Fractures of the Neck of Talus:
Most common talus fracture (50% of talus fractures); anatomically the neck is the weakest part (small x-section and porosity).
‘Aviators astragalus’ – during world war one, in plane crashes the talus neck was fractured by forced dorsiflexion of the forefoot on the rearfoot.
Mechanism of fracture is thought to be a force on the plantar surface of the foot just distal to the talus, with the ankle in its neutral position.
Clinical features:
Intense pain; unable to move STJ, MTJ or bear weight; history of vehicle accident, fall from height or similar mechanism.
Hawkin’s Classification:
Type 1 – vertical fracture of neck with minimal displacement (~20%)
Type 2 – vertical fracture of neck with subtalar joint subluxation or dislocation
Type 3 – fracture of neck with dislocation of talus from ankle joint (~30%)
Type 4 – fracture of neck of talus with dislocation of talonavicular joint (~4%)
Avascular necrosis (AVN) is a common complication as there is often damage/trauma to vascular supply – higher probability of progressing to AVN with higher Hawkin’s type.
Hawkin’s sign – sclerotic appearance in subchondral area of talar dome that occurs 6-8weeks after a fracture in neck of talus; seen on AP of ankle. As talus has a tenuous blood supply easily disrupted in cases of trauma high risk of avascular necrosis. Hawkin’s sign appears during healing process.
Management:
Difficult to involvement of other joints
Type 1 immobilised in nonweightbearing cast for 6-10 weeks; non-union and AVN is rare
Types 2-4 initially closed reduction, but most need open reduction and internal fixation (depends on amount of displacement
Long term complications:
• Joint osteoarthritis – especially if had AVN (commonly associated with poor outcomes; pain in STJ on pronation and supination NSAID’s, foot orthoses, intra-articular corticosteroids)
• Ankylosis
• Non-union – most are in a varus and/or dorsal angulation ( has implications for long term function when healed)
• Avascular necrosis – more common in more severe injuries, especially following displaced fracture (up to 90% of Type 4); can be quantified by MRI – need to be kept non-weightbearing for up to 8 months
• Neurovascular injury
• Skin problems- pressure necrosis from displaced fragments
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