, and it is maximally loaded with the ankle plantarflexed and the great toe pushing off. Repetitive plantarflexion and hallux motion produce stenosing tenosynovitis, thickening of the tendon and sheath that can trigger or lock the hallux: "dancer's tendinitis". Impingement and FHL pathology frequently coexist but behave as distinct entities, and either may occur in isolation.

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History. Ballet dancers describe posterior ankle pain, particularly with en pointe work; footballers may feel it on downward kicking and swimmers on push-off. The pain is worse with plantarflexion and may come with triggering of the great toe if the FHL is involved.

The posterior impingement test (van Dijk's test). With the patient seated or prone and the knee flexed to relax the gastrocnemius, grasp the foot and perform a quick, repetitive passive forced hyperplantarflexion of the ankle. Recognisable reproduction of the patient's deep posterior pain is a positive test. A small rotatory "grinding" movement at end-range increases posterior compression and heightens sensitivity, and the manoeuvre is often repeated in slight external and internal rotation.

Reading the result. The test has high sensitivity, so a negative, pain-free test essentially rules out bony posterior impingement. Its specificity is lower, because forced plantarflexion also loads the FHL, Achilles and posterior capsule; a positive test is not by itself diagnostic and should be correlated with imaging and, when equivocal, a diagnostic injection.

The rest of the examination.

• Palpate the posterolateral ankle, between the Achilles and peroneal tendons, for tenderness
• Move the great toe with the ankle plantarflexed: passive flexion and extension may reproduce symptoms or show triggering, and pain or triggering on passive hallux dorsiflexion and resisted hallux flexion points to coexisting FHL tenosynovitis rather than pure osseous impingement
• Exclude Achilles pathology: tenderness at the insertion, Thompson test

Radiographs. The lateral view shows an os trigonum as a separate ossicle or a prominent Stieda process as an elongated tubercle, and both are best assessed on a true lateral.

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CT better defines the anatomy, particularly for surgical planning, and shows the relationship of the ossicle to the talus.

MRI shows bone oedema in the os trigonum or lateral tubercle, FHL tenosynovitis and associated soft-tissue inflammation.

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Ultrasound can assess the FHL tendon dynamically.

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Diagnostic injection. An image-guided local anaesthetic injection to the posterior ankle that relieves symptoms confirms the pain source. Greater than 70% relief of the pain on the posterior impingement test supports the diagnosis, particularly when imaging is equivocal.

The incidental ossicle. An os trigonum is a common asymptomatic anatomical variant. Imaging findings must correlate with a positive impingement test, and ideally a confirmatory diagnostic injection, before symptoms are attributed to it.

Differential Diagnosis

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Algorithm

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Start without surgery. Non-operative care consists of:

• Activity modification, avoiding provocative plantarflexion
• Physiotherapy for ankle conditioning, avoiding excessive plantarflexion
• NSAIDs or analgesia for symptomatic relief
• A corticosteroid injection to the posterior ankle, which may provide relief and is both diagnostic and therapeutic

Conservative treatment may be successful in mild cases, but dancers and athletes often require surgery to return to activity. The evidence for non-operative treatment is very weak (few patients, retrospective), so no evidence-based protocol exists; a trial of activity modification, physiotherapy and image-guided injection remains reasonable before surgery in non-elite patients.

When to operate. Surgery is indicated for:

• Failed conservative treatment
• Athletes and dancers who require plantarflexion
• Confirmed posterior impingement with an identifiable cause

Endoscopic excision is the preferred method, with less morbidity and faster recovery than open surgery. Two portals, posterolateral and posteromedial, are placed on either side of the Achilles tendon; the os trigonum or Stieda process is excised, and FHL tenosynovitis, if present, is addressed in the same procedure by releasing the tendon.

Open excision goes through a posterolateral or posteromedial approach, with similar outcomes but a longer recovery.

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Outcomes. Results are good to excellent. In a systematic review of operated dancers 89% had a good-to-excellent outcome, and in an endoscopic series 94% returned to their previous sport.

Of the untreated condition.

• Persistent posterior ankle pain limiting plantarflexion-dependent activity such as dance and kicking sports
• Progressive FHL tenosynovitis or stenosis, with hallux triggering or locking
• Synchondrosis disruption or chronic fragmentation of the os trigonum, with ongoing mechanical symptoms
• Career-limiting loss of performance in elite dancers and athletes

Of surgery. Nerve injury is the most important. Portal-related neurological complications run at about 1.9% overall in large ankle arthroscopy series, the sural nerve at risk laterally and the tibial nerve with its medial calcaneal and plantar branches medially; most are transient and resolve within about 6 months.

• Incomplete excision: a residual os trigonum or Stieda fragment is the commonest cause of persistent symptoms and surgical failure (overall failure about 5-15%)
• Untreated coexisting FHL pathology, a recognised cause of surgical failure, with symptoms persisting despite osseous excision
• Posterior tibial vessel injury or haematoma, wound problems, infection (rare)
• Stiffness and scarring of the posterior recess; FHL weakness if excessive tendon is debrided, critical to avoid in dancers
• Persistent neuritis or scar dysaesthesia at portal sites, reported transiently in up to about 15% in some series

The protocol is staged, and its key principle is early motion:

• Early phase (0-2 weeks). A short period in a removable boot or backslab with protected weight-bearing; endoscopic patients often weight-bear as comfort allows within days. Begin early active ankle plantar- and dorsiflexion and hallux motion as soon as the wounds allow, to prevent re-scarring and adhesion of the posterior recess, a recognised cause of recurrent symptoms and stiffness.
• Intermediate phase (2-6 weeks). Progress to full weight-bearing out of the boot, restore the full range including the plantarflexion arc, and add calf and FHL strengthening and proprioception. After an FHL release or tenosynovectomy, protect against forced hallux dorsiflexion early but keep the toe gliding to avoid adhesion.
• Return to sport (6 weeks onward). Introduce sport-specific plantarflexion loading in a graded manner: relevé and pointe work for dancers, kicking for footballers, turn push-off for swimmers.

How long. Typical return is around 6-12 weeks for general sport and around 12-16 weeks (or longer) for elite dance and forced-plantarflexion athletes. Isolated FHL tendinopathy recovers more slowly than osseous impingement, at about 16 weeks (Rietveld). In the one randomised trial, endoscopic excision returned athletes to their previous level in about 7 weeks against 11-12 weeks after open excision.

Setting this staged, early-motion protocol, and counselling the longer timeline when the FHL is involved, is what delivers high return-to-sport figures.

Global Epidemiology

Posterior ankle impingement is predominantly an overuse condition of athletes who repetitively plantarflex — classically ballet dancers (en pointe / relevé) and football/soccer players (instep kicking), and also gymnasts, divers, swimmers (turn push-off) and downhill runners. An os trigonum is present in roughly 9% of feet worldwide (highest in East Asian populations), but is asymptomatic in most. There is no dedicated implant registry for this soft-tissue/osseous procedure; outcome evidence comes from case series, one RCT and systematic reviews rather than national arthroplasty registries.

Society Guidance — Side by Side

There are no disease-specific clinical practice guidelines from the major bodies for posterior ankle impingement; recommendations are derived from expert/society positions on hindfoot endoscopy and from sports-medicine consensus:

Registry & Outcome Notes

No joint registry captures this procedure. The strongest data point is the single RCT (endoscopic vs open, Level II) plus Level IV series and a complications study reporting an overall ankle-arthroscopy complication rate of ~3.5% with portal-related neurological injury ~1.9%.

High- vs Limited-Resource Practice Variation

• Well-resourced settings: MRI and image-guided diagnostic injection are standard, and endoscopic two-portal excision is widely available, allowing faster return to sport in elite athletes.
• Limited-resource settings: Diagnosis often rests on clinical examination and plain lateral radiographs; open excision through a posterolateral or posteromedial approach remains an entirely valid, effective treatment where endoscopic equipment or expertise is unavailable, with the trade-off of slower recovery and a higher (but still acceptable) complication rate.

Related pages: Os Trigonum Syndrome covers the commonest single bony cause in full - it and this page describe largely the same entity, and are registered as a duplicate pair pending merge; Ankle Impingement Syndromes is the umbrella covering both ends of the joint, and Anterior Ankle Impingement the mirror-image problem of forced dorsiflexion in footballers; FHL Tendinitis and Flexor Hallucis Longus Anatomy for the tendon that shares the fibro-osseous tunnel and coexists with bony impingement often enough that the two are treated in the same sitting; Talus Fractures for the lateral tubercle fracture (Shepherd fracture) that an os trigonum is misread as, and vice versa; Achilles Tendinopathy for the other cause of posterior ankle pain in the same athletes, and the one that must be excluded before a hindfoot endoscopy is planned; and Lateral Ankle Instability for the coexisting pathology that changes both the diagnosis and the operation.

Endoscopic versus open excision. Only one randomised trial exists (Georgiannos and Bisbinas, Level II), and it favours endoscopy for faster return and fewer complications; most other evidence is Level IV/V. Open excision remains acceptable, especially where endoscopic expertise is limited or extensive FHL work is anticipated.

Posteromedial versus posterolateral open approach. The posteromedial approach gives direct access to the FHL but risks the tibial nerve and posterior tibial vessels; the posterolateral is simpler, but FHL access is harder. There are no high-level comparative data, and the choice is surgeon-dependent.

Routine FHL release. Whether to release or decompress an FHL that looks normal intraoperatively is debated, because the failures from untreated FHL disease have to be weighed against the morbidity an unnecessary release adds. Current practice is to address the FHL only when pre-operative or intraoperative pathology is demonstrated.