Posterior Process Talus Fractures

The posterior process of the talus has two parts, a lateral tubercle and a medial tubercle, with the groove for flexor hallucis longus (FHL) running between them. A fracture of the lateral tubercle is the Shepherd fracture and a fracture of the medial tubercle the Cedell fracture, named after Shepherd and Cedell. The Shepherd fracture is the more common and can cause FHL impingement; the Cedell fracture is rare. Both are often missed initially.

Incidence. Posterior process fractures are quoted at less than 1% of talus fractures. The 21% posterior tubercle figure in the CT evidence below is a share of talar body fractures in one trauma-centre cohort, not a population incidence. The peak age is 20-40 years, in sport and trauma, with no clear sex predominance.

Mechanism. Forced plantarflexion is the classic mechanism. Direct trauma to the posterior ankle and a ligament avulsion, by the posterior talofibular or deep deltoid ligament, are the others. Associated injuries are ankle injuries and other foot trauma, surveyed below.

The posterior process. It projects from the posterior aspect of the talar body, gives attachment to ligaments and forms the FHL groove. The lateral tubercle is the larger of the two and forms the lateral border of the groove, and its fracture is the more common. The medial tubercle is smaller and forms the medial border.

The tendon in the groove. FHL, the flexor of the great toe, runs between the two tubercles. A lateral tubercle fracture fragment can impinge on it, which is why great toe flexion hurts, and ORIF or excision of the fragment relieves the impingement.

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The fracture is described three ways. Location names it and determines the treatment approach, displacement decides between conservative and operative care, and fragment size decides between fixation and excision.

Displacement. A step-off of less than 2mm is treated conservatively, and one greater than 2mm by ORIF or excision. The 2mm figure is a working threshold borrowed from intra-articular fracture practice, not one validated for this fracture: no cited series defines a numeric cut-off, and fragment size, cartilage damage and subtalar instability weigh alongside it.

Fragment size. A large fragment is reconstructible and ORIF is preferred, with better outcomes than excision. A small fragment may not be reconstructible, and excision is then acceptable, with a good outcome if there is no impingement.

Morphology. The posterior process itself varies in shape, and one label can conceal different fragment geometry.

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History. Posterior ankle pain after forced plantarflexion, direct trauma to the posterior ankle or a sports injury. The swelling is localised to the posterior ankle and weight bearing is painful, so walking is difficult. A lateral tubercle fracture impinging on FHL adds pain on great toe flexion.

Examination. There is swelling in the posterior ankle and ecchymosis, which may be delayed; deformity is rare. The tenderness is over the posterior process, and the ankle joint itself is usually not tender. Ankle range of motion may be limited, and so may plantarflexion.

The FHL signs. The FHL impingement test is pain with active great toe flexion, and it is the key clinical test. Pain on passive hallux movement, which stretches FHL, is the other clue, and in the reported Cedell case it was a key clinical clue.

Differential diagnosis. The single most important distinction is an acute fracture versus a symptomatic os trigonum, because the treatment, prognosis and medicolegal consequences of a missed fracture differ greatly.

Why it is missed. Plain films detect only around three-quarters of talar fractures, a radiographic sensitivity of roughly 74% against CT. The posterior process is among the hardest regions to see, because the fibula, normal ossification variants and overlapping tarsal bones obscure it on routine projections, and the fracture is misdiagnosed as an os trigonum or an ankle sprain. A high index of suspicion is needed, and CT is often what makes the diagnosis.

Radiographs. A few tailored views materially improve detection before cross-sectional imaging:

• Lateral - the best plain view. It profiles the posterior process, but the fracture is often subtle and is easily mistaken for an os trigonum synchondrosis or overlooked entirely
• External-rotation lateral - taken with the foot in approximately 30 degrees of external rotation, it rotates the posteromedial (Cedell) tubercle clear of overlapping bone. In the reported Cedell case it revealed a hypolucent shadow posterior to the talus that routine views had missed, and CT then confirmed the fracture
• AP - may show the fracture, but is less reliable than the lateral
• AP/mortise and oblique - help localise the tubercle and exclude a lateral process fracture or a malleolar injury
• Contralateral comparison films - help distinguish a smooth, corticated, often-bilateral os trigonum from a sharp, non-corticated acute fracture line

The os trigonum and Stieda process as normal variants are covered in the os trigonum and posterior ankle impingement topics; here the point is how to make the fracture visible.

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CT. CT is the reference standard, and it added information in 93% of talar fractures in trauma-centre data. It is recommended when the fracture is suspected clinically but the radiographs are negative, when displacement is unclear on the radiographs, and when planning surgery. It shows the fracture pattern, the displacement (the step-off is measured), the fragment size and the fragment's relationship to FHL.

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A sentinel injury. A posterior process fracture is frequently a marker of a higher-energy hindfoot injury rather than an isolated event. In a CT-based trauma-centre series, talar fractures were accompanied by adjacent joint subluxation or dislocation in more than 66% of cases and by an adjacent fracture in more than 72%. Fall from height was the commonest mechanism (44.8%) in the largest posterior-process outcome series, and the visible fragment may be the least of the patient's problems.

What to look for. Deliberately exclude each of these, and route to the dedicated topics:

• Subtalar (peritalar) dislocation - the posterior process can avulse during a subtalar dislocation, so reduction and stability of the subtalar joint take priority (see subtalar-dislocations)
• Other talus fractures - lateral process (snowboarder's), talar neck and talar body fractures frequently coexist and change the whole management plan (see lateral-process-talus-fractures, talus-fractures, talar-body-fractures)
• Calcaneal and malleolar fractures - high-energy plantarflexion and inversion loads the entire hindfoot, so scrutinise the calcaneus and malleoli
• Chondral and subtalar facet damage - posterior process fragments involve the posterior subtalar facet, and articular involvement drives both the fixation decision and the later risk of post-traumatic subtalar arthritis (see subtalar-arthritis)

In practice. Keep a low threshold for whole-foot CT in any suspected posterior process fracture, and document the neurovascular and soft-tissue assessment: the posteromedial neurovascular bundle and the skin over a displaced fragment. Never plan fixation of the visible fragment in isolation; exclude subtalar dislocation and lateral process, neck and body fractures first. Counsel that prognosis is often set by the associated injury rather than by the process fragment, and in the delayed or high-energy case it usually is.

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The decision. Suspicion comes first, because the fracture is often missed. Once it is confirmed, displacement, FHL impingement and fragment size set the treatment:

1. Non-displaced (less than 2mm step-off) with no FHL impingement - conservative treatment
2. Displaced (greater than 2mm) with a large fragment - ORIF is preferred. It relieves FHL impingement and prevents nonunion
3. Displaced with a small fragment, or causing FHL impingement - excision is acceptable. It relieves the impingement and is better than malunion

Non-operative treatment. The indications are a non-displaced fracture (less than 2mm step-off), no FHL impingement, and patient preference. The protocol is a short leg cast, non-weight bearing, for 6-8 weeks, with serial radiographs to monitor healing.

Surgical indications. Operate within 2 weeks if possible.

• Absolute: displacement greater than 2mm step-off, FHL impingement (pain with great toe flexion), a large fragment
• Relative: a small fragment that is symptomatic, failed conservative treatment

The incidence figures below are conventional teaching ranges, not rates measured in any cited series.

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Immobilisation. A short leg cast or boot, with the foot non-weight bearing for 6-8 weeks. Ankle range-of-motion exercises start in the first six weeks only if stable; otherwise ankle movement waits for cast removal. Physiotherapy covers FHL stretching and strengthening.

Protocol. Rehabilitation is staged by week:

• Weeks 0-6 - short leg cast, non-weight bearing, elevation to reduce swelling, ankle range-of-motion exercises if stable
• Weeks 6-8 - cast removal, transition to a walking boot, progressive weight bearing
• Weeks 8-12 - full weight bearing and progressive activity, with return to sport at 3-4 months

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The percentages below are conventional teaching ranges; the cited literature (case reports and series of 29-33 patients) does not validate any numeric rate. For displaced fractures as a group, treated by ORIF or excision, the conventional figure is 75-85% good results.

Long-term prognosis. Displacement and delayed treatment are the risk factors for chronic FHL impingement.

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These are rare injuries with no dedicated society guideline and no registry capture (talar process fractures are not separately tracked by arthroplasty registries such as the NJR, AJRR or AOANJRR, which record joint replacements rather than fixation of small process fractures). Practice is therefore guided by trauma principles and the small published literature, summarised below for a global readership.

Global epidemiology and practice variation

• Rarity and demographics: posterior process fractures are uncommon (the posterior tubercle accounts for around 21% of talar body fractures in CT-based trauma-centre data, but isolated process fractures are far rarer). They cluster in young, active adults — sport (especially football, dance, running and climbing) and falls from height are the dominant mechanisms worldwide.
• High-resource settings: ready CT/MRI access, fluoroscopy and hindfoot endoscopy support early diagnosis and minimally invasive excision or fixation; missed-diagnosis rates fall when CT is used liberally for unresolving posterior ankle pain.
• Limited-resource settings: reliance on plain radiographs increases missed and delayed diagnoses; pragmatic management leans toward immobilisation for presumed minor injuries and open excision/ORIF when surgery is indicated, since advanced imaging and endoscopic equipment may be unavailable.

Related pages: Talus Fractures is the umbrella covering neck, body and dome injuries, and the Hawkins classification that does NOT apply here; Lateral Process Talus Fractures for the snowboarder's fracture at the other corner of the talus - the same story of a missed "sprain", a different mechanism and a different approach; Os Trigonum and Posterior Ankle Impingement for the single most important differential: a smooth, corticated, rounded ossicle is an os trigonum, a sharp irregular non-corticated edge is a Shepherd fracture, and CT is what separates them; FHL Tendinitis for the tendon running in the groove between the two tubercles, whose pain on passive hallux movement is the clinical clue here; Subtalar Arthritis for the endpoint of an intra-articular fragment left unreduced, and Subtalar Dislocations for the injury these fractures accompany; Osteochondral Lesion of the Talus for the other cause of persistent post-sprain ankle pain with normal radiographs; and Lateral Ankle Instability for the diagnosis these are routinely mislabelled as.

The evidence base for posterior process talus fractures is limited to small retrospective series and case reports — there are no randomised trials. The following points are genuine areas of debate worth raising in a viva.