Sustentaculum Tali Fractures

Sustentaculum tali fractures are rare injuries involving the medial shelf of the calcaneus, which serves as a stable reference for calcaneal fracture reduction and has important structures (FHL tendon and medial plantar nerve) at risk during surgical approach.

Definition

Sustentaculum tali fracture: Fracture of the sustentaculum tali, which:

• Location: Medial shelf of calcaneus
• Function: Forms part of subtalar joint (middle facet)
• Attachment: Spring ligament and deltoid ligament
• Stability: Usually stays attached to talus via interosseous ligament

Sustentaculum tali anatomy:

• Medial shelf: Projects medially from calcaneus
• Subtalar joint: Forms middle facet (articulates with talus)
• FHL groove: FHL tendon runs beneath sustentaculum
• Stable reference: For calcaneal fracture reduction

Epidemiology

• Incidence: Less than 1% of calcaneus fractures
• Age: Peak 20-40 years (trauma population)
• Gender: No clear predominance
• Mechanism: High-energy trauma, inversion injury, or part of calcaneal fracture
• Associated injuries: Calcaneal fractures, ankle injuries

Beneath and medial to the sustentaculum run the long flexors: the flexor hallucis longus (FHL) in its fibro-osseous groove directly on the undersurface of the shelf, and the flexor digitorum longus (FDL) passing more medially, superficial to the FHL. Either tendon can become incarcerated within a displaced sustentaculum fracture line - a complication the reference operative series (Dürr, Zwipp and Rammelt) lists explicitly, alongside articular incongruity, as a formal indication to operate.

Why entrapment changes the plan

• It blocks reduction. An interposed tendon acts as a soft-tissue block; the fragment cannot be seated congruently until the tendon is retrieved, so any closed or percutaneous attempt will fail.
• It abolishes active toe flexion. Incarceration of the FHL tethers the great-toe flexor and abolishes active hallux flexion; FDL entrapment does the same for the lesser toes. This is the mechanical basis for the classic "cannot flex the great toe" sign, and is far more often entrapment than a primary tendon rupture.
• It removes the millimetre debate. Because interposition both blocks reduction and disables the tendon, entrapment is an absolute operative indication whatever the amount of displacement - the usual step-off threshold simply does not apply.

Recognising and dealing with it

• Clinically: test active great-toe and lesser-toe flexion in every medial hindfoot injury; loss of hallux flexion after a fall demands scrutiny rather than reassurance.
• On CT: look for the tendon lying within the fracture gap and for a fragment that will not seat; MRI confirms tendon incarceration and distinguishes entrapment from rupture.
• Intra-operatively: through the direct medial approach, identify, retract and free the FHL (and FDL where involved) from the fracture before reduction, then reduce to the medial facet and cortical outline and fix with two small-fragment screws directed medial to lateral. A tendon left entrapped risks adhesion, a flexion contracture or clawing of the hallux, and late attritional rupture.

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Sustentaculum Tali Anatomy

Sustentaculum tali:

• Location: Medial shelf of calcaneus
• Size: 1-2cm projection medially
• Function: Forms part of subtalar joint (middle facet)
• Attachments: Spring ligament, deltoid ligament

Subtalar joint:

• Three facets: Anterior, middle (sustentaculum), posterior
• Sustentaculum: Middle facet, articulates with talus
• Function: Inversion/eversion, stability

FHL (Flexor Hallucis Longus) tendon:

• Course: Runs beneath sustentaculum tali
• Function: Flexes great toe
• Risk: At risk in medial approach

Medial plantar nerve:

• Location: Medial to sustentaculum
• Course: Between abductor hallucis and flexor digitorum brevis
• Function: Sensory to medial foot, motor to intrinsic muscles
• Risk: At risk in medial approach

Pathophysiology

Injury mechanism:

• High-energy trauma: Part of calcaneal fracture
• Inversion injury: Isolated sustentaculum fracture
• Direct trauma: To medial heel

Why sustentaculum is stable:

• Interosseous ligament: Attaches sustentaculum to talus
• Strong attachment: Ligament usually intact
• Template: Serves as reference for reduction

Why displacement matters:

• Subtalar joint: Sustentaculum is part of subtalar joint
• Articular surface: Displacement causes joint incongruity
• Arthritis risk: Malunion leads to subtalar arthritis

History

Symptoms:

• Medial heel pain: Pain on medial side of heel
• FHL dysfunction: Loss of great toe flexion (if FHL injured)
• Swelling: Localised to medial heel
• Difficulty weight bearing: Pain with weight bearing

Mechanism:

• High-energy trauma (calcaneal fracture)
• Inversion injury (isolated)
• Direct trauma to medial heel

Physical Examination

Inspection:

• Swelling on medial heel
• Ecchymosis (may be delayed)
• Deformity (rare)

Palpation:

• Tenderness over sustentaculum (medial to calcaneus)
• FHL dysfunction (loss of great toe flexion if injured)
• Subtalar joint tenderness

Range of Motion:

• Subtalar ROM limited and painful
• Great toe flexion limited (if FHL injured)
• Inversion/eversion painful

Special tests:

• FHL function: Test active great toe flexion
• Medial plantar nerve: Test sensation to medial foot
• Subtalar joint stress: Pain with inversion/eversion

Differential Diagnosis

Medial hindfoot pain after trauma is easily mislabelled as an ankle sprain. CT distinguishes a sustentaculum fracture from its mimics.

The single most important normal variant to separate from an acute sustentaculum fracture is the os sustentaculi, an accessory ossicle at the posterior margin of the sustentaculum tali. It arises from a secondary ossification centre that fails to fuse and is joined to the sustentaculum by a fibrocartilaginous synchondrosis. It is frequently bilateral - a feature that is itself a valuable clue.

When the ossicle is the problem

An os sustentaculi is usually an asymptomatic incidental finding, but it is not always innocent. A painful synchondrosis - whether degenerate or disrupted by an acute injury - can itself generate medial subtalar pain that mimics a fracture, and the variant has been linked to symptomatic middle-facet subtalar pathology. The rule is therefore two-way: do not label a smooth, bilateral, non-oedematous ossicle as a fresh fracture, but equally do not dismiss persistent medial hindfoot pain in a patient who happens to have one - the junction can be the pain generator.

FHL Injury

5-10% incidence:

• Cause: Medial approach, FHL runs beneath sustentaculum
• Prevention: Identify and protect FHL tendon during approach
• Management: Repair if injured, may need FHL transfer if severe

Medial Plantar Nerve Injury

5-10% incidence:

• Cause: Medial approach, nerve runs medial to sustentaculum
• Prevention: Identify and protect medial plantar nerve during approach
• Management: Neuroma excision if symptomatic

Immediate Postoperative

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

• Success rate: 80-85% (union, pain relief)
• Functional outcomes: 75-80% return to pre-injury level
• Subtalar arthritis: 10-15% develop arthritis

ORIF (part of calcaneal):

• Success rate: 75-85% (union, pain relief)
• Functional outcomes: 70-75% return to pre-injury level
• Subtalar arthritis: 15-20% develop arthritis

Conservative (non-displaced):

• Success rate: 85-90% (union, pain relief)
• Functional outcomes: 80-85% return to pre-injury level
• Subtalar arthritis: 5-10% develop arthritis

Long-Term Prognosis

Subtalar arthritis progression:

• With proper treatment: 10-15% develop subtalar arthritis
• Without treatment: 20-30% develop subtalar arthritis
• Risk factors: Displacement, malunion, delayed treatment

Global Epidemiology

• Rarity: Isolated sustentaculum tali fractures are reported globally as under 1% of all calcaneal fractures.
• Pattern: The sustentaculum is fractured in roughly a third (around 34 to 36%) of intra-articular calcaneal fractures, rising with Sanders grade.
• Demographics: Typically young-to-middle-aged adults (peak ~20 to 45 years) after a fall from height or road-traffic trauma; a male predominance mirrors the wider calcaneal-fracture population.
• Resource link: Incidence tracks high falls and motorcycle/road trauma, so the burden is proportionally higher in regions with high road-injury rates and occupational falls.

Guidelines and Society Positions — Side by Side

No orthopaedic society publishes a sustentaculum-specific guideline; practice is extrapolated from calcaneal-fracture and intra-articular fracture principles.

Registry and Trial Evidence

• Registries: Arthroplasty/implant registries (NJR, AJRR, AOANJRR, Swedish/Norwegian) do not capture sustentaculum or calcaneal fracture fixation, so there is no implant-survival data for this injury - a point worth stating explicitly in a viva.
• Best trial evidence: The UK Heel Fracture Trial (Griffin, BMJ 2014) found no two-year functional advantage of ORIF over non-operative care for typical displaced intra-articular calcaneal fractures, with far higher complication and reoperation rates after surgery. It frames the global caution around routine calcaneal surgery but does not address isolated sustentaculum fractures, where middle-facet incongruity and tendon entrapment remain operative indications.

High- vs Limited-Resource Practice

• High-resource: Routine CT for diagnosis and planning, fluoroscopy-guided or open anatomical fixation, foot-and-ankle subspecialist input, structured rehabilitation.
• Limited-resource: CT may be unavailable, so missed diagnoses are commoner; non-displaced and many displaced fractures are managed in a cast with non-weight-bearing; percutaneous screw fixation is favoured over extensile approaches to limit wound and infection risk where soft-tissue and perioperative support are constrained.

The evidence base is thin (small series, biomechanical and anatomical studies, no fracture-specific RCT), so several questions remain genuinely open.