CALCANEAL AVULSION FRACTURES

 

Avulsion fractures of the calcaneal tuberosity are uncommon, accounting for 1.3–2.7% of all calcaneal fractures.

The calcaneus is the primary weight bearing bone in the heel, and its many surface contours render it a relatively difficult bone to visualize in its entirety. The stabilizing ligaments that hold the calcaneus in place occupy very specific locations, and the Achilles tendon enthesis is in a relatively constant location; therefore, avulsion fractures occur in reproducible locations.

Fractures of the tuberosity are either from an avulsion or shear-compression mechanism of injury, with the latter constituting most fractures. Avulsion may occur from sudden tension on the Achilles tendon from falling on a plantarflexed foot when the calf muscles are actively contracted, hyperextension of the ankle, or while pushing off a dorsiflexed foot such as in a sprinter beginning a race.

There are four types of avulsion fractures: type 1, simple avulsion with a variable-sized bone fragment; type 2, beak fracture with a horizontal fracture extending into the posterior body; type 3, infrabursal avulsion by the superficial fibers of the middle third of the Achilles tendon; and type 4, small beak fracture avulsed from the deep fibers of the tendon.

An important pitfall is a neuropathic avulsion fracture of the tuberosity in a patient with long-term diabetes mellitus. In these patients, the fracture occurs without a history of significant trauma or overuse activity. The primary fracture line is parallel to the apophyseal scar, and the fracture affects the superior cortex but not always the inferior cortex.

The fracture also tends to extend posteriorly with a horizontal component immediately distal to the enthesis of the Achilles tendon. When the fracture is imaged sequentially, distraction and fragmentation are common later findings. Neuropathic fractures are important because they have a much higher incidence of infection, nonunion, malunion, and failure of fixation and require a much longer time to heal than nonneuropathic insufficiency fractures.

Another pitfall occurs in children. A Salter 3 fracture of the apophysis in a skeletally immature patient may mimic Sever disease when it is not significantly displaced. A systematic evaluation of the calcaneus with attention to areas of vulnerability will assist those who interpret ankle and foot radiographs in maintaining a high diagnostic accuracy for these fractures.

Typically, treatment is with open reduction-internal fixation (ORIF), although minimally displaced fractures may be treated with closed reduction.

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