Hawkins Classification of Talar Neck Fractures

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The Hawkins classification (1970), with the Type IV addition by Canale and Kelly (1978), stratifies talar neck fractures by displacement and the pattern of associated peri-talar dislocation. The talus has a precarious, largely retrograde blood supply through the neck, so each step up in grade represents further disruption of that supply and a higher likelihood of avascular necrosis.

The talus has no muscular or tendinous attachments and depends entirely on capsular and ligamentous vessels. Understanding this anatomy explains why AVN rates climb with each Hawkins grade.

• Artery of the tarsal sinus (anastomosis of the lateral tarsal artery and a branch of the perforating peroneal artery): supplies the lateral talar neck and part of the body. Disrupted with subtalar dislocation (type II onwards).
• Deltoid branch of the posterior tibial artery: enters the medial talar body deep to the deltoid ligament. This is the single most important vessel for talar body perfusion and the last remaining supply in high-grade injuries.
• Artery of the tarsal canal (from the posterior tibial artery): the dominant supply to the central talar body, running in the canal between the talar neck and body.
• Superior neck vessels from the anterior tibial (dorsalis pedis) artery: supply the dorsal talar neck and are torn in any displaced neck fracture.

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The Hawkins sign is a radiographic indicator of revascularisation of the talar dome and, by implication, a reduced likelihood of AVN.

• Appearance: a subchondral radiolucent line in the talar dome, visible on an anteroposterior view of the ankle, typically at 6 to 8 weeks after injury.
• Mechanism: the lucency reflects subchondral resorption (disuse osteopenia) in the revascularised, living talar dome — bone that is dead cannot become osteopenic.
• Interpretation: the Hawkins sign indicates a living blood supply — AVN is unlikely if the sign is present (lucency = life).
• Limitation: absence of the Hawkins sign does not confirm AVN. MRI is the definitive investigation for AVN when clinically suspected, particularly after 8 to 12 weeks. The Hawkins sign is useful but not sufficient on its own.

The three major complications are AVN, post-traumatic arthritis, and malunion.

• Avascular necrosis of the talar body: the defining complication, rising with Hawkins grade (meta-analytic rates ~10% type I to ~53% type III). Importantly, partial AVN often revascularises without collapse — in Vallier's series, 37% of patients with radiographic osteonecrosis revascularised without collapse, so only a minority (~31%) developed collapse. If the body collapses, salvage options include tibiotalar arthrodesis (Blair fusion), tibiocalcaneal/tibiotalocalcaneal fusion, talar prosthesis, or (less successfully) talectomy.
• Post-traumatic arthritis: the subtalar joint is affected in most displaced fractures — subtalar arthritis is actually the commonest late sequela (up to ~80% at longer follow-up), often exceeding AVN. The ankle is additionally involved in types III–IV.
• Malunion: varus angulation of the talar neck causes anterior/medial impingement and altered biomechanics; corrected by osteotomy if symptomatic, but technically demanding.