Posterior Process Talus Fractures

Posterior process talus fractures are rare injuries involving the posterior process of the talus, which has two parts: the lateral tubercle (Shepherd fracture) and the medial tubercle (Cedell fracture). These fractures can cause FHL impingement and are often missed initially.

Definition

Posterior process talus fracture: Fracture of the posterior process of the talus, which has:

• Lateral tubercle: More common, Shepherd fracture
• Medial tubercle: Rare, Cedell fracture
• FHL groove: Between the two tubercles

Shepherd fracture: Lateral tubercle of posterior process

• More common than medial
• Causes FHL impingement
• Named after Shepherd

Cedell fracture: Medial tubercle of posterior process

• Rare
• Less common than lateral
• Named after Cedell

Epidemiology

• Incidence: Less than 1% of talus fractures
• Age: Peak 20-40 years (sports, trauma)
• Gender: No clear predominance
• Mechanism: Forced plantarflexion, direct trauma
• Associated injuries: Ankle injuries, other foot trauma

Posterior Process Anatomy

Posterior process of talus:

• Location: Posterior aspect of talus body
• Two parts: Lateral tubercle and medial tubercle
• FHL groove: Between the two tubercles
• Function: Attachment site for ligaments, forms FHL groove

Lateral tubercle (Shepherd):

• Size: Larger than medial
• Location: Lateral aspect of posterior process
• Function: Forms lateral border of FHL groove
• Fracture: More common, causes FHL impingement

Medial tubercle (Cedell):

• Size: Smaller than lateral
• Location: Medial aspect of posterior process
• Function: Forms medial border of FHL groove
• Fracture: Rare, less common than lateral

FHL (Flexor Hallucis Longus) tendon:

• Course: Runs between lateral and medial tubercles
• Function: Flexes great toe
• Impingement: Fracture can cause impingement

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Pathophysiology

Injury mechanism:

• Forced plantarflexion: Classic mechanism
• Direct trauma: To posterior ankle
• Avulsion: Ligament avulsion

FHL impingement:

• Mechanism: Fracture fragment impinges on FHL tendon
• Symptoms: Pain with great toe flexion
• Treatment: ORIF or excision relieves impingement

Why often missed:

• Subtle on X-ray: May be obscured
• Misdiagnosed: As os trigonum or ankle sprain
• CT needed: Often requires CT for diagnosis

History

Symptoms:

• Posterior ankle pain: Pain in posterior ankle
• FHL impingement: Pain with great toe flexion (lateral tubercle)
• Swelling: Localised to posterior ankle
• Difficulty walking: Pain with weight bearing

Mechanism:

• Forced plantarflexion
• Direct trauma to posterior ankle
• Sports injuries

Physical Examination

Inspection:

• Swelling in posterior ankle
• Ecchymosis (may be delayed)
• Deformity (rare)

Palpation:

• Tenderness over posterior process
• FHL impingement test (pain with great toe flexion)
• Ankle joint usually not tender

Range of Motion:

• Ankle ROM may be limited
• Great toe flexion painful (FHL impingement)
• Plantarflexion may be limited

Special tests:

• FHL impingement test: Pain with active great toe flexion
• Posterior process palpation: Tenderness over posterior process

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. Use the table below to structure the differential in the viva.

Plain films detect only around three-quarters of talar fractures (radiographic sensitivity roughly 74% against CT), and 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. Before defaulting to cross-sectional imaging, a few tailored radiographs materially improve detection — a point the topic's own case evidence relies on but the standard-view protocol above does not develop.

• Standard lateral: the single best plain view — it profiles the posterior process, but the fracture line is easily mistaken for an os trigonum synchondrosis or overlooked entirely.
• External-rotation lateral: a lateral taken with the foot in approximately 30 degrees of external rotation rotates the posteromedial (Cedell) tubercle clear of overlapping bone. In the reported Cedell case this projection revealed a hypolucent shadow posterior to the talus that routine views had missed, and CT then confirmed the fracture.
• AP/mortise and oblique views: help localise the tubercle and exclude differentials such as a lateral process fracture or a malleolar injury.
• Contralateral comparison films: imaging the uninjured foot helps distinguish a smooth, corticated, often-bilateral os trigonum from a sharp, non-corticated acute fracture line.
• Escalate rather than repeat: when doubt persists, proceed to CT (the reference standard, which added information in 93% of talar fractures in trauma-centre data) rather than repeating the same unhelpful plain film.

The detailed anatomy of the os trigonum / Stieda process as a normal variant is developed in the dedicated os trigonum and posterior ankle impingement topics; here the point is purely how to make the fracture visible.

A posterior process fracture is frequently a marker of a higher-energy hindfoot injury rather than an isolated event — a fact implied by the epidemiology above ("associated injuries: ankle injuries, other foot trauma") but never developed. 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%, and fall from height was the commonest mechanism (44.8%) in the largest posterior-process outcome series. The visible fragment may therefore be the least of the patient's problems.

Deliberately look for, 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).

Practically this means a low threshold for whole-foot CT in any suspected posterior process fracture, a documented neurovascular and soft-tissue assessment (the posteromedial neurovascular bundle and the skin over a displaced fragment), and counselling that prognosis is often set by the associated injury rather than by the process fragment itself.

FHL Impingement

20-30% incidence (if untreated):

• Cause: Lateral tubercle fracture impinges on FHL tendon
• Symptoms: Pain with great toe flexion
• Prevention: ORIF or excision relieves impingement
• Management: Surgical treatment (ORIF or excision)

Nonunion

10-15% incidence:

• Cause: Displacement, inadequate fixation
• Prevention: Rigid fixation, bone graft if needed
• Management: Revision fixation with bone graft

Immediate Postoperative

• Immobilisation: Short leg cast or boot
• Weight bearing: Non-weight bearing (6-8 weeks)
• ROM: Ankle ROM after cast removal
• PT: FHL stretching and strengthening

Rehabilitation Protocol

Weeks 0-6:

• Short leg cast, non-weight bearing
• Elevation to reduce swelling
• Ankle ROM exercises (if stable)

Weeks 6-8:

• Cast removal
• Transition to walking boot
• Progressive weight bearing

Weeks 8-12:

• Full weight bearing
• Progressive activity
• Return to sport (3-4 months)

Overall Outcomes

ORIF (large fragments):

• Success rate: 80-90% (union, pain relief)
• Functional outcomes: 75-85% return to pre-injury level
• FHL impingement: Relieved in 90-95%

Excision (small fragments):

• Success rate: 75-85% (pain relief)
• Functional outcomes: 70-80% return to pre-injury level
• FHL impingement: Relieved in 85-90%

Conservative (non-displaced):

• Success rate: 85-90% (union, pain relief)
• Functional outcomes: 80-85% return to pre-injury level
• FHL impingement: Rare if non-displaced

Long-Term Prognosis

FHL impingement resolution:

• With proper treatment: 90-95% relief of impingement
• Without treatment: 20-30% develop chronic impingement
• Risk factors: Displacement, delayed treatment

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.

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.