What is your diagnosis?

Talar dome fracture, likely osteochondral defect

At first glance, this is a straight-forward lateral low-ankle sprain.  She is tender over the lateral ligaments (ATFL and CFL). And the x-rays appear to be negative for acute fracture or dislocation. But are they really? On closer look, there is an avulsed bony fragment over the superior lateral talar dome, seen best on the AP and mortise projections (Image 2). 

Image 2. Same images as previous with annotation

• Pearl: Look closely at the entirety of the talar dome when (independently!) reviewing ankle x-rays after an inversion injury. 

• Pearl: Although not visible on plain radiographs, there is articular cartilage covering the entirety of the articular talar dome. The small bony fragment also contains a chunk of the articular cartilage.

• Pearl: The fractured piece of bone and cartilage, termed an osteochondral defect (OCD), is at risk for non-union and eventual displacement from the talar dome and into the joint space, constituting a bothersome and destructive intra-articular loose body.

What is your management in the ED?

Radiographs should routinely be obtained to look for underlying fracture or malalignment after an inversion injury associated with inability to bear weight. Patients with talar dome fractures should be immobilized in either a walking boot or a splint pending Orthopedics follow up in order to decrease chances that the fragment displaces, causing an intra-articular loose body.

• Pearl: Unlike low ankle sprains in which early weightbearing and mobilization is important for healing, in the presence of a talar dome injury, it is best to immobilize the patient initially. 

Does Orthopedics need to see this patient acutely in the ED?

No

• Pearl: Prompt Orthopedics follow up (1-2 weeks) should be arranged to ensure that the OCD is healing appropriately.