Posterior process

This fracture is often confused with an ankle sprain. The mechanism of this injury is an axial load. Diagnosis is often very difficult.

A plain x-ray may be diagnostic, but coronal CT scans are often necessary for a complete definition of the injury.
The presence of an os trigonum which is a developmental failure of the fusion of the posterior tubercle of the talus with its body may be very confusing in making a diagnosis. The aspect of the os trigonum facing the rest of the talus is corticated whereas a fresh fracture is not. If there is any doubt, a bone scan or an MRI would be definitive.
Case by courtesy of Dr. Steven Steinlauf, Florida, USA.